Impacts of Atmospheric Ammonia Volatilized from the Cattle Feedlot on Nitrogen Deposition onto Japanese Cypress Canopy

Abstract

The dry deposition of atmospheric ammonia (NH₃) volatilized from feedlots, one of major loads of nitrogen into the basin, has been rarely observed at the tree canopies close to the feedlot in Ibaraki, Japan. We made multi-point annual observations of the NH₃ concentration using passive samplers within and surrounding the cattle feedlot in Ibaraki. The throughfall and wet deposition of ammonium-nitrogen (NH₄⁺-N) was also measured by bulk samplers under Japanese cypress trees near the feedlot. The annual mean NH₃ concentration measured inside the feedlot (322 ppbv) was lower than that expected from the cattle density, suggesting the requirement for monitoring the micrometeorological environment and management processes inside the feedlot. The results also indicated that the local-scale spatial distributions of the NH₃ concentration may be influenced by not only horizontal wind directions but also air temperature and humidity, buildings, and trees. The annual throughfall deposition of NH₄⁺-N (27.5 kgN/ha/yr) was clearly greater than those observed in the Japanese forests in past studies, suggesting the high impact of the dry deposition of NH₃ volatilized from the feedlot. The deposition velocity of NH₃ was estimated to be 3.4±2.5 cm/s, which was the highest range level of literature values for coniferous forests.