Multi-approach investigation of macrophytes of Iseo Lake combing remote sensing with structural and elemental data

In the framework of the project funded by the CARIPLO Foundation "ISEO: Improving the lake Status from Eutrophy towards Oligotrophy", a multi-approach characterization of the macrophyte communities of the Iseo Lake (northern Italy) were carried out. Based on a systematic investigation of available data, mainly collected in the frame of WFD monitoring activities performed by ARPA Lombardia, a standardized protocol was developed to map the spatial gradients of macrophytes and to estimate their contribution to the littoral metabolism. During the period 2015-2017, based on satellite data (Sentinel 2 A-B) and in-situ measurements, we have reconstructed the extent and density of littoral vegetation - largely dominated by Vallisneria spiralis, Najas marina and Ceratophyllum demersum. We focused our attention to the southern sector of the lake (between Iseo and Clusane) which was the one characterized by shallower waters and higher macrophyte colonization rates. In total, 20 different sites were identified for six different macrophytes (V. spiralis, N. marina, C. demersum, Lagarosiphon major, Myriophyllum spicatum, Chara globularis) for each of which biomass samples were collected using known surface frames by SCUBA diving or by modified rakes. In addition, a series of random samplings (n = 12 for both years) were carried out aimed at measuring the species' elemental content of nitrogen, phosphorous, and carbon. Samples were analyzed in laboratory for determining fresh and dried biomass and nutrient content using standard procedures. Here we presented the main outputs of the work, discussing the reliability of satellite-derived maps, biomass evaluation and the role of macrophytes in regulating the lacustrine nutrient cyclization.