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Widespread Summertime N2O Undersaturation in U.S. Lakes and Reservoirs
Citation:
Beaulieu, J., M. McManus, AND R. Martin. Widespread Summertime N2O Undersaturation in U.S. Lakes and Reservoirs. 2021 ASLO Aquatic Sciences Meeting, Virtual, NC, June 22 - 27, 2021.
Impact/Purpose:
Inland waters are thought to be a globally significant source of nitrous oxide (N2O), a potent greenhouse gas, but most of the research in this area has focused on streams and rivers, with few measurements available from lakes and reservoirs. In this study we measured N2O concentrations in 1185 lakes and reservoirs (hereafter lakes) distributed across the conterminous US. We found that 75% of US lakes were functioning as a sink for atmospheric N2O. These findings suggest that current estimates of N2O emissions from inland waters may be an overestimate. These findings will be of interest to organizations responsible for compiling greenhouse gas inventories.
Description:
Inland waters are a globally significant source of nitrous oxide (N2O), a potent greenhouse gas. Most measurements have been performed in lotic waters, however, and data from lakes and reservoirs are relatively limited, despite their much greater spatial extent. To improve understanding of N2O dynamics in lentic waters, a probabilistic survey of summertime dissolved N2O concentrations (dN2O) was conducted at 1185 waterbodies distributed across the nine major U.S. ecoregions as a component of EPA’s National Lakes Assessment, a survey of chemical, physical, and biological indicators in U.S. waterbodies. We estimated that dN2O was undersaturated in approximately 75% of U.S. waterbodies during the sampling period, indicating that most U.S. waterbodies function as N2O sinks during the summer months. Despite widespread N2O undersaturation, the national average dN2O was 110% saturation (95% C.I.: 95 - 124%), indicating that N2O supersaturation in a minority of U.S. waterbodies was sufficient to offset undersaturation in the majority. Based on a semivariogram, spatial autocorrelation was not detected among the sampled lakes, suggesting that variation in N2O biogeochemistry may be controlled primarily by local as opposed to landscape scale drivers.
