Term of Award

Summer 2017

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

Risa Cohen

Committee Member 1

J. Checo Colon-Gaud

Committee Member 2

Asli Aslan


Streams across the United States and globally are influenced by environmental contamination, including antibiotics, which enter streams due to widespread use and multiple pathways into the environment. Antibiotics are also likely to enter streams in mixture with other contaminants that alter the effects on aquatic organisms. Furthermore, antibiotic-resistant bacteria enter streams through similar pathways as antibiotics with implications for natural microbial communities. Therefore, understanding the presence and effects of antibiotic-contaminant mixtures and antibiotic-resistant bacteria in streams is important for resource management.

Chapter one describes an experiment that tested the hypothesis that the antibiotic tetracycline (TC) alone influences phytoplankton communities differently than in mixture with excess nutrients. Environmental conditions including season and flow regime were also manipulated to determine the effect of these variables. Artificial streams and ponds were inoculated with phytoplankton and exposed to one of four treatments: no-addition control, TC-only, nutrients-only, and TC + nutrients in fall 2015 and summer 2016. TC and nutrients individually had positive, negative, or neutral effects depending on the experiment, and TC-nutrient mixtures increased growth under certain conditions. Thus, the direction and scale of TC and nutrient effects are likely dependent upon seasonal changes in temperature and flow. Results from this study demonstrate the importance of considering antibiotic-nutrient mixtures and environmental conditions in toxicity tests to more accurately predict how phytoplankton communities will respond to inputs of these contaminants.

Chapter two describes a field study that tested the hypotheses that: 1) land use influences TC-resistant bacteria abundance in southeastern coastal plain streams; 2) TC-resistant bacterial abundance is related to temperature, precipitation, and nutrient concentration; and 3) phytoplankton abundance and community composition are related to TC-resistant bacterial abundance. Water samples were collected from streams within the Ogeechee River Basin (ORB), southeastern GA, USA to examine relationships between land use, resistant bacterial abundance, phytoplankton communities, and environmental variables over time. Results suggested that agricultural locations are local sources of fecal bacteria and WWTPs are likely local sources of both fecal bacteria and resistant bacteria into surface waters. These findings also indicate that major precipitation events affect ARB delivery to streams. In addition, phytoplankton within ORB streams are influenced by light attenuation and nutrient concentration rather than altered competitive dynamics with resistant bacteria.

Research Data and Supplementary Material