Ecological quality of snowmaking reservoirs in the Alps and management perspectives

Abstract

Alpine freshwater ecosystems are biodiversity hotspots providing key ecosystem services. These ecosystems face threats from climate change and anthropogenic activities. Snowmaking reservoirs have emerged across the globe as a response to snow rarefaction and increasing winter tourism, and despite efforts to assess their environmental impact, our understanding of their ecological quality after being built remains limited. In the present study, we evaluated representative snowmaking reservoirs in French Alpine counties (départements) and their potential to serve as aquatic ecosystems. A comprehensive approach was employed encompassing ski resort surveys and geographical analyses of 136 reservoirs, complemented by investigations into abiotic characteristics and biodiversity surveys in 28 sampled reservoirs. The findings indicated that the multiplication and proximity of these reservoirs to freshwater habitats make them components of the alpine aquatic landscape. Terrestrial vegetation, although sparse, was commonly present on the banks of these reservoirs, but they systematically lacked aquatic vegetation. Faunal diversity appeared to be limited, and consisted of both indigenous and non-native species. Comparisons of snowmaking reservoirs with mountain lakes revealed similarities in water quality, implying the potential for similar oligotrophy and biotic communities. However, differences in conductivity, alkalimetry and pH were observed, possibly linked to distinct differences in water sources or retention times. Snowmaking reservoirs displayed unique habitat features through their structure and functioning. Although these reservoirs are attractive in terms of their biodiversity, there are concerns regarding their capacity to support species due to observations of drowned mammals and stranded amphibians and dragonflies. Our observations reveal potential ecological traps in the design, exploitation and uses of snowmaking reservoirs. Recommendations are made to enhance existing structures and future designs by increasing ecological processes and better protecting biodiversity.