Impacts of freshwater flushing on anammox community structure and activities in the New River Estuary, USA

Anaerobic ammonium oxidation (anammox) and denitrification are 2 microbial nitrogen removal processes that may play an important role in controlling the intensity and duration of estuarine and coastal eutrophication. Sediment communities in the New River Estuary, North Carolina were investigated to determine the dynamics of anammox activity and community structure in conjunction with environmental conditions. N-15 tracer incubation experiments with sediment slurries were used to measure anammox and denitrification rates and estimate anammox contribution to total N-2 production. Molecular analyses targeting the hydrazine oxidoreductase (hzo) gene were conducted to examine the structure of anammox communities and quantify the abundance of anammox bacteria in sediments. Potential anammox rates ranged from 0.02 to 1.4 nmol N-2 g(-1) h(-1), with the highest potential activities observed during winter and spring when the estuary received large doses of nitrogen from the watershed. Anammox contributed up to 14.1% of total N-2 production in upstream estuarine sediments and abundance of anammox communities ranged from 1.55 x 10(2) to 2.59 x 10(5) hzo gene copies g(-1) sediment. Both activities and abundance of anammox communities were correlated with percent sediment organics (% organics) and the porewater concentrations of hydrogen sulfide. Based on hzo sequence analysis, anammox bacteria related to \u27Candidatus Jettenia spp.\u27 were widespread in estuarine sediments, which may be attributed to freshwater flushing and associated changes in environmental parameters as well as the geomorphology of the estuary. This is the first study to describe a dominance of \u27Candidatus Jettenia spp.\u27 in relation to % organics and hydrogen sulfide in an estuarine ecosystem driven by meteorological forcing