Groundwater anammox at an industrial site in Calgary

Ammonium and nitrate concentrations in an alluvial aquifer adjacent to the Bow River, beneath and downgradient of a fertilizer plant have largely decrease over the past decade suggesting the plume is being 'flushed' likely by upgradient N-poor groundwater. Possible biochemical nitrogen processes were evaluated which might be influencing these concentrations including denitrification, dissimilatory nitrate reduction to ammonium (DNRA), nitrification and anaerobic ammonium oxidation (anammox). Different biochemical and isotopic signatures contribute to an understanding of the behaviour of the various N compounds. The decreasing groundwater ammonium and nitrate concentrations are attributed in part to the anammox process through several lines of evidence: (1) elevated delta 15NNO3 and delta15NNH4 with decreasing nitrate and ammonium concentrations, (2) higher delta 15NNO3 values than delta15NNH4 values, (3) N2 production with concentrations above atmospheric levels (4) delta15NN2 in 15N depleted in the downgradient groundwater relative to the source groundwater and (5) the presence of the required anammox bacteria.