Quantification of nitrate reduction potential and kinetics of soil samples obtained from sandy aquifers, Schleswig-Holstein, Germany

Alexandra Giber1, Christine Kübeck1, Christoph Schüth2, Frank Steinmann3, Thomas Olderog3
1 IWW Rhenisch-Westfalian Institute for Water Consulting and Development Services Department Water resources Management Water Catchment, Biebesheim am Rhein, Germany
2 Technical University of Darmstadt, Institute for Applied Geosciences, Darmstadt, Germany
3 Landesamt für Landwirtschaft, Umwelt und ländliche Räume des Landes Schleswig-Holstein, Germany

P 13.2 in Nitrate and the importance of denitrification for water supply

Today, the majority of European farmland is dominated by industrial agriculture – an intensive food production featuring enormous single-crop farms and animal production facilities – causing an agricultural nutrient surplus especially in nitrogen within the environment. As a consequence, this intense agricultural activity has already led to high nitrate concentrations above the drinking water limits of 50 mg/l in nearly 30 % of the shallow groundwater bodies in Germany. Still a large number of groundwater bodies show low nitrate concentrations due to natural attenuation processes. With continuing input of nutrients the denitrification capacity within these aquifers decreases and may lead to an rapid increase of nitrate concentrations. In this context, we analysed the content of denitrification capacity (sulfide-/disulfide sulfur and organic carbon) and its reactivity at 60 locations in Schleswig-Holstein. Sediment samples were collected within the upper groundwater layer up to 12 m depth. The content of sulfide-disulfide and organic carbon were quantified by solid phase analysis. Furthermore, under scanning electrone microscope (SEM) analysis, different structures of iron- and sulfur rich compounds were observed and in some cases, pyrite framboids could be identified. Denitrification potential was investigated from laboratory batch experiments that contained sediments with different concentrations of the above-mentioned electron donors. The autolitotrophic and heterotrophic denitrification reactions were modelled and the kinetic rates were determined with the usage of the hydrogeochemical transport model, PHREEQC.