Document Type

Thesis - Open Access

Award Date

2019

Degree Name

Master of Science (MS)

Department

Geography

First Advisor

Darrell Napton

Keywords

Big Sioux River basin, land use/land cover, Mann-Kendall test, NASS CDL dataset, Nitrates, water quality

Abstract

Between 2006 and 2012, conversion of 485,000 acres of grassland to cropland in eastern South Dakota was reported. In 2012, the Big Sioux River (BSR) running through most of eastern South Dakota was listed among the dirtiest rivers in the nation. This rating convinced state authorities to study trends of land cover changes in the BSR watershed and its association with BSR water quality with respect to increases in nitrate levels. This research i) quantifies spatial and temporal changes in the land cover types within the BSR watershed, and ii) identifies any correlation between these changes and changes in BSR nitrate levels. It uses the Cropland Data Layer (CDL) to characterize and determine rates of Land Cover Changes (LCC), and the non-parametric Mann-Kendall test to identify statistically significant increasing and decreasing LCC trends within the BSR watershed. Similarly, nitrate data collected from 11 gauging stations operating in the BSR watershed were analyzed using the Mann-Kendall test to identify any trends. For all the land cover classes and gauging stations that were identified as statistically significant, a Sen’s Slope estimate was used to estimate their magnitudes. Only Corn/Soybean and Grassland acreage displayed a significant increasing and decreasing trends, respectively whereas remaining classes including Other Crops, Water, and Developed didn’t show any trends and were considered as classes having “No Trend”. Similarly, out of 11 gauging stations, one station (SD Codington K06) showed a significant increasing trend, one station (MN Pipestone 099) showed a decreasing trend and remaining other stations didn’t show any trends and were considered as gauging stations having “No Trend”. In general, there was insufficient evidence to conclusively link changes in Corn/Soybean LCC to changes in nitrate levels. The results of this research suggest that changes should be made to gauging station locations and sampling frequency, particularly on smaller tributary rivers and streams within the watershed.

Library of Congress Subject Headings

Water quality -- Big Sioux River (S.D. and Iowa)
Landscape changes -- South Dakota.
Landscape changes -- Big Sioux River Watershed (S.D. and Iowa)
Land use, Rural -- South Dakota.
Land use, Rural -- Big Sioux River Watershed (S.D. and Iowa)

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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