Dualism of denitrification and dissimilatory nitrate reduction to ammonium in sediment of nitrate-polluted aquatic ecosystems

点击翻译按钮获取中文摘要

Dissimilatory nitrate reduction by sediment bacteria is the quantitatively most important sink for nitrate that promotes the eutrophication of aquatic ecosystems. Incomprehensibly, in most cases only denitrification (DEN) that converts nitrate into nitrogen gas has been subject of research. In this study, however, the dissimilatory nitrate reduction to ammonium (DNRA), which maybe is quantitatively important in many aquatic ecosystems, will be investigated. DNRA is not effective against eutrophication because the ammonium produced is preserved in the ecosystem. The central goal of this study is the comparative and equitable investigation of DNRA and DEN in order to better understand the controlling abiotic factors (e.g., nitrate, sulfide, organic carbon, iron). In a novel approach, the vertical distribution of both DNRA and DEN in the sediment will be analysed with microsensors, gel probes, and mass spectrometry. Abundance and activity of the nitrate-reducing microbial community will be studied on the level of functional genes (here: nitrite reductases) with molecular techniques. Results obtained in laboratory experiments using benthic gradient chambers, natural sediments, and bacterial isolates will be validated at relevant field sites.