The aim of the EU water framwork directive (EU WFD) is to achieve a good chemical and ecological status for European water bodies (till 2015). However, to choose the appropriate actions to improve the ecological status, the cause for the poor status has to be identified. For this purpose, tools, such as weight-of-evidence (WoE) approaches, are required that are able to detect chemical induced effects in a multi-stress situation, which is common in anthropogenically modified water bodies. Indices that consider chemical induced changes in in situ communities are important components of WoE approaches (Fig. 1).
In fine, cohasive sediments (often hotspots of chemical pollution) common macroinvertebrate based indices (e.g. SPEAR[%]-Index; Saprobic Index) can rarely be used, as only few macrobenthic species occur in these habitats. Here, meiobenthic invertebrates, such as nematodes, should be used for bioindication. For this purpose, the NemaSPEAR[%]-Index was developed, that uses the percentage of nematode species at risk (NemaSPEAR), that had shown to occur mainly in lowly contaminated (Fig. 2), and rarely in contaminated freshwater sediments. The NemaSPEAR[%]-index has shown to be a suitable measure to assess chemical induced changes in benthic invertebrate communities (Höss et al. 2011; Wolfram et al. 2012). Höss et al. (2017) revised and validated the index and provided index-based classes of ecological quality (Fig. 3). The NemaSPEAR[%] index was already applied for assessing the ecological status of urban streams that are influences by contaminated groundwater (Sonne et al. 2018). Moreover, in Swedish streams, the ecological risks of pesticides were evaluated with biofilm-inhabiting nematode communities (Bighiu et al. 2020). Recent studies showed that the NemaSPEAR[%] index has an added value to macrofauna-based indices to assess the ecological quality of fine sediments (Brüchner-Hüttemann et al. 2021).
Moreover, it is possible to determine the the NemaSPEAR[%]-Index on the basis of molecular taxonomy. Schenk et al. (2020a, 2020b, 2022) showed a good coherence of NemaSPEARmorphological and NemaSPEARmolecular for assessing the ecological quality of freshwater sediments.