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Double-check of dissimilatory nitrate reduction to either ammonium or dinitrogen in aquatic habitats

Final Activity Report Summary - DOUBLECHECK (Double-check of Dissimilatory Nitrate Reduction to either Ammonium or Dinitrogen in Aquatic Habitats)

The project focused on the comparative investigation of denitrification and dissimilatory nitrate reduction to ammonium (DNRA), two benthic microbial processes of great importance for nitrogen cycling in aquatic ecosystems. The metabolic control of both processes was simultaneously studied in benthic gradient chambers in which natural conditions, i.e. the microenvironment for sediment bacteria, are much better represented than in the commonly used slurry assays. By implementing a newly developed gel-probe technique in this experimental set-up, it was possible for the first time to determine the vertical distribution of both processes relative to each other.

It was proven that the two processes can coexist in one and the same sediment by means of spatial separation along vertical nitrate and sulfide gradients. We can thereby revise the current notion that in a given environment only one of the two processes will dominate due to the competitive exclusion principle. It was also demonstrated that denitrifying sediments can be shifted towards DNRA by increasing the sulfide supply from deep sediment strata.

This implies that the deterioration of aquatic ecosystems due to organic pollution can trigger the intensification of eutrophication due to nitrogen compounds (i.e. ammonium produced by DNRA) that are not eliminated from the ecosystem in the form of gas (i.e. dinitrogen produced by denitrification).