Spatial Variability in Biogenic Gas Releases from Subtropical Wetland Ecosystems is Revealed from Ground Penetrating Radar (GPR) at the Lab and Field Scale

English Abstract:

Peatlands are key contributors of greenhouse gases into the atmosphere that are capable of producing and releasing significant amounts of free-phase biogenic gases (CO₂ ,CH­₄). Over the past two decades many studies have investigated gas flux dynamics in peat soils, however the spatial distribution of these fluxes are still highly uncertain, particularly for tropical and subtropical peatlands. This study implements an array of hydrogeophysical methods to investigate the spatial variability in biogenic gas accumulation and release in three 0.027 m³ peat monoliths from three different wetland ecosystems in central Florida (sawgrass peatland, a wet prairie, and a depressional wetland within a pine flatwood). Over a period of five months gas content variability (i.e. build-up and release) within the peat matrix was estimated using a series of ground penetrating radar (GPR) transects along each sample about three times a week using high frequency (1.2 GHz) antennas. GPR measurements were constrained with an array of gas traps (eight per sample) fitted with time-lapse cameras in order to capture gas releases at 15 minute intervals. A gas chromatograph was used to determine CH₄ and CO₂ content of the gas collected in the gas traps. A grid of surface deformation points was also collected concurrently to monitor changes in the peat surface associated with gas build up and release. The approach was further upscaled to the field within the Blue Cypress Preserve (BC) where high temporal resolution datasets were implemented. The aim of this study is to investigate the spatial and temporal variability in gas accumulation and release of biogenic gases in subtropical peat soils at the lab and field scales and how they are potentially related to structural changes within the peat matrix. This work has implications for better understanding carbon dynamics in subtropical freshwater peatlands and how climate change may alter such dynamics.