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Abstract Title: Biogeochemical Controls on Hg Dynamics in Sediments and Suspended Particulate Matter of Contaminated German Rivers
Presenter Name: Jan G. Wiederhold
Company/Institution: German Federal Institute of Hydrology (BfG)
Session: Mercury in Freshwater Ecosystems
Co-Authors: Jan G. Wiederhold,Stephan Krisch,Lorenz Gfeller,Andreas Breidenbach,Alexandra Alten,Harald Biester,Jens Hahn,Andreas Schttler,Sebastian Buchinger,Arne Wick,Lars Duester

Abstract Information :

Despite the implementation of strict environmental regulations and large efforts to improve the water quality over the last decades, the chemical status of all large rivers in Germany is still classified as ?not good?. This is often primarily caused by the exceedance of the environmental quality standard of the EU Water Framework Directive for mercury (Hg) in biota. Even though direct Hg releases into rivers have been greatly reduced, the targeted further decreases in Hg levels appear to be impeded by continuous remobilization from the large pool of legacy Hg residing in historically deposited bottom sediments. However, the biogeochemical controls on the transformation and mobility of different Hg species in riverine sediments and suspended particulate matter are only poorly understood. This includes for example the important influence of microorganisms on Hg species dynamics as well as the effects of dredging and resuspension in managed waterways. Here, we present the new interdisciplinary research project QUISS aiming to elucidate the biogeochemical Hg cycling in historically contaminated river systems in Germany with a focus on sediments and suspended particulate matter using a variety of methods and study approaches. The analysis of inorganic and organic Hg species (e.g., methyl-Hg) as well as their spatial and seasonal variability and bioavailability in samples collected from contaminated river systems will be accompanied by the molecular characterization of microbial community structure/function (e.g., detection of Hg (de)methylation genes). In addition, laboratory incubation studies investigating Hg species dynamics at the sediment-water interface using micro-/meso-profiling systems to obtain porewater samples at high spatial resolution will be conducted and used to assess the effect of management actions (e.g., disturbance due to dredging). Our new project will provide new insights about the biogeochemical controls and mechanisms of riverine Hg species dynamics as well as recommendations for the management of contaminated river systems.

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