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La traduction en langue en anglaise a été réalisée par Bernard D.Reeves.


To the memory

To the memory of those who have passed away and who played an important role in my professional development as a teacher and researcher, and with whom I developed friendships and shared true feelings of affection.
 
 
Bernard Roché (1948-2004): An excellent scientist and an activist, committed to preserving the biodiversity of the island's natural environments. He passed away too soon. I had the chance and the privilege to carry out scientific research with him on the fresh waters of Corsica.
 
Jean Giudicelli (1936-2021): An exceptional man, an immense researcher of extraordinary intellectual power. The body of knowledge on Mediterranean running waters owes him a great debt. I owe him my passion for aquatic environments. Like a spiritual father, he guided me along the path of ecology.
 
Arlette Cazaubon (1942-2022): The greatest specialist in Mediterranean freshwater algae, particularly from the south-east of France (Provence and Corsica). An exceptional personality. A shining example of courage and generosity. She felt more joy in giving than in receiving. She passed on to me her passion for seaweed.
 
 
 
 
 
 
I would like to thank the people who helped and supported me in writing this book:
 
My wife Sylvie (Chou)
My daughters Sophie, Alicia and Manon
My beloved grand-daughter Bianca
My sons-in-law François Tramoni and François Colonna
Nicolas Alfaro
 
A special thanks to my friend and photographer Philippe Pierangeli for 
his remarkable photographic work in this book
 
Thanks also to Jean Christophe Barbier, Martin Boone, Morgan Calu, François Colonna, Frank Fetzner, Alain Gauthier, Stéphane Muracciole (ONF), Thomas Pesquet and the European Space Agency for their contribution to the photographic illustrations


PREFACE
  
                  Antoine Orsini is a hydrobiologist. As a meteorologist I deal with meteors and water falling from the sky, his interest is in the clear water of rivers, lakes and mountain streams. We were destined to meet.
 
            Above and beyond the demanding scientist from whom I have learned so much, Antoine is also a child of water and of Corsica. In this respect, he confided to me that he studied the fauna of the rivers of the Restonica valley in his early years in a rather unusual way.
 
He is a demanding and passionate scientist. His enthusiasm runs through this meticulous work. He evokes the complex economic, ecological, cultural and spiritual relationships between mankind and water.
 
He takes us on a journey from the Amazon and the Nile to Golu and Tavignani; from Lakes Baikal and Tanganyika to Melu and Capitellu. The author presents the mineral and thermo-mineral waters of Corsica, a largely under-exploited heritage.
 
This work reveals the particularities of the aquatic fauna of Corsica: faunistic gaps and a high rate of endemism. And its curiosities: freshwater jellyfish, invulnerable tardigrades, the planaria (immortal worms), the Corsican gordian (a manipulative parasite). But this biodiversity is threatened by extreme natural events (floods and low water). And by direct anthropisation (dams, pollution, contamination) and indirect anthropisation (climate change).
 
The author shows the importance of alluvial forests, riparian forests and pozzines in the process of carbon sequestration, an issue related to resistance and resilience to the consequences of climate change. This book is also a journey through time, the evolution of pozzines over 2000 years is presented.
 
            We learn about past and future water use. It is acknowledged that water in Corsica is a resource to be preserved, as are its fauna and ecosystems. This asset is fragile, and has come under pressure from both human activity and the natural disturbances of rivers, such as floods.
. This chapter undoubtedly leads us to a growing awareness of this crucial issue, to considering our attitudes to preserving this water, which is an essential element, in both quantity and quality, for our environment...  and for life.
 
 
 Patrick REBILLOUT
Director of Météo France, Ajaccio



Table of contents
 
Introduction
I. The geographic and topographical situation of Corsica
II. The climatology of Corsica 
III. Geology : Corsica, two mountains in the sea
IV. Surface water
. Permanent environments
- Running water: rivers and streams
- Stagnant water: lakes
Natural lakes: mountain lakes
Artificial lakes: dam reservoirs
. Temporary environments; Mediterranean temporary pools
V. Groundwater: spring water, mineral water and thermos-mineral water
VI. The particularities of the aquatic fauna of Corsica
. Fauna gaps
. The high rate of endemism
VII. Biodiversity of Corsica's fresh waters
. Fish
. Amphibians or batrachians
. Reptiles (turtles and aquatic snakes)
. Invertebrates
. Aquatic flora
VIII. Terrestrial vegetation in hydrosystems
. Alluvial forests and riparian forests
. Pozzines
IX. Biodiversity under threat
                  . Extreme natural events: floods and low water
                  . Direct anthropisation: dams, pollution and contamination
                  . Indirect anthropisation: climate change
X. Water use in Corsica
. Past use
. Current use
XI. Water and human health
XII. Climate change
 
Bibliographic references



INTRODUCTION
 
Freshwater, the future of humanity
 
Water is the predominant element on the planet Earth; oceans cover 70 % of the world's surface. But freshwater accounts for only 2.5 % of all water. Almost 70 % of freshwater is stored in ice, so the available freshwater is less than 1 % of the Earth's water.
 
Water is LIFE
The age of the Earth is estimated at 4.55 billion years. The appearance of life on our planet dates back 3.85 billion years. The first land animals appeared 440 million years ago (“Out of the water”). Life in water alone has therefore lasted 3.41 billion years.
 
But water is also DEATH
Today, 2.5 to 3 billion people do not have access to safe drinking water. The consumption of poor quality water leads to the deaths of one million people per year, including 360,000 children under the age of five. There are several causes, including the presence of biological agents such as bacteria, viruses or parasites, along with both natural and man-made chemical elements such as arsenic, antimony, nitrates, pesticides, etc.
 
The relationship between man and water is complex, due to the economic, ecological, cultural and spiritual relationships that exist with water. In the most ancient civilisations, water is seen as a sacred source of life. Water holds an important place in both mythology and religion. Its combined powers of life and death make it a metaphysical element.
 
Great flourishing civilisations have developed in the valleys of great rivers. Most of the great ancient civilisations are described as “water civilisations”. Their levels of development were directly linked to their degree of control of water management. Conversely, the weakening of this social mastery of water automatically led to their decline and disappearance.
 
Religions and water
In the Judeo-Christian tradition, water occupies a significant place in the Book of Genesis in the Bible: “darkness was upon the face of the deep; and the spirit of God moved over the waters”. God organised the universe out of water: “let the waters under heaven be gathered together unto one place and let the dry land appear”. The first baptisms were performed in nature – in springs and rivers. This was followed by the building of specific baptismal fonts. The word “font” comes from the Latin “fons”, which means both along with the source of the water and the god who lives there.
 
For the Hebrews, cleanliness was a moral obligation: “Cleanliness is next to godliness”. Before entering a sacred place, rabbis wash their hands and feet. Ritual baths are used for washing and purification before religious events.
 
The origins of Christian baptism have parallels in Egypt, Greece and the ancient East, including India with the bathing in the river Ganges.
 
References to water are also prominent in the Qur'an: “We made from water every living thing”. In the Qur'an, water, along with the sky and the earth, is an essential element that testifies to the existence of the Prophet. The Islamic custom of performing ablutions before entering the mosque originally came from a concern for hygiene and it gradually evolved into a prayer to Allah. In the heart of Mecca is the Zamzam spring. According to Islamic legend, Ishmael, the son of Abraham, and Hagar, his mother, while fleeing in the desert, were making a plea for water when a spring suddenly appeared. Since then, part of the pilgrimage to Mecca is to pay homage to the Zamzam spring, whose waters are drunk.
 
 
Water, the great challenge of the 21st century
Water is an essential factor for development, particularly in islands of the Mediterranean. Water, which used to be part of the natural heritage, has become an economic element, a commodity and a source of conflict. The various antagonistic interests are social (rich / poor), economic (domestic / industrial / agricultural) and political (international conflicts).
 
An increase in greenhouse gas emissions has led to a rise in both global temperatures and sea levels. The effects of climate change must be factored into the management of water resources.
 
Extreme climatic events, such as droughts and floods, highlight the acute vulnerability of the aquatic ecosystem.
 
Human health is threatened by emerging or re-emerging infectious and vector-borne diseases, such as malaria, chikungunya, dengue, zika, and so on.
 
The consequences of climate change will have an impact on the energy sector. The low filling rate of hydroelectric dams will compromise the energy mix, leading to an increase in the share represented by thermal energy, in particularly the use of oil and coal.
 
The scarcity of water resources will lead to an increase in prices of domestic and agricultural water and consequently an increase food prices. Social inequalities will arise linked to the distribution and pricing of water.
 
In the long term, the current system for governing of water resources will be called into question. Changes in behaviour and lifestyles as well as upheavals in the agricultural sector will become inevitable.
 
 
Water in Corsica
On the island, the main users of water resources are the human population, including tourists, and farmers, particularly with irrigated agriculture. As the region is not highly industrialised, the other main activities related to aquatic environments are large-scale hydroelectricity (from which produces 25 % Corsica’s energy needs).
 
In 2019, the surface water bodies with a good or very good ecological status have an exceptional rate of 88 % (50 % for the other French basins). However, the quantitative status of some groundwater bodies on the island's eastern coast is deteriorating. The overexploitation of resources in summer and the consequences of climate change go to explaining this degradation. Nevertheless, 98 % of surface water bodies and 100 % of groundwater bodies are in good chemical condition.
 
 
In this book, the typology chosen for freshwater is as follows: firstly groundwater, and secondly surface water. 
 
These are classified as:
1. In permanent environments: these are flowing waters (rivers) and stagnant waters, natural lakes (such as mountain lakes), and artificial lakes (such as reservoirs and dams).
2. In temporary environments: these are temporary watercourses and temporary Mediterranean pools.
 
The presentation of running water (rivers) and stagnant water (lakes and reservoirs) ecosystems begins with an overview of these hydrosystems on a global, European and national scale.
 
 
 
 

Antoine ORSINI, Hydrobiologist.
Senior Lecturer at the University of Corsica.
Director of the Hydrobiology Laboratory UMR-CNRS 6134 SPE.
Board member of the RM&C Water Agency.
Former board member of the Corsican Environment Office.
President of the Scientific and Environmental Committee of the Project for the Development of the new infrastructures for the port of Bastia.
Member of the Corsica Basin Committee.
Member of the Regional Scientific Council of the Natural Heritage of Corsica.
Member of the Scientific Council of the Regional Natural Park of Corsica.
Former President of the Scientific Councils of (1) the Corsican Regional Nature Park, (2) the Scandola Nature Reserve, (3) the UNESCO MAB Fango Nature Reserve.
 
President of the Central Corsica Community of Communes. 

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I. The geographic and topographical situation of Corsica 
 
The Mediterranean is an inland sea that communicates with the Atlantic Ocean through the Straits of Gibraltar. The Italian peninsula and Sicily divide the Mediterranean into two basins of differing size. The larger, eastern basin extends to the Middle East; the western basin is smaller. In the latter, Corsica and Sardinia occupy a meridian position bordering the Tyrrhenian Sea.
Corsica lies at a latitude of between 41° and 43° north. Stretching in a north-south direction, it is about 160 km from Provence, as is at a distance of 82 km from Tuscany and only 12 km from Sardinia. With almost 1,000 km of coastline, 183 km in length and 84.5 km at its widest point, it has a surface area of 8,748 km². Corsica is the most mountainous island in the Mediterranean, although it does not have the highest peak, Monte Cintu (2,707 m), is surpassed by Mount Etna, which rises to 3,323 m in Sicily. But in Corsica, half of the territory has an altitude of over 400 metres and the island has almost 120 peaks over 2,000 metres.
 
 
Corsica photographed by Thomas Pesquet on 6 July 2021 during the Alpha space mission, with the following comment: “Corsica in majesty. It's always surprising to realise that it's closer to Italy than to France – looking at weather maps or geography books where it's closer to the mainland, I grew up thinking it was 200m off Nice, and I was surprised to find that it has a close sister, Sardinia, a stone's throw to the south. This photo is a perfect example of what astronauts like to photograph from space: landscapes that are recognisable at a glance, an almost perfect vertical, and the reflection of the sun on the sea.
 
Note that the white spots on the centre of the island are not snow but clouds.  However, they cling remarkably well to the highest relief.

 


 



 

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II. The climatology of Corsica
 
Corsica and Sardinia are located on the path of air masses coming from the Atlantic on the one hand and the Sahara on the other. With its 120 peaks above 2,000 metres, Corsica is more mountainous than Sardinia. Altitude plays an important role in rainfall, as rainfall in Corsica is largely orographic. The summits form a screen to the clouds causing condensation on the relief.
The altitude, the general direction of the main ridge line and the influence of the sea are the main factors that determine the climatic originality of Corsica.
 
Rainfall patterns:
 
Precipitation is characterised by variability in space and time.
Spatially speaking, altitude has a strong influence on the rainfall regime, with average annual water levels rising from 700 mm at sea level to 1,300 mm above 1,400 m.
 
Rainfall patterns in Corsica
 
 
In terms of time, the amount of annual rainfall varies greatly from one year to another, with autumn and winter being the wettest seasons.
 
Drought is a complex phenomenon that results from the combined effects of several factors, including rainfall patterns, soil type and the particular stage of plant development. The quantity of water supply from precipitation is the determining factor. The intensity of the phenomenon depends on other meteorological factors such as temperature, duration of insolation and wind.
 
The impact of climate change on cumulative annual rainfall is not clearly established. Nevertheless, the intensity of extreme rainfall in the Mediterranean region is increasing.
 
Snow:
 
Corsica is the most mountainous island in the Mediterranean, with nearly 120 peaks over 2,000 metres, and has a considerable snow cover in winter.
From the coast to 300 m in altitude, snow is rare and exceptional. From 300 to 600 m (600 to 900 m on the south side), snow normally falls every winter, the layer frequently reaches 20 to 30 cm in depth, with periods of total melting following snowy episodes. From 1,100 m to 1,500 m altitude (1,400 to 1,800 m on the south side) snow cover is more continuous, with falls occurring from October to April and depth sometimes exceeding 2 metres. Above 1,500 m (1,800 m on the south face) the increase in snow cover is progressive, average depth is 2 metres with a maximum of 6 metres. At these altitudes, the action of the wind is preponderant and favours the formation of drifts, areas of high accumulation and cornices; melting is very slow and it is not rare to encounter large patches of snow on north-facing slopes until the end of July.
Snow cover plays an important role in the hydrological system by reducing the amplitude of low water in certain Corsican rivers. However, since the 1990s, the regime of rivers has been much less influenced by snow, as snow cover is falling in surface area and depth, due to global warming.
 
Thermal regimes:
 
Due to its geographic situation, and depending on the season, Corsica falls under the influence of tropical, oceanic or continental air masses. The relief and the maritime influence play, once again, an important role: the relief accentuates the temperature differences whereas the sea moderates them.
The average annual temperature ranges from 15.3°C in the lowlands to 8.5°C in the mountains.
In addition to the relief, the sea breeze plays an important role in the average annual maximum temperatures. In fact, the sea breeze “relativises the maximum temperatures by adding humidity and limits a good part of the coastal fringe to average maximum values of almost 20°C” (Bruno et al., 2001).
 
 
Thermal regimes in Corsica
 
Wind:
 
Given its insularity, Corsica is particularly sensitive to the wind regimes that blow over this part of the Mediterranean basin, both for the main currents and for the local breezes.
In winter (westerly circulation), the temperate air masses coming in from the Atlantic Ocean are filled with moisture as they cross the Mediterranean; the flow is therefore cool and humid (e.g., the mistral).
In summer (south-easterly circulation), subtropical air masses from the Sahara generate a hot, dry flow (e.g., the sciroccu).
The influence of the relief on the winds is reflected in orographic effects. The acceleration of the wind due to the Venturi effect has two sources: vertical constriction (between the summits and the lower limit of the tropopause), and horizontal constriction (in the valleys, between the main relief).
Secondary relief and composition effects with breeze phenomena disturb the wind flow causing turbulence and deviations.
 
The map of local winds observed in Corsica shows seven different winds:
 
 U grecale, north-easterly, is a strong Tyrrhenian wind. It is frequent in autumn and spring and very much linked to storms in the Mediterranean. It brings a lot of rain to the eastern side of Corsica.
 U levante is an easterly wind; when it is very strong, it often crosses the line of the Corsican summits and reaches the western coasts.
 U libecciu is the great Corsican wind; its effects are felt throughout the island but to varying degrees. From a south-westerly direction in the south of Corsica, it becomes a westerly wind in Balagne and on the western side of Cap Corse due to the orientation of the relief. In summer, it is generally dry, whereas in winter it becomes wet and brings rain mainly to the western slopes.
 U maestrale, from the northwest, is a sudden, violent wind, dry in summer and wetter in winter.
 U punente is the east wind; it often mixes with libecciu.
 U sciroccu is a warm and humid southerly wind; it is often accompanied by red dust from the Sahara, fog and coastal mist.
 A tramuntana is the great north wind, violent, dry and cold; it blows in long gusts in winter and purifies the air.
 
 
The climates of Corsica
 
The significant variations in temperature and precipitation, moving from the coast to the island's peaks, mean that it is possible to distinguish separate climate systems. Simi (1964) proposes to three:
 
 From 0 to 600 m, a mild and humid Mediterranean climate with average annual temperatures varying from 14 to 17°C, abundant but irregular rainfall, a long dry season in summer.
 From 600 to 1,200 m, a high Mediterranean climate with average annual temperatures varying from 10 to 13 °C, abundant rainfall and a less marked dry season.
 Above 1,200 m, an alpine climate with harsh winters, characterised by temperature contrasts and very heavy precipitation, particularly in the form of snow.
 
Gamisans (1991) speaks of a high-altitude Mediterranean climate because the alpine tone proposed by Simi (1964) is in fact based solely on thermal criteria (harsh winters); precipitation does not have an alpine tone but still has a Mediterranean tone, even if it is attenuated.
 

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III. Geology: Corsica, two mountains in the sea
 
Corsica is remarkable for the diversity and complexity of its geological aspect. Although detailed surveys and structural interpretations are still open to discussion, the main geological formations are now well known.
 
Geologically and historically, Corsica corresponds to two mountains in the sea (Gauthier, 1998). A high western mountain, made up of granite and rhyolite, and a lower eastern mountain made up of schist. The former includes Corsica in a sweep from the Calvados region in north-western France to the extreme south, culminating at Monte Cintu at 2,707 m, and with 120 peaks exceeding 2,000 m. The second is part of the formation of Cap Corse and Castagniccia. It is separated from the first by the central furrow, a depressed area of lower altitude. A cross-section of Corsica, from the west coast (Galéria) to the east coast (Moriani), via Monte Cintu and San Pedrone, is a good illustration of the expression “two mountains in the sea”.
 
 
 
Schematic cross-section of Corsica (West — East)
 
 
The simplified geological map shows four main units separated from each other by major tectonic faults:
 The oldest (primary era) and most extensive covers the south-western part, roughly two thirds, of the island; it is “Hercynian ” or “ancient” Corsica, essentially made up of plutonic rocks (granite, diorite, gabbro) and a rhyolitic volcanic complex in the Cintu and Osani massifs.
 The north-eastern third of the island is called “Alpine Corsica” on account of the tertiary age of the layer of lustrous schists that it is made up of. Ophiolites and a very diverse range of metamorphic rocks are found here: sericite schist, prasinite (green schist), cipolin, quartzite, serpentinite, gneiss, etc.
 The central depression or Corti zone marks the contact between the two previous groups. This zone presents very diverse facies, broken up by numerous deep tectonic faults creating scale-like structures.
 A final unit is formed by the tertiary and quaternary sedimentary terrain of the eastern plains and the calcareous-sandstone basins of Saint Florent and Bonifacio.
 
 
 
Simplified geological map of Corsica

 
 

Page 42/43
 
IV. Surface water
. Permanent environments
Running water: rivers and streams
 
In the World
 
The Amazon is the longest river in the world at 6,992 km and flows through Peru, Ecuador and Brazil.
The Nile, previously considered as the longest, comes in second place with a length of 6,852 km. Its huge watershed extends over 12 African countries: Burundi, Tanzania, Rwanda, Kenya, Congo, Uganda, Central African Republic, South Sudan, Ethiopia, Sudan, Eritrea and Egypt.
The Yangtze River in China and the Mississippi River in the United States follow with 6,380 and 6,275 km respectively.
 
In continental France ... and in Europe
 
The longest river in France is the Loire with 1,012 km. The Seine comes second with a length of 776 km. 
 
The Rhine flows for 1,320 km through Switzerland, Liechtenstein, Austria, Germany, France, and the Netherlands.
 
The Meuse is 950 km long and flows through France, Belgium and the Netherlands.
The Rhône (812 km) runs through Switzerland and France.
 
In Corsica
 
The island's hydrographic network comprises 3,000 linear kilometres of waterways. The longest are the Golu and the Tavignanu with 89 and 88 km respectively.
 
 
The main rivers of Corsica
 
 
Strahler Stream Order
 
A stream ordering system is a method for ranking portions of streams according to their position in the river system by assigning them a numerical code, based on a hierarchy of tributaries. The most common, and the easiest to use, is the Strahler stream Order (1957), which consists of assigning rank 1 to the rivers at the head of the basin, and then, progressing downstream, each river which receives a river of the same rank has its own rank increased by one unit.
 
 
Strahler Stream Order
 
In the Strahler stream order, rank 1 corresponds to spring outfalls. Ranks 2 and 3 are for very small and small streams respectively. Medium-sized streams are ranked 4 and large streams are ranked 5. Above rank 5, they are called very large rivers.
 
The application of the Strahler system to Corsican rivers shows that rank 5, for the Golu and the Tavignanu, is the highest rating given. In continental France, rank 8 is obtained for the Loire and the Rhône. On a global level, the Amazon and the Nile are rivers of 12 and 11 respectively.
 
The typology of Corsican watercourses
 
Six main types of watercourse can be distinguished in Corsica:
 
The Golu and the Tavignanu are the largest rivers on the island both in terms of length (89 and 88 km) and the surface area of their catchment areas (1,036 and 693 km²). These two rivers originate on the eastern slopes of hercynian Corsica; the altitude of the highest point of each catchment area is very high (2622 and 2707 m). These rivers then flow through the central depression, the shale and green rocks of alpine Corsica and finally through the eastern plain before flowing into the Tyrrhenian Sea. The average gradient is about 2 %; the low gradient of the lower course (0.3 to 0.4 %) reflects the presence of an alluvial plain on the sedimentary terrain of the eastern plain.
 
The Travu, Sulenzara, Osu and Cavu rivers originate on the eastern slopes of hercynian Corsica; the altitude of the highest point of the catchment area (50 to 128 km²) is high (1,377 to 2,134 m), and lengths of the rivers ranges from 22 to 32 km. The average slope is between 4.3 and 6.3 %, the dominant substratum is granite.
 
The Taravu, Rizzanese, Gravona, Prunelli and Liamone are the major rivers (41 to 65 km long and 276 to 482 km² in catchment area) of the western slopes of hercynian Corsica. The average slope varies from 2.2 to 4.4 %; the altitude of the highest point of the catchment area, where granites dominate, is high (2,041 m to 2,352 m).
 
The small rivers of the western slope of hercynian Corsica have lengths of between 19 and 32 km, the catchment area is between 130 and 150 km².
The Alisu, Ortolo, Ostriconi and Reginu rivers have the following characteristics: altitude of the highest point (1,314 to 1,680 m), average slope (3.1 to 5.6 %), slope of the lower course (0.3 to 0.8 %).
The Fangu, Figarella and Portu rivers are characterised by (i) a high altitude of the highest point of the catchment area (2,108 to 2,547 m), (ii) a high average slope (6.3 to 9.1 %), (iii) a very high headwater slope (10.4 to 25.3 %) and (iv) the presence of rhyolite in the catchment area.
 
The Alisgiani, Bevincu, Bravone and Fium'Altu are the biggest rivers of alpine Corsica. The main characteristics are: length (24 to 37 km), surface area of the catchment area (54 to 180 km²), altitude of the highest point (1,469 to 1,767 m), average gradient (4.1 to 5.2 %).
The Luri is a small river on Cap Corse, which is 11 km long, and characterised by a high upper slope.
 
Flow variations: the hydrological regime
 
The rivers of Corsica have a pluvio-nival-Mediterranean hydrological regime. This regime is influenced by rain and snow and has a severe summer low water level, characteristic of Mediterranean rivers.
 
The pluvio-nival-Mediterranean regime has two periods of low water and two periods of high water. The winter low water period, which is not very marked, corresponds to the storage of water in the form of snow; the summer low water period, which is more severe, coincides with the minimum rainfall.
 
The periods of high water correspond in spring to the melting of the snow and in autumn to heavy rainfall. This hydrological regime is marked by considerable and very sudden variations in flow, leading to sudden and violent floods.
 
 
 
Average daily flows (m3/s) of the Tavignanu in 2002
 
For flooding of the rivers in Corsica, the maximums known by the HYDRO database are presented in a later table.
The maximum instantaneous flow exceeds 800 m3/s for the Golu, Tavignanu, Solenzara, Liamone and Fium Altu.
The record is held by the Sulenzara (at Sari-Sulenzara) with 1,580 m3/s on 31 October 1993 at 23:59. In the classification of Corsican rivers, the Sulenzara is not one of the major rivers, in fact, it is in 21st position for length, 18th for catchment area surface and 11th for average annual flow. The magnitude of this flood was due to the high intensity of precipitation localised in a particular catchment area.
 
Floods, maximums known by the HYDRO database
(Ministry of Ecology, Sustainable Development and Energy)
 
However, according to a document entitled: “L'Evaluation Préliminaire des Risques d'Inondation 2011, Bassin corse” (Ministry of Ecology, Sustainable Development, Transport and Housing), the Corsican record is held by the Tavignanu. In October 1976, the Tavignanu (at Caterraggiu) had an instantaneous flow of 3,500 m3/s. For the record, the average flow of the Seine is 480 m³/s, that of the Loire 900 m3/s and that of the Rhône 1,700 m3/s.
 
The maximum instantaneous height during flood periods (recorded by the HYDRO database) exceeds 8 metres in the Golu, Tavignanu, Sulenzara, Fium'Orbu and Fangu. The record is held by the Fangu (at Galéria) with 10 metres, on 21 October 1992 at 08:28. In the ranking of Corsican rivers, the Fangu is in 17th position for the length and 12th average annual flow.
 
But the record is held by the largest river in Corsica, the Golu. In September 1938, water levels reached 12.50 m at Barchetta (EPRI, 2011).
 
During the 20th century, floods caused many victims and significant damage. In September 1974, 8 people were swept away by the Tavignanu at Baliri in Corti.
 
The major disaster on All Saints’ Day 1993 will be stay in people’s memories for a long time. Between 31 October and 2 November, the Sulenzara, Travu and Rizzanesi rivers bursting their banks caused 7 victims and significant damage (160 communes affected) estimated at a cost of some €420 million.
 
 
Longitudinal and cross-sectional profile (riverbed and floodplain)
 
The considerable and very abrupt variations in flow, leading to sudden and violent floods, come from the high gradient of the watercourses, resulting in a very short reaction time, particularly during autumn rains.
 
 
 
Longitudinal profile of some Corsican rivers
 
 
The bed of a river is the space covered by the water flowing in normal times before overflow; the floodplain corresponds to the flood expansion zone.
The floodplain is a buffer space that allows natural flood control and the slowing down of the speed of floods.
 
 
 
 
 
Cross-section of the Tavignanu downstream from Corti
 
 
 
 
The riverbed and floodplain of the Tavignanu downstream from Corti
 
 
The floodplain in flood (Tavignanu downstream from Corti)
 
 
 
 
 
Flow impacted by hydroelectric schemes
 
The hydrological regime of a river can be affected by the operation of a hydroelectric structure (dam). The impact is reflected in a significant reduction in flow in the instream flow section (short-circuited section downstream of the dam). But it is more marked in the part of the river subject to hydropeaking (downstream of the hydroelectric plant). Hydropeaks are daily variations in the flow, linked to the operation of the hydroelectric plant. This is referred to as a regulated flow.
 
 
 
Hydrograph of the Golu and Tavignanu rivers, from 9 to 13 January 2017.
 
The lower course of the Golu (downstream of Castirla) has a regulated hydraulic regime subject to locks, in relation to the operation of the Calacuccia-Corscia hydroelectric complex. This hydroelectric development has several units, in order from upstream to downstream: (i) the Sovenzia power station fed by the inflow from the Tavignanu, diverted through an intake located at 1084 NGF (French National Level reference) and with a capacity of 6 m3/s; (ii) the Calacuccia dam and its reservoir; (iii) the Corscia plant fed by the water from the Calacuccia reservoir; (iv) the Corscia dam and its reservoir and (v) the Castirla plant fed by the water from the Corscia reservoir.
 
Hydropeaks are artificial, sudden and frequent variations in flow rates, linked to the use of water from dams for hydroelectricity production. The Golu hydrograph shows variations between 4 and 11 m3/s, i.e. an increase of 275 %. At the same time, the natural flow of the Tavignanu oscillates between 6 and 7 m3/s.
 
In the Golu, changes in the hydrodynamic characteristics of the flow (water level, current speed) lead to changes in the habitat of aquatic organisms: fish, invertebrates, algae (see elsewhere).
 
In addition to the ecological impact, there is a potential risk to those who use the waterways (for fishing or swimming, for example) and who may be unaware of a potential water release.
Every summer, the EDF (the French national electricity company) carries out a communication campaign to warn the general public of risks associated with dam releases by recruiting hydroguides to raise public awareness.
 
 
Flow influenced by snowmelt
 
 
Hydrograph of the Restonica, at Corti, from 18 to 22 April 2018.
 
 
The Restonica, a major tributary of the Tavignanu, has its source at Lake Melu at an altitude of 1,711 metres. The highest point of its watershed is Monte Ritondu (2,622 m). The upper Restonica valley is covered by snow for a good part of the winter.
The hydrograph (graph representing the variations of flow in relation to time) of the Restonica, at the Rivisecu bridge, in Corti from 18 to 22 April 2018 shows daily cyclical variations of the flow. They are characterised by peaks between 17:00 and 18:00. These oscillations are between 5 and 6 m3/s, the amplitude of the intraday variation in flow is 20 %.
These cyclical variations reflect the daily periodicity of the liquid inflow in relation to the snow melting. The flow therefore varies in significant proportions between the sunniest hours of the day and the coldest hours of the night.
 
 
Solid transportation or sediment transit
 
Rivers, especially during floods, transport large quantities of sediment. There are two forms of transportation: bed load and suspension. 
Bed load takes place on the bottom of the riverbed and concerns hard substrates such as blocks, stones or pebbles which are coarse granulometric elements.
Suspension is the transport of loose substrates such as sand, silts, silt or clay, in other words fine granulometric elements.
 
For the rivers of Corsica we have estimated the level of solid transportation to be between 200 and 400 tonnes per km² per year.
For the Golu, with a catchment area of around 1,000 km², annual solid transportation is somewhere between 200,000 and 400,000 tonnes per year. During exceptional floods, values can exceed 1 million tonnes.
 
Under certain conditions (e.g. with very steep slopes between 30 and 40 %, and following fires), water runoff leads to significant quantities of ash. When the density of the mixture of water and matter is close to 2, the transported elements almost float. This is the phenomenon of hyper-concentrated bed load or debris flow.
In this type of situation, damage to both people and property can be significant. This has been the case in Corsica on a number of occasions: (i) August 1943, Ocana, 5 dead; (ii) November 1994, Canavaggia (4 houses washed away), damage in Santa Lucia di Mercuriu and Lentu; (iii) November 2000, damage in Restonica after the great fire.
 
In terms of the matter transported by rivers, sand with a diameter varying from 50 µm to 2 mm (fine to coarse sand), is at the origin of the beaches in the coastal areas.
 
The salinity of the sea and oceans is caused by dissolved salts transported by rivers. While the concentration of salts in freshwater is low (0.02 to 0.04 g/l), in the sea, evaporation of the water leads to a concentration (by a factor of 1,000) of these salts and therefore to an increase in salinity (Mediterranean: 38 g/l).
 
In the solid transportation or sediment transit discussed above, natural elements have been taken into account. Unfortunately, it is nowadays necessary to add anthropogenic elements, and particularly plastic waste.
This inorganic particulate waste is the source of chemical contaminants in water and in the food chain in the aquatic environment. Among these contaminants are PCBs (Polychlorinated biphenyls), PAHs (Polycyclic aromatic hydrocarbons), organochlorine pesticides, PBDEs (Polybrominated diphenyl ethers), Bisphenol A, Alkylphenols...
 
In rivers, plastic waste is visible in the form of macroplastics (bottles, etc.). Given that act a massive crushing machines, they not only break up stones But rivers, which are real crushing machines, not only break up stones, turning them into sand, but also macroplastics, fragmenting them into microplastics.
This plastic waste pollution has an impact on aquatic fauna. Invertebrates and fish ingest these microplastics and chemical contaminants, which are released in their digestive tract. These toxic substances concentrate in the organs including the muscles (fillets) of fish that is later consumer by humans.
If these microplastics remain in the intestines of the fish, without breaking the muscle tissue, they break down into nanoplastics and pass the intestinal barrier. They are therefore present in the fish we eat.
 
It should be remembered that the lifetime of plastic waste in the natural environment varies, depending on the type, from between 100 to over 1,000 years.
 
We are all aware today of plastic waste pollution affecting rivers, seas and oceans. Even though the pollution may be at sea, the solutions can be found on land. Saving water and aquatic ecosystems is also a question of protecting human health. We need to show solidarity with people living in the lower reaches of rivers and on the coasts.

 
Stagnant water: lakes
Natural lakes: mountain lakes
 
In the World
The largest lake is the Caspian Sea, wrongly named by geographers. Its volume is 78,000 km3 (1 km3 = 1 billion m3), its surface area is 374,000 km2, i.e. 2/3 of France. The salinity of the water is 12.5 g/l. As a reminder, the Mediterranean Sea has a salinity of 38 g/l. The maximum depth of the lake is 1,025 m. The shores of the Caspian Sea are shared by Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan,
 
The deepest lakes are Baikal and Tanganyika.
Lake Baikal is located in Siberia, Russia, with a maximum depth of 1,740 m and a volume of 23,000 km3. With a surface area of 31,500 km2, it is 3.5 times the size of Corsica. Salinity is 0.1 g/l.
Lake Tanganyika in Africa has a maximum depth of 1,471 m and a surface area of 32,900 km2. Salinity is 0.4 g/l. The lake forms a natural border between four countries: Burundi, Tanzania, Zambia and the Democratic Republic of Congo.
 
 
In Europe
Lake Geneva is the largest lake in Western Europe with a surface area of 580 km2 and a maximum depth of 310 m. It is located between France and Switzerland, where it is called Lac Léman.
Lakes Constance (Germany) and Maggiore (Italy) have surface areas of 538 km2 and 213 kmrespectively; their maximum depths are 252 m and 370 m respectively.
 
 
In mainland France
The Lac d’Hourtin et Carcans (which straddles two communes, hence the name) has a surface area of 57 km2but is shallow (maximum 10 m). With a surface area of 45 km2, the Lac du Bourget is a little smaller, but its maximum depth is 147 m.
 
 
In Corsica
 
In the Corsican mountains there are about forty permanent bodies of water, but only 15 lakes have a maximum depth of more than 3 metres and a surface area of more than 0.5 hectares.
 
These mountain lakes are glacial. About 14,000 years ago, they were formed either by glacial erosion (Melu, Capitellu) or by the accumulation of moraines (Bastani).
 
Glaciers have often left traces such as striations (grooves) and gouges.
 
The deepest are Capitellu (44 m), Bellebone (or Ritondu, or Betaniella) (35 m) and Bastani (24 m). The largest are Bellebone (or Ritondu, or Betaniella) (7.4 ha), Ninu (6.5 ha), Melu (6.2 ha) and Capitellu (5.5 ha).
 
The water balance classifies these lakes as fluvial, i.e. inflows and outflows are mainly through tributaries and surface outfalls.
 
These lakes spend the winter under the ice, resulting in a slowdown of biological activity.
 
With two mixes a year (spring and autumn) these mountain lakes are dimictic; the stratification phase (thermal and chemical) takes place in summer.
 
 
Thermal stratification of mountain lakes
 
 
 
 
 
Alpine chough at Lake Melu
 
This image shows the bathymetry of the lake. Bathymetry (from the ancient Greek “bathys” meaning “deep”) is the science that deals with the relief and depth of lakes and oceans.
 
The alpine chough (a tacula) is a paleo-montane species, belonging to the crow family which lives in mountain ranges in Europe (Pyrenees, Alps, Corsica, Caucasus) and also Asia and North Africa. In the Alps it can be found at the summit of Mont Blanc (4,809 metres). It is a protected species throughout France. 
It is listed in Appendix II of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention). It is considered “in decline” by the Birds Directive Assessment (2013).
 
The vegetation of the catchment area depends on the altitude. The Corsican pine (pinus nigra corsicana) is present around the lakes below 1,700 m (Crenu); between 1,700 and 2,100 m altitude the Corsican sweet alder (alnus alnobetula suavolens) the dominant species of the shrub layer (Melu); above 2,100 m vegetation is rare and represented by a small number of thorny plants (Maggiore, Cintu).
 
These lakes sometimes have an original formation called a pozzines. These are hygrophilous and meso-hygrophilous grasslands located on substrates resulting from the complete or near-complete natural filling of glacial lakes. They are essentially formed by the subterranean organs of grasses, cyperaceae and dwarf juncaceae with sphagnum moss. Stream that meander through pozzines have a gentle slope, their substrate is sandy and gravelly, and the water flows without turbulence. This provides ideal conditions for trout spawning grounds. This hydrosystem plays an essential role in the reproduction of the endemic trout Salmo trutta macrostigma (species of community importance, European Habitats Directive 92/43EEC). The headwaters often constitute a nursery, on which a large part of the trout populations of many rivers depend.
 
The aquatic plantlife is mainly represented by microscopic algae and mosses. Macrophytes are rare, swimming pondweed is present in Ninu and Gialicatapiani lakes. The white waterlily is only present in Lake Crenu.
 
Aquatic invertebrates are dominated by insects, oligochaetes and crustacea. Vertebrates are represented by trout, brook salmon, Corsican mountain newts, salamanders and painted frogs. This fauna is characterised by a high level of endemism.
 
Typology of mountain lakes in Corsica
 
 
Typology of mountain lakes in Corsica
 
The typology proposed takes the following abiotic parameters into account: Altitude (m), Lake area (ha), Perimeter (m), Maximum depth (m), Distance from the sea (km), Distance from the Vaziu power plant (km), Watershed area (ha), Exposure to the Barrier, Duration of frost (months), Source of watercourse.
 
The projection of the lake points shows 3 groups of lakes:
Group 1: Bellebone (or Ritondu or Betaniella), Capitellu, Goria, Bastani, Ninu, Melu
This group includes large (lake area between 4.38 and 7.40 ha), deep (maximum depth between 7 and 42 m), east-facing lakes in relation to the barrier.
Group 2: Bracca, Crenu, Vitalaca
This group includes small lakes (lake area between 0.62 and 2.30 ha), shallow (maximum depth between 3.5 and 6.5 m), exposed to the west in relation to the barrier.
Group 3: Niellucciu, Oru, Gialicatapianu, Oriente, Cavacciole, Maggiore.
This group includes small lakes (lake area between 0.30 and 1.15 ha), shallow (maximum depth between 1.5 and 15.0 m), exposed to the east in relation to the barrier.
 
Exposure to the barrier may play an important role, particularly in considering the potential impact of particulate matter from the Vaziu power plant.
 
Groups 1a and 2a include the Ninu, Melu and Vitalaca lakes, which are the source of major rivers, the Tavignanu, Restonica and Prunelli respectively. These lakes are therefore an important challenge in the quantitative and qualitative management of these rivers.

 
Artificial lakes: dam reservoirs
 
In the World
 
Dams are built to store large quantities of water. The oldest dates back to 2600 BC, the Sadd-el-Kafara Dam, built in the Garawi Valley in Egypt. The dam was 14 metres high and 110 metres long, with a volume of 500,000 m3. The remains of this dam, now no longer in use, show a thickness of 98 metres at the base of the structure.
 
The oldest dam still in operation dates from 1594, the Tibi Dam in Alicante, Spain, has a height of 46 metres, a length of 65 metres and a base thickness of 30 metres.
 
The highest structure, 335 metres, is the Roghun Dam in Tajikistan. The dam is 70 km long and can store 11,600 million m3.
 
The highest in Europe (285 metres) is the Grande Dixence Dam in Switzerland. The dam’s volume is 400 million m3.
 
 
In mainland France
 
The highest in France (180 m) is the Chevril (or Tignes) Dam in Savoie. This structure can store 235 million m3. The downstream face of the dam has the largest fresco in the world (18,000 m2); it is the work of Pierret (1989) and represents Hercules.
 
 
In Corsica
 
Corsica has 48 dams, 12 of which are class A dams, with a height of over 50 m.
 
The Tolla, Calacuccia, Corscia, Sampolo, Trevadine and Rizzanèse dams are managed by EDF (Electricité De France), mainly for hydroelectricity production.
 
The dams of Teppe Rosse, Alzitone, Bacciana, Guazza, Peri, Alesani, Padula, Codule, Figari, Ortolo and Ospedale are managed by the OEHC (Office d'Equipement Hydraulique de la Corse) for irrigation and drinking water supplies.
 
Teppe Rosse, Alzitone, Bacciana, Guazza, Peri and Padula are hill reservoirs, i.e. artificial reserves, often located outside the hydrographic network, closed by a dam and fed either during the rainy period by run-off or by a permanent or temporary watercourse. This type of structure has no downstream release of water (no instream flow).
 
 
 
Dams and reservoirs managed by EDF (Electricité De France)
 
Dams and reservoirs managed by the OEHC (Office d'Equipement Hydraulique de la Corse)

 
. Temporary environments; Mediterranean temporary pools
 
Temporary pools are hydrosystems found in almost all regions of the world. They are characterised by a dry period of variable duration that affects these bodies of water cyclically. This type of temporary habitat is particularly common in the circum-Mediterranean area.
The plant groups are dominated by species of the genus Isoetes.
The dynamic evolution of the temporary pools consists of three successive phases: the filling, intermediate and drying phases.
Each phase corresponds to a characteristic aquatic population. The filling phase reveals the importance of Crustacea, the invertebrate fauna is dominated by Anostraca Tanymastix stagnalis and Chirocephalus sp. as well as Cladocera of the genus Daphnia.
The intermediate phase is characterised by the proliferation of Chironomidae Diptera larvae. Cladocera crustaceans play an important role in the aquatic population. This phase is marked by the appearance of Gyrinidae, Haliplidae and Dytiscidae Coleoptera. As well as the Heteroptera Notonectidae and Corixidae. The Odonata Lestidae and Libellulidae are less important at this stage.
The drying phase is characterised by the dominance of predatory invertebrates: Diptera Tanypodinae; Odonata Lestidae, Aeschnidae and Libellulidae; Coleoptera Dyticidae; Heteroptera Notonectidae and Corixidae.
Coring of the sediment during the de-watered phase shows the presence of resistant forms, in particular the megaspores of a Pteridophyte of the genus Isoetes, as well as encysted forms of the crustacean Tanymastix stagnalis.
The Corsican Environment Office, in partnership with the Corsican Regional Environment Directorate and the Rhône Méditerranée & Corse Water Agency, has launched an Action Programme for the Conservation of the island's Temporary Pools, designed to ensure the preservation of this original and fragile ecosystem, listed as a priority habitat under the Habitats Directive. 
This action programme will enable us to study the dynamic evolution of these environments and develop knowledge in the managing these environments and in the field of the conservation biology of the rare animal and plant species they host.
  
Padulellu temporary pool (Porti Vecchiu)
 
Isoetes megaspores
Tanymastix stagnalis cysts
 
 

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V. Groundwater: spring water, mineral water and thermo-mineral water
 
The geological nature of Corsica does not favour the existence of significant groundwater. The plutonic rocks (granite, diorite, gabbro, etc.) and volcanic rocks (rhyolite, etc.) of hercynian Corsica, as well as metamorphic rocks (schist, cipolin, gneiss, etc.) and magmatic rocks (serpentinite, etc.) of Alpine Corsica, are not very permeable if at all. Corsica’s groundwater is therefore characterised by the absence of large aquifers of regional importance and the weakness of spring flows.
Nevertheless, these fractured rocks offer possibilities for water infiltration, but do not allow for the establishment of large reserves.
 
Spring, mineral and thermo-mineral waters
 
Definition:
Spring water is water of underground origin. Mineral water is of underground origin with stable physico-chemical composition over time. Thermo-mineral water is hot water, of underground origin, with stable physico-chemical composition.
Some mineral or thermo-mineral waters can health benefits which are recognised by the Academy of Medicine.
 
Mineral and thermo-mineral waters of Corsica
 
There are many thermal springs in Corsica with long-standing therapeutic properties, attested to by Roman remains.
These waters are of medical, socio-economic and tourist interest.
 
More than 40 springs are known in Corsica, and can be classified in 3 groups:
 
(1) Mineral waters with a temperature range of 12 to 19°C: La Porta, Caldane d'Ampugnani, Ferriera, Orezza, Pardina, Moïta, Puzzichellu, Cordozza, Vadina, Ornasu (Aquacetosa), Funtanella.
 
(2) Thermal waters with a temperature range of 32 to 57°C: Guagnu-les-Bains, Caldanella, Pietrapola, Vignola, Caldaniccia, Guitera-les-Bains, Urbalacone, Baraci, Caldane de Tallano.
 
(3) Radioactive water: Dirza (Uragiu).
 
From a chemical point of view, these sources are classified into 5 groups corresponding to different therapeutic indications.
 
(1) Sodium sulphide waters: Guagnu-les-Bains, Caldanella, Cardozza, Vadina, Pietrapola, Vignola, Funtanella, Caldaniccia, Guitera-les-Bains, Urbalacone, Baraci, Caldane de Tallano.
 
(2) Calcium sulphide waters: Puzzichellu.
 
(3) Calcium bicarbonate waters: Ornasu (Aquacetosa).
 
(4) Ferruginous waters: La Porta, Caldane d'Ampugnani, Ferriera, Orezza, Pardina, Moïta.
 
(5) Radioactive waters: Dirza (Uragiu).
 
The therapeutic effectiveness of thermal waters is due to the high temperature but also to the chemistry of the water, particularly the presence of numerous trace elements. However, thermal plankton plays a fundamental role; glairin or baregin is a nitrogenous gelatinous substance of essentially bacterial origin made up of sulpho-bacteria and microscopic algae such as diatoms. This thermal plankton has an antioxidant, anti-inflammatory and healing action.
 
The mineral and thermo-mineral waters of Corsica are a largely under-exploited heritage. We can only deplore the very low use and sometimes even the abandonment of sites, since our springs have a medical, socio-economic and tourist interest.
 
Mineral and thermo-mineral waters of Corsica: the main sources
Mineral and thermos-mineral waters of Corsica: water chemistry
 

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VI. The particularities of the aquatic fauna of Corsica
 
The geological history of Corsica (with the drift and rotation of the Corso-Sardinian block around 25 million years ago) is one of the reasons for the particularities of the flora and fauna of Corsica.
The originality of the aquatic fauna is reflected in: (i) the presence of numerous faunal gaps and (ii) a high rate of endemism, the highest in Europe after the Caucasus and ahead of the Iberian Peninsula.
 
  1. Fauna gaps
As far as fish are concerned, the fresh waters of mainland France have 167 species (including 64 introduced species), whereas in Corsica the fish population is poorer with only 25 species (including 21 introduced species).
Amphibians in metropolitan France include 39 species with 21 species in the Alps and 18 in the Pyrenees. The freshwater systems of Corsica have only 7 species.
The faunistic gaps are particularly marked for aquatic invertebrates. While the inventory of the freshwater fauna of the Alps includes about 2,200 species and that of the Pyrenees nearly 1,000 species, in Corsica only 650 species have been catalogued.
As a reminder, the terrestrial fauna of Corsica is marked by numerous faunistic gaps. There is an absence on the island of magpies, vipers, chamois, isards, ibexes, roe deer, squirrels, badgers, marmots, wolves, bears and lynxes, all of which are frequently found in the Alps or the Pyrenees.
 
  1. A high rate of endemism
Among the species of fish, the presence of the endemic strain of Salmo trutta macrostigma can be noted.
As for batrachians, 6 of the 7 species present in Corsica are endemic, corresponding to an endemism rate of almost 86%.
For invertebrates, out of the 650 species present in the fresh waters of Corsica, 200 species are endemic, i.e. a rate of endemism of almost 31%. Among the 200 endemic species, 105 are Corsican endemics and 50 are Corso-Sardinian endemics.
In the upper reaches of rivers and in springs, the rate of endemism reaches 60%.
This biodiversity is now threatened by dams, domestic discharges, fertilisers and pesticides used in agriculture, livestock farming, aggregate extraction, water sports, species introductions (e.g. fish) and the consequences of climate change.
Climate change is reducing the ecological niche of many cold-water species, restricting their range to riverheads and springs.

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VII. Biodiversity of Corsica’s fresh waters
 
A. Fish
 
Corsica’s rivers are dominated by three species: trout (Salmo trutta), eel (Anguilla anguilla) and freshwater blenny (Salaria fluviatilis).
 
The common trout is a species of salmonid native to Eurasia and North Africa. It is widely distributed throughout Europe. Genetic studies have shown that there are several genetic types. In continental France, a distinction is made between the Atlantic strain (domesticated and bred in fish farms) and the Mediterranean strain.
 
In Corsica, in addition to the Atlantic and Mediterranean strains, there is an endemic Corsican strain belonging to the macrostigma subspecies. The European “Habitat” Directive 92/43/EEC classifies Salmo trutta macrostigma as a “species of community interest” in Annex II. This species mainly frequents the apical parts of river basins as well as certain high-altitude wetlands called pozzines.
 
In Corsican rivers, trout growth is less than 5 cm per year, due to the low mineralisation rate of the water (low calcium and bicarbonate content) and the oligotrophic nature of the water (invertebrate biomass is low). The proliferation of these aquatic organisms depends on the geology, altitude, anthropic inputs and the overall nature of the riparian zone (deciduous or coniferous). The influence of allochthonous inputs of organic matter from the riparian zone on fish populations in forested rivers has been demonstrated.
 
The eel is an amphibiotic, thalassotactic species. It leaves continental and coastal waters and makes a transoceanic breeding migration towards the Sargasso Sea, its only presumed spawning area. In the rivers of Corsica, the eel has been recorded at altitudes of up to 1,300 m.
 
The freshwater blenny is a fish from the Mediterranean region and is more frequent in Corsica than on the mainland. This species is present in the large coastal rivers up to an altitude of 200 m.
 
These three native fish species are distributed in Corsica’s waterways corresponding to 4 different altitude zones:
 
 The upper trout zone, above 800 m altitude, is dominated by trout, eels are often absent.
 
 The lower trout zone, between 800 and 200 m altitude, where the population consists of trout and eel.
 
 The eel zone, below 200 m altitude, is dominated by eels, coexisting with the freshwater blenny; the number of trout is considerably reduced.
 
 The marine influence zone includes the estuary and the part of the river which receives an influx of salt water. In addition to the eel and the stickleback (Gasterosteus aculeatus), there are amphibiotic species that migrate from the sea to the rivers to reproduce: the twait shad (Alosa fallax), the big-scale sand smelt (Atherina boyeri), the European bass (Dicentrarchus labrax), and various mullets (Chelon labrosusLiza aurataLiza ramadaMugil cephalus).
The Mediterranean killifish (Aphanius fasciatus) frequents salty or brackish coastal lagoons.
Fish zoning in the Tavignanu
1. Trout; 2. Eel; 3; River blenny
4. Stickleback; 5. Twait shad; 6. Sand smelt; 7. Bass; 8. Mullet.

Introduced species:
 
Whereas in 1900 there was only one introduced species (the Eastern mosquitofish, Gambusia holbrooki) in Corsica’s fresh waters, there are now 21 introduced species. The mosquitofish was introduced as part of a programme to combat malaria.
The cumulative number of introduced species per year is as follows: 1900 (1); 1970 (8); 1980 (12); 1990 (15); 2000 (20); 2010 (21).
 
There are 21 introduced species in Corsica’s fresh waters: the common sturgeon (Acipenser sturio), pike (Esox lucius), crucian carp (Carassius carassius), goldfish (Carassius auratus), European carp (Cyprinus carpio), Marmara chub (Leuciscus cephalus), common roach (Rutilus rutilus), gudgeon (Gobio gobio), topmouth gudgeon (Pseudorasbora parva), Eurasion ruffe (Gymnocephalus cernuus), minnow (Phoxinus phoxinus), catfish (Ictalurus punctatus), common rudd (Scardinius erythrophtalmus), pikeperch (Sander lucioperca), wels catfish (Silurus glanis), tench (Tinca tinca), common perch (Perca fluviatilis), largemouth bass (Micropterus salmoides).
 
These introduced species have been catalogued in the lower reaches of rivers impacted by the exploitation of aggregates (gravel pits) and in a few artificial reservoirs managed by Electricité de France or the Office d’Equipement Hydraulique de la Corse.
 
The charr or brook trout (Salvelinus fontinalis) was introduced in the early 1970s in some high-altitude lakes. The rainbow trout (Oncorhynchus mykiss) is regularly released into Corsica’s waterways before the opening of fishing season by the Fédération Interdépartementale de Pêche et de Pisciculture.
 
The consequences of introducing fish species:
These introductions are a threat to native fish, including the macrostigma trout (Corsican strain), as they bring predation, competition, pathogens (viruses and bacteria) and parasites.
 
At the beginning of the 1970s in Corsica, the brook trout (Salvelinus fontinalis) was introduced into mountain lakes. The consequences of this were catastrophic, resulting in the disappearance of the native trout (Salmo trutta), as the brook trout, which reaches almost 40 cm in length, is extremely voracious. This introduction is most probably responsible for the significant decline in the numbers of the Corsican brook salamander (Euproctus montanus).
 
The parasitic rosette agent (Sphareothecum destruens) has been identified in fish from the Calacuccia dam. The species concerned are the topmouth gudgeon and the minnow, two species introduced into Corsica. The topmouth gudgeon (Pseudorasbora parva) is a fish species originating from China. This infectious intracellular eukaryotic pathogen at the fungus-animal border is said to be the cause of mortality in the common rudd population present in this large artificial lake in Niolu.
This multi-host pathogen affects not only topmouth gudgeon and minnows but also other fish introduced into Corsican freshwater such as bream, common carp, gudgeon, roach, pond perch, rainbow trout and brook trout.
In continental France, the rosette agent also affects farmed sea bass, which benefits from the Label Rouge in Corsica. This infectious pathogen could, in the future, threaten the aquaculture sector in Corsica.
 
On the mainland, rainbow trout are involved in the spread of viral diseases such as viral haemorrhagic septicaemia and infectious haematopoietic necrosis. These are both rhabdoviruses, as the viruses belong to the genus Novirhabdovirus.
 
Carp are affected by spring viremia virus and Koi herpes virus. They can also carry monogenic (Diplozoon nipponicum) and cestode (Bothriocephalus acheilognathi) parasites. The latter also affects the Eastern mosquitofish.
 
The roach is the vector of a parasitic disease, ligulosis, caused by Ligula intestinalis. The pikeperch is the host of a trematode parasite (Bucephalus polymorphus) responsible for larval bucephalosis.
 
The safeguarding of our aquatic ecosystem requires a ban on the introduction of new species of fish and increased protection of the headwaters of the watershed where the Corsican trout live.
 
Some elements of trout and eel biology
 
Trout: Size / Weight Relationship
 
The relationship between the size and weight of trout is summarised by a mathematical equation that enables the weight of the fish to be determined by its length. A 10 cm trout weighs about 10 grams, a 30 cm trout 200 g and a 60 cm fish 1.6 kg.
 
 
Trout: Size / Age relationship (polygon of increasing cumulative frequencies)
 
The polygon of increasing cumulative frequencies enables a rapid determination of the age of the fish. The breaks in the slope are marked in order to determine the limits of the different age classes.

Size / Age relationship of trout (size class boundaries)
Size (mm) Age (year)
65 to 83 0+ (fry of the year)
84 to 125 1+ (yearling trout)
126 to 152 2+
153 to 207 3+
208 to 266 4+
267 to 327 5+
 
 
 
 
Eel: Size/Weight Relationship
 
 
The relationship between the size and weight of eels is modelled in a mathematical equation. It enables their weight to be determined in relation to their length. A 10 cm eel weighs just over one gram, a 40 cm eel 100 g and an 80 cm eel 900 g.
 
 
Eel: Size / Age relationship (polygon of increasing cumulative frequencies)
 
 
The polygon of increasing cumulative frequencies enables a quick determination of the age of the fish. The breaks in the slope are marked in order to determine the limits of the different age classes.
 
Size / Age relationship of eels (size class boundaries)
Size (mm) Age (year)
55 to 149 0+ (elver of the year)
150 to 212 1+ (one-year-old eel)
213 to 309 2+
310 to 399 3+
400 to 500 4+
501 to 601 5+
602 to 800 6+
 
 
Fish in mountain lakes
 
At the beginning of the 20th century, only the Ninu and Melu lakes were known for their trout populations. The other lakes were considered, probably wrongly, as apiscicultural, i.e. sterile for fish.
 
Lake Gialicatapianu, which has not been affected by breeding programmes, has a good population of brown trout. The connection with the Manganellu, a tributary stream of the Vecchiu (tributary of the Tavignanu) may explain this situation. Other mountain lakes in Corsica are possibly in the same situation.
 
At the end of the 1950s, a breeding programme of brown trout was carried out in the Crenu and Vitalaca lakes. At the beginning of the 1970s, breeding of brown trout and brook trout was carried out: (i) in the Ritondu massif in the lakes of Melu, Capitellu, Goria, Bellebone (or Ritondu, or Betaniella) and Oriente; (ii) in the Rinosu massif in the lakes of Bastani, Bracca and Vitalaca
 
In lakes where brook trout have been introduced and where there was a pre-existing population of brown trout, cohabitation between the two species lasted for a short time. The alien (introduced) species eliminated the native species, as is the case in Lake Melu.
 
Nowadays, in the lakes of Ninu, Vitalaca, Gialicatapianu, Oriente, Crenu and Braca, the fish population is only represented by the brown trout. The fish fauna of the Oriente, Crenu and Braca lakes is endangered.
Brook trout is the only species of fish present in the lakes of Melu, Bastani and Capitellu.
The lakes with the most fish are, in descending order: Melu, Ninu, Bastani, Capitellu, Vitalaca and Gialicatapianu.
 
The absence of fish in the lakes of Cavaciole, Maggiore, Niellucciu and Oru is probably due to the very low mineralisation of the waters and consequently to reduced primary production.
The conductivity value, which reflects the mineralisation of the water, is 42 μS/cm at Lake Ninu. Conductivity recorded at Cavaciole, Maggiore, Niellucciu and Oru (13 to 26 μS/cm) are lower and are characteristic of very weakly mineralised waters.
The Dissolved Organic Carbon content of water is an approach to the primary production of an aquatic ecosystem. At Lake Ninu, the value obtained is 6.7 mg/l, those found at Cavaciole, Maggiore, Niellucciu and Oru (0.6 to 0.8 mg/l) are ten times lower, they translate the low primary productivity of these mountain hydrosystems.
The failure of fry breeding in Goria and Bellebone (or Ritondu, or Betaniella) may have the same explanation.

B. Amphibians and Batrachians
 
In the freshwater ecosystems of Corsica, the two main groups of amphibians are represented. The Urodeles, which have a tail, and the Anurans, which do not have a tail in their adult stage.
 
Anurans:
Balearic green toad (Bufotes viridis balearicus): endemic to the Balearic Islands, Corsica and southern Italy
The Corsican painted frog (Discoglossus montalentii): endemic to Corsica
The Tyrrhenian painted frog (Discoglossus sardus): endemic to the Tyrrhenian
The Italian pool frog (Pelophylax lessonae bergeri)
The Sardinian tree frog (Hyla sarda): endemic to Corsica, Sardinia and the Tuscan archipelago
 
Urodeles:
The Corsican brook salamander (Euproctus montanus): endemic to Corsica
The Corsican fire salamander (Salamandra corsica): endemic to Corsica.


C. Reptiles (Turtles and aquatic snakes)
 
Turtles:
The European pond terrapin (Emys orbicularis)
 
Exotic species:
The red-eared terrapin (Trachemys scripta elegans)
The yellow-bellied slider (Trachemys scripta scripta)
The common snapping turtle (Chelydra serpentina)
 
 
Snakes (water snakes):
The Corsican garter snake (Natrix natrix corsa): endemic to Corsica
The viperine water snake (Natrix maura).

D. Invertebrates
 
The invertebrate population of Corsica’s fresh waters is characterised by the existence of numerous faunal gaps and a very high percentage of endemic species.
 
The specific composition of the fauna of Corsica’s fresh waters (650 species) is one of the poorest in Western Europe. The rivers of the Alps have nearly 2,200 species, and the Pyrenees nearly 1,000.
The faunal gaps vary depending on the order, and are very numerous in the Plecoptera, Diptera and Trichoptera, but less marked in the Ephemeroptera, Odonata, Coleoptera and Hydracaria.
 
The existence of these faunal gaps is explained by the fact that none of the continental species that are missing in Corsica have ever reached the island. 
It was during the Quaternary period that the fauna and flora of the Holarctic regions became most diverse. At that time, great climatic waves caused fauna and flora to move over vast areas, as the taxa followed the advance and retreat of the glaciers. These exchanges between different regions resulted in a great wealth of species in middle Europe. However, at the same time, Corsica remained outside these faunistic and floristic movements because it was already geographically isolated, the drift of the Corso-Sardinian block dating from the Oligocene-Miocene period (Tertiary).
 
The aquatic fauna of Corsica is characterised by a very high percentage of endemic species. In Europe there are three major centres of endemism for running water fauna: the Caucasus, the Tyrrhenian (which includes peninsular Italy, Sicily, Sardinia and Corsica) and the Iberian Peninsula.
With nearly 200 endemic species, the fauna of Corsica contains, given the small size of the island, the highest concentration of endemics in Europe. The originality of the entomo-hydro-fauna is unevenly marked in the various groups. In Corsica, the Plecoptera, Trichoptera and Diptera Blephariceridae contain the highest percentage of endemic species.
Endemism is mainly found in spring communities and in the upper reaches of rivers, where the endemism rate approaches 60%. The spring biotope provides a refuge and conditions for the survival of ancient species.
 
The majority of aquatic invertebrates have larval and pupal stages in the water and the adult stage (imago) in the air.
 
The fauna of rivers has two ways of adapting to the current: (i) ethological, by taking shelter under stones, and (ii) morphological (dorso-ventral flattening, claws, hooks, pseudopods, suction cups, reinforced envelopes).
 
In rivers, aquatic plants (algae and macrophytes) provide only a relatively small proportion of the organic substances needed by feeders. The ecosystem receives most of its primary energy from the surrounding vegetation cover (riparian and catchment vegetation) and possibly from various organic waste products.
Decomposing leaves are the staple diet of detritivorous aquatic invertebrates (fragmenters) that consume large plant debris, transforming it and breaking it down into finer debris. The presence of colonies of micro-organisms increases the nutritional value of this organic matter.
The fine elements resulting from this fragmentation serve as food for the collecting organisms, which obtain them either by filtering particles suspended in the water or by collecting fine elements deposited on the substrate.
A very specialised category of invertebrates known as bottom feeders, or grazers, feed on epilithic algae (Diatoms).
Invertebrate predators and parasites feed on fragmenters, collectors and grazers.
Salmonids, such as trout, are predators of aquatic invertebrates.

Curiositites
 
Peach blossom jellyfish (Craspedacusta sowerbii)
Originally from the Yangtze River in China, it was catalogued in 1880 in England in the pond of a botanical garden. It was transported with tropical water plants imported into England, including the water hyacinth. In 1928, it was present outside ponds in other bodies of water in England. It has now colonised all 5 continents through the aquarium plant market.
In France it appeared in 1962 in Lake Geneva, followed by Lake Annecy in 1990. In 2009 it appeared in Corsica in the Teppe Rosse and Coti-Chiavari dams.
 
 
Tardigrades
Tardigrades (water bears) are found in fresh, brackish and salt water, and also in humid terrestrial environments. The aquatic fauna of Corsica includes 19 species of tardigrades. The most represented families are the Echiniscidae and the Hypsibiidae. These very small organisms (between 0.05 mm and 1.2 mm) feed mainly on mosses and stringy algae, some rare species are carnivorous.
Tardigrades are resistant to extreme temperatures, from -272°C to +150°C. Some even survived a spacewalk during a Russian orbital mission, resisting both the vacuum of space and UV radiation.
These animals can enter into a slowed-down life, cryptobiosis, through extensive dehydration. In this biological phenomenon, water is replaced by a sugar-based “biological antifreeze”.
Tardigrades have the ability to repair DNA. Genome sequencing of this creature opens up interesting prospects, particularly in research programmes on DNA repair mechanisms and carcinogenesis in humans.
 
 
Molluscs
“On the abandoned beach, shellfish and crustaceans” is how the song “La Madrague”, sung by Brigitte Bardot in 1963, begins, words by Jean-Max Rivière and music by Gérard Bourgeois. Molluscs and crustaceans are clearly identified with the marine environment.
In the fresh waters of Corsica, 36 species of molluscs have been catalogued, 5 of which are endemic.
There is even a freshwater mussel (Unio elongatulus) in the lower Tavignanu.
 
 
Crustaceans
This faunal group is represented by 6 species, 4 of which are endemic. The presence of two introduced species should be noted: the white-clawed crayfish (Austropotamobius pallipes) and the spinycheek crayfish (Faxonius limosus). The latter is included in the list of invasive alien species of concern for the European Union. The spinycheek crayfish is a threat to native species either through competition or through the transmission of a type of water mould called Aphanomyces astaci, or crayfish plague, of which it is a healthy carrier. The spinycheek crayfish also weakens dykes and banks by digging deep burrows, thus threatening hydraulic structures.

Planaria, immortal worms
Planaria are aquatic flatworms (Plathelminths), they are represented in the fresh waters of Corsica by three endemic species: Crenobia alpina corsica endemic to Corsica, Dugesia benazzii endemic to Corsica, Sardinia and peninsular Italy, and Dugesia mediterranea endemic to Corsica, Sardinia, Sicily and Spain.
These organisms have the ability to regenerate any damaged part of their body and even regenerate a complete individual from a fragment of a body.
Recent studies have shown that this regeneration process is governed by stem cells called “neoblasts”. The result of this research opens up perspectives for humans on the regeneration of tissue and cells and the maintenance of vital functions despite ageing.
 
 
Gordionus cyrnensis, a manipulative parasite
The Corsican gordian worm (Gordionus cyrnensis) is a non-segmented parasitic worm with a cylindrical body (phylum Nematomorpha). It wraps around itself forming a living “Gordian knot”, hence its name.
In its larval stage, the parasite develops in the body of a terrestrial orthopteran insect (such as grasshoppers or crickets) or beetles. The gordian manipulates the behaviour of the host, causing it to “commit suicide” by drowning, so that it can return to its breeding environment.
In the aquatic environment, it first parasitises aquatic vertebrates such as amphibians or fish; it then parasitises the larvae of aquatic invertebrates such as wood-boring beetles. The parasitised caddisfly larva develops into an aquatic nymph and then into a terrestrial, aerial, adult that is eaten by a cricket or beetle. The life cycle of the Gordian beetle is thus completed.
 
 
Hydrachnidia, regulating mosquito populations
Aquatic mites are arachnids (best-known representatives of arachnids being spiders and scorpions) that are parasites or predators of aquatic insect larvae including diptera (mosquitoes and others).
In the fresh waters of the island, there are nearly 70 species, 41 of which are endemic to Corsica. The population is dominated by the genera Torrenticola and Hygrobates.
These aquatic organisms are present throughout the entire hydrographic network, from the spring to the mouth of a watercourse. They frequent not only running water (rivers) but also stagnant water in the plains (lower reaches of rivers, ponds, temporary pools) and in the mountains (high-altitude lakes).
It should be remembered that mosquitoes are vectors of malaria, chikungunya, dengue, zika, among other diseases.
 

E. Aquatic flora: macrophytes and microalgae
 
1) Macrophytes: are large aquatic plants. They are present in several plant phyla and groups. 
Among the Spermatophytes (seed plants) is pondweed (Potamogeton sp.), of which 13 species are present in Corsica.
Among the Pteridophytes (ferns, horsetails and lycopods), the pilularia minuta should be mentioned.
Among the Bryophytes (mosses, liverworts and anthocerotae), the genus Fontinalis is represented in Corsica by 3 species.
Among the macro-algae, i.e. those visible to and identifiable by the naked eye in the field, the genera Cladophora and Chara are noteworthy.
 
Macrophytes can be classified into two groups: helophytes and hydrophytes.
 
Helophytes are emergent plants that can withstand partial immersion. They are also called mud plants, amphibious plants or amphiphytes.
The most common species are: Phragmites australis (reed), Typha latifolia (broadleaf cattail), Scirpus lacustris (lakeshore bullrush), Juncus acutus (spiny rush), Osmunda regalis (royal fern), Nasturtium officinale (watercress), Mentha aquatica (water mint) and Carex nigra (black sedge).
 
Hydrophytes are submerged or floating plants.
This group of macrophytes consists of 4 types:
  1. Submerged fixed and fully immersed hydrophytes
  2. Fixed submerged hydrophytes with floating leaves
  3. Free floating surface hydrophytes
  4. Submerged free floating hydrophytes.
 
Submerged fixed and fully immersed 
Elodea canadensis (Canadian waterweed): present in the lower reaches of rivers, this alien (exotic species) has probably “escaped” from aquariums.
 
Fixed submerged hydrophytes with floating leaves
Nymphaea alba (White waterlily): present at the mouths of some rivers and at Lake Crenu, probably transported by air by the little grebe (Tachybaptus ruficollis) which breeds in the lake’s reed beds.
 
Pondweeds: 13 species are present in the hydrosystems of Corsica (rivers, ponds, canals, peat bogs). The best represented species are: Potamogeton natans (floating pondweed), Potamogeton pectinatus (sago pondweed), Potamogeton pusillus (lesser pondweed).
 
Free floating surface hydrophytes
Duckweed: Lemna minor (common duckweed) and Lemna gibba (gibbous duckweed).
 
Submerged free floating hydrophytes
Utricularia australis (southern bladderwort)
 
 
Macrophytes and popular naturalist knowledge
 
Aquatic plants were frequently used in traditional pharmacopoeias (Greeks, Romans, European herbalists, etc.).
Hippocrates (460-377) prescribed the rhizome of the sweet flag (Acorus calamus) to treat eye diseases, indigestion, toothache, colds, coughs and fevers.
The sweet flag essential oil is used in Egypt and India to treat skin diseases, coughs, asthma and haemorrhoids. The roots of this macrophyte have laxative and diuretic properties.
Traditional Chinese and Japanese medicine uses the dried rhizomes of two species of waterlilies (Nuphar japonicum and Nuphar pumila) for their tonic, haemostatic and diuretic properties.
In France, the rhizome of the yellow waterlily (Nuphar lutea) was used to treat skin ailments: insect bites, sunburn, superficial burns, etc.
In Sudan, the root and leaf of the Egyptian or tiger lotus (Nymphaea lotus) are used to treat dysentery and tumours. It is also used for its antibacterial properties.
 
In Corsica:
Watercress is eaten raw in salads or cooked in soups and herb pies. But it was also used to treat skin diseases.
Water mint can be used in the preparation of soups, herb pies, fritters, omelettes. 
Rushes are used to make cheese moulds and fishermen’s traps.
Wicker or purple willow is used to make baskets.

Ludwigia: invasive plants in France and in the Mediterranean region (including Corsica)
 
Ludwigia palustris is a species of evening primrose that has a wide geographical distribution. It is present in continental France and in Corsica in ponds and rivers. This species does not pose any particular problem.
But Ludwigia peploides is an invasive plant that causes serious damage to aquatic ecosystems. This species, originating from South America, was accidentally introduced around 1830 in the Montpellier region. It has since colonised the whole of France, the first observation in Corsica (Figari, South Corsica) dates from 2007.
Dense and extensive meadows lead to:
  1. A decrease in biodiversity (competition with native flora);
  2. A change in the physico-chemical nature of the water;
  3. A hydraulic disturbance (flow).
The Conservatoire Botanique National de Corse (CBNC), a department of the Office de l’Environnement, is engaged in a strategy of fighting against invasive species in general and ludwigia in particular.
 
2) Microalgae
 
In aquatic environments, microalgae occupy two compartments: the water column and the sediment. The algae in the open water make phytoplankton, the algae attached to the bottom (benthic or epilithic algae) make up the periphyton.
 
Microalgae in waterways
 
In the waterways of Corsica nearly 280 species of microalgae have been catalogued. The Diatomophyceae are the best represented with nearly 70% of the species counted; the genera Navicula and Nitzschia dominate the diatomic population.
For many southern European rivers, the number of species is much lower.
 
Microalgae in high-altitude lakes
 
For all the lakes we studied, nearly 150 species of algae, phytoplanktonic and periphytic, were catalogued.
With nearly 130 species, Chlorophyceae and Diatomophyceae dominate the algal population. The development of a flora rich in Diatoms attests to the presence of silica in the water. The phytoplankton community is more diverse than the epilithic community.
In the lakes of Melu and Ninu, the proliferation of cyanobacteria during the summer period is evidence of pollution related to the overuse of the sites.
 
Microalgae in artificial reservoirs
 
In the reservoirs of the artificial lakes studied, more than 200 species were recorded, with Diatomophyceae and Chlorophyceae being the dominant groups during a very large part of the annual cycle.
During the summer period, there is a phytoplankton bloom resulting from the proliferation of cyanobacteria, which represents more than 90% of the microalgae sampled.

Cyanobacteria
 
Cyanobacteria, also known as cyanophyta, are autotrophic prokaryotes, systematically classified in the kingdom Eubacteria. These micro-organisms are distinguished from bacteria by the presence of chlorophyll and other pigments.
 
Cyanobacteria occur naturally in small numbers all over the world, and in virtually all environments, even the most extreme. Wherever there is water, there can be cyanobacteria.
 
The proliferation of cyanobacteria is the consequence of a combination of their adaptation systems and environmental factors. These factors are mainly:
            - a high concentration of phosphorus in the environment;
            - good stability of the water column;
            - high water temperature.
 
The growth of cyanobacteria can have an impact on water quality, as some cyanobacteria have the ability to produce toxins called cyanotoxins.
 
 
 
 

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VIII. Terrestrial vegetation in hydro-systems
 
A. Alluvial forests and riparian forests
 
An alluvial forest is a wooded formation on alluvium, in relation with the underlying water table, subject to the influence of floods.
A riparian forest is an ecosystem dominated by trees bordering the channel of a watercourse.
Alluvial forests and riparian forests have two categories of woody species: softwood (willow, alder, poplar) and hardwood (oak, maple, ash).
The combination of watercourses and trees constitutes an “ecocomplex”, i.e. a set of interactive ecosystems.
 
Alluvial forests and riparian forests play an important role in: (i) Soil formation in alluvial plains; (ii) Controlling surface and groundwater flow; (iii) Transporting sediment and coarse organic matter; (iv) Filtering pollution by contributing to the self-cleaning capacity of rivers.
 
The tree species of the riparian zone influence the hydrological, hydraulic and morphological conditions of the watercourse: the aerial system modifies flow conditions in the flood plain (attenuating the effects of floods) and the root system controls the shape and stability of the riverbed.
 
Riparian forests play a role in the movement of species (ecological corridors), especially birds and insects.
Undergrowth shelters, formed by the roots of the riparian trees, influence fish behaviour: (i) habitat and refuge (during floods); (ii) lower temperature and therefore better oxygenated water; (iii) trophic relationship, since the larvae of aquatic invertebrates that feed on dead leaves are the food for the fish.
 
Alluvial forests and riparian zones are in decline due to: (i) agriculture and urbanisation; (ii) aggregate exploitation (gravel pits); (iii) the consequences of climate change.
 
 
The alluvial forest at the mouth of the Fangu
 
The mouth of the Fangu is one of the few places on the island where an alluvial forest is found. The forest is dominated by evergreen oak (Quercus ilex), strawberry tree (Arbutus unedo) and tree heather (Erica arborea). On the banks of the river, the riparian vegetation is mainly composed of black alder (Alnus glutinosa), pussy willow (Salix cinerea) and bay trees (Laurus nobilis).
 
 
The riparian forests of the Restonica-Tavignanu river system
 
From downstream to upstream, there is a succession of riverine plant formations.
 
At the mouth of the Tavignanu, the riparian zone with ash and poplar has been severely damaged by human activity. The Caucasian ash (Fraxinus angustifolia subsp. oxycarpa), black alder (Alnus glutinosa), common oak (Quercus rubor), pussy willow (Salix cinerea), pubescent oak (Quercus pubescens), white willow (Salix alba), field elm (Ulmus minor), black poplar (Populus nigra) and white poplar (Populus alba) are the most represented trees.
 
At the Altiani bridge, the riparian zone is dominated by Caucasian ash (Fraxinus angustifolia subsp. oxycarpa), black alder (Alnus glutinosa) and black poplar (Populus nigra).
In areas where sediment has accumulated (pebbles, gravel, sand and silt), willow stand can develop. These are characterised by purple willow (Salix purpurea subsp. purpurea), white willow (Salix alba), pussy willow (Salix cinerea), crack willow (Salix fragilis), black poplar (Populus nigra), holly (Ilex aquifolium), black alder (Alnus glutinosa) and fig trees (Ficus carica).
 
In the area around Corte, the tree layer of the riparian zone is dominated by black alder (Alnus glutinosa), Italian alder (Alnus cordata), walnut (Juglans regia) and fig (Ficus carica). The shrub layer is populated by: stinking tutsan (Hypericum hircinum), Corsican heath (Erica terminalis) and boxwood (Buxus sempervirens).
 
In the Restonica valley, at Tragone bridge, where the banks are rocky, the riparian vegetation is narrow and discontinuous. The forest trees (beech, Laricio pine) reach the edge of the watercourse.
The riparian layer is characterised by black alder (Alnus glutinosa), Italian alder (Alnus cordata), manna ash (Fraxinus ornus), holly (Ilex aquifolium), common beech (Fagus sylvatica), silver fir (Abies alba) and yew (Taxus baccata). In the shrub layer, Corsican sweet alder (Alnus viridis subsp. suaveolens) appears.
 
At the Grutelle sheepland, black alder and Italian alder disappear, probably due to the unfavourable edaphic and thermal conditions. At this altitude, the riparian vegetation is dominated by Corsican sweet alder, which grows as far as Lake Capitellu.

B. The pozzines of Corsica
 
Pozzines are specialised hygrophilous groups, situated in the subalpine or, in exceptional circumstances, the montane levels. These peaty areas are found in the upper valleys of the main rivers. Pozzines are hygrophilous and meso-hygrophilous grasslands installed on substrates resulting from the more or less complete filling of glacial lakes. Located on an impermeable subsoil (glacial mud) with peat saturated with water, pozzines are essentially formed by the underground organs of grasses, Cyperaceae and dwarf Joncaceae with sphagnum.
 
Pozzines are largely populated by Euro-Siberian species (around 65%), accompanied by a significant number of endemic species (35%). These peaty soils constitute a difficult environment for many plants because they are asphyxiated, poorly mineralised and very poor in assimilable nitrogen in particular. This is why they have a flora that is not very rich and is highly specialised. This is the case of (i) bilberries, which have mycorrhizae, i.e. an association of a lower fungus with the plant’s roots; (ii) drosera, (“carnivorous”, or more correctly insectivorous, plants) which feed on insects.
 
Pozzines are made up of three physiognomically distinct groups: (i) a sedge marsh dominated by black sedge, bluegrass and marsh violet; (ii) a butterwort and tufted bulrush marsh dominated by Corsican butterwort, tufted bulrush, black sedge and bluegrass; and (iii) a mat grass grassland dominated by mat grass and Corso-Sardinian pearlwort.
 
This asphyxiating, more or less acidic environment is very unfavourable to the presence of micro-organisms responsible for breaking down and mineralising dead plant debris. Undegraded organic matter (peat) has been accumulating since the retreat of the last glaciers, about twelve thousand years ago. The peat layer can be 3 to 6 metres thick, and the pH of the upper parts is always acidic, between 5 and 5.7.
 
Origin and evolution of pozzine groups:
 
The retreat of the glaciers during the last cold climatic phases led to the formation of basins and the creation of lakes. The sedimentation process, with the addition of torrential alluvial deposits, gradually took place in these lakes.
 
The first gravel and lake mud banks to emerge were then colonised by grasslands with Corsican butterwort (Pinguicula corsica) and tufted bulrush (Scirpus cespitosus). A marshy grassland with black sedge (Carex nigra f. intricata) then gradually established. The alluvium and the overlying grasslands gained ground over open water. This process led to the formation of peat and sometimes to the fragmentation of the glacial lake into several basins or “pozzi” connected by a network of channels.
 
If the process of sedimentation and vegetation growth continues, the “pozzi” may be filled in; some of them, isolated from the general flow of water, only play the role of temporary pools.
When they are almost completely filled in, they are colonised by black sedge (Carex nigra f. intricata). This results in a landscape of flat areas uniformly covered with herbaceous vegetation, where mat grass (Nardus stricta) is dominant, with a few small streams draining the whole.
 
Pozzines and carbon sequestration
 
At the 21st meeting of the Conference of the Parties (CoP 21), all participants adopted the “Paris Agreement” in December 2015. This agreement, which aims to contain global warming “well below 2°C above pre-industrial levels”, specifies in Article 5 that “Parties shall take action to conserve and, where appropriate, enhance greenhouse gas sinks and reservoirs”.
 
Corsica is home to two key ecosystems in terms of carbon fixing and above all sequestration, with the presence of very large Posidonia meadows and pozzines (high-altitude peat bogs). Recent scientific work has made it possible to classify ecosystems according to their carbon sequestration potential. Posidonia meadows come out on top with almost 2,100 tonnes of CO2 per hectare. This is followed by peatlands (1,300 T.CO2/ha) and mangroves (1,100 T.CO2/ha). Tropical and boreal forests store less than 200 T.CO2/ha.
 
Within the framework of a research programme entitled “PADDUC-CHANGE” and financed by the Collectivité de Corse, soil sampling was carried out in the pozzine of Lake Ninu.
The exploration bore was drilled to a depth of 4 metres and provided (i) the soil profile of this pozzine and (ii) samples to be taken at various depths for C-N isotope ratio analysis and carbon-14 dating.
 
The soil profile includes:
(i) The first ten centimetres are herbaceous vegetation dominated by mat grass (Nardus stricta). In places, black sedge (Carex nigra f. intricata) is present.
(ii) The thickness of the peat reaches 3.4 metres. This more or less acidic asphyxial environment (the pH of the upper horizons is between 5 and 5.7) is very hostile to the presence of micro-organisms which break down and mineralise dead plant material. Undegraded organic matter has been accumulating since the retreat of the last glaciers. The peat is essentially formed by the undegraded underground organs of grasses, Cyperaceae and dwarf juncaceae with sphagnum.
(iii) At a depth of 3.5 m, the glacial moraine, which is almost 1 metre thick, is represented by a blue clay forming an impermeable stratum.
(iv) The Hercynian basement, composed of biotite-amphibole granodiorites and enclaves, appears at a depth of 5.5 metres.
 
The estimated age of the different strata of the pozzine soil profile is as follows:
At a depth of 0.5 m the estimated age of the peat is 2,500 years (cal.BP); at 3.4 m it is 8,500 years.
Depending on the depth, the age of the glacial moraine varies from 9,000 to 14,000 years (cal.BP). It is worth remembering that the last glaciation in Corsica dates from the Dryas (-17,000 to -10,000) and that the complete retreat of the glacier in the upper Tavignanu (where Lake Ninu is located) is estimated at -10,000 years.
We also made a 3D model of the north-western pozzine of Lake Ninu.
 
 
 
 
Evolution of the pozzines over time (reconstruction)
 
Core drilling of the pozzines of Lake Ninu
 
Ninu Lake pozzine core: blue clay (glacial moraine) at depth of 4 m 
 
 
Lake Ninu pozzine core: peat at depth of 3 m 

3D modelling of the north-western pozzine of Lake Ninu
 
Depth (m) Estimated age (Ka cal.BP)  
 
   
0.0       Pozzine
0.5 2.5      
1.0 3.9      
1.5 5.4      
2.0 6.5     PEAT
2.5 7.4      
3.0 8.0      
3.5 8.6      
4.0 9.0     Glacial moraine
4.5 10.0     BLUE CLAY
5.0 12.0      
5.5 14.0      
6.0        
6.5        
7.0 250 000     Hercynian base
7.5       GRANODIORITES
8.0        
8.5        
9.0        
9.5        

Soil profile and age estimation
 

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IX. Biodiversity under threat
 
The fauna of Corsica’s fresh waters is marked by a high rate of endemism. Among the vertebrates, apart from the Corsican strain of Salmo trutta macrostigma, batrachians have six endemic species.
Among the invertebrates, 200 species are endemic, including 105 Corsican endemics and 50 Corso-Sardinian endemics.
This exceptional biodiversity is threatened by extreme natural events such as floods and low water, but also by human activities. We will discuss the different forms of anthropisation, whether direct (dams, pollution, contamination) or indirect (climate change due to greenhouse gas emissions).
As we shall see later, one of the consequences of climate change is the increase in the frequency and magnitude of extreme events (floods and low water).
 
1. Extreme natural events: floods and low water
 
The hydrological regime (evolution of flows during an annual cycle) of Mediterranean rivers is marked by extreme events: high and low water. These natural parameters of the functioning of the aquatic ecosystem can have destructive effects, but the return to a normal situation occurs at differing speeds.
 
 
Evolution of the average daily flow (in m3/s) of the Tavignanu in 2017 (source Banque Hydro)
 
 
(i) Floods
Heavy autumn precipitation and, to a lesser extent, snowmelt in the spring can lead to an increase in the flow rate and consequently in the speed of the current.
 
Floods have a positive effect on the aquatic ecosystem because the flushing effect removes accumulated natural and man-made material from the river.
 
But aquatic flora and fauna are impacted because exceptional floods wash away aquatic organisms and, above all, destroy habitats.
 
Macrophytes, large aquatic plants, such as pondweeds, mosses, macroalgae, etc., are often torn up and carried away by the current.
Microalgae, such as diatoms, are more difficult to detach from the substrate, but some exceptional floods completely eliminate the biofilm (microflora).
 
Exceptional floods with a return period of one hundred years, cause not only considerable material and human damage, but also major disturbances to aquatic fauna.
However, fish and invertebrates have developed adaptations (ethological, morphological and anatomical) in order to resist the strong hydrodynamics during the flood (Resistance) and to recolonise the environment after the flood (Resilience).
 
Resistance in fish
During flooding, fish avoid the axial course of the river and position themselves near the banks in the flood plain, where the speed of the current is slowed down by the trunks of the riparian forest. The presence of shelters under the banks limits the impact on the fish population. Fish use these shelters not only to rest (under normal hydrological conditions) but also during floods.
The presence of natural or artificial flood plains plays an important role in this phase of resistance. Despite the fact that when the flood recedes there is a risk of fish becoming trapped in areas disconnected from the river.
Fish may also migrate to smaller tributaries which are often less affected by the effects of flooding.
 
Unfortunately, every flood is accompanied by water pollution from hydrocarbons, trace elements (heavy metals), medicines, or cleaning products. Fish, especially salmonids such as trout, are very sensitive to pollution. Although specific, this pollution reduces the ability of these organisms to resist.

Resilience in fish
 
After flooding, fish that have migrated return to their preferred habitat. If the fish population is virtually wiped out, the environment is recolonised from the small tributaries by the downstream migration of fish fry. In a river system, tributaries act as biological reservoirs from which the biotopes are recolonised and the ecological structure is rebuilt.
 
 
Resistance in invertebrates
 
During flooding, the aquatic invertebrate population has various strategies. It can take refuge in the flood plain where the current speed is lower, and shelters under the banks make good refuge zones.
But invertebrates, being small in size, migrate into the underflow of the riverbed.
Resistance to strong currents is conditioned by the presence, in certain benthic invertebrates, of morphological (dorso-ventral flattening) and/or anatomical (claws, hooks, suckers) adaptations.
Despite this struggle for survival, part of the aquatic invertebrate population is subject to catastrophic drift (passive dispersion under the effect of the current), which drags individuals downstream.
 
Resilience in invertebrates
 
After flooding, aquatic invertebrates, which have migrated into the flood plain and underflow, return to their original habitats. But the fundamental element of resilience is the ordinary drift from smaller tributaries which are less impacted by the flood.
 
The catastrophic drift of aquatic invertebrate larvae is compensated for by adults (imagos) that fly upstream and lay eggs.
 
The rapid recolonisation of the environment is favoured by the presence of asynchronous species (several sub-populations at different stages) and polyvoltine species (several generations per year).
 
In case of pollution, often associated with flooding, the resilience time is considerably extended.

Low water
 
During the hydrological cycle, the drop in flow during the summer period leads to major changes in the way rivers function. A severe and prolonged low water level can lead to complete dryness. This may be periodic in the case of temporary rivers, and results from evaporation and/or outflow of water.
 
During low water, environmental conditions become unfavourable and lead to selection in species. Slow flow limits the mixing of the water and jeopardises good oxygenation.
In summer, low flows cause the water to warm up and the dissolved oxygen level in the water to fall even further.
The low water period encourages the accumulation of organic matter in the riverbed. As this organic matter breaks down it will consume even more oxygen in the water. The high water temperature and the accumulation of organic matter can create anoxic conditions.
Low runoff in summer periods results in an increase in the concentration of pollutants in the water.
This deterioration in environmental conditions can lead to a weakening of aquatic organisms and even mortality. During this critical phase, the fauna is more vulnerable to pathogens such as viruses and bacteria, along with parasites and pollution.
 
During periods of low water, the reduction in the habitat of species and the thickness of the water surface limit the free movement of individuals.
 
 
Complete dry out: the case of temporary Mediterranean rivers
 
In the case of a complete draining of the riverbed, the recolonisation of the environment, after the water has been restored, takes place in 4 successive stages:
 
The first corresponds to colonisation by aquatic invertebrates that have survived the complete dry period, in a state of “suspended” life, such as the Gastropod mollusc Ancylus fluviatilis, the Oligochaete Eiseniella tetraedra and the Diptera Chironomidae.
 
The second stage is achieved by the hatching of the first eggs of the Ephemeroptera Habrophlebia fusca and Caenis martae, as well as the Trichoptera Tinodes agaricinus.
 
The third phase corresponds to the arrival, by air, of adult beetles such as Helichus substriatus and Deronectes moestus.
 
The final stage sees the appearance of new species arriving by ordinary drift from the benthic populations of the zones that remain in the water, located upstream. These zones constitute biological reservoirs which play a fundamental role in the recolonisation of the environment. However, obstacles to ecological continuity disrupt conditions for the movement of species. The restoration of ecological continuity (levelling of dams, etc.) is therefore essential for the resilience of the aquatic ecosystem.

2. Direct anthropisation (dams, pollution, contamination)
 
Dams
 
Here we deal with the case of a hydroelectric complex comprising a dam and its reservoir as well as a hydroelectric plant, located downstream of the dam and fed by the hypolimnetic water of this reservoir.
 
The impact of the dam on the physico-chemical and biological characteristics of the watercourses is reflected in:
(i) A disturbance of the thermal regime;
(ii) A change in the physico-chemical nature of the water, in particular conductivity;
(iii) A decrease in the taxonomic richness of benthic invertebrate communities;
(iv) Depletion of Trichoptera, Ephemeroptera, Plecoptera and Molluscs.
(v) The proliferation of Diptera (Simuliidae and Chironomidae) and Oligochaetes.
 
 
Variation in the structure of benthic invertebrate populations in a river impacted by hydroelectric developments
 
 
The impact of the hydroelectric schemes is more pronounced in the section of the river subject to hydropeaking (short-circuited section downstream of the plant) than in the instream flow sections (downstream of the dam). Hydropeaks are daily variations in flow, linked to the operation of the hydroelectric plant.
 
 
 
Evolution of the hourly flow (in m3/s) of the Golu from 23 to 29 July 2021 (source Banque Hydro)
 
 
 
Pollution
 
In Corsica’s rivers, the steepness of the slope results in a rapid and turbulent flow that ensures good oxygenation of the water through mixing, meaning the self-purification of the rivers is very effective.
But urban discharges, whether treated or not, cause disturbances. The significant input of grey water or domestic water modifies the characteristics of the abiotic (water chemistry, substrate) and biotic (algae, invertebrates, fish) factors of the aquatic ecosystem.
 
The impact of pollution on the physico-chemical parameters of water is manifested by the appearance of nitrogen and phosphorus salts.
 
The change in the composition of benthic invertebrate communities is reflected in:
 
(i) The increase in diversity for some taxocenoses (Hirudinae, Oligochaetes, Diptera) while it is reduced for others (Ephemeroptera, Plecoptera, Trichoptera and Coleoptera);
(ii) The disappearance or reduction in numbers of pollutant-sensitive taxa;
(iii) The appearance of taxa strictly dependent on organic matter;
(iv) The increase in the density of pollutant-resistant and saprobiont taxa (Oligochaetes and Diptera Chironomidae);
(v) Increasing the density of the settlement of lenite habitats;
(vi) The increase in predators of certain saprobionts such as Hirudinae that feed on Oligochaetes and Chironomid larvae;
(vii) The significant increase in the relative abundance of collectors (Orthocladiinae and Chironomini) in relation to the enrichment of water with suspended organic particles;
(viii) A net decrease in the relative abundance of grazing invertebrates (bottom feeders) as benthic diatoms disappear in favour of bacteria.
 
The impact of organic discharges on the drifting community results in:
(i) Reduction in faunal diversity and drift density;
(ii) The increase in the relative abundance of Diptera;
(iii) The decrease in the relative abundance of Ephemeroptera, Trichoptera and Coleoptera;
(iv) The disappearance of pollutant-sensitive organisms while they are still represented in the benthos;
(v) Increased drift of pollutant-resistant or saprophilic taxa (OrthocladiinaeChironominiPsychoda).
 
The variation in the faunal composition of the drift is therefore a relevant parameter for assessing the impact of organic pollution.
 
 
Variation in the structure of benthic invertebrate populations in a river impacted by urban discharges

Contamination
 
The impact of a former arsenic mine, located on the banks of the Presa, a tributary of the Bravona, has resulted in arsenic and antimony contamination of the physico-chemical and biological compartments of the water.
 
Downstream of the mine, the average arsenic concentration in the water is 1,000 times higher than that obtained in the reference station.
 
The contamination of the environment has led to the disappearance of 19 species of benthic invertebrates as well as a clear reduction in the number of about 10 species.
 
In the invertebrates present downstream of the mine, the larvae of Plecoptera show the highest concentrations of arsenic and antimony.
For Leuctra plecoptera, the value of the bioaccumulation factor (which is the ratio between the concentration of arsenic or antimony in the invertebrates and the average water contents) is 800 for arsenic and 1,300 for antimony.
 
At the most contaminated station, the average arsenic and antimony concentrations of the bryophyte Fontinalis antipyretica are 353 and 48 µg/g respectively; the arsenic and antimony contents in the mosses increase with those in the water. The bioaccumulation factor is 160 for arsenic and 370 for antimony.
 
Trout living downstream of the mine have an average concentration of 1.92 µg/g of arsenic and 0.45 µg/g of antimony. The phenomenon of organotropism has been highlighted, with classification in descending order of the various fish organs studied according to bioaccumulation is (i) for arsenic: operculum > liver > gills > axial skeleton > muscle and (ii) for antimony: operculum > gills > axial skeleton > liver > muscle. The arsenic and antimony concentrations for all organs correlate closely with those found in the water.
 
In the contaminated station, the study of the evolution of arsenic and antimony concentrations in the food chain shows that bioaccumulation decreases with increasing trophic levels.
 
 
3. Indirect anthropisation (climate change)
 
The consequences of global warming on the aquatic invertebrate populations of Corsica’s waterways are reflected in the modification of the altitudinal limits of the distribution area of certain species.
 
Climate change is reducing the ecological niche of many cold-water species, restricting their range to upper rivers and springs.

Altitudinal limits of some “cold” stenothermic organisms
 
The planarian Crenobia alpina corsica and the Deronectes lareynieri beetle, whose lower limit of distribution was 650 metres in 1964, have not descended below 1,000 metres since 2010.
 
The Graptodytes sexgattatus beetle and the Baetis cyrneus mayfly have also seen their range restricted. The lower limit of the range has increased from 400 m to 800 m in 48 years.
 
 
As the water warms at higher altitudes, the upper limit of the range of warm-water species is moving upwards. In the upper reaches of rivers, interspecific competition is increasing and the survival of endemic species, which are numerous at high altitudes, is threatened.
 
Altitudinal limits of some “warm” stenothermic organisms
 
The Yola bicarinata obscurior and Eubria pallustris beetles are “warm” stenothermic organisms. In the early 1960s, the upper limit of their range was around 500 m in altitude. Since 2010, these invertebrates have moved up to 1,000 metres.
 
The upper limit of the range of the Diptera Liponeura cortensis has increased from 800 m to 1300 m in 48 years.
 
The Ephemeroptera Serratella ignita, which did not exceed 1,000 m in 1964, has risen to 1,450 m since 2010.
 

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X. Water uses in Corsica
 
A. Past uses
 
The mills, washhouses and fountains which bear witness to the past use of water, remain an invaluable built heritage.
 
Aqueducts are more consequent structures reveal the past mastery of water management.
In the Ajaccio region, the twenty or so aqueducts of the Gravona canal played a fundamental role in supplying water to the town of Aiacciu, but also in the farming of the land crossed by the canal. Built under Napoleon III, this 20 km long canal has some major works such as the aqueducts of Ponte Bonello, Mezzavia and Mulinu Biancu.
 
The Aqueduct of Moriani (commune of San Niculau), also called Canal de la Forge, is a Genoese structure built in 1578, about one kilometre long. It fed the Moriani Forge, which used hydraulic power to operate its equipment, from a catchment in the Pietrignani river.
 
In Ghisoni, an irrigation canal of almost 3 km, called “u fossu”, built around 1860, enabled the irrigation of several hundred hectares of agricultural land. It is still in use today.
 
 
Old dams show the importance of storing water in winter for use during the particularly dry summer period.
 
The Caprioni dam, known as the Coti-Chiavari penitentiary dam, was built between 1870 and 1871 at the place called "Caprioni" on the stream called "Furmiculosa". The dam is 19 m high, 55 m long and has a wall width of 5.50 m at the face. It has an overflow device located on the left side of the structure. Its volume is estimated at 24,000 m3. It was built as a gravity dam using ashlar masonry and hydraulic lime.
 
The Argentella mine dam is located in the communes of Galeria and Calenzana.
Although the exploitation of silver ore dates from the Genoese period, the construction of the dam dates from 1869. The dam, 20 m high and 144 m long, creates a reservoir with a capacity of 80,000 m3.
 
Another mining operation, the former Matra arsenic mine, is another example of industrial water use. A river intake was used to transport water to the ore washing plant. Unfortunately, the former Matra arsenic mine is a perfect example of a past activity that hinders the current development of the eastern plain due to arsenic and antimony contamination of the water.
 
 
B. Current uses
 
Water is a renewable natural resource, but it is not inexhaustible. In view of the consequences of climate change, it must be saved.
 
Water used corresponds to water drawn for a given use; water consumed corresponds to the part that is not returned to the environment.
In the case of hydroelectricity production, the vast majority of this water is discharged into the environment; we therefore speak of use and not consumption. In Corsica, the annual volume of water turbinated varies from 500 to 900 million cubic metres.
Water that is discharged after its use (domestic water) is called wastewater.
 
The uses of water and aquatic environments
 
Domestic use: 
            Drinking water (drinking, hygiene, washing, sanitary disposal);
Vegetable gardens;
Fire fighting;
Recreation (aquatic environments, private swimming pools).
 
Economic use:
Agriculture (including irrigation);
Energy production (hydroelectricity, cooling of thermal power plants);
Extraction of alluvial materials (gravel pits);
Public administration;
Agri-food;
Shellfish farming;
Recreation (public swimming pools).
 
 
Annual water consumption by use
 
In Corsica, the annual volume of liquid precipitation (rain) and solid precipitation (snow, hail) is around 8 billion m³. After evapotranspiration (physical evaporation and transpiration by vegetation) and infiltration, the flow in all the watercourses is 3 billion m3, i.e. a flow rate of 100 m3/s.
The eight most productive catchment areas alone account for nearly 75% of the resource (Golu, Tavignanu, Taravu, Liamone, Gravona, Prunelli, Rizzanese and Fium’Orbu).
 
In Corsica, gross annual withdrawals are between 90 and 110 million cubic metres, of which 70 to 90 million cubic metres come from surface water. For groundwater, the volume withdrawn is 25 Mm3 per year.
 
1) Agriculture: 58 Mm3 of which 46 Mm3 for irrigation; withdrawals are made from surface water (dams and rivers).
The Eastern Plain is the sector of the island where consumption is the highest (35 to 50 Mm3).
 
The PADDUC (Plan d’Aménagement et de Développement Durable de la Corse) was approved by the Assembly of Corsica on 5 November 2020. One of the objectives of this strategic document is to protect agricultural and forestry areas in order to double agricultural and forestry production in thirty years. The mapping of ESAs (Strategic Agricultural Areas) shows a total surface of about 100,000 ha; today, only 20% of ESAs are irrigated.
 
2) Drinking water supply: 45 Mm3 of which 22 Mm3 from surface water (rivers and artificial reservoirs) and 23 Mm3from groundwater (springs, boreholes in alluvial aquifers and basement aquifers).
The resident population consumes 80% of this resource and the tourist population 20%.
 
3) Industry: for the cooling of the engines of the Vaziu and Lucciana thermal power plants, EDF uses nearly 0.1 Mm3.

Network efficiency
 
In 2015, the efficiency of the raw water networks was close to 70%. It does not exceed 50% in the Eastern Plain, which is the sector of the island where consumption is the highest (35 to 50 Mm3).
For drinking water networks, the efficiency value is between 80 and 90%.
 
 
Hydroelectricity
 
The total power of EDF’s hydroelectric production is 199 MW. This energy is produced from the infrastructures (3 dams and 7 hydroelectric power stations) located in the Golu, Fium’Orbu and Prunelli valleys.
Small-scale hydro, not managed by EDF, represents less than 30 MW.
 
The electricity mix is based on a more or less balanced mix of thermal (369 MW), interconnection with Italy (150 MW) and renewable energies.
Thermal energy is the foundation of the electricity mix, with fuel oil accounting for 41% of electricity production.
Hydropower is the leading renewable energy source, accounting for 20% of electricity production.
With 30%, the interconnections with Italy (SARCO and SACOI cables) are essential for the safety of Corsica’s electricity system (Sardinia-Corsica and Sardinia-Corsica-Italy cables).
Renewable energies other than hydroelectricity are developing: Solar (6%), Wind (2%) and Biogas (0.5%).
 
The consequences of climate change have an impact on the energy sector. Indeed, the low filling rate of the reservoirs managed by EDF mortgages the energy mix, which leads to an increase in the share represented by thermal energy, particularly the use of fuel oil.
The low snowfall in our mountains leads to low river flows and limited hydropower production. In 2017, large-scale hydropower accounted for only 15% of the electricity mix due to severe summer low water levels in rivers.
 
Thanks to global warming and its mild winters, energy savings for heating are real. But we must not forget the increase in energy consumption in the summer period, due to tourist activity and the development of air conditioning.
The maximum power demand on the grid in winter varies from 400 to 450 MW. In summer, it approaches 350 MW, with a record of 379 MW reached in August 2017.
This increase in summer consumption has an impact on production costs. Indeed, in Corsica, the average annual cost is €200/MWh but it varies from €150/MWh in February to €250/MWh in August when hydraulic production is very low and thermal oil represents 60% of the total electricity production.
 
 
Water reserves stored in reservoirs
 
In Corsica, the total volume of nearly 109 Mm3
Edf 61.6 Mm3
OEHC 47.3 Mm3
 
In Corsica, gross annual withdrawals are between 90 and 110 million cubic metres, of which 70 to 90 million cubic metres come from surface water. For groundwater, the volume withdrawn is 25 Mm3 per year.
 
Current and future needs global warming
 
In Sardinia
 
1.65 million inhabitants, 3.44 million tourists
 
Water consumption is estimated at 1,160 Mm3 per year
 
The Regional Agency of the Hydrographic District of the Autonomous Region of Sardinia has a department responsible for the management of (i) water resources, (ii) water services and (iii) drought.
 
 
34 dams with man-made reservoirs providing storage of nearly 1,900 Mm3
 
The largest reservoirs Omodeo (450 Mm3 ), Monte su rei (323 Mm3 ), Nuraghe arrubiu (263 Mm3 ), Muzzone (224 Mm3), Calamaiu (104 Mm3 ) account for 72% of the total.
 
Crisis management plan
Ordinary regime, vigilance level, danger level, emergency level
 
filling
cyano temperature
eutrophication and anoxia
 
Agriculture 60-70%, domestic 20%.
Low network efficiency 50 to 60% agricultural, 35 to 40 water supply.
 
Most were eutrophic, with phytoplankton communities dominated by cyanobacteria. The presence of cyanotoxins was assessed in a number of Sardinian reservoirs, with microcystins (MC) being the most frequently detected cyanotoxin.
 
Complex interactions between eutrophication and climate change, although it is likely that climate factors will lead to larger and more frequent proliferation events.
 
Average annual rainfall ranges from 400 mm near the coast to 900 mm inland, with an average of 50 rainy days per year; average annual temperature is 15°C (RAS, 1998). River water collected in artificial basins accounts for about 70% of the water supply for agriculture, industrial and domestic uses for a population of about 1.6 million people. The availability of reservoir water is very low in the Iglesiente (SW Sardinia), while the Cambrian carbonate formations host important aquifers due to intense fracturing and karst processes.
 

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XI. Water and human health
Corsica’s surface and ground waters contain traces of pesticides, drugs (antibiotics, anti-inflammatory drugs), endocrine disruptors (hormone-mimetic properties capable of interacting with the hormonal system), and plastic microparticles.
Biological agents such as bacteria, viruses and parasites are identified in these waters. As well as natural or anthropogenic chemical elements such as arsenic, antimony, nitrates...
 
1. Water intended for human consumption (EDCH)
The chemical quality of water distributed in Corsica is generally good and the main cause of non-compliance is linked to the presence of germs indicating faecal contamination. The 2020 assessment reveals that 90% of the population in Corsica is served by water that meets bacteriological quality requirements (ARS, 2021).
However, tap water quality problems still exist in rural areas due to: (i) the obsolescence of the networks, (ii) the lack of appropriate treatment facilities and (iii) inadequate maintenance and operating conditions.
Why should you drink tap water?
3 arguments exist:
(i) Water quality. Bottled water is no purer than tap water. A scientific study was conducted by American researchers on bottled and tap water in 9 countries including the USA, China, India, Mexico and Brazil. The study shows that water in plastic bottles contains twice as many plastic microparticles as in tap water.
(ii) Economy. Bottled water is 500 times more expensive than tap water. Consuming bottled water is a double penalty. The infrastructure (pipes, reservoirs, treatment systems) is financed by our taxes and fees (water bills). And then there is the backache of carrying the water packs.
(iii) Ecology. The production of one plastic bottle requires the consumption of 100 ml of oil. Since the first plastic bottle in 1960, billions of units have been manufactured. In Corsica, plastic bottles represent about 7,000 tonnes per year, with recycling only 50%. Many bottles end up in rivers and the sea. Time taken for plastic bottles to break down varies from 100 to 1000 years. Plastic microparticles are found throughout the food chain: shellfish, fish, cetaceans, humans.
 
2. The natural geochemical background
In pollution-free waters, the geological nature of the terrain through which the water flows determines its physico-chemical characteristics. The ionic load of water can be acquired in many ways, the most important being the alteration of the minerals that make up the rocks by carbonic acid from the atmosphere and organic acids from the percolating water in the soil.
Trace elements, formerly called heavy metals, have natural background concentrations that are sometimes high in relation to quality standards (global, supranational, national). For a given trace element, the natural soil-geochemical background corresponds to the natural endogenous concentration related to the nature of the bedrock and soils.
As the geological nature plays a fundamental role in this “background noise”, the situation for “Hercynian Corsica” and for “Alpine Corsica”, separated by a line connecting Saint Florent to Solenzara via Corti, are presented separately.
To the north of this line, “Alpine Corsica” is made up of lustrous schists of Tertiary age. Ophiolites (green rocks) and a very diverse range of metamorphic rocks are found here. In places, the surface and underground waters of the north of the island have high levels of trace elements.
This is particularly the case in Cap Corse where the presence of shale causes high levels of antimony, iron and manganese.
The presence of antimony and arsenic in the waters of the Bravone valley is natural, but is accentuated by past mining activity (Matra realgar mine).
In the upper Fium’Altu valley (Orezza micro-region), the high iron content in the ground and surface water is linked to the presence of lustrous schist, serpentine, calcschist and cipolin.
To the south of the line linking San Fiurenzu to Sulenzara via Corti “Hercynian Corsica”, or “ancient Corsica”, extends over more than two thirds of the island and dates from the primary era. This geological unit is essentially made up of plutonic rocks (granite, diorite, gabbro) and a rhyolitic volcanic complex in the Cintu and Osani massifs. 
The presence of trace elements in the water is less frequent than in “Alpine Corsica”. High levels are related to past mining activities. This is the case in Balagne, where the water can have significant concentrations of arsenic, copper, manganese, lead and zinc.
Rhyolites and volcanic tuffs are the source of copper, lead and zinc in groundwater and surface water.
Water flowing over gabbro and diorites can have high copper contents. In the Cintu massif, the presence of nickel in the water is linked to the natural pedogeochemical background.
In the Prunelli valley, the presence of fluorite seams within the granite explains the high concentration of fluorine in the water.
In the Southern Corsica micro-region, the presence of gneiss and migmatite is the reason for the arsenic, copper, iron and manganese content. The last two elements are also present in the waters of the Ortolu valley.

Antimony. Acute intoxication is characterised by digestive problems (vomiting, stomach cramps and diarrhoea); chronic intoxication causes haematological disorders. High doses cause cardiac toxicity (changes in repolarisation).
Arsenic. Acute intoxication is characterised by gastrointestinal disorders, followed by severe neurological disorders, liver and kidney disorders and cardiovascular manifestations of hypertension and tachycardia. Chronic intoxication results in digestive disorders, melanodermic and neurological syndromes. Arsenic and its inorganic compounds are classified as proven human carcinogens. Epidemiological studies have shown that exposure to arsenic through ingestion of contaminated water can cause lung, skin and bladder cancer, and possibly kidney and colon cancer. Other studies suggest an association between exposure to arsenic in drinking water and the development of prostate and liver cancers.
Copper. Copper is an essential element for the human metabolism but is toxic at high levels. Copper intoxication results in gastrointestinal problems. New-borns are particularly vulnerable to excess copper. Zinc and iron levels can influence copper absorption.
Iron. Iron is an essential element for our body as it is involved in the biosynthesis of haemoglobin. But ingesting high doses can lead to a progressive accumulation of iron. Iron overload increases the risk of cancer, especially colon cancer.
Fluoride. Fluoride is important for dental health, as it promotes mineralisation and protects against tooth decay through its antibacterial action. However, ingestion of high doses can cause abdominal pain, nausea, vomiting and diarrhoea.
Manganese. Manganese poisoning is extremely rare, but high levels can give water an unpleasant taste.
Nickel. Nickel has a relatively low digestive absorption and is therefore not very toxic via the digestive tract.
Lead. The passage of lead through the enteral epithelium is low in adults but enteral absorption is more active in children, resulting in more severe intoxication: abdominal pain, constipation, encephalopathy, intellectual deficiencies, stagnation of the growth curve, anaemia, (lead poisoning). Lead crossing the placental barrier is said to be responsible for miscarriages and foeto-toxicity.
Zinc. Zinc is an essential element in the human metabolism, as it is involved in the biosynthesis of DNA and RNA. However, ingestion of high doses of zinc affects the immune system, lowers blood levels of good cholesterol and increases oxidative stress; it can lead to genito-urinary disorders.
 
3. Pesticides

Pesticides are used to control harmful organisms (animals, plants, fungi). Pesticides are mainly used in agriculture and are referred to as phytosanitary or phytopharmaceutical products. They are also used in non-agricultural applications, particularly by local authorities and private individuals, and are known as biocides. We should not forget human antiparasitics (lice treatments, etc.).
The quantities sold in Corsica amount to 300 tonnes in Upper Corsica (mainly in the eastern plain) and 50 tonnes in Southern Corsica (Source: BNVD). Per year, hazardous organic substances represent 50 to 60 tonnes, including 25 tonnes of the herbicide glyphosate. The annual sale of dangerous mineral substances, mainly copper (fungicide), is 15 tonnes.
From 2010 to 2017, the quantity of toxic, highly toxic, carcinogenic, mutagenic and reprotoxic substances amounted to 800 tonnes (Source: BNVD).
Glyphosate and AMPA (Amino-Methyl-Phosphonic-Acid), which is the main degradation product of glyphosate, are the most frequent pesticides in the waterways of mainland France, including Corsica. Pesticides banned in France are found in these waters, such as atrazine, a herbicide banned since 2001. The persistence of this substance in hydrosystems is very high.
In Corsica, AMPA is present in the water column and in the sediment at the bottom of dams; this stored water is intended for human consumption. This pesticide has consequences on health. Several studies have shown the role of glyphosate in the appearance of lymphomas. It is classified as a probable carcinogen by the WHO.
Although banned since 2001, atrazine is found in trace amounts in running water. The atrazine molecule is transformed into metabolites by the action of micro-organisms. One of the specific metabolites is desethylatrazine (DEA), which is found in groundwater.
Although atrazine is classified as non-carcinogenic by the International Agency for Research on Cancer, DEA appears to be more toxic than the parent molecule. It is known that this metabolite affects foetal growth in mammals.
Apart from the problem of pesticides in water, the first people exposed to the dangers of pesticides are farmers and even amateur gardeners. Farmers tend to depend on pesticides in the same way some doctors do on antibiotics.
There is a strong link between exposure to pesticides and numerous pathologies in adults, notably cancers, neurodegenerative diseases and anxiety disorders. Since the 1970s, the French agricultural world has experienced an excess of deaths by suicide (one suicide every two days). The causes are not only economic and financial. The link between suicide and the use of pesticides has been noted in numerous scientific studies, particularly in India, the United States, Canada and Brazil.
The annual quantity of chlorpyrifos-methyl sold in Corsica is 3 to 4 tonnes. Exposure to this neurotoxic and endocrine disrupting insecticide can cause leukaemia in adults and has an impact on neurodevelopment in children.
A scientific study conducted in the USA concluded that there is a relationship between exposure to chlorpyrifos in pregnant women and autism, with the risk being multiplied by 6. The critical period is weeks 1 to 8 of pregnancy, i.e. the period of development of the foetus’s nervous system.
Fosetyl-aluminium and folpel are fungicides where quantities sold in Corsica vary from 25 to 30 tonnes per year. The safety data sheet, provided by the seller, specifies the “Hazard warning”. It is clearly stated that this category of fungicide is “Very toxic to aquatic organisms”. Even more seriously, the carcinogenicity statement of the product leaves no doubt: “Suspected of causing cancer”. These fungicides are suspected of causing duodenal adenocarcinoma (cancer of the duodenum).

4. Cyanobacteria
 
Cyanobacteria, also known as cyanophyceae, are autotrophic prokaryotes, systematically classified in the kingdom Eubacteria. These micro-organisms are distinguished from bacteria by the presence of chlorophyll and accessory pigments.
 
They appeared about 3.8 billion years ago and are among the organisms that are responsible for the expansion of life on Earth through their production of oxygen and their contribution to the first biological carbon sink that reduced the greenhouse effect.
 
Cyanobacteria occur naturally in small numbers all over the world, and in virtually all environments, even the most extreme. Wherever there is water, there can be cyanobacteria.
 
The proliferation of cyanobacteria is the consequence of a combination of their adaptations and environmental factors. These factors are mainly:
            - a high concentration of phosphorus in the medium;
            - good stability of the water column
            - high water temperature.
 
The growth of cyanobacteria can have an impact on water quality, as some cyanobacteria have the ability to produce toxins called cyanotoxins.
 
There are three main groups of cyanotoxins classified according to their mode of action:
- dermatotoxins have the skin as a target organ (irritants);
- Neurotoxins mainly affect the nervous system (headache, dizziness, muscle cramps, paralysis, respiratory or heart failure);
- Hepatotoxins mainly affect the liver (inflammation), but can also affect other organs, such as the kidneys or intestines (diarrhoea, stomachache, nausea and vomiting).
 
Hepatotoxins are the most common and harmful toxins in cyanobacterial blooms. Among them, microcystins are the cyanotoxins most frequently involved in cases of animal or human poisoning.

Good and bad cyanobacteria
 
The production of cyanotoxins by cyanobacteria represents a danger to human and animal health. These microalgae are therefore considered potentially dangerous. But we must not forget the important role they play in certain situations.
(i) Cyanobacteria are the origin of aerobic life on Earth through the production of oxygen by photolysis of water.
(ii) In rice cultivation, they are considered as a green manure; cyanobacteria are microbial biofertilisers, i.e. microorganisms that fix atmospheric nitrogen, and have thus played a fundamental role in rice production for centuries without the use of nitrogen fertiliser.
(iii) The use of dietary supplements based on spirulina, which is a cyanobacteria, is growing rapidly.
 
5. Indigenous urogenital bilharzia (schistosomiasis) (see Climate Change)

6. The tiger mosquito, Aedes albopictus, and vector-borne diseases (see Climate Change)
 
7. The precautionary principle

There are two such principles, the first of which was introduced into French law by the Barnier Act of 2 February 1995 and was enshrined in the 1958 Constitution when it was revised on 1 March 2005. This precautionary principle has an objective dimension: “When the occurrence of damage, although uncertain in the light of scientific knowledge, could seriously and irreversibly affect the environment, the public authorities shall ensure, by application of the precautionary principle and within their areas of competence, the implementation of risk assessment procedures and the adoption of provisional and proportionate measures in order to prevent the occurrence of damage.” The concrete conditions of application of the precautionary principle remain unclear.
But the second precautionary principle has a subjective dimension, it allows us to claim the right to live serenely, not to be exposed to a worry. And we must all claim this right.
We must remember that the constitutional law of 1 March 2005 relating to the Charter of the Environment, proclaims in article 1 that: “Every person has the right to live in a balanced environment that respects health”.