Valutazione ambientale del fiume Merse (Toscana) associata a campionamenti del granchio di fiume Potamon fluviatile

The River Merse basin is situated between the provinces of Siena and Grosseto. During the last few centuries, it has been subjected to intense mining operations. Being polluted because of this mining activity since the times of Industrial Revolution, the river has recently received renewed media coverage that has led to a process of decontamination, ended in 2009. According to the studies on the environmental quality run by the ARPAT between 2011 and 2012, the result of the decontamination has been only partially successful, as the environmental quality of the river ranges from "moderately deteriorated" to "deeply deteriorated". In this study, we carried out an analysis of the environmental quality of the hydrographic system of the Merse river in five transects falling in the tract between the municipalities Montieri and Pari. We analysed the abiotic features of each site before carrying on a sampling of both the benthic macroinvertebrate fauna (Extended Biotic Index) and river crabs Potamon fluviatile, correlating the data obtained through crab sampling to the composition of the substrate of the river bed, and assessing the degree of similarity of the different locations. The results showed an environment where the alteration is still visible, even though the general environmental conditions seem to have improved since 2011/2012, as shown by the finding of Aphelocheirus (s.str.) aestivalis (Fabricius, 1794) (Hemiptera Heteroptera Aphelocheiridae) specimens in two out of five sampling sites, confirming the only partial success of the decontamination process. The overall reduced quantity of river crabs that were sampled could reflect low environmental quality, but this scarcity has probably to be ascribed to an inadequate management of its population, which is constantly endangered by poaching. In detail, the situation imposes the redefinition of a new management strategy aimed to preserve the river crabs as well as a long-term monitoring project in order to achieve and maintain an adequate environmental quality.