Atmospheric Wet And Dry Deposition And Its Impacts Onagricultural Soils In Northern China

Dry and wet deposition is one of major pathway for removal of air pollutants from atmosphere, atmospheric pollutants are not only affect the Earth's biogeochemical cycles, but also accumulate through the food chain after they go into the aquatic and terrestrial ecosystems,and cause harm to humans health in the end. Following the rapid economical growth, acceleration of industrialization and urbanization, China has been faced with a gradual deterioration of air quality and extreme air pollution events occur frequently, Beijing, Tinajin and Hebei Province region has become China's most polluted areas. As the region's air pollution worsen and worsen, it will have a serious impact on regional agricultural ecosystems. It is a technical difficulties to estimates species, flux and ecological effects of atmospheric pollutants which transported to the the land surface species.In this paper, active and passive sampling methods were used to collect precipitation samples synchronously from June 2013 to August 2014 in Beijing. Soluble ions( Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42- etc) p H, and conductivity were analyzed and Metal elements(Be, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Ba, Ti, Pb, Th, U)were also analyzed. Results show that it is rational and reliable to evaluate atmospheric deposition by the traditional passive method and evaluate dry deposition by two different methods. We also use three- year concentration of soil profile and total settlement data of Luancheng and Yucheng agricultural station in North China to analyze the enrichment contribution rate of heavy metals, which transport from atmospheric depositon to agricultural system. This paper obtained the following results:(1) The traditional passive sampling method(bulk deposition) was gradually replaced by active sampling technique(wet-only deposition), because the passive method was vulnerable to dry deposition of aerosols and gaseous pollutants, thereby affecting the chemical composition of precipitation and the quantification of wet deposition fluxes. Here, a wet-only device was co-located with a bulk collector in urban Beijing, allowing the contribution of dry deposition to the bulk collector to be inferred. The results showed that the concentrations of NO3-, Mg2+, Ca2+, K+, Cl-, SO42-, Na+ and NH4+ observed by bulk sampler were 65%, 58%, 43%, 41%, 35%, 26%, 10% and 9% higher than those of wet-only deposition, respectively. Passive sampling method has a tendency to get a settlement substance acidification of precipitation, but because of the precipitation of alkaline substances carry higher background content; acidic dry deposition of atmospheric pollutants introduced did not significantly alter the p H of precipitation by passive sampling method.Due to the interferences of dry deposition, bulk deposition flux of NO3-, NH4+ and SO42- was 79%, 18% and 35% higher than that of wet-only deposition, respectively. Bulk deposition measured by open rain collectors can capture most nitrogen(N) and sulfur(S) compounds via wet deposition, but incomplete dry deposition of gases and particles. The total deposition(wet plus dry) of N and S to ecosystems will therefore be underestimated by the use of bulk collectors in urban areas, with underestimated values of 23 kg/(hm2·a)(39%) and 20 kg/(hm2·a)(40%)..(2) The passive method was vulnerable to dry deposition of aerosols pollutants, thereby can use two kind of sampling methods estimation of atmospheric dry deposition flux indirectly. The results showed that the dry deposition flux of Na, Mg, Ca, K, V, U, Mo, Cu, Ni, Se, Th, Sb, Fe, Ti, As 15 kinds of metal elements deposition fluxes of 57 %,51%,42%,36%,33%,30%,27%,25%,23%,22%,20%,20%,17%,17%and17% of the total flux, respectively, by using two sampling methods can estimate the atmospheric dry deposition fluxes. Thus, it is rational to estimate the amount of dry deposition flux indirectly by the differences of two sampling ways.(3) In North China dry and wet deposition fluxes of heavy metals is higher than other foreign countries and other areas in China, North agricultural regions contaminated metal elements of different degrees of enrichment on the soil surface, that showed significantly affected by the presence industrial emission sources. Yucheng station Mn, Cu, Fe, Ni and As enrichment at 40-60 cm, Mo, Zn, Cr and Ni enrichment at 20-40 cm, heavy metal pollution significantly affect agricultural topsoil. Yucheng atmospheric deposition of anthropogenic soil metal element Cu, Se, Cd and As the contribution rate is 78%,11%, 8% and 10%, respectively, less impact on the other metal elements; Luancheng station atmospheric deposition of Zn soil settlement the contribution rate of 20%,Cr element almost entirely from atmospheric deposition.Atmospheric dry and wet deposition carried high concentrations of pollutants in North China, which constitute a serious threat on regional water and soil ecosystem. In this paper, a method to help the scientific evaluation of atmospheric pollutants by precipitation, dry deposition of dust and gas input to the reliability and feasibility of flux over ground environmental, the results conducive to cognitive spatial variation of air pollution in North China and deposition fluxes potential impacts on ecosystems, regional atmospheric pollution and thus can provide some scientific basis for cooperative control.