Abstract

Microbial denitrification contributes significantly to the mitigation of nitrate contamination in sedimentary aquifers by reducing nitrate coupled to the consumption of organic carbon (heterotrophic) and iron sulphides like pyrite (autotrophic). However, these phases are often only present in trace amounts and can become depleted, so that denitrification will eventually cease. In order to implement measures within the EC-Water Framework Directive, we investigated the denitrification potential and the denitrification processes in the sediments of the Hessian Ried. The reduction potential was quantified and characterized by solid-phase analyses of drill core samples. Depth-oriented investigations of hydrochemistry (i.e. stable isotopes, N_2Excess) allowed determining nitrate input, reduction progress and average reduction kinetics upstream of selected wells. Despite low sulphide contents (max. 123 mg-S/kg), autotrophic denitrification was typically the dominant process. The results can be used to delineate risk areas, downstream of which denitrification can be expected to cease in the near future.