Abstract:
Water quality degradation has been a significant concern in the White River watershed of
Indiana. As a consequence of long-term inputs of industrial and domestic effluents, and urban and
agricultural runoff, the White River has been adversely affected. Some major on-going concerns
include excess nutrients, organic compounds, and salinity. Water quality degradation effects
extend beyond the local scale, as the White River is a headwater stream and drains into the
Mississippi River. Water quality issues become more complex with changing climate, which shifts
streamflow regime and water quality. One emerging water quality concern regarding climate
change is irrigation suitability of water under the potential shift from rain-fed agriculture to
irrigation agriculture in the Midwest. To address these issues, this thesis research: 1) analyzed the
long-term secondary water quality data using a novel approach, Weighted Regression on Time,
Discharge and Seasons; and 2) collected bi-weekly water samples from the White River during the
crop growing season of 2019, and comprehensively analyzed the irrigation suitability of the water.
Long-term water quality data analysis of five monitoring sites show that overall flow-normalized
concentration and flux of biochemical oxygen demand (BOD) and nitrate-nitrite nitrogen increased
from 2002 to 2018. The only exception occurred at the Walnut monitoring site where both nitratenitrite nitrogen concentration and flux decreased. Analysis of pollutant sources indicates that point
source pollution and combined sewage outflows may have a substantial contribution to nutrient
pollution, and agricultural and urban runoff has a big impact on the both the nutrient and BOD
load in the river. Irrigation suitability analysis concludes that the water is mostly suitable for
irrigation; however, suitability exhibits distinct patterns between May–July and August–October.
An average of 7.8% of samples from May-July are unsuitable for irrigation, while an average of
24.5% of samples from August-October are unsuitable for irrigation. Considering that AugustOctober is the dry and low-flow season when water demand is high, the results suggest a notable
possibility that water is unsuitable for irrigation when most needed. This is the first comprehensive
study to evaluate irrigation suitability of surface water in the Midwest United States. Meanwhile,
the long-term water quality analysis and identification of pollution sources are critical for
understanding the driver of water quality in the context of climate and streamflow changes. The
results of this study will inform water resources managers responsible for formulating future
conservation plans.
