USING GIS TO EVALUATE EROSION AS A POTENTIAL PATHWAY FOR NUTRIENT POLLUTION OF LITTLE KICKAPOO CREEK IN BLOOMINGTON, ILLINOIS

Since the 1960s, application of fertilizers to agricultural fields has increased significantly, and as a result, nutrient loading of Midwestern streams has degraded water quality and threated aquatic life. Excess nutrients are able to enter stream systems through a variety of pathways, including: erosion of soil from fertilized fields, surface runoff, leaching to groundwater, and agricultural tile drainage systems. This paper examines the potential for erosion as a pathway for nutrients to enter Little Kickapoo Creek (LKC) in Bloomington Illinois. Using GIS, the LKC watershed was delineated, the land cover was determined, and the stream power index (SPI) was calculated for the watershed. SPI measures overland flow and is based on topography. Overland flow can be used as a proxy for erosion, for high levels of overland flow result in high levels of erosion. The results illustrate that the stream’s headwaters are located in an urban environment, but the majority, 60%, of the stream flows through row crops of corn and soybeans. The slope of the land is generally flatter in the urban section of the watershed and increases slightly in the central and southern sections of the watershed. The SPI calculation revealed that the land along the stream channel had the highest risk for erosions. Nutrients may enter streams from urban runoff, but erosion of extensively fertilized agricultural fields contributes significantly more nutrients to streams. Higher nitrate concentrations within the stream water correspond to areas along the stream with higher erosion potential. This study determined that due to the majority of erosion occurring in close proximity to agricultural fields, the eroded soil entering LKC will be high in nutrients from the fertilizers, making erosion a likely pathway for nutrient loading of the stream.