Emily K. Joynt, Weon Shik Han, Erik L. Gulbranson and Jackson P. Graham
Department of Geosciences, UW-Milwaukee. joynt.emily@gmail.com, hanw@uwm.edu, gulbrans@uwm.edu, jpgraham@uwm.edu
Wetlands are vital components of the carbon cycle containing an estimated 20-30% of the global soil carbon store. The Cedarburg Bog of southeastern Wisconsin boasts a myriad of wetland habitats including the southernmost string bog found in North America. Carbon dioxide (CO2 ) behavior in these systems is the response of multiple interdependent variables that are, collectively, not well understood. Modeling this behavior in future climate scenarios requires detailed representation of relationships within highly diverse environments. In 2014 a LI-COR 8100A automated soil gas flux system was installed in a hollow of the Cedarburg Bog string bog, measuring diffusive CO2 concentration and flux. Groundwater data, soil temperature, and weather data (temperature, pressure, etc.) were included to elucidate correlations between soil CO2 flux/CO2 concentration and external forces. In 2015 field data were complemented with soil moisture data and depth profile sampling of pore water chemistry and stable carbon isotopes from peat and gaseous media in order to discern the source and evolution of CO2 at depth. Preliminary LI-COR data analysis reveals distinct diurnal and seasonal trends; CO2 concentration builds overnight while flux increases during the day. CO2 flux magnitude and CO2 concentration range peak in mid-summer, but frequency of increased CO2 flux events is greatest in spring. Overall flux averages 7.55 mgCO2 /min-m2during the day but reaches 530 mgCO2 /min-m2 , and in several instances negative flux events are observed. Increased atmospheric and soil temperatures and decreasing atmospheric pressure are all observed to prelude increasing CO2 flux intensity, though correlation significance yields a wide array of strengths. Initial gaseous δ13C(CO2 ) data show average δ13C of ~18‰ with depleting values overnight, suggesting increasing microbial metabolic efficiency. Soil media reveal a microbial biomass δ13C of roughly -21 to -22‰. Further interpretation of data trends will utilize the HYDRUS-1D model to quantify relationships under changing environmental conditions. M.S. Thesis research, Dr. Weon Shik Han, Major Advisor.