Spatial variability in surface N2O fluxes across a riparian zone and relationships with soil environmental conditions and nutrient supply

Riparian zones often serve to buffer nutrient loading from agricultural uplands but may also release greenhouse gases such as nitrous oxide (N2O) to the atmosphere. Riparian zone topography, combined with lateral chemical inputs from fields, is expected to cause variable hydrochemical environments which may lead to spatially variable N2O emissions. We examined spatial patterns in the simultaneous measurements of subsurface nutrient supply in groundwater, subsurface N2O production and surface N2O fluxes along two transects across a forested riparian zone adjacent to an agricultural field. Although subsurface N2O concentrations and ground water nitrate (NO3-) concentrations displayed distinct spatial trends across the riparian zone, with larger concentrations near the riparian zone-field interface and smaller concentrations in the riparian zone interior, surface N2O fluxes did not reflect this pattern. Instantaneous N2O fluxes measured during this study ranged from -0.28 to 1.3 nmol m(-2) s(-1) and were as variable within a site as they were among sites. Surface N2O fluxes were most strongly correlated with air and soil temperatures and N2O concentrations in soil pores in the top 15 cm of the soil profile, and were generally not correlated with conditions found in deeper soil throughout the riparian zone, suggesting that lateral inputs in runoff from the agricultural uplands are not increasing N2O fluxes at this site. Further research and analysis is required for a better understanding of the production and consequent movement of N2O. as well as an improved understanding of the effects of agriculture on N2O emissions from riparian areas. (C) 2010 Elsevier B.V. All rights reserved.