Nitrous Oxide Accumulation in Soils from Riparian Buffers of a Coastal Plain Watershed–Carbon/Nitrogen Ratio Control
2007
Hunt, P. G. | Matheny, T. A. | Ro, K. S.
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 μg 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 μg 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 (r ² = 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.
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