Burgin, A. J., S. K. Hamilton, W. Gardner, and M. McCarthy. 2013. Nitrate reduction, denitrification, and dissimilatory nitrate reduction to ammonium in wetland sediments. Pages 519-537 in R. D. Delaune, R. Reddy, C. J. Richardson, and P. Megonigal, eds. Methods in biogeochemistry of wetlands. Soil Science Society of America, Madison, Wisconsin, USA.
Nitrate loading to aquatic ecosystems has increased dramatically in response to anthropogenic N pollution. Nitrate can be removed from aquatic ecosystems through a variety of processes including denitrification and dissimilatory nitrate reduction to ammonium (DNRA). In this chapter, we present two methods used in combination with the stable isotope of NO3− (15NO3−) to quantify the relative importance of DNRA and denitrification to overall NO3− uptake. First, we describe how continuous flow-through sediment cores can be used for controlled manipulations involving the addition of 15NO3− and measurement of resultant 15N2 and 15NH4+ (products of denitrification and DNRA). We also describe the “push–pull” method for determining denitrification and DNRA in situ for a variety of aquatic ecosystem sediment types. Both continuous flow-through cores and push–pull methods can be useful for comparing the N removal capacity of different aquatic ecosystems when full-scale ecosystem isotope additions are impossible due to methodological or resource limitations. Finally, these methods are suitable for comparing the multiple processes that can be responsible for NO3− removal (e.g., denitrification and DNRA). More studies incorporating a comparative analysis of the processes will yield greater understanding of their ecosystem-level importance and controls.
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