Abstract
BackgroundIn Germany and the EU, most headwaters are still far from reaching a good chemical and ecological status as it is required by the European Water Framework Directive (WFD), until 2027 the latest. Particularly, in densely populated areas, impacts from municipal and industrial wastewater discharges or diffuse agricultural emissions are still a matter of concern. This also applies to the Nidda River which is considered to be in a moderate to rather poor condition. In our study, we investigated short-term and long-term consequences of anthropogenic pollution on fish health via one monitoring with caged fish (CF) and two field sampling campaigns (FF). In the CF monitoring, rainbow trout (Oncorhynchus mykiss) were caged for seven weeks at four selected sites along the Nidda, whereas in the FF monitoring approach, feral fish, including brown trout (Salmo trutta f. fario), European chub (Leuciscus cephalus) and stone loach (Barbatula barbatula) were caught in June and September 2016.ResultsHistopathological analyses of liver and gills were conducted, accompanied by measurements of hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity to assess the cytochrome P450 (CYP1A1) function, and genotoxicity via the micronucleus assay. Caged as well as field-captured fish exhibited impaired health conditions showing lesions particularly in the liver, and a presumably overwhelmed CYP1A1 system, whereas genotoxicity was not induced. The variation between sampling sites and seasons was rather low, but two trends were recognisable: (a) liver condition was poorest around spawning season and (b) tissue integrity and EROD activity were most affected downstream of industrial dischargers. Furthermore, effects were species dependent: the generally highly sensitive S. trutta f. fario proved to be impacted most, whereas L. cephalus with its pelagic lifestyle was affected less than the benthic B. barbatula, indicating a relevant contamination of sediments.ConclusionOur results confirm the impaired ecological state of the Nidda and emphasise that a sustainable improvement of aquatic ecosystem health needs to include both water quality and sediment contamination to approach the ambitious WFD goal.
Highlights
In Germany and the EU, most headwaters are still far from reaching a good chemical and ecological status as it is required by the European Water Framework Directive (WFD), until 2027 the latest
We studied the health of field-captured feral fish (CF) (Salmo trutta f. fario, Leuciscus cephalus and Barbatula barbatula) mirroring long-term exposure, and chronic effects at four sites along the Nidda River in two monitoring campaigns in spring and autumn 2016
At the end of the experiment, caged fish were in the same mean weight and size range as fish from HC1 that were sampled in parallel to the start of the exposure, whereas individuals from HC2, fed at the hatchery and sampled at the same time point as the Nidda-exposed fish, increased in mean size and weight (Table 3)
Summary
In Germany and the EU, most headwaters are still far from reaching a good chemical and ecological status as it is required by the European Water Framework Directive (WFD), until 2027 the latest. In densely populated areas, impacts from municipal and industrial wastewater discharges or diffuse agricultural emissions are still a matter of concern. This applies to the Nidda River which is considered to be in a moderate to rather poor condition. The project network NiddaMan aimed at comprehensively investigating the ecosystem health of a highly anthropogenically influenced river system in Central Hesse, Germany, and at identifying potential key factors of pollution to support and advise authorities in their effort to improve the ecological state. Combined with various natural stressors (e.g. temperature, food availability, predation, reproduction and parasites) which often act synergistically [47] and potentially enhance adverse effects by lowering organismal resilience, mixture toxicity cannot be extrapolated from (physico-)chemical parameters, but have to be assessed by measuring biological responses in exposed organisms, e.g. by using biomarkers [3, 6, 20, 21, 90, 110, 120]
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