Burgin, A. and S.K. Hamilton
Presented at the ASM at Estes Park (2006-09-01 to 2012-09-23 )
Nitrate disappearance in sediments, an important process for improving water quality, is usually assumed to be due to respiratory denitrification. While performing tracer experiments in freshwater sediments of Michigan, we found that nitrate removal coincided with sulfate production, and that sulfate removal commenced only after nitrate was depleted. Because this activity appears to be biological, we hypothesize that the nitrate removal is due to sulfur oxidizing bacteria that use nitrate as an oxidant in the production of sulfate. Sulfur oxidizers do not necessarily denitrify nitrate to dinitrogen, but may instead produce ammonium via a form of dissimilatory nitrate reduction to ammonium (DNRA). Push-pull experiments in streams, lakes and wetlands (23 sites) often showed sulfate production during nitrate removal. The nitrate introduction also yielded significant ammonium production and sulfide removal compared to controls. Further analysis using stable isotope tracers in 9 sites have also revealed the importance of DNRA as a proximate sediment nitrate removal process, but have shown that anaerobic ammonium oxidation (Anammox) is relatively unimportant. These alternative pathways of nitrate removal have important implications for water quality management, especially in the highly agricultural areas of the Midwestern US.
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