Monitoring the impact of landslide aftermath on aquatic vegetation in Lake Mezzola using Sentinel-2

A time series of multi-spectral optical satellite data covering three years (2016-2018), acquired from the satellites of the Sentinel-2 constellation managed by the European Space Agency (ESA) and the EU Copernicus program, with cloud cover above 50% on Lake Mezzola were discarded has been gathered and processed. In addition, hydrological and meteorological parameters (temperature, incoming radiation, precipitation and water level) were retrieved from sampling stations located nearby the study area, and an in situ survey has been carried out (26 September 2018) for documenting the macrophyte conditions in the southern portion of the lake in terms of species presence, density, phenological stage, and traces of impact. The analysis of time series of Sentinel-2 derived maps have shown that both submerged and riparian macrophyte communities of Lake Mezzola and Pian di Spagna wetland were impacted by increased turbidity and sediment transport due to the August 2017 landslide events. Submerged vegetation of the southern part of the lake has exhibited a decrement in 2018, compared to previous years, in terms of total area covered and plant density, together with some signs of shifts in community composition in the littoral area. Riparian helophytes instead have shown evidence of stress during the growing season following the landslide, translated into a delay in green-up for 2018 season, i.e. reaching WAVI = 0.3, varying between 10 and 40 days compared to previous years. Although last year has shown and unusually cold early Spring in North of Italy, the late development of riparian reed beds in 2018 is not attributable only to this weather anomaly, since terrestrial reeds of Pian di Spagna wetland did not show the same growth delay from time series of WAVI scores.