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SOIL NITROUS OXIDE, NITRIC OXIDE, AND AMMONIA EMISSIONS FROM A RECOVERING RIPARIAN ECOSYSTEM IN SOUTHERN APPALACHIA
Walker*, J T., C D. Geron*, J. M. Vose, AND W. T. Swank. SOIL NITROUS OXIDE, NITRIC OXIDE, AND AMMONIA EMISSIONS FROM A RECOVERING RIPARIAN ECOSYSTEM IN SOUTHERN APPALACHIA. CHEMOSPHERE. Elsevier Science BV, Amsterdam, Netherlands, 49(10):1389-1398, (2002).
The paper presents two years of seasonal nitric oxide, ammonia, and nitrous oxide trace gas fluxes measured in a recovering riparian zone with cattle excluded and in an adjacent riparian zone grazed by cattle. In the recovering riparian zone, average nitric oxide, ammonia, and nitrous oxide fluxes were 5.8, 2.0, and 76.7 ng N/m2-s (1.83, 0.63, and 24.19 kg N/ha-y), respectively. Fluxes in the grazed riparian zone were larger, especially for nitric oxide and ammonia, measuring 9.1, 4.3, and 77.6 ng N/m2-s (2.87, 1.35, and 24.50 kg N/ha- y) for nitric oxide, ammonia, and nitrous oxide, respectively. On average, nitrous oxide accounted for greater than 85% of total trace gas flux in both the recovering and grazed riparian zones, though nitrous oxide fluxes were highly variable temporally. In the recovering riparian zone, variability in seasonal average fluxes is explained by variability in soil nitrogen (N) concentrations. Nitric oxide flux was positively correlated with soil ammonium concentration, while nitrous oxide flux was positively correlated with soil nitrate concentration. Ammonia flux was positively correlated with the ratio of ammonium to nitrate. In the grazed riparian zone, average ammonia and nitrous oxide fluxes were not correlated with soil temperature, N concentrations, or moisture. This was likely due to high variability in soil microsite conditions related to cattle effects such as compaction and N input. Nitric oxide flux in the grazed riparian zone was positively correlated with soil temperature and nitrate concentration. Restoration appeared to significantly affect nitric oxide flux, which increased approximately 600% during the first year following restoration and decreased during the second year to levels encountered at the onset of restoration. By comparing the ratio of total trace gas flux to soil N concentration, we show that the restored riparian zone is likely more efficient than the grazed riparian zone at diverting upper-soil N from the receiving stream to the atmosphere. This is likely due to the recovery of microbiological communities following changes in soil physical characteristics.