Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 48, Issue 8, Pages 4425-4434Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es4056005
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Funding
- Natural Environment Research Council [NE/F006063/1]
- Queen Mary University of London [NE/F004753/1]
- AXA Research Fund
- NERC [NE/F004753/1, NE/F006063/1] Funding Source: UKRI
- Natural Environment Research Council [ceh010010, NE/F006063/1, NE/F004753/1] Funding Source: researchfish
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Alteration of the global nitrogen cycle by man has increased nitrogen loading in waterways considerably, often with harmful consequences for aquatic ecosystems. Dynamic redox conditions within riverbeds support a variety of nitrogen transformations, some of which can attenuate this burden. In reality, however, assessing the importance of processes besides perhaps denitrification is difficult, due to a sparseness of data, especially in situ, where sediment structure and hydrologic pathways are intact. Here we show in situ within a permeable riverbed, through injections of N-15-labeled substrates, that nitrate can be either consumed through denitrification or produced through nitrification, at a previously unresolved fine (centimeter) scale. Nitrification and denitrification occupy different niches in the riverbed, with denitrification occurring across a broad chemical gradient while nitrification is restricted to more oxic sediments. The narrow niche width for nitrification is in effect a break point, with the switch from activity on to activity off regulated by interactions between subsurface chemistry and hydrology. Although maxima for denitrification and nitrification occur at opposing ends of a chemical gradient, high potentials for both nitrate production and consumption can overlap when groundwater upwelling is strong.
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