The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

[摘要] The stoichiometry of dissolved inorganic carbon (DIC) and nutrients duringbiological uptake is widely assumed to follow the Redfield ratios(especially the C / N ratio) in large river plume ecosystems. However, thisassumption has not been systematically examined and documented, because DICand nutrients are rarely studied simultaneously in river plume areas andinterpretation of ratios can be confounded by strong river–ocean mixing aswell as intense biological activity. We examined stoichiometric ratios ofDIC and nutrients (NO₃^-, PO₄^3- and Si[OH]₄) in theMississippi River plume and adjacent continental shelf in June 2003 andAugust 2004 and calculated biological removal as the difference betweenobserved concentrations and those predicted from conservative mixing, asdetermined from a multi-end-member mixing model and observed salinity andtotal alkalinity. Despite complex physical and biogeochemical influences,relationships between DIC and nutrients were strongly dependent on salinityrange and geographic location, and influenced by biological removal. LowerC / Si and N / Si ratios in one nearshore area were likely due to localizedinput of high Si and low NO₃^- water from adjacent wetlands orpreferential removal of nitrogen in the area. When net biological uptake wasseparated from river–ocean mixing and corrected for preferential N removal,the stoichiometric ratio of C / N / Si was similar to the Redfield ratio, thussupporting the applicability of the Redfield-type C / N / Si ratios inriver-plume biogeochemical models.

[学科分类] 地球化学与岩石