Distribution Process And Major Influencing Factors Of Wet Deposition Pollutants By Typical Forest Communities In Northern Subtropical Region Of China

In the present study,Phyllostachys edulis plantation,Cunninghamia lanceolata plantation,and Cyclobalanopsis glauca broadleaf forest,three typical forest types in northern subtropical China,were selected to investigate the fate and transport processes of inorganic nitrogen（NH₄⁺-N,NO₃^--N,NO₂^--N）,TP,SO₄^2-,F^-,Cl^-,four kind of base cations（Na,Mg,Ca,K）and seven heavy metals（Pb,Cd,As,Cu,Zn,Mn,and Ni）in various hydrological components（i.e.precipitation,throughfall,stemflow,litterfall,and surface runoff）.In order to provide experimental basis for the structural transformation of the forest ecosystem in the subtropical region and the improvement of the ecological service function,the effects and the underlying mechanisms of forest canopy,litter and soil layer on precipitation quality was monitored,analyzed and discussed,combined with the characteristics of precipitation and forest communities.The results are as follows:（1）The rainfall of Miaoshanwu was apparently acidic,with average p H of 5.97.The annual average concentration of NH₄⁺-N,NO₃^--N,NO₂^--N,TP,SO₄^2-,F^-,Cl^-was 1.06,0.63,0.04,0.06,1.86,0.16,0.38 mg/L,respectively.While the annual average concentration of Na,K,Ca,and Mg was 0.27,0.36,0.89,0.17mg/L,respectively.And the annual average concentration of Pb,Cd,As,Cu,Zn,Mn,Ni was 1.00,0.12,0.52,3.35,36.73,8.39,1.89μg/L Because the concentration of cations such as NH4⁺,K and Ca in precipitation decreased,acidic pollutants such as NO3^--N and SO4^2-accumulated in large amounts,the precipitation in the non-growth season was more acidic.（2）The canopies could increase p H of precipitation,and kept stable throughout the year,which absorbed TP,NH4⁺-N,F^-,Na,Cu and Ni in rain water and leached Cl^-,K,Ca,Mg,Mn,and Zn strongly.A large amount of base cations leached from the forest canopies neutralized acidic precipitation and increased the p H of the throughfall.The canopy of P.edulis plantation had the stronger interception capacity for various substances and a low leaching rate than C.lanceolata and C.glauca,the maximun interception rate was 81.81%.On the contrary,the canopy of C.lanceolata plantation had a strong leaching capacity and the weakest interception ability.（3）The litter layer was the major releasing sources of nutrient under the forests.The litter layer of C.glauca broadleaf forest had the strongest leaching ability to nitrogen,phosphorus,Cu and Ni,and the maximum leaching rate was 158.29%,and the litter layer of C.lanceolata plantation had the strongest leaching ability to four kinds of base cations,and the maximum leaching rate was 125.82%.（4）The surface runoff of the three forest communities accounted for 0.08—0.37%of atmospheric precipitation,while 28.37—59.49%of atmospheric precipitation was the forest soil percolation water of 0—5 cm soil layer.Compared with litterfall,the concentrations of NO3^--N,phosphorus and sulfur in surface runoff increased,and the concentrations of base cations in surface runoff was 4.24—68.28 times those of atmospheric precipitation.Similar to the p H value of forest soil,the p H of soil percolation water was 4.07—4.84,and the concentration of NO3^--N in soil percolation water was 21.16—35.09 times that of atmospheric precipitation.Comparing surface runoff and soil percolation water（output）and atmospheric precipitation（input）fluxes,the three forest communities all showed the trapping effect on Na,NH4⁺-N,F^-,Cl^-and TP,and the strong leaching effect on K,Ca,Mg and NO3^--N.C.glauca broadleaf forest had the strongest interception ability to NH4⁺-N and TP,and the interception rate was 99.00%and 95.90,respectively,and the strongest leaching effect to NO3^--N,K and Mg,the interception rate was 690.13%,164.01%and 310.13%,respectively.（5）The main indicators that affected the quantity and quality of the throughfall were precipitation and LAI.Atmospheric precipitation increased linearly with the throughfall volume of the three forest communities,and the precipitation was negatively correlated with the concentrations of various elements in the throughfall.LAI was positively correlated with Cl^-,TP,and NH4⁺-N,and negatively correlated with other anions,base cations,and seven heavy metals.The main indicators that affected the concentrations of litterfall were litter moisture and precipitation.The amount of atmospheric precipitation increases linearly with the litterfall volume of the three forest communities.The moisture content of litter was negatively correlated with nitrogen,phosphorus,sulfur and base cations in the permeate water.Soil moisture content,herb coverage,forest density were negatively correlated with NO3^--N concentration in surface runoff,and forest density was also negatively correlated with concentrations of NH4⁺-N,SO4^2-,NO2^--N,and seven kind of heavy metals,while the surface herb coverage was positively correlated with the concentration of seven heavy metals in surface runoff.