Date of Award

Winter 2016

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Wilfred M Wollheim

Second Advisor

Stephen H Jones

Third Advisor

Robert J Stewart

Abstract

Fecal bacteria have a significant impact on downstream water quality. Removal of fecal bacteria in river systems potentially attenuates downstream impairments and would represent an important ecosystem service. However, few studies aimed to quantify in-stream removal of fecal bacteria. The goal of this study is to understand the ecosystem service of fecal bacteria removal at the river network scale in both water column and hyporheic zone across hydrologic conditions. I developed a module for routing fecal indicator bacteria (FIB) through river networks in the Framework for Aquatic Modeling of the Earth System (FrAMES) model to understand the fate and transport of FIB. This study focuses on Escherichia coli (E. coli), which is the freshwater indicator for fecal contamination. E. coli loading from land and aquatic removal in both water column and hyporheic zone was simulated for every river grid cell throughout the river network. This study found that the hyporheic zone is important in removing E. coli. The water column and the hyporheic zone removed approximately 10-30% and 30-50% of E. coli input, respectively, during the summer period. Watershed size, land use distribution, and hydrology interact to determine network-scale E. coli removal, but hydrology has the most significant impact. Low-frequency but high-magnitude hydrologic events mobilize a disproportionate amount of E. coli. The attenuation efficiency of river networks decreases as the flow increases, but remains relatively high at higher flows common during critical summer periods. This study found that the ecosystem service of E. coli removal reduces E. coli levels at critical downstream water bodies, such as recreational lakes and estuaries. These results have important implications for managing bacteria contamination.

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