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Carbon dioxide dynamics and community metabolism in the Mississippi River plume
Citation:
GUO, X., W. CAI, W. HUANG, Y. WANG, F. CHEN, M. C. MURRELL, S. E. LOHRENZ, L. JIANG, M. DAI, J. HARTMANN, Q. LIN, AND R. CULP. Carbon dioxide dynamics and community metabolism in the Mississippi River plume. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 57(1):1-17, (2012).
Impact/Purpose:
This study measured dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, and DO in the Mississippi River plume in spring, summer, and fall. Results from this study allowed us to estimate the production of labile organic carbon required for the development of the mid-summer hypoxia of the northern Gulf of Mexico. Results from this and related studies support development of nutrient criteria under the Clean Water Act, Water Quality Multi-Year Plan, Long-Term Goal 1. It also supports the goals of the Gulf of Mexico, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force when was established under the Harmful Algal Bloom and Hypoxia Control Act (HABHRCA).
Description:
Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, and DO were measured in the Mississippi River plume during five cruises conducted in spring, summer and fall. In contrast to many other large rivers, both DIC and TAlk were higher at the river end-member than in seawater. Substantial losses of DIC occurred within the plume, particularly at intermediate salinities. DIC removal was accompanied by high dissolved oxygen (DO), high pH, and nutrient depletion, and was attributed to high phytoplankton production. On several occasions, TAlk was also removed within the plume, indicating significant CaCO3 precipitation. Net community production (NCP) rates were estimated from calculated DIC and TAlk removal and water transit times. NCP peaked during summer at 3.6 g C m-2 d-1, which is the highest reported for large river plumes studied to date. In summer and fall, biological production in the turbidity plume consumed the majority (62-73%) of available nutrients, while during spring only 18% of the available nutrients were utilized in the plume. Seasonal and spatial patterns of NCP suggest that nutrient supply, light availability, and water residence time strongly influenced net biological production. We also estimated that plume productivity during March-June was sufficient to supply ~2/3 of labile organic carbon demand required for the development of the mid-summer hypoxia of the northern Gulf of Mexico.