Date of Award
Master of Science
Geography and Environmental Resources
Persistently elevated nitrogen loads discharged to the Gulf of Mexico from the Mississippi and Atchafalaya rivers have been shown by a vast body of literature to be the cause of recurring hypoxic conditions in the Gulf of Mexico. Riverine wetlands have been shown to be important ecosystems capable of substantially reducing nitrogen loads delivered downstream through N removal processes including denitrification, anaerobic ammonium oxidation, and plant uptake. In order to assess the relative potential of wetland sites for nitrogen attenuation, a suitability analysis was performed to identify the relative nitrogen attenuation potential of wetlands within the Middle Mississippi River (MMR) floodplain. For this assessment, the literature on nitrogen cycling in riverine wetlands was used to identify variables which are associated with denitrification potential. Data for these variables were sourced from publicly available geospatial datasets and floodplain inundation frequency estimates using a hydraulic model. The variables compiled for this analysis included flood frequency, soil drainage class, soil hydrologic class, soil pH, soil texture, land use, and soil organic carbon. Principle component analysis was applied to the dataset to reduce the number of variables in the suitability model. The results of the principle components analysis revealed that the first four components explained 77% of the variation within the dataset of potential denitrification variables. As a result of the PCA analysis, the variables Soil Hydrologic Class, Soil Organic Carbon, Land Cover, Soil pH, SSURGO’s Flood Frequency, and Flood Exceedance Probability were used to evaluate riverine wetland areas potential for denitrification under two hydrologic connection scenarios, a “with-levee” and a “no-levee” condition. For the with levee scenario, there were 66,146 ha of floodplain that attained a suitability rating of average potential, an additional 16,937 ha of floodplain attained high potential, and 706 ha of floodplain were rated as having very-high potential. The second scenario assumed removal of levees in the study area. In this scenario, there were 65,897 ha in the floodplain that attained a suitability rating of average potential. There were 34,457 ha in the study segment that attained a rating of high potential, whereas 510 ha attained a very-high potential on the suitability scale. These results were then analyzed by levee system, comparing economic and population data with the results of the suitability analysis. In particular, the amount of area within a levee system achieving a rating of high potential vs. the total property value within the levee system was compared to determine which systems would be best candidates for strategic reconnection. This analysis suggests that the Bois & Brule, the Big Five, and the Grand Tower / Degonia Levee systems are the most suitable systems for strategic reconnection efforts in the study area.
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