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 andGrosseto. During the last few centuries, it has been subjected to intensemining operations. Being polluted because of this mining activity sincethe times of Industrial Revolution, the river has recently received renewedmedia coverage that has led to a process of decontamination,ended in 2009. According to the studies on the environmental qualityrun by the ARPAT between 2011 and 2012, the result of the decontaminationhas been only partially successful, as the environmental qualityof the river ranges from "moderately deteriorated" to "deeply deteriorated".In this study, we carried out an analysis of the environmentalquality of the hydrographic system of the Merse river in five transectsfalling in the tract between the municipalities Montieri and Pari.We analysed the abiotic features of each site before carrying on a samplingof both the benthic macroinvertebrate fauna (Extended BioticIndex) and river crabs Potamon fluviatile, correlating the data obtainedthrough crab sampling to the composition of the substrate of the riverbed, 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 haveimproved 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 onlypartial success of the decontamination process.The overall reduced quantity of river crabs that were sampled couldreflect low environmental quality, but this scarcity has probably to beascribed to an inadequate management of its population, which is constantlyendangered by poaching.In detail, the situation imposes the redefinition of a new managementstrategy aimed to preserve the river crabs as well as a long-term monitoringproject in order to achieve and maintain an adequate environmentalquality.