| The requirement of resource and inferior resource consumption are constantly increasing with the rapid development of China’s economy, then furthure resulting in explosive growth of pollutants emitted into the atmosphere; increased cars and industrial emissions also lead to a serious acid rain and fog-haze in China. The atmospheric pollutants reach to the land accompanying with the dry and wet deposition, and forest ecological system as the biggest land ecosystem is a big receiver of atmospheric pollutants.Previous studies have indicated that forest has the ability to purify rainwater, as rainwater can be filtered through various forest layers (such as canopy and litter) before entering into surface water, and filtered rainwater by forest can be further purified by soil layers during its transportation to ground water, and the forest ecosystem on water conservation and purification and soil maintenance also play an important role. This combination of forest and soil layers usually can produce the maximum hydrological function of forest ecosystems.The southwest region is the second largest district with a high forest coverage rate (95.41%) in China, and the annual rainfall here ranges from 900 mm to 1522 mm. The Simian mountain national nature reserve has the most representative zonal vegetation types in the region, but also the largest and the most preserved subtropical evergreen broad-leaved forest of the earth at the same latitude.Therefore, the typical subtropical evergreen broad leaf forest forest were chosen to study and analyze the retention characteristics of nitrogen, sulfide, base cations and Pb, Cd in precipitation by this forest and to better understand the role of this type of interception purification forest ecosystems and other areas of precipitation and the different types of forest ecosystems to do comparative analysis, in order to more fully understand the ecology of the forest important role in economic and social development.The Luosi Mountain (altitude:1 440m) in Simian Mountain is a representative area with high forest coverage (canopy density:0.91) in southwest region, which is an appropriate site to study the water quality and purification of heavy metals by forest.The pH, nitrogen (N) and sulfur (S) ions (NO3-,NO2-, NH4+, SO42-), base cations (Ca2+, Mg2+, Na+, K+), and two common harmful heavy metals (Pb and Cd), mainly released from industrial waste gas and automobile exhaust, were chosen to analyze their dynamic characteristics in this evergreen broad-leaved forest. Also, the interception abilities of different ecosystems for those were also compared. Precipitation, forest precipitation (throughfall and dropping off), litterfall, and soil leachate of the evergreen broad-leaved forest in Simian Mountain were investigated from September 2012 to August 2013, with sampling twice a month. The results showed that:1) the rainfall of Simian Mountain was apparently acidic,with average pH of 4.89 and maximum pH of 5.14. The soil, canopies and trunks could increase pH of precipitation,with soils having the maximum increment, followed by the forest canopy. The nitrogen and sulfur ions and base cations were the reason of acidizing precipitation, and the high concentrations of NO3- and SO42- were one of the main cause that acidizing precipitation in this survey region.2) during the research period, the concentrations of NO3-, NO2-, NH4+, SO42-, Ca2+, Mg2+, Na+, K+ in precipitation were 1.40 ± 0.42 mg·L-1,0.07 ± 0.04 mg·L-1,1.12 ± 0.42 mg·L-1,8.01 ± 3.13 mg·L-1,3.43 ± 1.46 mg·L-1,0.32 ±0.16 mg·L-1,0.76 ± 0.48 mg·L-1 and 1.55 ± 0.70 mg·L-1, respectively, all exceeding more than several times than the Lijiang background; and the Pb and Cd levels in precipitation were 22.92 ± 13.57 μg·L-1 and 2.82 ± 1.46 μg·L-1, respectively, and the monthly average deposition fluxes of Pb and Cd were 3.06 ± 2.74 mg·m-2 and 0.32 ± 0.27 mg·m-2, higher than those in other regions, such as Tangshan in china, New Jersey in USA and North Sea in Belgium. Rain water in this forest was to some extent polluted by Pb, with concentration of Pb in precipitation meeting the third water quality standard of the Quality Criteria of Ground Surface Water Environment (GB3838-88), but it was not polluted by Cd. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model analysis Combining with the wind roses in study area showed:the Simian mountain was mainly influenced by the air masses from the northwest direction in fall and the northeast direction in summer, which brought pollutants from industrial developed cities to the study area.3) the forest canopy could work well on intercepting NO3-, NO2-, SO42-, Na+, Pb and Cd in rain water, especially had a strong ability interception for Pb and Cd with the interception rate of 91.67% and 86.84%; however the average concentration of NH4+, Ca2+, Mg2+,K+ and pH were showed increased tendency. The average concentration of NO3-, NO2-, SO42- were decreased and the average concentration of Ca2+, Mg2+, K+ were increased were one of main causes of the increase pH in rain water. The forest canopy intercept ability is the strongest level in the forest ecosystem. Precipitation through forest canopy was not for all the material had the effect of the intercept, atmospheric precipitation was leached NH4+, Ca2+, Mg2+, K+ that on forest canopy leaf excreta, when atmospheric precipitation through forest canopy leaf surface.4) the Simian Mountain evergreen broadleaf forest earth surface had a very thick litter layer and the litter saved plentiful water. In the muggy and hot environment, the trunks and leaf were very easy decomposed and released organics and inorganic matter, therefor the average concentration of NO3-, NO2-, NH4+, SO42-, Ca2+, Mg2+, Na+, K+ had various extent rise. The vast acid ions and increase of organic acid made the pH rised, so the litter has the lowest pH. But the organic compounds had adsorbed and intercepted Pb and Cd in litterfall.5) long-term acid rain in mountain Simian made the soid acidized. The colloform and other groups in soid adsorbed NO3-, SO42-, NH4+, K+, Cd, but the low pH surroundings made part of NO2-, Ca2+, Mg2+, Na+, Pb were released to soil leachate. 6) the Evergreen broad-leaved forest ecosystem had very good intercept purification effect of pollutants in precipitation, especially for the interception of toxic heavy metals Pb and Cd had a strong interception effect, the total intercept rate were as high as 98.52%,98.52%, respectively. At the same time, the forest ecological system also made good regulating role for acid precipitation, and high forest crown density and long-term humid environment enhanced the forest canopy interception ability. |
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