Nitrous oxide (N
2O) has 265 times greater greenhouse potential than carbon dioxide and its atmospheric concentration has increased by about 20% since industrialization; however, N
2O production and emissions from aquatic systems are poorly constrained. To evaluate N
2O
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Nitrous oxide (N
2O) has 265 times greater greenhouse potential than carbon dioxide and its atmospheric concentration has increased by about 20% since industrialization; however, N
2O production and emissions from aquatic systems are poorly constrained. To evaluate N
2O fluxes associated with meteoric groundwater discharge to coastal zones, we measured N
2O concentrations in May and October 2011 from two discharge points of the Upper Glacial aquifer on Long Island, NY, USA. One coastal zone contains only fresh water and the other contains an upper saline zone. N
2O concentrations decreased by around 40% for the fresh water and a factor of two for the salt water from May to October, 2011. Fluxes were around 100 to 200 times greater from the freshwater (246 to 448 µmol/m shoreline/day) than saltwater aquifer (26.1 to 26.5 µmol/m shoreline/day). N
2O concentrations correlate positively with NO
3− and dissolved oxygen concentrations and negatively with salinity, dissolved organic carbon (DOC) and N
2 denitrification concentrations. The smaller saltwater N
2O export resulted from DOC enrichment in the upper saline zone, which appears to have driven denitrification to completion, removed N
2O, and increased N
2 denitrification. DOC concentrations should be considered in global N
2O flux estimates for coastal aquifers.
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