Dynamic Change Characteristics Of Mercury In Litter Of Typical Subtropical Forest System In Southwest China

Mercury,a special heavy metal,can be carried out long-range migration and spread to the rest of the world through atmospheric movement.Even in the fish in the waters of inaccessible area,the studies found that much more accumulation of mercury in the fish there.The main reason is that mercury accumulation is caused by the enrichment of the food chain after the atmosphere has been brought and settled.Different forms of mercury,methylmercury,ethylmercury and other organic mercury,are so easily biologically absorbed and accumulated in fish that harm biological nervous system severely.Thus,mercury,as a pollutant that can spread around the world with atmospheric motion,has always been highly valued by the relevant scholars for a long time.Terrestrial ecosystems are considered to have complex biological systems and large biomes,and are important areas of research for this widespread global mercury pollution problem.This also includes forest ecosystems that are the largest,and the species and the richest terrestrial regions.The forest ecosystem is also considered to be the active pool of mercury because it absorbs mercury from the dry and wet deposits while releases mercury to the outside,and through the release of leaves,leaching of precipitation,etc.Therefore,the study of the mechanism of mercury uptake and release in forest vegetation-atmosphere interface is very important for mastering the mercury cycle in nature.In recent years,more and more studies on the migration and transformation laws of mercury in atmospheric-forest vegetation-soil interface have improved people's understanding of the problems.However,due to the complexity of forest ecosystems,there are still many problems to be further explored.Particularly,around the world there is not too much relevant research about litter layers,an important component of forest ecosystems.It will be more helpful to master the mechanism and regulation of the dynamics of mercury migration and transformation in the forest systems within the further understanding of the relevant mechanisms.The results are as follows:(1)In the litter of evergreen broad-leaved forest and coniferous forest,total mercury decreases with the litter,and its mass and unit concentration are increased.After 12 months of decomposition,the average mercury content in litter of evergreen broad-leaved forest increased to 125% of its original value,while the average mercury content in coniferous litter was increased to 120 %.(2)The change range of methylmercury is larger in litter decomposition,and the amount of litter is decreasing at a relatively consistent rate during the development of trees.The analysis of the segmentation regression model shows that the accumulation of mercury is seasonal and decreases in the season of the cessation of growth,but there is a significant increase in the other seasons.This is the case in the two types of forest land.The accumulation reflects a certain seasonal.(3)During the whole decomposition process,the change of methylmercury content and concentration was larger than that of total mercury,and the final methylmercury content of the two stands showed a significant increase trend compared with their initial contents The The decomposition rate of methylmercury in the coniferous and broad-leaved mixed forest reached 3.4 times of the original concentration,and the concentration of methylmercury in the evergreen broad-leaved forest reached 2.38 times of the original concentration.(4)At the early and late stages of decomposition,the proportion of medium-inert mercury in litter is the highest,which leads to a decrease in the ratio of mercury to other active states in litter,where the complexes are stable and mercury migrates And its toxicity and ecological risk also decreased.(Hg-w,Hg-o,Hg-e and Hg-s)increased with the increase of Hg-w and Hg-h in the middle of the decomposition,and the other four kinds of mercury It has a high ecological risk.(5)The change in the content of nitrogen between litter and mercury varies to a certain extent,showing the biotransformation process of mercury.That is,the nitrogenfixing microorganisms in the litter accumulate the protein by the accumulation of nitrogen,resulting in the conversion of the reducing sulfur group to the mercury.In the process of microbial absorption and fixation of nitrogen,mercury flux also increased significantly.This suggests that the migration of mercury in litter and the process of transformation may be affected by the type of microorganisms therein.