Author: Jake J Beaulieu,   (USEPA)

Designation: 

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 concentrations in lentic waters, a probabilistic survey of summertime dissolved N₂O concentrations (dN₂O) was conducted at 1090 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.  We used classical survey inference and multilevel regression and poststratification methods to estimate parameters related to dN₂O for the population of US lakes and reservoirs.  dN₂O was undersaturated in 75% (95% C.I.: 68.9 – 80.7%) of U.S. waterbodies during the sampling period, indicating that most U.S. waterbodies functioned as N₂O sinks during those summer months. Despite widespread N₂O undersaturation, the national average dN₂O was 110% saturation (95% C.I.: 104 - 123%).  Mean N₂O saturation varied spatially across the conterminous US, with lowest N₂O saturation in the Northern Plains ecoregion (95% C.I. 85 – 97%) and highest in the Coastal Plains ecoregion (95% C.I. 109 - 160%).  Despite regional variation in N₂O saturation, a semivariogram did not detect spatial autocorrelation among the sampled lakes, suggesting that variation in dN₂O may be controlled primarily by local as opposed to landscape scale drivers.  Nitrate concentration was the best predictor of dN₂O.

Category: Scientific Program Abstract > Special Sessions > CS10 Gas Fluxes