Semester of Graduation

Summer 2019

Degree

Master of Science (MS)

Department

Department of Oceanography and Coastal Science

Document Type

Thesis

Abstract

Sediment, nutrient deprivation and salt water intrusion, among other factors, are driving widespread organic soil collapse and marsh loss in the Mississippi River Delta. Freshwater diversions were designed to reintroduce Mississippi River water and dissolved nutrients into the adjacent basins to manage salinity and slow land loss by maintaining marsh vegetation and nutrient cycling functions. These diversions are controversial by a few, suggesting that nutrient enrichment without a sediment subsidy can lead to further wetland loss in the receiving basins. In this study, a soil characterization is presented for the receiving marsh of the Davis Pond diversion in 2007, just as full-scale operation began, and again in 2018 after 11 years of diversion influence. Data for the top 10 cm of soil from 140 stations in both years were used in spatial analysis to create maps of soil properties. As a result of sedimentation from the diversion, there has been a significant increase of soil mineral content, and consequently soil bulk density. Elevated soil δ15N isotope values and increased inorganic phosphorus stocks suggest elevated rates of nutrient enrichment in the wetland, leading to increased mean organic matter and carbon content, especially in those immediate areas of diversion influence. Changes to biogeochemical cycling is apparent in altered soil nutrient ratios. Multivariate methods demonstrate the effectiveness of certain soil parameters for monitoring impacts of river diversions in wetlands. The δ15N isotope is an important indicator of river water-influenced soils, whereas mineral content and inorganic phosphorus can identify in which areas a river sediment subsidy was provided. Previous to this study, the long-term impacts of lower Mississippi River hydrologic restoration projects had yet to be statistically quantified due to little or no pre-sampling. The results of this study have implications for monitoring diversion impacts, providing guidance for continued use of freshwater diversions in Louisiana, and informing future management strategies in coastal areas around the world.

Committee Chair

White, John R

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