The Combination of a Biotic and a Chemical- Microbiological Index Shows the Environmental Risks of a high Quality Mediterranean Stream (Tellesimo; S.C.I. ITA090018; Sicily, Italy)
Mediterranean river ecosystems have a highly endangered biodiversity;consequently, a monitoring activity is neededto identify the most impacted areas, the risk factors and to evaluate the efficacyof protection and restoring activities. This is particularly true for tributaries that are often overlooked by public agencies, while they are central elements for the protection of biodiversity. According to the Water Framework Directive (W.F.D.) this requires a multidisciplinary approach, linked to the study of the physicochemical, hydromorphological and biological characters of the water environments. In this study the results are reported of a monitoring activity in the Tellesimo Stream, a high quality Sicilian water course, wheretwo fish species included in the I.U.C.N. Red List as Critically Endangered (Anguilla Anguilla)and Near-Threatened (Salmo cettii) live. According to the WFD multidisciplinary approach, both a biological quality index (I.B.E.), using benthic macroinvertebrates as indicators, and a chemical-microbiological quality index (L.I.M.) were used. The two indexes gave different and sometimes contrasting results. This led to ascertaindifferent environmental risks for this stream: a seasonal (autumn) pollution, detected by I.B.E., probably due to the illegal discharge of olive mills waste water into the karst system, and a lighter but more chronicalteration, detected by L.I.M., probably due to theagricultural and/or small industrialactivities existingin the catchment area. These results highlight the need to use different methods to evaluate stream quality: in fact this allows the identification ofdifferent risk factors that sometimes can act in a very subtle or unseen way.