Nitrogen loads alter the N_2 production between denitrification and anammox in Min River Estuary, a highly impacted estuary in southeast China

摘要

Estuarine sediment denitrification and anammox in response to increased nitrogen (N) loads remain poorly understood. In this study, we used N isotope tracer approach to investigate the spatial distribution of denitrification and anammox and identified the crucial controls on the partitioning of dinitrogen gas (N-2) production along the Min River Estuary (MRE), a highly impacted estuary in southeast China. The results indicated that denitrification and anammox rates ranged from 10.5 to 70.7 nmol g(-1) h(-1) and from 0.44 to 4.31 nmol g(-1) h(-1), respectively. Relative contribution of anammox to N-2 production (R-a) was in a range of 1.04-15.1%, tending to increase toward estuary mouth. Denitrification rates were significantly higher in upper (high N loads) than in lower estuary (low N loads), while anammox rates and R-a showed inverse distributions along the MRE. Wastewater discharge caused the N point pollution triggering denitrification but inhibiting anammox. The best predictor of the variations in denitrification rates was total nitrogen, whereas pH and NH4+ could explained the variations in anammox rates across the estuary. The crucial predictors for the partitioning of N-2 production between denitrification and anammox were NH4+ and NOx. These results suggest that the increase in human activities intensity can alter the partitioning of N-2 production between denitrification and anammox, and the magnitude of this switch can be predicted by N loads in MRE and other highly impacted estuaries. (c) 2021 Elsevier Ltd. All rights reserved.