Sentinel-2 reveals spatiotemporal dynamics of submerged aquatic vegetation in Lake Iseo (Italy)

Our main objectives were to map the distribution of SAV in the southern part of the Lake Iseo (a deep subalpine lake in Northern Italy) in the period 2015-2017, and to evaluate its spatiotemporal variations and the possible factors of change. Specifically, we focused our attention to the bathymetric layer between 0 and 10 m of depth dominated by Vallisneria spiralis, Najas marina and Ceratophyllum demersum. To the aim 17 Sentinel-2A/B images, at 10m spatial resolution, were atmospherically corrected through the radiative transfer code 6SV to produce the Remote Sensing Reflectance (RRS) that were then used as input of the code BOMBER (Bio-Optical Model-Based tool for Estimating water quality and bottom properties from Remote sensing images) for estimating the substrate type and coverage. The results show that the southern part of Lake Iseo is characterized by significant coverage of SAV: between 0 and 5 meters deep there are the major coverings, which decrease with increasing depth, moreover the spatial analysis has shown that close to the coast there are mainly sparse macrophytes, while dense macrophytes are usually located between 10 and 50 meters from the coast line. The temporal analysis showed a decrease in the area of SAV between 2015 and 2017, equal to 19% of the rate of coverage of the bottom. Decrease that is also confirmed by the presence of floating macrophyte stands on the surface of water.