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Dual Isotope Measurements Reveal Zoning of Nitrate Processing in the Summer Changjiang (Yangtze) River Plume
Author(s) -
Yan Xiuli,
Xu Min Nina,
Wan Xianhui Sean,
Yang JinYu Terence,
Trull Thomas W.,
Dai Minhan,
Kao ShuhJi
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl075951
Subject(s) - plume , nitrate , environmental science , panache , denitrification , submarine pipeline , isotope analysis , oceanography , nitrogen , hydrology (agriculture) , environmental chemistry , geology , atmospheric sciences , ecology , chemistry , meteorology , geography , geotechnical engineering , organic chemistry , biology
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.