PHOTOCHEMICAL EFFECTS ON THE QUANTITY AND QUALITY OF DISSOLVED ORGANIC CARBON IN STREAMS OF NORTHERN VERMONT

Lake Champlain, a regional source of drinking water and recreation in Northern Vermont, is plagued by nutrient imbalances that lead to environmental problems, such as seasonal algal blooms. Understanding the dynamics of one of these nutrients, dissolved organic carbon (DOC), is important for both a locally healthy aquatic ecosystem and at a larger scale the global carbon cycle and its connection to climate change. Specifically, this study examines the photochemical transformation of DOC in terms of both carbon quantity (concentration) and carbon quality (bioavailability). Initial experiments used filtered water from streams originating from different land use types that lead into Lake Champlain: Urban (Potash Brook), Agricultural (Hungerford), Forested (Wade), and a combination of the three (Swanton). These water samples were exposed to simulated sunlight for a total of 96 hours. Samples were removed every 24 hours for analysis of total DOC concentration, the UV-visible spectrum, and 3D fluorescence excitation-emission matrices (EEM). To monitor the changes in bioavailability of DOC in water samples after exposure to light, EEMs were post processed with PARAFAC modeling to determine the change in the percentage of protein-like DOC (typically more bioavailable) vs. humic-like DOC. DOC bioavailability was also measured pre and post exposure to light by inoculation with a 1:1 bacterial inoculum obtained from a local stream and then stored in the dark for a 28-day period. The difference between initial and final DOC for each incubation pair was inferred as the bioavailable DOC pool.

Additionally, to better understand the impact of leaf fall on DOC photochemistry leaf litter was collected from 5 different tree types: Shagbark Hickory, Yellow Birch, Sugar Maple, White Oak, and Beech. After leaching leaves in water for 24 hours the DOC was characterized then subjected to the same photo irradiation process described above. Data from these experiments will show the significance of photochemistry on DOC transformation as a function of watershed land use and leaf fall.