Climate change effects on hatching success and embryonic development of fish: Assessing multiple stressor responses in a large-scale mesocosm study.

Climate change threatens freshwater fish species due to predicted changes in thermal, sedimentary and hydrological properties of stream ecosystems. Gravel-spawning fish are particularly sensitive to such alterations as warming, higher inputs of fine sediment and low-flow all have potentially negative effects on the functionality of their reproductive habitat, the hyporheic zone. Multiple stressors can interact in synergistic and antagonistic manners, causing surprise-effects that cannot be predicted from the additive consideration of individual stressors. For obtaining reliable, yet realistic data on the climate change stressor effects warming (+3-4 °C), fine sediment (increase in <0.85 mm by 22 %) and low-flow (eightfold discharge-reduction), we constructed a unique large-scale outdoor-mesocosm facility consisting of 24 flumes to study individual and combined stressor responses in a fully-crossed, 3-way-replicated design. To acquire representative results reflecting individual susceptibilities of gravel-spawning fish species due to taxonomic affiliation or spawning seasonality, we studied hatching success and embryonic development in the three fish species brown trout (Salmo trutta L.), common nase (Chondrostoma nasus L.) and Danube salmon (Hucho hucho L.). Fine sediment had the most significant single negative effect on both hatching rates and embryonic development (-80 % in brown trout, -50 % in nase, -60 % in Danube salmon). When fine sediment was combined with one or both of the other stressors, we observed strongly synergistic stressor responses, being distinctly stronger in the two salmonid species than in the cyprinid nase. Danube salmon was most susceptible to synergistic effects due to warmer spring water temperatures exacerbating the fine sediment-induced hypoxia, hence leading to complete mortality of fish eggs. This study highlights that individual and multiple-stressor effects depend strongly on life-history traits of respective species and that climate change stressors have to be assessed in combination to obtain representative results due to the high level of synergisms and antagonisms detected in this study.

Demonstration of an aggregated biomarker response approach to assess the impact of point and diffuse contaminant sources in feral fish in a small river case study.

The assessment of the exposure of aquatic wildlife to complex environmental mixtures of chemicals originating from both point and diffuse sources and evaluating the potential impact thereof constitutes a significant step towards mitigating toxic pressure and the improvement of ecological status. In the current proof-of-concept study, we demonstrate the potential of a novel Aggregated Biomarker Response (ABR) approach involving a comprehensive set of biomarkers to identify complex exposure and impacts on wild brown trout (Salmo trutta fario). Our scenario used a small lowland river in Germany (Holtemme river in the Elbe river catchment) impacted by two wastewater treatment plants (WWTP) and diffuse agricultural runoff as a case study. The trout were collected along a pollution gradient (characterised in a parallel study) in the river. Compared to fish from the reference site upstream of the first WWTP, the trout collected downstream of the WWTPs showed a significant increase in micronucleus formation, phase I and II enzyme activities, and oxidative stress parameters in agreement with increasing exposure to various chemicals. By integrating single biomarker responses into an aggregated biomarker response, the two WWTPs' contribution to the observed toxicity could be clearly differentiated. The ABR results were supported by chemical analyses and whole transcriptome data, which revealed alterations of steroid biosynthesis and associated pathways, including an anti-androgenic effect, as some of the key drivers of the observed toxicity. Overall, this combined approach of in situ biomarker responses complemented with molecular pathway analysis allowed for a comprehensive ecotoxicological assessment of fish along the river. This study provides evidence for specific hazard potentials caused by mixtures of agricultural and WWTP derived chemicals at sublethal concentrations. Using aggregated biomarker responses combined with chemical analyses enabled an evidence-based ranking of sites with different degrees of pollution according to toxic stress and observed effects.

Disentangling multiple chemical and non-chemical stressors in a lotic ecosystem using a longitudinal approach.

Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysis, we aimed here to disentangle the effects of multiple chemical and non-chemical stressors along a longitudinal land use gradient in a third-order river in Germany. We distinguished and evaluated four dominant stressor categories along this gradient: (1) Hydromorphological alterations: Flow diversity and substrate diversity correlated with the EU-Water Framework Directive based indicators for the quality element macroinvertebrates, which deteriorated at the transition from near-natural reference sites to urban sites. (2) Elevated nutrient levels and eutrophication: Low to moderate nutrient concentrations together with complete canopy cover at the reference sites correlated with low densities of benthic algae (biofilms). We found no more systematic relation of algal density with nutrient concentrations at the downstream sites, suggesting that limiting concentrations are exceeded already at moderate nutrient concentrations and reduced shading by riparian vegetation. (3) Elevated organic matter levels: Wastewater treatment plants (WWTP) and stormwater drainage systems were the primary sources of bioavailable dissolved organic carbon. Consequently, planktonic bacterial production and especially extracellular enzyme activity increased downstream of those effluents showing local peaks. (4) Micropollutants and toxicity-related stress: WWTPs were the predominant source of toxic stress, resulting in a rapid increase of the toxicity for invertebrates and algae with only one order of magnitude below the acute toxic levels. This toxicity correlates negatively with the contribution of invertebrate species being sensitive towards pesticides (SPEARpesticides index), probably contributing to the loss of biodiversity recorded in response to WWTP effluents. Our longitudinal approach highlights the potential of coordinated community efforts in supplementing established monitoring methods to tackle the complex phenomenon of multiple stress.

Tandem Action of Natural and Chemical Stressors in Stream Ecosystems: Insights from a Population Genetic Perspective.

Agricultural and urban land use has dramatically increased over the last century and one consequence is the release of anthropogenic chemicals into aquatic ecosystems. One of the rarely studied consequences is the effect of land use change on internal concentrations of organic micropollutants (OMPs) in aquatic invertebrates and its effects on their genotype diversity. Here, we applied population genetic and internal concentrations of OMPs analyses to determine evolutionary implications of chemical pollution on Gammarus pulex populations from a natural and two agricultural streams. Along 14 consecutive months sampled, 26 different OMPs were quantified in G. pulex extracts with the highest number, concentration, and toxic pressure in the anthropogenically stressed stream ecosystems. Our results indicate distinct internal OMP profiles and changes in both genetic variation and genetic structure in streams affected by anthropogenic activity. Genetic variation was attributed to chemical pollution whereas changes in the genetic structure were attributed to environmental disturbances, such as changes in discharge in the impacted stream ecosystems, which worked both independently and in tandem. Finally, we conclude that human-impacted streams are subjected to severe alterations in their population genetic patterns compared to nonimpacted stream ecosystems.

Limited impact of an invasive oyster on intertidal assemblage structure and biodiversity: the importance of environmental context and functional equivalency with native species.

Impacts of invasive species are context dependent and linked to the ecosystem they occur within. To broaden the understanding of the impact of a globally widespread invasive oyster, Crassostrea (Magallana) gigas, intertidal surveys were carried out at 15 different sites in Europe. The impact of C. gigas on macro- (taxa surrounding oyster > 1 cm) and epifaunal (taxa on oyster < 1 cm) benthic communities and α and ß-diversity was assessed and compared to those associated with native ecosystem engineers, including the flat oyster Ostrea edulis. Whilst the effect of C. gigas on benthic community structures was dependent on habitat type, epifaunal communities associated with low densities of O. edulis and C. gigas did not differ and changes in benthic assemblage structure owing to the abundance of C. gigas were therefore attributed to the presence of oyster shells. Macrofaunal α-diversity increased with C. gigas cover in muddy habitats, while epifaunal α-diversity decreased at greater oyster densities. Macrofaunal ß-diversity was greatest at low densities of C. gigas; however, it did not differ between samples without and increased densities of oysters. In contrast, epifaunal ß-diversity decreased with increasing oyster cover. Different environmental contexts enabled more independent predictions of the effect of C. gigas on native communities. These were found to be low and more importantly not differing from O. edulis. This indicates that, at low densities, C. gigas may be functionally equivalent to the declining native oyster in terms of biodiversity facilitation and aid in re-establishing benthic communities on shores where O. edulis has become extinct.

Chemical activity and distribution of emerging pollutants: Insights from a multi-compartment analysis of a freshwater system.

Emerging pollutants are ubiquitous in the aquatic system and may pose risks to aquatic ecosystems. The quantification and prediction of environmental partitioning of these chemicals in aquatic systems between water, sediment and biota is an important step in the comprehensive assessment of their sources and final fates in the environment. In this multi-compartment field study, we applied equilibrium partitioning theory and chemical activity estimates to investigate the predictability of concentrations in Gammarus pulex as a model invertebrate from water and sediment in a typical small central European river. Furthermore, KOW-based and LSER approaches were assessed for the calculation of sediment organic carbon-, lipid-, and protein-water partitioning coefficients and activity ratios between the different compartments. Gammarid-water activity ratios close to unity have been observed for many chemicals, while sediment-water and sediment-biota chemical activity ratios exceeded unity by up to six orders of magnitudes. Causes may be: disequilibrium due to slow desorption kinetics and/or an underestimation of partition coefficients due to the presence of strongly adsorbing phases in the sediments. Water concentrations, particularly when using LSER for prediction of partition coefficients were good predictors of internal concentrations in gammarids for most emerging pollutants. Some hydrophilic chemicals such as the neonicotinoid imidacloprid tend to accumulate more in G. pulex than expected from equilibrium partitioning. This conclusion holds both for KOW as well as for LSER-based predictions and suggests previously unidentified mechanisms of bio-accumulation which may include binding to specific protein structures.

Biogeochemical patterns in a river network along a land use gradient.

The Bode catchment (Germany) shows strong land use gradients from forested parts of the National Park (23% of total land cover) to agricultural (70%) and urbanised areas (7%). It is part of the Terrestrial Environmental Observatories of the German Helmholtz association. We performed a biogeochemical analysis of the entire river network. Surface water was sampled at 21 headwaters and at ten downstream sites, before (in early spring) and during the growing season (in late summer). Many parameters showed lower concentrations in headwaters than in downstream reaches, among them nutrients (ammonium, nitrate and phosphorus), dissolved copper and seston dry mass. Nitrate and phosphorus concentrations were positively related to the proportion of agricultural area within the catchment. Punctual anthropogenic loads affected some parameters such as chloride and arsenic. Chlorophyll a concentration and total phosphorus in surface waters were positively related. The concentration of dissolved organic carbon (DOC) was higher in summer than in spring, whereas the molecular size of DOC was lower in summer. The specific UV absorption at 254 nm, indicating the content of humic substances, was higher in headwaters than in downstream reaches and was positively related to the proportion of forest within the catchment. CO2 oversaturation of the water was higher downstream compared with headwaters and was higher in summer than in spring. It was correlated negatively with oxygen saturation and positively with DOC concentration but negatively with DOC quality (molecular size and humic content). A principle component analysis clearly separated the effects of site (44%) and season (15%), demonstrating the strong effect of land use on biogeochemical parameters.