Light Exposure, Nutrients, and Microbial Assemblages Alter the Uptake of Dissolved Organic Carbon in Wyoming Water Bodies

Dissolved organic carbon (DOC) is a major downstream carbon flux in rivers. The variety of sources from which organic carbon enters aquatic ecosystems influences the carbon structure and thus carbon bioavailability. Our goal was to identify the role that light, microbes, and limiting nutrients play in DOC processing. We leached terrestrial material into water and calculated DOC uptake from short-term bioassays, which were exposed to light to evaluate the effects of photo-degradation on microbial uptake of DOC. In the Laramie River, the rate of microbial DOC uptake leached from cottonwood leaves was 0.022 per day (stdev=0.014). While DOC concentrations did not significantly change after light exposure, DOC uptake rates were 3X higher compared to pre-light bioassays (0.074 per day, stdev=0.028). Preliminary results suggest that light plays an important role in increasing microbial uptake of DOC. We will expand our comparisons using data from microbial DNA extractions, which will be used to compare different microbial assemblages to differences in DOC uptake. Nutrient amendment assays will also be used to assess the potential for nutrient limitation to alter microbial uptake of DOC. This research allows us to identify human impacts on ecosystem processes by analyzing changes in DOC levels.