USING HYDROGEOPHYSICAL METHODS FOR ESTIMATING RATES OF BIOGENIC GAS PRODUCTION IN PEAT SOILS OF THE FLORIDA EVERGLADES

Peat soils are known to release significant amounts of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere. However, uncertainties still remain regarding the spatial and-temporal distribution of gas production and release from peat soils, especially in low-latitude and subtropical peatlands like the Everglades. Ground penetrating radar (GPR) is a hydrogeophysical tool that has successfully been used in the last decade to non-invasively investigate several aspects related to carbon dynamics in peat soils such as the release of biogenic gasses. Most research work has focused on northern peat soils, and has only recently been used in subtropical systems. In this study we use a combination of GPR and gas flux measurements to estimate methane production rates at four field sites, spanning two different peat types of the Florida Everglades over a 4 month period. At each site, gas contents within the soil are monitored using the GPR method and gas release is monitored using flux chambers. A weekly gas production rate is estimated using a mass balance approach accounting for in-situ changes in soil gas content using the GPR method, gas flux to the atmosphere using static flux chambers, and expected rates of diffusion and methanotrophic consumption found in literature. Resulting production rates for all observations range between 0.02 and 0.47 g CH4 m^-2 d^-1, and highlight the spatial and temporal heterogeneity of gas dynamics between peat soil types. Methane production and flux results are then compared to outputs from a gas flux model developed with each site’s characteristics. Better understanding rates of biogenic methane gas production and release from wetlands has implications regarding the role of wetlands and peat soils in large scale carbon cycling studies.