Semester

Summer

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Division of Plant and Soil Sciences

Committee Chair

Jason A. Hubbart

Committee Member

Eugenia Pena-Yewtukhiw

Committee Member

Zachary B. Freedman

Committee Member

Michael Strager

Abstract

A scarcity of field-based research investigating the relationships between E. coli (fecal matter) concentration, suspended particulate matter (SPM; including size distribution), physicochemical parameters (water temperature, pH, SPC, DO, chloride) and land use practices and the importance of these relationships, particularly for human health, policy makers, and water resource managers, provided the impetus for this research. A 22-site, nested-scale, experimental watershed study design was implemented to investigate E. coli concentrations and the aforementioned relationships in a contemporary mixed land use watershed in the Appalachian region of the eastern United States. Results from a reduced (n=4 sites) study showed SPM in the µm interval to be the most important for E. coli with more than 90% of E. coli data found in this smallest interval. An annual study including all 22 sites revealed elevated E. coli concentrations in agricultural sub-catchments (avg. 560 CFU per 100 mL) relative to mixed development (avg. 330 CFU per 100 mL) and forested (avg. 206 CFU per 100 mL) sub-catchments. Additionally, annual E. coli and SPM concentration data displayed a statically significant relationship (p < 0.01) in agricultural areas. Results reflect the impact of historic land use practices (e.g. AMD caused by mining) as Spearman’s correlation coefficient (SCC) results showed significant correlation (p < 0.05) between water pH and E. coli concentrations at 77% of sample sites. Furthermore, a pH tipping point (threshold) in the range of 7.68–7.76 was identified in the current investigation, with pH values below this range including significant negative correlations (p < 0.05) with E. coli concentrations. A land cover tipping point of 25–30% was also identified for mixed development land use practices and significant (p < 0.05) negative correlations between E. coli and chloride concentrations. This research provides validation of the use of the experimental watershed study design to advance understanding of fecal contamination regimes in contemporary mixed land use watersheds. Results from the work can inform policy makers and land use managers about factors impacting fecal microbes in mixed land use watersheds, thereby aiding in effective water quality management.

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