4.7 Article

Human activity intensity controls the relative importance of denitrification and anaerobic ammonium oxidation across subtropical estuaries

Journal

CATENA
Volume 202, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.catena.2021.105260

Keywords

Denitrification; Anammox; N-2 partitioning; N2O; Human activity intensity; Subtropical estuaries

Funding

  1. National Natural Science Foundation of China [41725002, 42071130, 41701548, 41761144062]
  2. Open Fund of Key Laboratory of Geographic Information Science (Ministry of Education), East China Normal University [KLGIS2020A01SPS:refid::GS2]

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Human activities significantly increase estuarine nitrogen loads, affecting denitrification and anammox rates differently. Anammox contribution to total N-2 production decreases towards the estuary mouth. Factors such as DO, NH4+, and NO3- play a key role in the partitioning of N-2 production between denitrification and anammox.
Human activities are dramatically increasing estuarine nitrogen (N) loads, further altering N processes. However, relative importance of denitrification and anaerobic ammonium oxidation (anammox) in response to human activities intensity gradient remains poorly understood for estuaries. In this study, we used a N-15 isotope tracer approach to characterize the variations in sediment denitrification and anammox rates and determined the crucial factors controlling the partitioning of N-2 production and regulating N2O production across five subtropical estuaries in southeast China. Denitrification rates increased significantly from 8.82 +/- 3.89 nmol N g(-1) h(-1) (low human activity intensity) to 41.2 +/- 11.5 nmol N g(-1) h(-1) (high human activity intensity) across the studied estuaries. Anammox rates not varied significantly between low (2.37 +/- 0.66 nmol N g(-1) h(-1)), moderate (3.96 +/- 0.91 nmol N g(-1) h(-1)), and high (4.04 +/- 1.09 nmol N g(-1) h(-1)) human activity intensity estuaries. Relative contribution of anammox to total N-2 production (R-a) decreased toward estuary mouth within each estuary. The Ra was also significantly lower in the estuaries characterized by high N loads and low DO. N2O production rates were in a range of 0.192-1.92 nmol N2O g(-1) h(-1) across the estuaries and controlled by water NO2-, salinity and TOC. DO, NH4+, and NO3- were the best predictors of the partitioning of N-2 production between denitrification and anammox. The high human activities intensity increased NH4+ and NO3- loads and further enhanced denitrification, leading to the decrease in Ra and increase in N2O production. These findings suggest that low DO and high N loads estuaries can increase denitrification and N2O emissions, whereas not affect anammox substantially under the higher intensity of human activities.

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