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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:	Refereed Article
Keywords:	Changjiang River, plume, dual isotope, nitrate, isotope effect
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Chemical Oceanography
Objective Division:	Environment
Objective Group:	Physical and Chemical Conditions of Water
Objective Field:	Physical and Chemical Conditions of Water in Marine Environments
UTAS Author:	Trull, TW (Professor Thomas Trull)
ID Code:	125812
Year Published:	2017
Web of Science® Times Cited:	5
Deposited By:	Ecology and Biodiversity
Deposited On:	2018-05-08
Last Modified:	2018-08-20
Downloads:	37 View Download Statistics