Evidence for microbial mediated nitrate cycling within floodplain sediments during groundwater fluctuations

Abstract

Abstract. The capillary fringe is a subsurface terrestrial-aquatic interface which can be a significant hotspot for biogeochemical cycling of terrestrially derived organic matter and nutrients. However, pathways of nitrogen (N) cycling within this environment are poorly understood, and observations of temporally discrete changes in nitrate concentrations lack the necessary resolution to partition between biotic or abiotic mechanisms. Here we take an experimental and mechanistic modeling approach to char- However, this relationship is dependent on the coupling between aerobic and anaerobic microbial guilds at the oxic-anoxic interface. Modeling insights also suggest that anammox might play a more prominent role in N loss under conditions where organic matter concentrations are low and rapidly depleted by aerobic heterotrophs prior to the rise of the water table.