ESTIMATING VULNERABILITY OF WATER BODY USING SENTINEL-2 IMAGES AND PREDICTIVE EUTROPHICATION MODELS: the STUDY CASE OF BRACCIANO LAKE (Italy)

Due to the concomitance of several factors related to progressive climate changes and to increased water management for anthropogenic usage, drastic fall in level of Bracciano Lake was reported in the summer of 2017. By November 2017, the water level decreased 0,198 meters below the hydrometric zero established at 163.04 meters s.l.m. Such alarming rate has not been detected in the last seventeen years. The consistent change in water level causes modifications in its environment, on the edge of the coasts and specifically, brings about an increase in the rate of eutrophication (trophic enrichment phenomenon). The determination of the volume of water contained in the lake basin was estimated with GIS tools modeling, by analysing the bathymetry of the water body and applying the supervised classification of Sentinel-2 images; this allowed to identify the reservoir and consequently to reconstruct the course of the coastline. Once defined the hydrometric reduction in the water body for the observed period, the Vollenweider model, that calculates the trophic state of a lake, was used to quantify nutrients concentration and relative increase of eutrophication status as a consequence of the anthropic activities practiced in the belonging basin. The quantification of the water level changes of Bracciano Lake, before and after the hydrometric crisis, occurred in 2017, related to the estimate of the level of eutrophication, allows us to define the degree of vulnerability of the lake ecosystem. The proposed methodology represents an efficient monitoring tool for assessing the vulnerability of water bodies influenced by eutrophication.