Carbon flow and ecosystem dynamics in the Mississippi River plume described by inverse analysis

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 95-101).Issued also on microfiche from Lange Micrographics.Planktonic ecosystem dynamics in the buoyant Mississippi River plume were investigated using inverse analysis, a technique that incorporates data describing ecosystem processes and calculates rates of unknown trophic flows and sedimentation in the plume ecosystem. The waters receiving the Mississippi River were divided into four subregions connected by water flow to discretize the gradient of ecosystem properties as river water mixed with ocean water. Each subregion was represented by eight interconnected compartments that were linked to adjacent subregions by advective carbon flow. Models were produced for 4 seasons. Solutions for three seasons (spring, summer, and fall) showed a small region of net autotrophy associated with mid-salinity waters (15-29 psu), surrounded by a larger region of net heterotrophic waters where production did not meet respiratory carbon demand. In addition to moving more than 20% of total plume primary productivity out of the study region, westward water flow moved excess organic carbon from autotrophic regions to heterotrophic regions. In contrast, the winter result indicated a plume that was net-heterotrophic in all 4 subregions with high aerobic bacterial respiration and relatively low primary production that did not meet respiratory demand. Inputs of riverine DOC and carbon from resuspended sediments were required to make up the deficit. Sedimentation of organic carbon was linked to primary production in the mid-salinity regions of the plume, with strongest sedimentation from the productive mid-salinity regions during most of the year. Sedimentation was enhanced beneath less productive, higher salinity areas, due to inputs of organic carbon advected from mid-salinity regions. During winter organic carbon sedimentation was calculated to be zero. The models indicated that a dynamic relationship between primary production and sedimentation exists and provide a good starting point for future development of models which directly address the relationships between nutrient inputs, primary production, sedimentation, and hypoxia in the economically and environmental important regions of the Louisiana Shelf