Rhône River ecosystem

• Category: Inland Aquatic Biomes.
• Geographic Location: Europe.
• Summary: This major European river supports fertile lands where wildlife and plants flourish.

Descending precipitously out of the western Alps from an altitude of nearly 1.1 miles (1,800 meters) high, winding below the Jungfrau, Matterhorn, and Mont Blanc peaks, the Rhône River’s relentless flow originates from the melting glacier bearing its name. The river then flows through a granite-based valley of braided streams and wooded flood plains, meandering 504 miles (812 kilometers) to its silt-strewn mouth at the Mediterranean Sea. From the soaring Alps in Switzerland, through France, and into the Mediterranean, the Rhône plummets sharply as it claims over 37,838 square miles (98,000 square kilometers) of watershed fed by incessant glacial meltwater enhanced by periodic rain and snowfall.

The river’s floods can be prodigious, rising to ten or more times its expected annual flow in just one season. The Rhône has long been the gift of the Alps to the awaiting Gulf of Lion coastal region in southern France, nourishing along the way the forests, fisheries and flyways of the seasonally drier Provence region. The river is one of the few major freshwater sources for this sea—since the Nile River was heavily dammed in the 1970s at Aswan.

The Rhône-Alps climate is continental and mediterranean, with temperatures averaging 38 F (3 C) in winter and 67 F (20 C) in summer. Rainfall averages 3 inches (71 millimeters) monthly in summer and 2 inches (56 millimeters) monthly in winter, with an annual total of 32 inches (825 millimeters).

Biodiversity

Agriculture in the Rhône valley largely covers the low areas, plains, and islands. The Rhône’s extensive flood plain provides wildlife with varied habitats: First, along the rapid descent through its alpine forested and glaciated valley, before abruptly bending southward at the city of Lyon, then watering mixed hardwood forests on its way into the wide brackish delta, the Camargue, south of Arles and west of Marseilles. Dry sclerophyll forests dominate the Mediterranean coastline around the Camargue; these areas are characterized by vegetation that is fire-adapted, if not fire-dependent, for reproduction.

The greater Rhône valley is a conduit for both native and invasive vegetation, wildlife, bird-flyways, and fisheries—from the warm, arid, southern Mediterranean climate to the cooler, more moist northwestern European maritime zone. The river valley is the only north-to-south watercourse in western Europe, suturing the landscapes that blend together the different flora and fauna from the North and Mediterranean Sea bioregions.

Fifteen types of forests have been identified in the upper Rhône, revealing the diversity of tree species that protect the soils of the watershed. Alpine species, such as grey alder, German tamarisk, and sea buckthorn, are replaced by ash, oak, hornbeam, and common apple as the river moves south between the Alps and the Massif Central through the warmer sections of Provence. There are stands of fire-tolerant Aleppo oak, as well as stone pine, which requires moderate fire for its cones to release seed and re-forest the landscape. Also prevalent are wild orchids, which thrive in the lime-rich soil.

Thus, the Rhône’s watershed provides habitat for both alpine and boreal forest vegetation, as well as ecotone, or overlap, areas. Oak, maple, ash, and alder are common in the rich uplands, while semiarid scrub forests and salt marshes are spread widely about the river’s convergence with the Mediterranean.

However, agriculture, irrigated croplands, and vineyards have replaced much of the riparian woodlands, extensive wetlands, and original alpine forests, beginning gradually in the late Middle Ages. By the 14th century, forested areas had been significantly reduced for cultivation purposes. Such activity from the lowlands to the alpine meadows has driven wildlife to the edges of the watershed. Wolves, lynx, ibex, chamois, European beaver, and mountain goats are among the more than 38 larger animal species still extant in the mountainous reaches of the watershed, which provide the most sheltered habitats.

The Rhône River basin is home to many protected species, nationally and locally, including amphibians, reptiles, birds, and mammals. The biome is frequented by such birds as the crested falcon, Egyptian vulture, Lammergeier or bearded vulture, and many species of falcon, eagle, buzzard, and owl. Black and royal kites and ospreys have also been spotted among the ranks of raptors.

Fish found in the Rhône include trout, pike, pike-perch, salmon, bream, catfish, and carp. The small, nocturnal Apron fish, sometimes called the Rhône streber, is only found in this river, but its populaion is endangered because of pollution and climate change. While sport fishing is common, the sport is strictly policed for ecological reasons, particularly for the presence of bioaccumulated toxic chemicals.

Human Influences

Approximately 58 million people live in the area near the river, with the river’s natural flow controlled by many dams that generate up to one-quarter of French hydroelectric power. Below its glacier source in Switzerland, the river flows into and out of Lake Geneva, where nearly the entire lakeshore has been affected by agriculture. Nuclear power plants use huge amounts of the river’s ample and mostly regulated flow of water to cool the fission reactors. However some curtailed power production in the early 2020s following the 2021 Russian invasion of Ukraine.

Large and small industries have been established throughout the region, most notably aluminum and chemical plants in Valais, oil refineries at Lyon, and the refineries and steel mills at Fos.

The Rhône has long attracted tourists, and this industry plays an increasingly important role in the regional economy. Recreational activities, from skiing and climbing in the Alps to horseback riding in the Camargue, help underpin the economy, but deliver various stresses to the biome.

Environmental Issues

Wetland loss exacerbates flooding and pollution from agriculture, industry, and nuclear power plants. Reporters noted in 2005 that sufficient polychlorinated biphenyls (PCBs) had been dumped in the river near Lyon to contaminate the river perch and other food fish to an extent such that fishing in the river had to be abandoned.

Deforestation, pollution, and erosion accompanying settlement, grazing, forestry, and agriculture have generated groundwater loss, which has triggered the retreat of native forest cover and altered the river’s course from braided streambeds to a dammed series of controlled reservoirs, decreasing the biotic diversity of its fisheries. Dams block shad, lampreys, and eels moving up and down the river. With extensive dam development, sturgeon became extirpated here in the 1970s, leading to a sturgeon recovery plan that is still in its incipient stage.

Climate change has upset the predictable amounts and timing of snowmelt that feeds the river and waters the valleys that nourish local wildlife and pasturelands. Research indicates that between 1960 and 2020, the average summer flow in the northern Rhône River near Lake Geneva decreased by 7 percent, and in the south, the flow decreased by 13 percent. Rising temperatures have driven many species to higher ground, where the flora base of the food web is under greater pressure to provide sustenance. Rainfall levels are more unpredictable; there have been many major floods of the Rhône and other Alps-sourced rivers in the first decades of the twenty-first century. However, some longer-term research suggests that drought could be the more severe threat.

As with other European rivers, in the early 2020s, the Rhône had decreased water levels caused by drought and an increase in average temperatures. As this trend continues, experts predict disputes will occur concerning the use of available water, and nuclear power production will decrease. Because the Rhône River is the primary water source for over two million individuals and the irrigation source of over 2,700 farms, this decrease is a large-scale concern for the region.

Bibliography

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