ENVIRONMENTAL CONTROLS OF METHANE CONCENTRATIONS IN STREAMS IN THE SOUTH CAROLINA PIEDMONT

Methane is a greenhouse gas 80 times more potent than carbon dioxide. Rivers and streams, though understudied, tend to be oversaturated with respect to methane and therefore a net contributor to atmospheric methane content. Our study focused on finding whether trends exist between methane concentrations in streams and variables such as elevation, climate, and land cover in the Piedmont region of South Carolina. We

also examined small-scale spatial variability within streams such as in riffles, pools, and runs. We collected over 80 samples in the summers of 2019 and 2023 from over 40 locations in the Enoree, Saluda, and Savannah River basins. Methane samples were collected using a modified oceanic procedure, and methane concentrations were measured using a gas chromatograph. Stream methane concentrations ranged from 5 μatm in mountainous areas to 3000 μatm in the lower-elevation Piedmont locations and near wetlands. Pools averaged a methane concentration of 479 μatm while riffles and runs averaged a concentration of 342 μatm, 40% lower than in pools. Streams draining wetlands had the highest methane concentrations. Sample site elevation had a moderate negative correlation with methane concentrations (r²= 0.55) indicating decreased methane at higher elevations. Temperature had moderate positive (r²= 0.53) and rainfall moderate negative (r²= 0.54) correlations with methane concentration, though both are related to elevation. Agricultural land cover and percentage of wetlands in watersheds had weak positive correlations and channel slope had a weak negative correlation with methane concentrations. Initial observations indicate that elevation is the most important control of methane concentration for individual sample locations. This observation runs counter to the literature, which suggests streams in urbanized land cover and low-order streams in general have the highest methane concentrations. However, our data may be skewed by high concentrations of methane in low order streams at the lowest elevations in our study area. Future research will focus on detailed analysis of individual watersheds and a comparison of methane concentrations in watersheds with different land covers but at similar elevations.