What is it about?
Coupled chemical dynamics of North Branch carbonate and DIN systems were studied. Water residence time of ∼30 d enhances estuarine respiration and CaCO3 dissolution. The North Branch biogeochemistry contributes to Changjiang element export fluxes. Biogeochemical controls of pCO2 in inner Changjiang Estuary were better understood.
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Why is it important?
The North Branch pCO2 distribution pattern is unique compared with many other estuaries where aquatic pCO2 normally declines with salinity increase. Furthermore, the biogeochemical additions of ammonium and alkalinity were identified in salinities between 4 and 16 in the North Branch. Based on field data analyses and simplified stoichiometric equations, we suggest that the relatively high North Branch pCO2 values and estuarine additions of dissolved inorganic nitrogen/carbon in the mid-salinity area were strongly associated with each other. These signals were primarily controlled by biogeochemical processes in the North Branch, combining biogenic organic matter decomposition (i.e. respiration), ammonia oxidation, CaCO3 dissolution, and CO2 degassing.
Perspectives
A case of estuarine DIC generation via organic matter decomposition and carbonate dissolution in the Ganga (Hooghly) River estuary, India showed that half of the DIC export flux from the Hooghly River is generated within the estuary, with CO2 degassing exhibiting minor influences on the observed variations in DIC. Our study, however, suggests that estuarine DIC/DIN generation had minor contributions to Changjiang export fluxes of biogenic elements, whereas CO2 loss via degassing accounted for 24.7% of the overall DIC generation in the North Branch of the inner Changjiang Estuary. Our study implies that estuarine DIC/DIN generation and the environmental impacts might vary in different systems, relying onwater residence times and other physical and biogeochemical conditions. Much remains to be investigated to quantitatively evaluate the significance of estuarine DIC/DIN generation on a global scale.
Dr Wei-Dong Zhai
Shandong University
Read the Original
This page is a summary of: Biogeochemical generation of dissolved inorganic carbon and nitrogen in the North Branch of inner Changjiang Estuary in a dry season, Estuarine Coastal and Shelf Science, October 2017, Elsevier,
DOI: 10.1016/j.ecss.2017.08.027.
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