Hydrological and meteorological controls on landscape scale nitrous oxide (N2O) emissions

Background/Question/Methods Nitrous oxide (N₂O) emissions at the landscape scale are poorly understood and this severely limits our ability to develop strategies for protecting estuaries and controlling global warming. We quantified N₂O emissions along a soil wetness sequence across a pasture-forest-alfalfa-riparian zone landscape in upstate New York. The wetness sequence has an approximate length of 725 m and a total relief of 50 m. The pasture has an average slope of 20% lying on the uphill section of the wetness gradient, followed by a nearly horizontal patch of forest, and an alfalfa field with slight relief. Hydrologic and meteorological patterns along this slope, including soil moisture (both volumetric and gravimetric), pH, texture, soil organic carbon (SOC), nitrate, ammonium, soil and air temperature, and precipitation were all monitored. N₂O fluxes were measured weekly during the late spring to early summer using the static chamber technique.

Results/Conclusions Our results showed that soil moisture increased along the slope from the top to bottom as we expected, except for the alfalfa field which was normally the driest among all sites. Soil nitrate in the alfalfa field, however, was significantly higher than the other sites despite its low levels of SOC and ammonium. The magnitude of N₂O emissions fell in the range of 1.0-5.0 kg N₂O ha^-1 yr^-1 with substantial difference among different research sites/landscapes. In addition, patterns of N₂O emissions most closely followed the patterns of soil moisture and SOC, highlighting the importance of topographic positions in the emissions of N₂O in the highly patchy landscapes.