Ecological characterization of the Clitunno River (Central Italy): a lowland stream fed by limnocrenic spring

The Clitunno River (Umbria, Tiber River basin) is a small river of great historical, landscaping and environmental value. The stream originates from a lowland spring system, characterized by a regular flow which is not able of removing the considerable deposits of fine sediments accumulated over the decades due to input of civil and productive discharges. The alteration condition has worsened in 2006 following the spill of oily substances and solvents due to a serious accident of an oil mill. Since 2011, the river is subject to hydraulic and environmental recovery by “Consorzio di Bonificazione Umbra” based mainly on the partial removal of sediment up to “Casco dell'Acqua” locality (floodgate site, 10 km from the spring). The aim of the study is an environmental quality assessment of the medium-high reach of Clitunno River. Nine monitoring stations were identified between the spring zone (St.1) and “Casco dell’Acqua” locality (St.9). In June 2011 and 2014, water and sediment samples for ionic and heavy metals analyses were collected, respectively. In March, June and September 2014 macroinvertebrate samples were collected, a total of about 49,000 specimens, belonging to 64 taxa. The limnocrenic spring affects the waterway until the St.3 (high levels of calcium, sulphates, magnesium and conductivity) with respect to the remaining downstream stations characterized by high values of sodium, nitrates, pH, water temperature and dissolved oxygen. The organic pollution is manifested in the downstream sites (St.7-St.9), while the heavy metal contamination is evident in the reach river near a small industrial area (St.5). The peculiar ecological condition of the upstream reach, i.e. minor amount of oxygen and high storage level of organic material of natural origin, showed an habitat similar to that of the downstream reach. However, the approach based on biological and ecological traits of benthic freshwater macroinvertebrates has allowed to differentiate well the natural condition status of the upstream reach from the pollution condition of the downstream reach of the Clitunno River. The study highlighted the peculiarity of Clitunno River biotope, practically unique in Central Italy, contributing to the knowledge of this particular freshwater ecosystem and therefore to its protection and conservation.