Degree
Doctor of Philosophy (PhD)
Department
Oceanography and Coastal Sciences
Document Type
Dissertation
Abstract
Coastal shelves such as the northern Gulf of Mexico (NGOM) are important systems for carbon burial and cycling. Shelf regions with strong river input are especially dynamic, often experiencing intense seasonal changes in water flow, nutrient loading, and carbon content. Most organic matter remineralization occurs within the sediment of coastal systems. However, the biogeochemical relationship between coastal sediment and water column processes remains poorly understood, particularly during seasonal hypoxia. In this study, we measured biogeochemical flux across the sediment-water interface in the NGOM within the region of Mississippi River influence during summertime hypoxia, as well as water column and sediment conditions.
We report that diffusive oxygen uptake (DOU) accounts for only 10-71%, averaging 33%, of total oxygen uptake (TOU) by sediments in the NGOM. This is a very low proportion compared to the two other studies around the globe that have measured DOU and TOU concurrently in river deltas (57-98%), which suggests that fauna-mediated oxygen uptake in this region may have been previously underestimated. We hypothesize that the movement associated with polychaete stress responses under hypoxic conditions may be responsible for this apparently elevated fauna-mediated oxygen uptake. There is evidence of benthic influence on bottom water conditions regarding dissolved inorganic carbon and pH, as well as a close relationship between dissolved oxygen and pH conditions. A budget of sediment biogeochemical processes remains enigmatic, however, as differing remineralization pathways is confounded by a complex environment of geochemical interactions. We urge future investigations of benthic-pelagic coupling to approach biogeochemical cycling as a holistic, interlocking system rather than adjacent compartments of remineralization. Flux of phosphorus across the sediment-water interface was negligible, likely due to the presence of oxidized iron near the sediment surface. Sediment phosphorus species were primarily mineral-bound, likely in the form of hydroxyapatite.
Date
11-3-2025
Recommended Citation
Beck, Hannah N., "Benthic-Pelagic Coupling for Sediment Biogeochemistry on the Northern Gulf of Mexico Shallow Continental Shelf" (2025). LSU Doctoral Dissertations. 6961.
https://repository.lsu.edu/gradschool_dissertations/6961
Committee Chair
Kanchan Maiti