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

Abstract

Anaerobic ammonium oxidation (anammox) and denitrification are 2 microbial nitro- gen 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 Car- olina were investigated to determine the dynamics of anammox activity and community structure in conjunction with environmental conditions. 15 N tracer incubation experiments with sediment slurries were used to measure anammox and denitrification rates and estimate anammox contri- bution to total N2 production. Molecular analyses targeting the hydrazine oxidoreductase (hzo) gene were conducted to examine the structure of anammox communities and quantify the abun- dance of anammox bacteria in sediments. Potential anammox rates ranged from 0.02 to 1.4 nmol N2 g �1 h �1 , with the highest potential activities observed during winter and spring when the estu- ary received large doses of nitrogen from the watershed. Anammox contributed up to 14.1% of total N2 production in upstream estuarine sediments and abundance of anammox communities ranged from 1.55 × 10 2 to 2.59 × 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 bacte- ria related to 'Candidatus Jettenia spp.' 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 'Candidatus Jettenia spp.' in relation to %organics and hydrogen sulfide in an estuarine ecosystem driven by meteorological forcing.