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Background: Approximately 90% of German surface waters do not meet the objectives of the European Water Framework Directive (EU-WFD). This is primarily due to deficits in water body structure and biological quality components, which in turn are negatively affected by chemical pollution. In this context, hydromorphological restoration measures have often been conducted to improve habitat and species diversity and, therefore, the ecological status of water bodies. However, habitat improvement is not necessarily accompanied by biota enhancement and thus by the improvement of the ecological status of rivers. To prioritize water management measures, decision criteria for the water management practice are necessary, which enable the prognosis, whether chemical pollution and its resulting effects or other factors, such as structural deficits of the water bodies, are the main cause for the failure to meet the objective of a good ecological status. Results:To address this need, we applied the freshwater mudsnail Potamopyrgus antipodarum and the amphipod Gammarus fossarum in active monitoring campaigns and in laboratory experiments with combined water/sediment samples and analyzed water and sediment samples with in vitro assays quarterly over the course of 1 year to provide evidence and guideline to assess if chemical contamination is a relevant stress factor for the aquatic biodiversity in rivers of the Nidda catchment (Hessen, Germany). On the basis of these results, an ecotoxicological, WFD-compliant assessment system was developed which, in comparison with the ecological status classes of the EU-WFD, permits the identification of the probable causes for the failure to meet the objectives of the EU-WFD. From these findings, recommendations for action were derived for the implementation of priority measures in water management practice. For the rivers Nidda, Usa, and Horloff, we identified a need for action to improve water and sediment quality at all investigated sampling sites except for the reference sites in the headwaters. The ecotoxicological assessment system also highlighted that hydromorphological restoration measures on their own will not lead to a good ecological status of rivers, as long as water and sediment quality are deficient. Conclusion:Hydromorphological restoration measures should be performed in conjunction with measures to reduce chemical contamination to achieve a good ecological status of the rivers Nidda, Usa, and Horloff. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 1 High Effects/values are as low as expected in the absence of disturbing influences or anthropogenic changes 2 Good Effects/values show minor anthropogenic changes, but deviate only slightly from the values that normally occur in the absence of disturbing influences 3 Moderate Effects/values indicate moderate anthropogenically induced change...

This paper presents the results from two ring-tests addressing the feasibility, robustness and reproducibility of a reproduction toxicity test with the freshwater gastropod Lymnaea stagnalis (RENILYS strain). Sixteen laboratories (from inexperienced to expert laboratories in mollusc testing) from nine countries participated in these ring-tests. Survival and reproduction were evaluated in L. stagnalis exposed to cadmium, tributyltin, prochloraz and trenbolone according to an OECD draft Test Guideline. In total, 49 datasets were analysed to assess the practicability of the proposed experimental protocol, and to estimate the between-laboratory reproducibility of toxicity endpoint values. The statistical analysis of count data (number of clutches or eggs per individual-day) leading to ECx estimation was specifically developed and automated through a free web-interface. Based on a complementary statistical analysis, the optimal test duration was established and the most sensitive and cost-effective reproduction toxicity endpoint was identified, to be used as the core endpoint. This validation process and the resulting optimized protocol were used to consolidate the OECD Test Guideline for the evaluation of reproductive effects of chemicals in L. stagnalis.

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Background: To date, only 8.2% of German surface waters achieve a good ecological status according to the European Water Framework Directive. This is primarily attributed to structural deficits, intensive land use, and chemical contaminations of water bodies. In this context, hydromorphological restoration measures are implemented with the aim to increase habitat and species diversity and thus improve the ecological status of water bodies. Nevertheless, existing studies show that restorations promote the reintroduction of individual species, but only in exceptional cases an improvement in the ecological status is achieved. Therefore, we examined the impact of the prevailing chemical contamination on the restoration success in the catchment of the river Nidda in Hessen (Germany) by comparing restored river sections at the rivers Nidda and Horloff with unrestored sections upstream (space-for-time-substitution) and a transect downstream the restoration measures. For this purpose, we conducted active biomonitoring campaigns with Potamopyrgus antipodarum and Gammarus fossarum and analyzed water and sediment samples with effect-based in vitro bioassays. Results: At the river Horloff, mortality of P. antipodarum and toxicity in water samples measured via the microtox assay were highest within the restoration. At the river Nidda, the reproduction of snails and gammarids significantly increased within the restorations, and reproduction of snails correlated positively and significantly with estrogenic activities. The microtox assay also exhibited the highest toxicities in water and sediment samples from the restorations and dioxin-like as well as estrogenic activities significantly increased compared to the unrestored reference site. On the basis of these results, the prevailing chemical contamination has negatively affected snails and gammarids in the active biomonitoring campaigns and consequently is likely to have also a negative impact on the local invertebrate community and thus endangers the restoration success. Conclusion:Hydromorphological restorations as a stand-alone measure are insufficient to improve the ecological status of a water body as long as the water and sediment quality remain deficient. Therefore, it is necessary to improve water and sediment quality in parallel with hydromorphological restoration measures to achieve the objectives of the EU-WFD. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.