Atmospheric Nitrogen Deposition And Acid Rain In Different Ecological Regions In Shaanxi Province

Atmospheric nitrogen deposition, a very important step in the nitrogen biogeochemical cycling, refers to the process that nitrogen components remove from atmosphere and deposit to the earth surface. With the anthropogenic influence, more and more reactive nitrogen emitted into atmosphere and deposited back to the earth. Atmospheric nitrogen deposition is not only an important agricultural and environmental research subject, but also occupies a decisive position in atmospheric chemistry. Atmospheric acid deposition generally refers to the precipitation with pH<5.6. The rapid development of industry and agriculture resulted in more and more acid rain, which ultimately caused a series of environmental problem such as water eutrophication, soil acidification and so on. The hazards of acid deposition on ecosystem and human health have become a world-renowned major problem. Shaanxi Province is the only province which located in the border of eastern humid area and western arid area of China. In recent years, serious soil erosion and dust storm problem often occurred in Shaanxi Province and made the ecological environment more fragile. So systematic research on atmospheric nitrogen deposition and acid deposition is not only helpful for us to make full use of environmental nutrients, but also provide basic data for environmental monitoring and assessment. In this paper, we used automated monitoring instrument, pot tests and long-term experiment to monitor the atmospheric nitrogen deposition, acid deposition and rain components in different ecological regions in Shaanxi Province. The main results were as follows:1.Five monitoring sites were chosen in four different ecological regions of Shaanxi Province to conduct a one-year monitoring research on wet and dry nitrogen deposition using automatic rain and dust sampler. The results showed that the amount of total inorganic nitrogen (TIN) ranged from 8.25 to 16.12 kg·hm^-2 in the 5 monitoring sites, and the maximum was in Yangling located in Wei River Agro-ecological Region, while the minimum was in Yulin situated in the Windy and Sandy Region along the Great Wall. The deposition rate of NH₄⁺-N was 3.10 kg·hm^-2 in Yulin, 3.66 kg·hm^-2 in Luoshuan, 8.60 kg·hm^-2 in Xi'an, 9.14 kg·hm^-2 in Yangling, 9.96 kg·hm^-2 in Ankang, while the NO₃^--N rate were 5.15,7.54,6.29,6.98 and 5.66 kg·hm^-2 respectively. Wet nitrogen deposition rate ranged from 6.57 to 14.43 kg·hm^-2 and dry nitrogen deposition rate varied from 1.19 to 2.74 kg·hm^-2. Both of them showed time variability. In summer and autumn, wet nitrogen deposition was higher than that in winter and spring because of the rainfall, whereas dry nitrogen deposition had opposite trend. This could be caused by the washing action of rainfall and greater amount of dust in winter and spring.2.In April, 2008 to March, 2009 the average deposition concentrations of NH₄⁺-N and NO₃^--N were 7.56μg·m^-3 and 4.65μg·m^-3 respectively in Guanzhong Area Shaanxi Province by collecting PM10 particles, and in each month, the concentration of NH₄⁺-N is greater than NO₃^--N. Total inorganic nitrogen was 9.22 kg·hm^-2, in which NO₃^--N and NH₄⁺-N account for 38.1% and 61.9% respectively. The amount of dry nitrogen deposition and PM10 particles showed a good positive correlation.3.Pot test and long-term experiment were used to estimate the total nitrogen deposition in Guanzhong Area Shaanxi Province. The results showed that in May, 2008 to September, 2008 and May, 2009 to October, 2009 total nitrogen deposition were 20.6 kg·hm^-2 and 21.4 kg·hm^-2 respectively. In the same period, the rain and dust sampler monitoring value were just accounted about half the estimated value. The annual nitrogen deposition was 40 kg·hm^-2·a^-1 through using long-term experiment, also larger than the monitoring value. As can be seen, the contribution of gas deposition and organic nitrogen deposition were very greater.4.The rainfall ranged from 333.7 mm to 1020.9 mm in the monitoring sites, and average annual pH varied from 4.96 to 5.91. The frequency of acid rain ranged from 14.3% to 21.2%, and the maximum was in Xi'an, while the minimum was in Yangling. The average conductivity was 0.133 mS·cm^-1. The anion and ion which had the highest substance concentration were NO₃^- and Ca²⁺ respectively. Compared with the southern acid rain area, the acid rain frequency in Shaanxi Province is lower, but with higher levels of various ions, air pollution is relatively serious.