Abundance, stable isotopic composition, and export fluxes of DOC, POC, and DIC from the Lower Mississippi River during 2006–2008

Journal of Geophysical Research: Biogeosciences
By: , and 

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Abstract

Sources, abundance, isotopic compositions, and export fluxes of dissolved inorganic carbon (DIC), dissolved and colloidal organic carbon (DOC and COC), and particulate organic carbon (POC), and their response to hydrologic regimes were examined through monthly sampling from the Lower Mississippi River during 2006–2008. DIC was the most abundant carbon species, followed by POC and DOC. Concentration and δ13C of DIC decreased with increasing river discharge, while those of DOC remained fairly stable. COC comprised 61 ± 3% of the bulk DOC with similar δ13C abundances but higher percentages of hydrophobic organic acids than DOC, suggesting its aromatic and diagenetically younger status. POC showed peak concentrations during medium flooding events and at the rising limb of large flooding events. While δ13C-POC increased, δ15N of particulate nitrogen decreased with increasing discharge. Overall, the differences in δ13C between DOC or DIC and POC show an inverse correlation with river discharge. The higher input of soil organic matter and respired CO2 during wet seasons was likely the main driver for the convergence of δ13C between DIC and DOC or POC, whereas enhanced in situ primary production and respiration during dry seasons might be responsible for their isotopic divergence. Carbon export fluxes from the Mississippi River were estimated to be 13.6 Tg C yr−1 for DIC, 1.88 Tg C yr−1 for DOC, and 2.30 Tg C yr−1 for POC during 2006–2008. The discharge-normalized DIC yield decreased during wet seasons, while those of POC and DOC increased and remained constant, respectively, implying variable responses in carbon export to the increasing discharge.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Abundance, stable isotopic composition, and export fluxes of DOC, POC, and DIC from the Lower Mississippi River during 2006–2008
Series title Journal of Geophysical Research: Biogeosciences
DOI 10.1002/2015JG003139
Volume 120
Issue 11
Year Published 2015
Language English
Publisher American Geophysical Union
Contributing office(s) National Research Program - Central Branch
Description 16 p.
First page 2273
Last page 2288
Country United States
State Louisiana