Date of Graduation

5-2020

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Michelle A. Evans-White

Committee Member

Daniel D. Magoulick

Second Committee Member

John D. Willson

Third Committee Member

Sally A. Entrekin

Keywords

Anthropogenic Pollutants, Aquatic Science, Detrital Biofilms, Detrital Processing, Freshwater, Priming Effect, Subsidy-Stress

Abstract

Anthropogenic activities associated with urbanization, agriculture, and resource extraction continue to increase to support increasing needs of the growing population. These activities increase the amounts of pollutants entering freshwater streams and put aquatic ecosystems at structural and functional risk. Aquatic microbes play an important role in detrital processing in streams as a key linkage in moving carbon from detrital stocks into aquatic food webs. My research investigates the effects of light, nutrients, and salts on detrital microbes and decomposition in freshwaters using a mesocosm approach. In chapter one, I modified a current priming effect (PE) hypothesis model to include light level, proposed a method for calculating quantitative values for potential PEs, and tested the PE hypothesis according to my model and proposed calculation methodology. I manipulated light level [ambient (full light available) or 19% of ambient] and phosphorus [P; added 10, 100, or 500μg/L dissolved inorganic P (DIP)], and measured the effects on autotrophic (algae) and heterotrophic (fungi) detrital microbial communities and decomposition of Quercus stellata (Post Oak) leaf litter in a 150-day experiment. The results illustrate the importance of considering light levels, nutrient ratios (rather than individual nutrients), and detrital recalcitrant organic matter (ROM) components in further PE model development and provide evidence that priming effects occur in aquatic systems. In chapter two, I compare two similar experiments investigating potential subsidy-stress responses of autotrophic (algae) and heterotrophic (fungi and bacteria) detrital microbial communities and decomposition of Liquidambar styraciflua (Sweet Gum) leaf litter to sub-lethal increases in two common sodium (Na) salts (i.e. NaCl and NaHCO3). Treatments included ambient streamwater (SW; ~3mg/L Na) and NaCl and NaHCO3 amended SW with target concentrations of 16, 32, and 64 mg/L Na salts. Experiment A was subjected to day/night light cycles and temperatures according to the season and ran for 134 days. Experiment B was subjected to 12hr light/dark cycles at a constant 4.5°C for 135 days. The data suggest low-level Na salt increases likely affect detrital biofilms and decomposition before toxicity occurs, may be ion- and species-specific, and temperature plays a significant role in the magnitude of these effects.

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