Date of Award

Summer 2017

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geography and Geology

Committee Chair

Dr Franklin Heitmuller

Committee Chair Department

Geography and Geology

Committee Member 2

Dr Jeremy Deans

Committee Member 2 Department

Geography and Geology

Committee Member 3

Dr Paul F. Hudson

Committee Member 3 Department

Geography and Geology

Committee Member 4

Dr Kevin A. Kuehn

Committee Member 4 Department

Biological Sciences

Abstract

The Mississippi River Basin is the largest river basin in North America and the third largest river basin in the world. Most of the corn, soybeans, wheat, cattle, and hogs harvested in the United States come from the Mississippi River Basin and about 58% of the entire drainage basin is croplands. Runoff from these lands carries sediments and nutrients, and the Mississippi River transports these downstream and ultimately deposits them in the Gulf of Mexico. The northern Gulf of Mexico is one of largest human-caused hypoxic zones in the world. Hypoxia is the phenomena where the dissolved oxygen level decreases in the water because of the eutrophication. Nutrients, particularly nitrogen (N) and phosphorus (P) are the main causes of eutrophication and the Mississippi River is the main source for nutrients in the Gulf of Mexico. The lower Mississippi River is frequently subjected to flooding during high discharge and floodwater sediments and nutrients are introduced into the floodplain. This study hypotheses that considerable concentration of nutrients are sequestrated in the Lower Mississippi Floodplain and the sequestration patterns are different in different sub-fluvial environments. Eight sediment cores recovered from three different sub-environments including levee backslope, point-bar and backswamp, taken from the Lower Mississippi floodplain were analyzed for their organic matter (OM), carbon (C), nitrogen (N), phosphorus (P), magnetic susceptibility, and particle size with depth. High concentrations of C, N, and OM are decreasing with depth and become low and relatively constant concentrations at depth no more than 25 cm. Levee backslope sediments consist of high silt and sand size particles, and have low concentration of C, N and OM. Backswamps and point-bar sediments are rich in clay size particles, C, N, and OM. C and N in the studied sediment samples were mainly originated from OM and total P is mainly from inorganic sources. Average concentration values in the topsoil for three sub-environments show moderate C and N concentrations and significantly high P concentrations compared to previous studies carried out in similar environments. Depth and OM concentration are the main factors governing the C and N concentrations while depth and clay fraction is more important in determining P concentrations. Results of this study show that floodplains are served as a sink for removing nutrients from further downstream movement effectively. Further study should be completed to understand the temporal changes in nutrient sequestration of the study area in order to quantify the amount of nutrients sequestrated within the floodplain.

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