29-2 Relative Controls of Spatial Variation of Methane Concentrations within Streams and Rivers in the South Carolina Piedmont

Session: Undergraduate Research, Part II (Posters)

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Streams and rivers are oversaturated with methane relative to the atmosphere. Previous research has suggested land cover, geomorphology, hydrology, organic matter, terminal electron acceptors, and temperature all influence methane concentrations. The importance of each factor in controlling methane concentrations within streams and rivers is unclear, particularly in temperate regions. Relative to tropical and boreal regions, temperate regions have been historically understudied. This study aimed to determine controls over spatial variability of stream methane concentrations in the South Carolina Piedmont. Samples were collected under baseflow conditions at 81 locations for a total of 129 samples in the summers of 2019, 2023, 2024, and 2025. Sample location elevations ranged from 239 to 306 m. The streams drained watersheds with a wide range of land covers, from mostly forested to mostly developed. Watersheds with urban land cover occurred in and around Greenville, South Carolina, with a population density of 570 people/km². Methane concentrations ranged from 5 to 5700 μatm/L (median of 569 μatm/L), and all samples were oversaturated. Methane concentrations had a moderate positive correlation with specific conductivity, a strong positive correlation with iron concentration, and a strong negative correlation with dissolved oxygen. Methane concentrations also had a moderate negative relationship with elevation and a strong negative correlation with channel slope, indicating the importance of geomorphology. Methane concentrations had a moderate positive relationship with turbidity. All types of land cover were weakly correlated with methane concentrations. Results suggest higher methane concentrations are associated with longer residence time in anoxic riparian zones in areas of shallower slopes.  Streams with steeper channel slopes at higher elevations have higher gas exchange rates and shorter hydraulic residence time in soils which limits methanogenesis. The population density and amount of high density development in Greenville may not be great enough to have a significant effect on methane generation. In the southeastern Piedmont, the combination of geomorphic controls and riparian soil conditions appears to be the strongest control over stream methane concentrations.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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