A fast-response methodological approach to assessing and managing nutrient loads in eutrophic Mediterranean reservoirs

With many lakes and other inland water bodies worldwide being increasingly affected by eutrophication resulting from excess nutrient input, there is an urgent need for improved monitoring and prediction methods of nutrient load effects in such ecosystems. In this study, we adopted a catchment-based approach to identify and estimate the direct effect of external nutrient loads originating in the drainage basin on the trophic state of a Mediterranean reservoir. We also evaluated the trophic state variations related to the theoretical manipulation of nutrient inputs. The study was conducted on Lake Cedrino, a typical warm monomictic reservoir, between 2010 and 2011. We assessed the hypereutrophic condition of the reservoir by monthly samplings of the water column and compared these results with the amount of nutrient load originating from anthropic activities in the drainage basin [42.6 t P y−1 for total phosphorus (P) and 531 t N y−1 for total nitrogen (N)]. We verified how the predictive OECD management model could be confidently applied to predict the P concentration in the reservoir on the basis of estimated loads from the drainage basin (98.7 mg P m−3 assessed versus 101 mg P m−3 estimated, approximately 2.5% over). Different scenarios are presented showing how it is possible to reduce approximately 62% P and 43% N, altering the condition of the ecosystem to become more mesotrophic. We also propose some management strategies to improve water quality in this lake ecosystem.