Satellite remote sensing of chl-a in subalpine Italian lakes in the last 15 years

Deep lakes overall represent an important socio-economic and environmental resource for the region in which they are placed. These lakes are generally characterised by large surface area and great depths and large volumes of water and generally have a low trophic status. However, although these lakes are less vulnerable to eutrophication than small shallow lakes, a continuous input of nutrients has led to increasing eutrophication in many of them. For measuring the changes of water conditions in lakes, satellite data play a crucial role. Within this study we exploit a set of optical satellite data (MERIS, Sentinel-3, Sentinel-2, and Landsat-8) to assess chlorophyll-a concentration, as proxy trophic status in the largest Italian lakes in the subalpine ecoregion. Chlorophyll-a was retrieved based on the state-of-the-art algorithms, while statistical analysis tools (as Sen Slope estimator) were applied to evaluate chl-a trends and , phenology and peak abundance. The time series overall show almost stable conditions of trophic status for all lakes, with slight increasing in Lake Maggiore. Higher resolutions spatial data allowed to capture phytoplankton blooms in different of sub-basins such as the southern-west of Garda. This study confirms how satellite technology might contribute to studies of the impacts from climate change that as regards the deep clear lakes, is still not well understood