Camargue wetlands

Category: Marine and Oceanic Biomes.

Geographic Location: Western Europe.

Summary: This ecosystem has lost one-third of its productive area in the past 50 years and is increasingly threatened by human activity.

The Rhône River spills into the northern Mediterranean Sea in a vast delta plain of sloping ridgelines, stranded riverbeds, salty lagoons, and coastal wetlands harboring significant biological diversity. This natural wealth in tangible forms of salt-tolerant herbs, rice fields, river and shore fisheries, birds, mineral salts, and livestock is associated with France's preeminent Mediterranean estuary. Flamingos, horses, rice, seasonal “mistral” winds, gypsies, bullfighting, and French faux cowboys are among the exotic subjects finding sanctuary in this remarkable wetland at the twin mouths of the Rhône, south and west of the city of Arles in the Languedoc region.

Extending behind 20 miles (30 kilometers) of dunes into the sea, the two diverging Rhône streams form the Grande Camargue. This sheltering core emerges as a mosaic of beaches, lagoons and marshes. Where rivers once flowed in slow loops, étangs, as these oxbows are called, evaporate under the Languedoc's simmering sun; the largest of these, Étang de Vaccares, forms the heart of this Biosphere Reserve. On the Rhône's west bank in the Petite Camargue lies Aigues-Morte, once a thriving medieval port, now stranded inland due to historically accumulating sediment that expanded the delta seaward. Since the Middle Ages, salt for curing food was dried on the flats.

The Rhône River mouth nourishes the Camargue's abundant diversity in an extensive estuary whose alpine-derived sediments are ensnared by shrubs, grasses, and halophytes. These maritime grasslands hold great biological wealth due to biotic nutrients trapped by a saltwater wedge, nourishing fish and birds attracted to the salt marshes and irrigated rice paddies. The expanse overflows into an area extending over 400 square miles (1,035 square kilometers) where the salt lagoons fed by the sea and dried by the summer sun persist beside the embanked rivers. Part of the Rhône's freshwater originates in glacial melt and snow, but is now diverted into 77 square miles (20,000 hectares) of cultivated rice in the Camargue's upland marshes.

Diversity

The unusual collection of estuarine plant communities here offers nesting or feeding for 35 bird species and 200,000 wintering ducks—making the Camargue a critical stopover point in their annual migrations. A fusion of fresh, brackish, and salt-water tolerant grasses, succulents, and diatoms thrive in an extended growing season, making for an uncommon amalgam of vegetative and bird species, some classified as threatened. Important bird rookeries were reserved dating from 1927, when nature preserves were created in the Rhône delta that later formed the essential wetlands protected in a 1962 agreement. The Camargue was designated a Ramsar site as a Wetland of International Importance on December 1, 1986.

The freshwater flow of the Rhône entering the lagoons works to stem the saltwater encroachment from the Mediterranean—but the sea is perhaps more relentless. In the 19th century the Digue à la Mer—a levee along 20 miles (30 kilometers) of the sea—was constructed to protect the Camargue's saline and hypersaline lagoons from the less salty Mediterranean seawater. Dams upstream of Arles along the Rhône's main stem have deprived the salt marshes of sediment in the last century, while providing hydroelectric power for the wine, chemical, salt, and tourist industries of the region. Less than a fifth of the sand, mud, and gravel historically provided by this northwestern Mediterranean river ever reaches the Camargue's sinuous waterways.

The loss of one-third of the productive marine wetlands over five decades in the Camargue has diminished the capacity of these salt marshes to absorb pollution while maintaining necessary productivity for livestock, fish, and birds. The Camargue's lagoons still give rise to a diversity of salt-tolerant succulents as well as brine shrimp that are a source of food for shore fisheries in the Gulf of Lyon, and also provide sustenance for the legendary flamingos and other wading birds. In 1997 an estimated 10,000 to 18,000 breeding pairs of flamingos nested here. Two threatened species have been documented in the Camargue: the European roller, which in 1997 was reduced to 50 to 100 breeding pairs, and the black-tailed godwit.

Shifting Influences

Despite the fact that ducks such as the teal (Anas crecca) help account for the spread of aquatic vegetation in the marshes, duck hunting has altered the hydrological character by introducing permanent freshwater ponds amid native salt marshes. Additionally horses and rabbits are agents of successional vegetation change in these wetlands, particularly by reducing the extent of rushes and sedges through grazing. Extensive rice cultivation—although helping to attract heron nesting—is responsible for pesticide contamination of the salt lagoons into which these paddies drain.

As a landscape shaped by the needs of salt industries, rice paddy farming, and livestock raising, these are contested grounds. Other forces also apply pressure, namely the region's chemical, steel, and petroleum refining interests and a preeminent port. Rice farmers allied with the native, evaporative, salt works have teamed up to defend regional biotic diversity. However, with declines in the nesting fowl of the Camargue, changes have developed due to both the hydrological alteration of the region's ecology and the pollution of its eel, wading bird, and microbial communities.

Clues to the shifting conditions of wildlife and fisheries reveal a complex disequilibrium creating the Camargue, strung out as it is between the Mediterranean-fed saline lagoons and diminishing sweet flows of the Rhône's watershed. Recent studies call for artificial buffers to retain freshwater runoff from rice fields to render persistent pesticide residues innocuous. This would assure some restoration of the natural cleansing capacity of the surrounding salt marshes to sustain rare plants and animals from the gradual, yet relentless, embayment from rising seas.

Bibliography

Arnaud-Fassetta, Gilles. “The Upper Rhône Delta Sedimentary Record in the Arles-Piton Core: Analysis of the Delta-Plain Subenvironments, Avulsion Frequency, Aggradation Rate, and Origin of Sediment Yield.” Geografiska Annaler: Series A, Physical Geography 86, no. 4 (2004).

Berlanga, Mercedes, et al. "Community Homeostasis of Coastal Microbial Mats from the Camargue during Winter (Cold) and Summer (Hot) Seasons." Ecosphere, 6 Feb. 2022, doi.org/10.1002/ecs2.3922. Accessed 23 July 2022.

Comoretto, L., et al. “Runoff of Pesticides From Rice Fields in the Ile de Camargue (Rhône River Delta, France): Field Study and Modeling.” Environmental Pollution 151, no. 3 (2008).

Golterman, H. L. “The Labyrinth of Nutrient Cycles and Buffers in Wetlands: Results Based on Research in the Camargue (Southern France).” Hydrobiologia 315, no. 1 (1995).

Roche, Helene, et al. “Rice Fields Regulate Organochlorine Pesticides and PCBs in Lagoons of the Nature Reserve of Camargue.” Chemosphere 75, no. 4 (2009).

Tourenq, Christophe, et al. “Spatial Relationships Between Tree-Nesting Heron Colonies and Rice Fields in the Camargue, France.” The Auk 121, no. 1 (2004).