Variables affecting macrophyte distribution in the Orbetello lagoon (Tuscany, central Italy)

The Orbetello Lagoon is an important transitional ecosystems which, due to particular environmental characteristics, host few, but abundant, submerged aquatic vegetation (SAV) species. The SAV communities abundance and distribution are known to be influenced by multiple biotic and abiotic factors. To evaluate factors affecting SAV, we related the major physico chemical characteristics of sediment (grain-size, pH, macronutrients, total carbonates) and biomasses (macronutrients) to the distribution and abundance of species. In summer 2008 we selected 6 sampling areas, based on the AVS levels in superficial water. In each area we collected sediments cores at four level (5 cm depth) and biomasses (acquiring data based on species); chemical analyses were performed in three replicates. Collected data were analyzed using a multivariate statistical approach to evaluate both variables distribution among sampling sites and their correlations to SAV. Results evidenced that the sampling areas influenced significantly sediment variables showing a relationship to AVS levels in water and a clear difference in variables assessment related to the level of analyses was observed in sediments. Concerning SAV, a significant differences were observed relating to the sampling area both for total biomass and species abundances, but there was not a clear dominance of a single specie. A significant correlation (p<0.01, R=0.76) was observed among total organic carbon in sediments and total biomass.