Environmental Drivers Influence Carbon Emissions and Storage of a Freshwater Lake

An eddy flux covariance system was constructed in June of 2013 over Douglas Lake, a freshwater lake at the University of Michigan Biological Station (UMBS), using open-path infra-red gas analyzers to continually monitor the CO2 fluxes and energy budget associated with the lake. In addition to the IRGA sensors, two water temperature sensors and dissolved oxygen sensors were installed in the water to determine the profiles within the lake. A pressure sensor was also used at a fixed height above the lake floor to determine the water level and provide 10 Hz estimate for surface waves at all times. The storage of CO2 in lakes can serve as a greenhouse gas source or sink depending on the time of year, the mixological events, and the microbial activity in the lake and its underlying sediment. Through long term observation of the fluxes, we will better describe the environmental factors contributing to CO2 dynamics of small freshwater lakes in the Midwest. The lake tower is roughly 1.5 and 2 km away from two other towers that measure carbon fluxes and energy budget in the forest that surrounds the lake. A built in assumption in the analysis of ecosystem fluxes from flux towers is that there are no large-scale horizontal gradients in the atmospheric concentration of CO2. The presence of lakes, with very different flux rates than forests may violate this assumption. We compare the total flux of CO2 from each of the ecosystems (lake and forest) and their none-synchronized seasonal and diurnal cycles. This synchronicity adds to the advection by creating temporary (both long and short term) CO2 concentration gradients from the air above the lake to the air above the forest. We used the season-long measurements of CO2 concentrations and fluxes at the lake and over the surrounding forest to determine the amount to carbon flux that is advected laterally from the air above the lake ecosystem to the forest.