The Functions Of Forests In Filtering Wet Deposition Of Pollutants And Their Hydro-chemical Characteristics

Effects of forest filter means that forests can eliminate and/or buffer contamination。This is one of the important functions of forest ecosystems. With the increase of pollution to water body and the air, more and more expectations have been paid to the self-cleaning functions of forest ecosystem。 Therefore, it is very necessary to study the process and mechanism of forest ecosystems to hold, absorb, and purify pollutants with their canopy, tree trunks, shrubs, herbs, litter and soil(microbe)。It is also an important to assess the hydrological service functions of forests。 This paper took the whole forest was taken as a filter system, which is divided the in several different sub-systems for this study,including plants,litter, soil and micro-organism。According to the purpose and content of this research, three types of plots are chosen: Cinnamomum camphora forest (broad-leave),Pinus massoniana forest (coniferous forest),bare field。All experimentations are made according to forests hydrological process research methods, Located Research Methods Of Forest System. Small catchment runoff method is used to study the filter function of forests. The results indicate that: ⑴the ionic concentrations of pollutants in the air precipitation is respectively: S042-30.36mg/L; N03-3.56mg/L; Cl-1.41mg/L; F-; 0.75mg/L , suggesting a higher contribution of SO2 to acid deposition the ionic concentrations of the throughfall and stem flows of forest communities are significantly higher than those in the precipitation。 in both types of forests, the pollutant concentrations in the underflows are significantly higher that those in the air precipitation。 by comparing the input and output system of the the ionic concentrations of pollutants, we found that the forests have a significant role in intercepting and accumulating wet deposition of air pollutants。 These observations support the supposition that "forests are filters to air wet deposition pollutants", in spite of the fact that the filtering effect is limited。 ⑵The total sulfur in soil is not high .The subsurface sulfur obviously is higher than the others soil horizon,the soluble sulfur mainly concentrates in the surface layer,the adsorpted sulfur mainly concentrates in 40-60cm. The adsorpted S is the dominance composition s in two kind of forest types,In the coniferous soil the adsorpted and soluble S is remarkably higher than the camphor tree forest along with prafile,but the bare land is dominanced by soluble S,Adsorpted S and the soluble S drop along with prafile.The soluble sulfur and the adsorpted sulfur do not remarkable relation with the total sulfur (P<0.001). pH and the adsorpted sulfate are negative relations. ⑶The relation between sulfur functional bacterium and the soil bulk density is not very close; but it is remarkable between sulfur functional bacterium and the soil pH; the soil moisture content and the sulfuric anaerobic bacterium quantity assumes remarkably positive correlation .The relation of sulfur bacteria and the soil organic matter is obviously (R=0.463),the sulfur anaerobic bacterium and the soil organic matter ′s correlation is not obviously。 The microorganism quantity is different in different soil types : Sulfur bacteria > sulfuric anaerobic bacteria; camphor forest > bare land > coniferous forest .The microorganism quantity distributes different soil horizons and types .The relations among soil sulfur bacteria , soluble sulfur (R=0.739) and the total sulfur relations(R=0.539) are close. But the sulfuric anaerobic bacteria is only closed with the total sulfur content (R=-0.458), not very closed with the soluble sulfur and theadsorpted sulfur。 ⑷The modelling experimentation indicated that soil percolation output is correlated with the total amount of precipitation and the rainfall duration, not correlated with the rainfall intensity. And along with rains hydroperiodism lengthening, average percolation output efficiency speeds up, vertical permeating is predominance,while lateral permeating is little。The soil percolation and SO42-have the "hysteresis phenomena" 。 Under the durative rainfall influence,the pH of soil percolation water change is firstly dropping and then rises along with precipitation increase and time lasting ; SO42-content also gradually increases,Thus soil pH and SO42-assumes the negative relations(R=-0.542); The sulfur bacteria is rises firstly,then drops gradually。The sulfuric anaerobic bacteria rise continuously,the regression equation may be seen,the sulfur bacteria,soil percolation water,the SO42-relevance is well,and the SO42-reduces along with the sulfur bacteria quantity increase,Thus it can be seen,The sulfur bacteria played an important role to degeneration the sulfur air pollution wet deposition ⑸The aboveground sorption and enrichment ability of major contaminants is stronger in Pinus massoniana than in Cinnamomum camphora forest, while the buffer ability in the canopy and trunk of the broad-leafed wood is greater than that of coniferous one. The soil of Pinus massoniana has stronger sorption and buffer ability to S than that of Cinnamomum camphora forest,while the whole sorption and buffer effect of S is greater in Cinnamomum camphora forest than in Pinus massoniana. The change of input and output contaminants concentrations indicates that the purification effect is better in Cinnamomum camphora forest than in Pinus massoniana. So in the practice of the forest management, the related department should appropriately mixed coniferous and broad-leafed forest to better the filter function.