The status of wet deposition of nitrogen compounds in an intensive dairy farming area in central Japan

Abstract

(pp. 47–52) The wet deposition of nitrogen compounds in the intensive dairy farming area and its environs in the northern part of the Kanto region in central Japan was investigated from April 2003 to April 2005. Open-bulk samplers were used to collect open-bulk precipitation, which approximates the sum of wet and dry deposition. Furthermore, wet-only samplers were applied to collect the precipitation for every 1 mm in a rainfall, termed the wet sample. The concentrations of total nitrogen and ammonium ions in the open-bulk precipitation were high in the central part of the dairy farming area and low in the remote mountainous area more than 15 km away the concentrations were generally high during winter and spring, and low during summer and autumn. There was a large difference in the annual deposition of nitrogen between the farming area and the surrounding area. The annual deposition of nitrogen in the farming area was significantly high compared to the values of existing data in Japan and Europe. The concentrations of respective nitrogen compounds in the wet sample, which accounted for 40 of the total rainfalls events, were notably high at the beginning of precipitation and rapidly decreased by 8 mm of continuous precipitation. The nitrogen concentrations at the beginning of precipitation were high in the farming area, and relatively low in the surrounding area. It was thought that the cause of the large wet deposition in the farming area was due to ammonia emissions, mainly from cattle manure produced at dairy farms. The factors of the seasonal changes were considered to be the frequency and the amount of precipitation, and the change in ammonia emissions from manure management performed by dairy farmers.