MS Thesis Defense


Justin Wiese

August 23, 2019


Determining Sources of E. coli Contamination in the Minnehaha Creek Watershed using Rep-PCR DNA Fingerprinting Technology

In 2013, total maximum daily load values for E. coli were not being met within the Minnehaha Creek Watershed District (MCWD) in Minnesota. Elevated levels of E. coli are of public health concern as they are used to indicate the possible presence of pathogenic bacteria that can cause illness in humans. The Minnehaha Creek, which occupies acres urban and suburban Minneapolis, empties into the Mississippi River - which ultimately flows out into the Gulf of Mexico. Poor water quality in the Minnehaha Creek, due in large part to microbial contamination, has the potential to impact larger regions and water bodies in the US and North American. Despite their importance, however, the sources of E. coli are not known. In this study I used rep-PCR DNA fingerprinting technology to determine the source(s) of elevated E. coli within the Minnehaha Creek during the years 2017 and 2018. Additionally, hydrological data was recorded to determine effects of altered hydrological flow regimes on change in diversity of E. coli. MANOVA and multidimensional scaling analysis suggested that Lake Minnetonka and sediment within the Minnehaha Creek are important sources of E. coli that are not greatly impacted by changing hydrological conditions. An analysis of 2017 vs 2018 data sets also showed that street gutters and grit chambers may also be an important source of E. coli contamination - but could be variable and dependent on higher hydrological flows to flush E. coli into the Creek. Results of this study showed that once E. coli and other fecal indicator bacteria enter water bodies, through a variety of sources including human, wildlife, pet, sewage, agricultural, etc, that these populations can grow and persist within both lake and sediment environments. This, together with new bacterial inputs, contribute to elevated E. coli counts leading to the impairment of water bodies. Variable hydrological flows have the possibility to move E. coli from surface biofilms into the water column leading to increased E. coli counts, particularly in structures such as street gutters and grit chambers.