Reservoirs represent a strategic resource which requires careful management of hydraulic networks and dams for the water-energy nexus without neglecting the protection of water quality and ecosystems. Reservoirs are typical sites where sediment accumulation is favored and desiltation is needed to maintain water storage capacity, as well as proper functioning. Accumulated sediments are frequently removed by flushing, causing physical-mechanical impacts on aquatic communities in the downstream rivers due to increased turbidity and fine-grained sediment deposition. Moreover, ammonia, organic compounds and metals adsorbed on sediments were proved to be released during flushing, potentially inducing toxic effects. In Lombardy Region (Central Alps, North Italy) more than 600 dams are present, mainly used for hydropower generation. A strong As and a moderate Cd, Hg and Pb enrichment in reservoir sediments was emphasized, with potential ecotoxicological risk according to PEC (Probable Effect Concentrations) quotients. In this framework, a technical board composed by researchers and environmental managers developed "PrATo". PrATo is a protocol designed for assessing the toxic potential of sediments released by flushing from reservoirs and includes methods for sampling, chemical analysis and ecotoxicological evaluation of sediments, as well as criteria for risk assessment, based on cross-interpretation of results deriving from chemical, ecotoxicological and ecological analyses. In particular, a proper sediment:water dilution coefficient to be applied during flushing can be derived from analyses, in order to prevent adverse effects on aquatic organisms. The trial of the PrATo protocol in some reservoirs helped disentangling some crucial issues. For example, the definition of threshold concentrations may be biased by high natural background values (particularly for trace elements; e.g. As), by different on-site bioavailability and by synergistic effects of pollutants. Toxicity bioassays were proved to be essential to define the toxic potential of sediments. PrATo is an example of analytical approach derived from science and transferred into management in order to be a cost-effective tool for decision making. The bases of this protocol have been recently included into the "Technical directives for the preparation, approval and implementation of Management Plans for reservoirs" by Lombardy Region.
Sediment flushing in North Italian reservoirs: matching research, governance and management
Laura Marziali;Lucia Valsecchi;Alfredo Schiavon;Stefano Tasselli;Gianni Tartari;
2020
Abstract
Reservoirs represent a strategic resource which requires careful management of hydraulic networks and dams for the water-energy nexus without neglecting the protection of water quality and ecosystems. Reservoirs are typical sites where sediment accumulation is favored and desiltation is needed to maintain water storage capacity, as well as proper functioning. Accumulated sediments are frequently removed by flushing, causing physical-mechanical impacts on aquatic communities in the downstream rivers due to increased turbidity and fine-grained sediment deposition. Moreover, ammonia, organic compounds and metals adsorbed on sediments were proved to be released during flushing, potentially inducing toxic effects. In Lombardy Region (Central Alps, North Italy) more than 600 dams are present, mainly used for hydropower generation. A strong As and a moderate Cd, Hg and Pb enrichment in reservoir sediments was emphasized, with potential ecotoxicological risk according to PEC (Probable Effect Concentrations) quotients. In this framework, a technical board composed by researchers and environmental managers developed "PrATo". PrATo is a protocol designed for assessing the toxic potential of sediments released by flushing from reservoirs and includes methods for sampling, chemical analysis and ecotoxicological evaluation of sediments, as well as criteria for risk assessment, based on cross-interpretation of results deriving from chemical, ecotoxicological and ecological analyses. In particular, a proper sediment:water dilution coefficient to be applied during flushing can be derived from analyses, in order to prevent adverse effects on aquatic organisms. The trial of the PrATo protocol in some reservoirs helped disentangling some crucial issues. For example, the definition of threshold concentrations may be biased by high natural background values (particularly for trace elements; e.g. As), by different on-site bioavailability and by synergistic effects of pollutants. Toxicity bioassays were proved to be essential to define the toxic potential of sediments. PrATo is an example of analytical approach derived from science and transferred into management in order to be a cost-effective tool for decision making. The bases of this protocol have been recently included into the "Technical directives for the preparation, approval and implementation of Management Plans for reservoirs" by Lombardy Region.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
