Factors Controlling Diffusive CO2 Transport and Production in the Cedarburg Bog, Saukville, Wisconsin: Field Observations

Abstract:

Wetland ecosystems 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. The behavior of carbon dioxide (CO₂) 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 such 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 and collectively measured diffusive CO₂ concentration and flux. Supplemental groundwater data, soil temperature, and weather data (temperature, pressure, precipitation, etc.) were also 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, both peaking in mid-summer. Flux events average 405 mg CO₂/m² per hour but reach over 31,800 mg CO₂/m² per hour in a single event and in several instances negative flux events are observed. Correlation significance also yields a wide array of strengths among variables. Initial δ¹³C data from gaseous CO₂ infer, on average, a more positive δ¹³C signature in the atmosphere compared to the surface and shallow subsurface. Temporal trends of these parameters are similar to one another, becoming depleted in δ¹³C through time. Further interpretation of data trends will utilize the HYDRUS-1D model to quantify relationships under changing environmental conditions.