Graduation Term

2022

Degree Name

Master of Science (MS)

Committee Chair

Wondwosen W.M Seyoum

Abstract

The demand for clean and potable water increases as the population number grows, and surface water serves as a significant source of water supply to many municipalities. However, the quality of surface waters is altered due to excess load of nutrients in the water bodies. For example, excess nitrate and dissolved phosphorus in water may lead to eutrophication. The 2019 bi-annual Illinois Nutrient Loss Reduction Strategies reported about 13% and 35% increases in nitrate and total phosphorus, respectively, across the statewide basins compared to the previous baseline data of 1980-1996. The biannual report stated that Illinois River basin was a major contributor of the nutrient increase in the statewide basin. Thus, understanding the factors driving nutrient load trends in the Illinois River basin is crucial for better nutrient reduction management.This study assessed trends in nutrient loading, specifically of nitrate and dissolved phosphorus, in the Illinois river basin and the factors driving the trends including climate (precipitation), hydrology (discharge), and land use. We used historical nutrient data from various sources, including USGS, to analyze the trends. First, load was estimated using simple and multiple linear regression models using the LOADEST (LOAD ESTimator) package developed by USGS in an R programming interface. The purpose is to produce accurate load estimates and obtain continuous load data later used for trend analysis. A non-parametric Mann-Kendall and Sen’s slope test were adopted to analyze and detect trends. Further, cross correlation was employed to understand the relationship between watershed characteristics and trends in nutrient load. The result of the load estimation model, the regmodel (9) in the LOADEST, shows the best fit across multiple stations with R2 values between (0.57, and 0.93 ), and the estimated mean flux rate of the point predictions of nitrate to be 41,600-337,000 kg/d and of dissolved phosphorus range from 4620-16,400 kg/d. Watersheds that displayed a positive trend for both nitrate and dissolved phosphorus loads displayed a significant correlation with stations with increasing trends of discharge, precipitations, and land use coverage area with much developed medium to high intensity. The results from this study will aid in better water quality management. Keywords: LOADEST, Water Quality, Nutrients, Load, Illinois River, Correlation

Access Type

Thesis-Open Access

DOI

https://doi.org/10.30707/ETD2022.20230207065834624389.999987

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