Air-water CO2 fluxes in the microtidal Neuse River Estuary, North Carolina

From June 2009 to July 2010, we conducted 27 continuous-flow surveys of surface water CO2 partial pressure (pCO(2)) along the longitudinal axis of the Neuse River Estuary (NRE), North Carolina ranging from the tidal freshwater region to the polyhaline border with the Pamlico Sound. Lateral transects were also conducted at the borders of each of three hydrologically distinct sections. The pCO(2) displayed considerable spatial-temporal variability. Likewise, net air-water CO2 fluxes showed high spatial and temporal variability, with a maximum [release] of 271 mmol C m(-2) d(-1) during high river flow conditions in fall and minimum [uptake] of -38 mmol C m(-2) d(-1) during wind-driven, high primary productivity conditions in late spring. During high-flow conditions, pCO(2) generally decreased from the river mouth to the Pamlico Sound, similar to patterns seen in well-mixed systems. During warm, low-flow conditions, surface water pCO(2) distributions were spatially variable and dissimilar to those patterns seen in most macrotidal, well-mixed estuaries. The annual air-water CO2 efflux from the study area was 4.7 mol C m(-2) yr(-1), an order of magnitude less than previously estimated for temperate estuaries. The CO2 fluxes observed in the NRE highlight the contrasts between macrotidal and microtidal systems and suggest that global estuarine CO2 emissions are likely overestimated by the current classification approaches. Scaling this lower efflux by the relative surface area of macrotidal and microtidal systems would reduce the global estuarine flux by 42%.