Distribution And Behavior Of Mercury In Terrestrial Ecosystem In Acid Deposition Area

A series of researches about mercury pollution have been conducted since the worldwide-shocked Minamata Disease happened in Japan in early I 950s, and some important aspects of mercury pollution to aquatic environment have also been understood clearly, such as the enrichment, transformation, transfer and endanger of aquatic food- chain etc. Since I 980s, mercury have been realized as a globe pollutant since large amounts of mercury from man-made sources such as the combustion of fossil fuels were emitted into the atmosphere and followed by long-distance transportation. Over 90% of mercury emitted into the atmosphere could eventually deposit back to the terrestrial ecosystems, and thus posed a great threat to human health via the terrestrial food chains. Investigations in the acid deposition areas demonstrated that the soil-plant systems were seriously polluted by mercury along with the occurring of acid deposition, and mercury was significantly bio-concentrated in the food chains. Thus, problems of mercury pollution in terrestrial ecosystems have come to be an important research subject. With the purpose of better understanding some weak links in this subject, we selected Chongqing, the acid deposition area with high consumption of coal and thus high emission of mercury, as the our research base to explore the distribution and behaviors of mercury as influenced by various environmental factors. Comprehensive methods including on-line investigation, on-site field monitoring and indoor simulation experiments were adopted for the purpose. The results may be taken as scientific references for the prediction and control of mercury pollution in terrestrial ecosystems. The investigation of this research covered an area of 556 kin2, which involved the urban district, its environs and the outer suburbs of Chongqing City. The distribution of mercury in the atmosphere close to land surface, the soil and plant in the regions suffering the influence of different acid deposition was monitored, the mercury emission from different anthropogenic sources was quantified, and the influences of atmosphere mercury on its contents in soil-plant systems were analyzed. Three field experiments were set in vegetable fields with different pollution degree by acid deposition for understanding mercury balance under different conditions. The experiments lasted from May 2000 to January 2001. Cowpea was planted followed by cabbage. During the experiment, samples of rainfall, deposited dust, leaching water, plant and soil were periodically taken for analyses of relevant parameters including mercury content. Pot experiment was designed to explore the effect regulation of air-Hg on soil-plant system and the transformation of Hg in soils. The experiment consisted of two groups, i.e. low air-Hg and high air-Hg, each with 8 treatments and four replications. Two seasons of young lettuce seedlings were planted. The investigation results showed that the distribution of Hg in the atmosphere with different surfaces underneath was in the order of urban area抐arming land>forest land; the concentrations of air-Hg were relevant to acid deposition: the air-Hg concentrations were higher in the areas suffering severer acid deposition; The vertical distribution of air-Hg monitored at the height of 0cm, 50,cm, 100cm and 150cm from the land surfaces consistently showed a sequence of SOcm>lOOcm>1 SOcm>Ocm regardless of the types of land surfaces underneath. However, Their magnitudes of concentrations of air-Hg were significantly af...