Jiyeong Hong

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

First Advisor

Laurent Ahiablame


Grassland is a valuable natural resource with many environmental benefits, which include erosion control, wildlife habitat promotion, water quality protection, and flood prevention. Conversion of grassland to cultivated cropland has been linked to environmental quality concerns. The goal of this study was to model the impacts of grassland establishment, depletion, and management on hydrology and water quality in Skunk Creek watershed in eastern South Dakota. The specific objectives are to quantify the impacts of grassland conversion and selected management regimes on streamflow and water quality, and explore the optimum grassland establishment location within a watershed to achieve water quality benefits. The Soil and Water Assessment Tool (SWAT) was used to evaluate “what if” scenarios to simulate streamflow, sediment, nitrate, and dissolved phosphorus loads at the outlet of the study watershed. Cropland Data Layer for the year 2011 was used as the existing land use condition, and 19 years of historical climate dataset (1996-2014) was used to create SWAT models for scenario simulations. Results indicate that grassland conversion to cropland and heavy grazing will likely result in water quality degradation in this watershed, while the best location for grassland establishment to attain water quality benefits within a watershed depends on the nutrient of interest and cropping systems. Grassland conversion to cropland scenarios resulted in 7% of increase in streamflow and sediment loading, 9% increase in dissolved phosphorus loading, and 25% decrease in nitrate loading. Grass-crop rotation shows increase in streamflow, and sediment loads by 12% and 19%, respectively, 13% decrease in nitrate loads, and a decrease in dissolved phosphorus loading. Grass-crop rotation scenarios with long-term grassland establishment resulted in 18% reduction in nitrate loads and less than 1% increase in dissolved phosphorus loads. Based on the simulations, heavy grazing reduced streamflow, sediment, and dissolved phosphorus, and nitrate loading by 7%, 8%, 2%, and 6%, while moderate grazing reduced streamflow, sediment, and dissolved phosphorus, and nitrate loading by 6%, 6%, 3%, and 6% compared to the baseline scenario. Heavy grazing (grazing on 100% of grassland) affected streamflow, sediment, and dissolved phosphorus loading by -1%, 2%, and 0.23% while nitrate loading remained similar compared to moderate grazing (grazing on 50% of grazing). The results of grassland establishment at downstream, midstream, and upstream areas of the watershed showed that the optimum locations for implementing grass cover in a watershed to attain water quality benefits varied depending on the nutrient and crop examined. Downstream, midstream, and upstream are respectively the optimum locations for reducing dissolved phosphorus, sediment, and nitrate loads in this watershed.

Library of Congress Subject Headings

Grasslands -- South Dakota -- Management.
Water quality management -- South Dakota -- Skunk Creek Watershed.
Streamflow -- South Dakota -- Skunk Creek Watershed.


Includes bibliographical references (pages 45-58)



Number of Pages



South Dakota State University



Rights Statement

In Copyright