An integrated approach to the toxicity assessment of Irish marine sediments: validation of established marine bioassays for the monitoring of Irish marine sediments

This paper describes the ecotoxicological evaluation of marine sediments from three sites around Ireland representative of a range of contaminant burdens. A comprehensive assessment of potential sediment toxicity requires the consideration of multiple exposure phases. In addition to the evaluation of multi-exposure phases the use of a battery of multi-trophic test species has been advocated by a number of researchers as testing of single or few organisms may not detect toxicants with a specific mode of action. The Microtox(R) solid phase test (SPT) and the 10-d acute amphipod test with Corophium volutator were used to assess whole sediment toxicity. Porewater and elutriates were assessed with the Microtox(R) acute test, the marine prasinophyte Tetraselmis suecica, and the marine copepod Tisbe battagliai. Solvent extracts were assayed with the Microtox(R) and T. battagliai acute tests. Alexandra Basin was identified as the most toxic site according to all tests, except the Microtox(R) SPT which identified the Dunmore East site as being more toxic. However, it was not possible to correlate the observed ecotoxicological effects with a specific and/or class of contaminants based on sediment chemistry alone. Therefore porewaters found to elicit significant toxicity (Dunmore East and Alexandra Basin) with the test battery were selected for further TIE assessment with T. battalgiai and the Microtox(R) system. The results of this study have important implications for risk assessment in estuarine and coastal waters in Ireland, where, at present the monitoring of sediment and water quality is predominantly reliant on chemical analysis alone.     

Pelagic-benthic coupling of the microbial food web modifies nutrient cycles along a cascade-dammed river

• Structure of multi-trophic microbial groups were analyzed using DNA metabarcoding. • Discontinuity and trophic interactions were observed along the dam-fragmented river. • C, N and P cycles are driven by top-down and bottom-up forces of microbial food web. • Pelagic-benthic coupling may intensify nutrient accumulation in the river system. Cascade dams disrupt the river continuum, altering hydrology, biodiversity and nutrient flux. Describing the diversity of multi-trophic microbiota and assessing microbial contributions to the ecosystem processes are prerequisites for the restoration of these aquatic systems. This study investigated the microbial food web structure along a cascade-dammed river, paying special attention to the multi-trophic relationships and the potential role of pelagic-benthic coupling in nutrient cycles. Our results revealed the discontinuity in bacterial and eukaryotic community composition, functional group proportion, as well as α-diversity due to fragmentation by damming. The high microbial dissimilarity along the river, with the total multi-trophic β-diversity was 0.84, was almost completely caused by species replacement. Synchronization among trophic levels suggests potential interactions of the pelagic and the benthic groups, of which the β-diversities were primarily influenced by geographic and environmental factors, respectively. Dam-induced environmental variations, especially hydrological and nutrient variables, potentially influence the microbial food web via both top-down and bottom-up forces. We proposed that the cycles of carbon, nitrogen and phosphorus are influenced by multi-trophic groups through autotrophic and heterotrophic processes, predator–prey relationships, as well as the release of nutrients mainly by microfauna. Our results advance the notion that pelagic-benthic trophic coupling may intensify the accumulation of organic carbon, ammonium and inorganic phosphorus, thereby changing the biogeochemical patterns along river systems. As a consequence, researchers should pay more attention to the multi-trophic studies when assessing the environmental impacts, and to provide the necessary guidance for the ecological conservation and restoration of the dam-regulated systems.