Validating the NemaSPEAR[%]-index for assessing sediment quality regarding chemical-induced effects on benthic communities in rivers

Abstract

Fine, cohesive sediments provide a habitat for a very diverse fauna and considerably contribute to important ecosystem services of aquatic ecosystems. As fine sediments are often hotspots of chemical contamination, the benthic fauna has to be protected in order to maintain its ecological functioning and thereby the proper provision of important ecosystem services. However, in these habitats usually meiofaunal organisms prevail, which are, so far, neglected in biomonitoring studies, while routine benthos monitoring (e.g. according to the EU Water Framework Directive) is solely based on macroinvertebrates. The recently developed NemaSPEAR[%]-index filled this methodological gap by providing a monitoring tool using freshwater nematodes, which are one of the most abundant and species rich invertebrates in fine sediments. In the present study the NemaSPEAR[%]-index was revised and validated based on a larger data set of nematode species and physico-chemical properties in river sediments in order to increase its applicability. The larger data set led to a similar categorization of nematode species at risk (NemaSPEAR). Validation of the NemaSPEAR[%] with an independent test data set, as well as external field data published by other authors and experimental microcosm data confirmed its usefulness as a specific index detecting chemical induced changes in benthic communities, whereas the index also worked at a higher taxonomic level (genus; NemaSPEAR[%]genus). A separation of the index for metal and organic pollution (NemaSPEAR[%]metal, NemaSPEAR[%]organic) showed no benefits for assessing sediments with mixed contamination, allowing the use of only one NemaSPEAR[%] for overall pollution. Moreover, based on its variance in lowly polluted reference sediments, class boundaries were set up for categorizing samples according to their ecological status, with a NemaSPEAR[%] higher or lower 30% indicating an acceptable or not acceptable ecological status, respectively. Overall, this study confirmed the robustness and relevance of the NemaSPEAR[%]-index for assessing the quality of fine sediments and using it as a line of evidence in a weight-of-evidence framework. Thus, the index can be a valuable tool for classification and prioritization of fine sediments supporting risk managers and regulators in making sediment management decisions.