Atmospheric Deposition And It's Chemic Consititute In Loess Plateau

As the industrial development increased sulfur content in atmosphere, the global acid rain caused by sulfur deposition affected the agricultural development badly. The in-depth study has been extended from acid deposition monitoring to atmospheric deposition monitoring. Compared with the developed countries, China left behind on the research of compositions of atmospheric deposition. At present, China is facing a serious problem of air pollution, therefore, taking measures to reduce air pollution and restore the original components has been put on the agenda.The most practical approach should be tracking the trend of the atmospheric compositions'changes, thereby forecasting their effects on the environment, ecosystems and various crops and finally making response measures. Therefore, in order to make full use of every advantage, the Shaanxi Provincial Meteorological Bureau and the Northwest A& F University cooperate to contribute to a monitoring net of atmospheric compositions in Shaanxi Province, hopefully, these studies would provide vital basis data for the research of atmospheric compositions and the change of environment. The locations of the monitoring experiments are Yangling and Luochuan in Shaanxi Province which are tipycally on behalf of the Guanzhong Plain and loess Dryland respectively. Atmospheric precipitation and deposition were collected by Automatically Sampling Implement of Precipitation and Deposition during 2006 to 2007. The mineral N content in the samples were measured. The main ions in the precipitation such as K+,Na+,Ca2+,Mg2+,NH4+,NO3-,SO42- were measured while deposition flux of various salts were also determined. The rainfall in Yangling in 2006 was 507.8 mm and the total N deposition flux was 20.6 kg/(hm2·a) which was equivalent to 51 kg urea. The annual rainfall in Luochuan was 579.5 mm and the total N deposition flux was 12.8 kg/(hm2·a) amounting to 32 kg urea. Wet deposition was the main form of deposition in both of the regions, whose dynamic monthly change performed simultaneously with the rainfall, achieving the peak between June and September. The rule of N input by dry deposition was not very clear. NH4+-N deposition in Yangling was significantly higher than that in Luochuan, which implied that the emissions and volatilization of NH3 in Yangling exceeded that in Luochuan. However, total N depositions in both areas were less than that in eastern China.During the year of 2006-2007, the average annual pH values of the rainfall in Yangling and Luochuan were 6.05 and 6.45 respectively with the frequencies of acid rain of 38% and 29%. Low pH appeared in the months of August, September and October which was basically the same as the trend of other areas.The conductivities of the rainfall in Yangling and Luochuan were 0.085 and 0.170m mS/cm respectively. They were slightly higher than that in eastern China and much higher than the background value in Waliguan Hill whose average conductivity was 0.015 mS/cm. Cations of precipitation in Yangling were listed orderly by the concentration of NH4+>Ca2+>Na+>K+>Mg2+ while in Luochuan it represented as Ca2+>Na+>Mg2+>NH4+>K+ . The concentration of NO3- was higher than that of SO42- in both of the precipitations in Yangling and Luochuan.The annual dry deposition in Yangling was103.0 t/km2a and the monthly average amount was 8.6 t/km2 mo. The maximum and minimum dry depositions were 10.2 t/km2 mo and 6.9 t/km2 mo respectively; the annual total dry deposition in Luochuan was 92.2 t/(km2 a). The monthly mean amount was 7.1 t/km2 mo and the maximum and minimum figures were 8.9 t/km2 mo and 6.5 t/km2 mo respectivelyThe soluble salts in dry deposition in Yangling totally was 10.97 kg/hm2 with the order of Na>Ca>NO3—-N>K>NH4+-N>Mg>S>P; the total soluble salts in dry deposition in Luochuan was11.59 kg/hm2 with the order of Ca>K>Na>NH4+-N>Mg>NO3—-N>S>P. Precipitation was the main input source for the active N and deposition was the main input channel for active P.The experiments showed that the input of nitrogen by the precipitation and deposition mainly because the development of agriculture, industry and transport. The amount of input should be given sufficient attention since it not only produced negative effects on agricultural production but also on the ecological environment. Although Shaanxi Province is not a region of heavy acid rain, the relative concentration of the rain resulted in low pH in the rainfall. The formative factors of acid precipitation were relatively complex one of which might be SO42-and Ca2+ existed as sedimentation. The precipitation and deposition is rich of salts. The vital function of deposition will be more apparent on the global atmospheric circulation.