Hunt P G, Matheny T A, Ro K S
USDA-ARS, Coastal Plains Soil, Water, and Plant Research Center, Florence, SC 29501, USA.
J Environ Qual. 2007 Jul 17;36(5):1368-76. doi: 10.2134/jeq2006.0255. Print 2007 Sep-Oct.
Riparian buffers are used throughout the world for the protection of water bodies from nonpoint-source nitrogen pollution. Few studies of riparian or treatment wetland denitrification consider the production of nitrous oxide (N2O). The objectives of this research were to ascertain the level of potential N2O production in riparian buffers and identify controlling factors for N2O accumulations within riparian soils of an agricultural watershed in the southeastern Coastal Plain of the USA. Soil samples were obtained from ten sites (site types) with different agronomic management and landscape position. Denitrification enzyme activity (DEA) was measured by the acetylene inhibition method. Nitrous oxide accumulations were measured after incubation with and without acetylene (baseline N2O production). The mean DEA (with acetylene) was 59 microg N2O-N kg(-1) soil h(-1) for all soil samples from the watershed. If no acetylene was added to block conversion of N2O to N2, only 15 microg N2O-N kg(-1) soil h(-1) were accumulated. Half of the samples accumulated no N2O. The highest level of denitrification was found in the soil surface layers and in buffers impacted by either livestock waste or nitrogen from legume production. Nitrous oxide accumulations (with acetylene inhibition) were correlated to soil nitrogen (r2=0.59). Without acetylene inhibition, correlations with soil and site characteristics were lower. Nitrous oxide accumulations were found to be essentially zero, if the soil C/N ratios>25. Soil C/N ratios may be an easily measured and widely applicable parameter for identification of potential hot spots of N2O productions from riparian buffers.
河岸缓冲带在世界各地被用于保护水体免受非点源氮污染。很少有关于河岸或处理湿地反硝化作用的研究考虑氧化亚氮（N₂O）的产生。本研究的目的是确定河岸缓冲带中潜在的N₂O产生水平，并确定美国东南沿海平原一个农业流域河岸土壤中N₂O积累的控制因素。从十个具有不同农艺管理和景观位置的地点（地点类型）采集土壤样本。采用乙炔抑制法测定反硝化酶活性（DEA）。在有无乙炔孵育后测量氧化亚氮积累量（基线N₂O产生量）。该流域所有土壤样本的平均DEA（有乙炔时）为59微克N₂O-N千克⁻¹土壤小时⁻¹。如果不添加乙炔来阻止N₂O转化为N₂，仅积累15微克N₂O-N千克⁻¹土壤小时⁻¹。一半的样本没有积累N₂O。在土壤表层以及受牲畜粪便或豆科植物生产的氮影响的缓冲带中发现了最高水平的反硝化作用。氧化亚氮积累量（有乙炔抑制时）与土壤氮相关（r² = 0.59）。没有乙炔抑制时，与土壤和地点特征的相关性较低。如果土壤碳氮比>25，氧化亚氮积累量基本为零。土壤碳氮比可能是一个易于测量且广泛适用的参数，用于识别河岸缓冲带中N₂O产生的潜在热点。
