Reservoirs are often characterized by high siltation rates which impair the storage capacity. Accumulated sediments are frequently removed by flushing, causing physical-mechanical impacts on aquatic organisms in the downstream rivers. In some cases, however, chemical compounds (organics and trace metals) adsorbed on sediments may induce toxic effects, mainly in a long-term perspective. Some researches emphasized that flushing operations may determine contaminant release from sediments, altering their bioavailability. Based on real case studies from Northern Italy, the "Analytical protocol for ecotoxicological and physical-chemical characterization of sediments in reservoirs" (PrATo) was developed in order to define proper methods for reservoir sediment characterization in the Lombardy Region, with the final purpose of a sustainable management of operations involving the release of sediments into downstream riverine ecosystems, i.e. the protection of aquatic communities. The protocol was developed by considering 30 reservoirs of Lombardy Region (Northern Italy), characterized by different degrees of silting and anthropogenic pressures. PrATo includes standard protocols for sampling, chemical analysis and ecotoxicological characterization of sediments of the reservoirs and of the downstream river stretches. It also includes criteria for risk assessment using an approach similar to TRIAD, which takes into account: 1) the comparison between micropollutant concentrations in sediments and quality thresholds selected from existing national legislation or from literature (e.g. cb-TEC and cb-PEC; MacDonalds et al., 2000); 2) the assessment of toxicity of sediments using ecotoxicological test batteries (for example, the chronic test with Heterocypris incongruens is considered as screening test); 3) the chemical and ecotoxicological assessment of sediments of the downstream river stretch before flushing as basis for planning proper operations, and after flushing as criteria to evaluate the results of these operations by comparison with the previous conditions. The final aim of the characterization is to provide practical information for a sustainable management of flushing operations. For example, a proper sediment: water dilution factor to be applied during flushing to prevent overcoming toxicity thresholds can be calculated. Preliminary trials of the protocol were carried out on 20 reservoirs. Results show that the definition of proper quality thresholds is rather difficult, since they are generally not representative of site-specific bioavailability. Therefore, the ecotoxicological characterization is necessary to assess sediment toxicity. PrATo provides a practical and efficient tool for a sustainable management of the flushing activities and will be adopted in Lombardy as technical guidance for the Reservoir Management Plans.
A protocol for assessing sediment toxicity in water reservoirs before flushing
Laura Marziali;Gianni Tartari;
2017
Abstract
Reservoirs are often characterized by high siltation rates which impair the storage capacity. Accumulated sediments are frequently removed by flushing, causing physical-mechanical impacts on aquatic organisms in the downstream rivers. In some cases, however, chemical compounds (organics and trace metals) adsorbed on sediments may induce toxic effects, mainly in a long-term perspective. Some researches emphasized that flushing operations may determine contaminant release from sediments, altering their bioavailability. Based on real case studies from Northern Italy, the "Analytical protocol for ecotoxicological and physical-chemical characterization of sediments in reservoirs" (PrATo) was developed in order to define proper methods for reservoir sediment characterization in the Lombardy Region, with the final purpose of a sustainable management of operations involving the release of sediments into downstream riverine ecosystems, i.e. the protection of aquatic communities. The protocol was developed by considering 30 reservoirs of Lombardy Region (Northern Italy), characterized by different degrees of silting and anthropogenic pressures. PrATo includes standard protocols for sampling, chemical analysis and ecotoxicological characterization of sediments of the reservoirs and of the downstream river stretches. It also includes criteria for risk assessment using an approach similar to TRIAD, which takes into account: 1) the comparison between micropollutant concentrations in sediments and quality thresholds selected from existing national legislation or from literature (e.g. cb-TEC and cb-PEC; MacDonalds et al., 2000); 2) the assessment of toxicity of sediments using ecotoxicological test batteries (for example, the chronic test with Heterocypris incongruens is considered as screening test); 3) the chemical and ecotoxicological assessment of sediments of the downstream river stretch before flushing as basis for planning proper operations, and after flushing as criteria to evaluate the results of these operations by comparison with the previous conditions. The final aim of the characterization is to provide practical information for a sustainable management of flushing operations. For example, a proper sediment: water dilution factor to be applied during flushing to prevent overcoming toxicity thresholds can be calculated. Preliminary trials of the protocol were carried out on 20 reservoirs. Results show that the definition of proper quality thresholds is rather difficult, since they are generally not representative of site-specific bioavailability. Therefore, the ecotoxicological characterization is necessary to assess sediment toxicity. PrATo provides a practical and efficient tool for a sustainable management of the flushing activities and will be adopted in Lombardy as technical guidance for the Reservoir Management Plans.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
