Coastal deltaic floodplains provide an important ecosystem service by removing or retaining nitrate from enriched riverine water. Wetland plants, soils, and microbes within these floodplains use nitrate through uptake, burial, and denitrification, thereby reducing the impact of nitrate on algal blooms and hypoxia in the Gulf of Mexico. However, these processes depend on the physical, biological, and chemical conditions within the floodplain. Understanding and characterizing the hydrodynamics of these systems and the relative impact of river, tide, and wind forcings are the first steps in understanding the biogeochemical processes controlling nitrate removal. Motivated by the desire to identify biogeochemical hotspots within coastal deltaic floodplains, this project focuses on modeling the hydrodynamics of these complex wetland ecosystems. Biogeochemical hotspots occur where anaerobic soils, sufficient organic carbon supply, longer residence times, and warmer water temperatures create optimal conditions for processes such as denitrification. The latter two conditions are strongly controlled by the hydrodynamics of the system. A Delft3D-FLOW model is developed for Wax Lake Delta, an actively prograding delta in southeastern Louisiana, in order to simulate daily and seasonal changes in water temperature and residence time within different hydrogeomoprhic zones of coastal deltaic floodplains. From January to March 2015, intertidal floodplains have warmer temperatures and longer residence times (up to 2.5 days) than subtidal floodplains (up to 1.5 days). However, when river discharge increases during spring floods, connectivity between channels and floodplains increases and residence times within all zones decreases as water is flushed more quickly to the Gulf of Mexico. Correctly simulating residence time of water within floodplains is essential to future efforts to model the transformation of nitrate in these systems.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-03272017-113450 |
| Date | 13 April 2017 |
| Creators | Christensen, Alexandra |
| Contributors | Larsen, Laurel G, Meselhe, Ehab A, Twilley, Robert R, Willson, Clinton S |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-03272017-113450/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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