| 1. |
- Laukert, G., et al.
(författare)
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Nutrient and Silicon Isotope Dynamics in the Laptev Sea and Implications for Nutrient Availability in the Transpolar Drift
- 2022
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 36:9
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Tidskriftsartikel (refereegranskat)abstract
- Realistic prediction of the near-future response of Arctic Ocean primary productivity to ongoing warming and sea ice loss requires a mechanistic understanding of the processes controlling nutrient bioavailability. To evaluate continental nutrient inputs, biological utilization, and the influence of mixing and winter processes in the Laptev Sea, the major source region of the Transpolar Drift (TPD), we compare observed with preformed concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP), silicic acid (DSi), and silicon isotope compositions of DSi (δ30SiDSi) obtained for two summers (2013 and 2014) and one winter (2012). In summer, preformed nutrient concentrations persisted in the surface layer of the southeastern Laptev Sea, while diatom-dominated utilization caused intense northward drawdown and a pronounced shift in δ30SiDSi from +0.91 to +3.82‰. The modeled Si isotope fractionation suggests that DSi in the northern Laptev Sea originated from the Lena River and was supplied during the spring freshet, while riverine DSi in the southeastern Laptev Sea was continuously supplied during the summer. Primary productivity fueled by river-borne nutrients was enhanced by admixture of DIN- and DIP-rich Atlantic-sourced waters to the surface, either by convective mixing during the previous winter or by occasional storm-induced stratification breakdowns in late summer. Substantial enrichments of DSi (+240%) and DIP (+90%) beneath the Lena River plume were caused by sea ice-driven redistribution and remineralization. Predicted weaker stratification on the outer Laptev Shelf will enhance DSi utilization and removal through greater vertical DIN supply, which will limit DSi export and reduce diatom-dominated primary productivity in the TPD.
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| 2. |
- Schmitz, M., et al.
(författare)
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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
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 804
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Tidskriftsartikel (refereegranskat)abstract
- 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 col-lected along a pollution gradient (characterised in a parallel study) in the river. Compared to fish from the refer-ence 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 agree-ment with increasing exposure to various chemicals. By integrating single biomarker responses into an aggre-gated 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 re-vealed 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. (c) 2021 Elsevier B.V. All rights reserved.
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