Regional Mountain Conference

Alpine lake chemical composition depends on several local and regional factors, including catchment cover. geographic and morphometric characteristics, atmospheric deposition and meteo-hydrological conditions. Local human activities may also lead to changes in the chemistry of lake water, by directly introducing allochthonous compounds, including toxic compounds, or indirectly triggering trophic cascades that can alter the lake’s trophic status. Fish introduction, livestock and other sources of nutrients and organic pollutants may indeed cause lake eutrophication or nutrient imbalances, with an overall effect on water quality.

The present study is based on 536 water samples collected over an 18-year monitoring period from 22 high altitude lakes in the protected areas of Gran Paradiso National Park and Monte Avic Natural Park. The monitoring, still ongoing, has been performed within the LIFE projects BIOAQUAE (Biodiversity improvement of Alpine aquatic ecosystems; 2012-2017) and RESQUE ALPYR (Restoration of aquatic ecosystems in protected areas in the Alps and Pyrenees; 2022- ). The study lakes are affected by several threats (livestock grazing, overtourism, introduced fish fauna) possibly interacting with each other. Sixteen lakes have been or are currently subject to fish eradication during the study period, representing an ideal direct test of the possible effects of non-native fish on nutrient concentrations.

The variability of chemical composition is assessed on a seasonal and interannual basis and analyzed in relation to environmental drivers, including lake morphology, catchment characteristics and anthropogenic pressures. Some lakes exhibit an increase in conductivity and major ions, that may be ascribed to a climate-related increase in weathering processes. Trends in nutrients are not evident, suggesting that in our study area there is no clear climate-driven increase in atmospheric nutrient deposition. We do, however, detect an effect of grazing livestock on nutrient levels, while the influence of fish presence and removal is less clear. This may indicate that lake responses to anthropogenic disturbances and restoration actions are either delayed or highly context-dependent, potentially confounded by multiple interacting factors such as benthic production and pelagic grazing. Long-term data collected with standard methods are confirmed as an invaluable tool to assess mountain lake chemical changes and their drivers.