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Abstract

Riverine nitrogen input into the coastal zone has increased remarkably in recent decades. Yet its transformation and recycling within hydrodynamically active regions remains unclear. Using observations of nitrate concentration and dual isotopic composition across the Changjiang River plume within a three end-member mixing model, we found deviations between the observed and expected values for mixing alone, revealing the nonconservative behavior of nitrate. Using cross correlations between concentrations and dual isotope deviations, we identified three nitrogen transformation zones, which correspond to separate portions of the plume. Nitrification and sedimentary denitrification occurred near the river mouth, nitrification prevailed further offshore under the plume, and finally, phytoplankton assimilation occurred in the outer surface plume (>100 km offshore), where it was fueled by nitrate that had already been strongly modified by microbial processes. Information was assembled into a conceptual model offering an overview of nitrogen transformations in a large river plume.

Item Type:	Article
Authors/Creators:	Yan, X and Xu, MN and Wan, XS and Yang, JYT and Trull, TW and Dai, M and Kao, SJ
Keywords:	Changjiang River, plume, dual isotope, nitrate, isotope effect
Journal or Publication Title:	Geophysical Research Letters
Publisher:	Amer Geophysical Union
ISSN:	0094-8276
DOI / ID Number:	https://doi.org/10.1002/2017GL075951
Copyright Information:	Copyright 2017 American Geophysical Union
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