Importance and controls of anaerobic ammonium oxidation influenced by riverbed geology

• Published in: Nature geoscience Vol. 9; no. 5; pp. 357 - 360
• Main Authors: Lansdown, K., McKew, B. A., Whitby, C., Heppell, C. M., Dumbrell, A. J., Binley, A., Olde, L., Trimmer, M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2016; Nature Publishing Group
• Subjects: 704/106/242; 704/106/694/1108; 704/106/694/2786; Ammonium; Anoxic conditions; Bioavailability; Brackish; Clay; Denitrification; Earth science; Earth Sciences; Earth System Sciences; Estuaries; Fluvial sediments; Geochemistry; Geology; Geophysics/Geodesy; letter; Marine environment; Microbial activity; Nitrification; Nitrogen; Oxidation; River beds; Rivers; Sediments; Soil permeability; United Kingdom > UK; British Isles, England, Avon; British Isles; British Isles, England, Hampshire
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo2684

Anammox, an important N 2 loss pathway in marine waters, is not well understood in rivers. In situ measurements of N 2 production in UK rivers reveal that anammox can be the dominant N 2 loss pathway in permeable but not in impermeable riverbeds. Rivers are an important global sink for excess bioavailable nitrogen: they convert approximately 40% of terrestrial N runoff per year (∼47 Tg) to biologically unavailable N 2 gas and return it to the atmosphere 1 . At present, riverine N 2 production is conceptualized and modelled as denitrification 2 , 3 , 4 . Anaerobic ammonium oxidation, known as anammox, is an alternative pathway of N 2 production important in marine environments, but its contribution to riverine N 2 production is not well understood 5 , 6 . Here we use in situ and laboratory measurements of anammox activity using 15 N tracers and molecular analyses of microbial communities to evaluate anammox in clay-, sand- and chalk-dominated river beds in the Hampshire Avon catchment, UK during summer 2013. Abundance of the hzo gene, which encodes an enzyme central to anammox metabolism, varied across the contrasting geologies. Anammox rates were similar across geologies but contributed different proportions of N 2 production because of variation in denitrification rates. In spite of requiring anoxic conditions, anammox, most likely coupled to partial nitrification, contributed up to 58% of in situ N 2 production in oxic, permeable riverbeds. In contrast, denitrification dominated in low-permeability clay-bed rivers, where anammox contributes roughly 7% to the production of N 2 gas. We conclude that anammox can represent an important nitrogen loss pathway in permeable river sediments.