Substantial nitrous oxide emissions from intertidal sediments and groundwater in anthropogenically-impacted XXXX Harbor, Massachusetts.

@entity739 @entity1568 @entity3727 @entity1507
Large @entity3727 emissions were observed from intertidal sediments in a coastal estuary, @entity739 Harbor, MA, USA. Average @entity3727 emission rates from 41 chambers during summer 2008 were 10.7mol N2Om(-2)h(-1)  4.43 mol N2Om(-2)h(-1) (standard error). Emissions were highest from sediments within a known wastewater plume, where a maximum @entity3727 emission rate was 155 mol N2Om(-2)h(-1). Intertidal @entity3727 fluxes were positively related to porewater ammonium concentrations at 10 and 25cm depths. In groundwater from 7 shoreline wells, dissolved @entity3727 ranged from 488% of saturation (56nM @entity3727 ) to more than 13000% of saturation (1529nM @entity3727 ) and was positively related to @entity1507 concentrations. Fresh and brackish porewater underlying 14 chambers was also supersaturated in @entity3727 , ranging from 2980% to 13175% of saturation. These observations support a relationship between anthropogenic nutrient loading and @entity3727 emissions in @entity739 Harbor, with both groundwater sources and also local @entity3727 production within nutrient-rich, intertidal sediments in the groundwater seepage face. @entity3727 emissions from intertidal "hotspot" in this harbor, together with estimated surface water emissions, constituted 2.4% of the average overall rate of @entity1568 export from the watershed to the estuary. This suggests that @entity3727 emissions factors from coastal ecosystems may be underestimated. Since anthropogenic nutrient loading affects estuaries worldwide, quantification of @entity3727 dynamics is warranted in other anthropogenically-impacted coastal ecosystems.
