Gas transfer velocities in small forested ponds

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Inland waters actively exchange gases with the atmosphere, and the gas exchange rate informs system biogeochemistry, ecology, and global carbon budgets. Gas exchange in medium- to large-sized lakes is largely regulated by wind; yet less is known about processes regulating gas transfer in small ponds where wind speeds are low. In this study, we determined the gas transfer velocity, k(600), in four small (<250m(2)) ponds by using a propane (C3H8) gas injection. When estimated across 12h periods, the average k(600) ranged from 0.19 to 0.72md(-1) across the ponds. We also estimated k(600) at 2 to 3h intervals during the day and evaluated the relationship with environmental conditions. The average daytime k(600) ranged from 0.33 to 1.83md(-1) across the ponds and was best predicted by wind speed and air or air-water temperature; however, the explanatory power was weak (R-2<0.27) with high variability within and among ponds. To compare our results to larger water bodies, we compiled direct measurements of k(600) from 67 ponds and lakes worldwide. Our k(600) estimates were within the range of estimates for other small ponds, and variability in k(600) increased with lake size. However, the majority of studies were conducted on medium-sized lakes (0.01 to 1km(2)), leaving small ponds and large lakes understudied. Overall, this study adds four small ponds to the existing body of research on gas transfer velocities from inland waters and highlights uncertainty in k(600), with implications for calculating metabolism and carbon emissions in inland waters.