Effects Of Typical Forest Stands On Water Qulity Of Runoff And Its Evaluation In Jinyun Mountain, Southwestern China

The research about effects of subtropical typical forests on runoff and water qulity in Jinyun Mountain was conducted, which are associated with the national 11th five-year key project of state forestry administration "Technology Research and Demonstration of Vegetation Construction with Water Conservation Function in Water district of northern Chongqing city" (2006BAD03A1802). The purpose of this paper is to provide evidence for water conservation forest construction in Chongqing city, southwest China.Based on analysis of forest communities of Jinyun Mountain,8 plots were set:Pinus massoniana×Gordonia acuminate mixed forest(I1), Gordonia acuminate×Symplocos setchuensis mixed forest(I2), Phyllostachys pubescens forest(I3), shrub forest(I4), Lindera kwangtungensis×Cunninghamia lanceolata mixed forest(I6), Phyllostachys pubescens×Symplocos setchuensis×Pinus massoniana mixed forest(I7), Pinus massoniana×Lindera kwangtungensis mixed forest(I8) and bareland(I5).In this study, firstly, the characteristics of rainfall and runoff yield were discovered by analyzing the precipitation and runoff monitoring data in 2002-2009. Secondly, air quality monitoring and cloud-fog water qulity monitoring were introduced into study to reaserch relationship between their qulity and rainwater qulity. During 2007-2009, according to the temporal and special orders of interaction between water and forest ecosystem, the ecosystem was divided into several layers and every layer water quality along rainfall-runoff process was studied by comparing, contrasting and mechanism analyzing. The rainwater, through fall water, surface runoff and inter flow were collected and chemically tested. The hydro-chemical properties of litter layers of typical forests were also studied by the simulated acid rain experiment. Thirdly, the nutrient and carbon storage of dominant trees leaves, litters and soil. The element content correlation among leaves litters and soil was studied. And the acid buffer potentiality of soil and litters in typical forests was comprehensive evaluated. Finally, the water qaulity of surface runoff and interflow was assessed by single-factor evaluation, comprehensive index method, principal component analysis and cluster analysis, grey correlation analysis and BP neural network method. The mainly results in the study were as follows:(1)During 2002-2009, the average precipitation in Jinyun Mountain was 1233.2mm, and mainly rained from April to October. Rain storm mainly occurred in June-September, and the precipitation and rainfall intensity were great. Runoff yields in plots were largest in May-August. In this period, surface runoff took 51.05%-65.90% of annual quantity, and interflow took 55%-68.4%. Regulatory effects of forest stands were better than bareland. And I3 had worst ability of regulatory; I1 and I2 had better abilities on this effect. (2)The dominant gaseous pollutant was SO2. Average pH of cloud-fog water (3.45) was smaller than rainwater (4.04) collected at the same time, but its ion content was larger. Acidification of rainfall in the region was serious. The acidrain in this area had a trend to transfer into combined pollution type.(3)The effects of different components of typical forests on water quality during the rainfall to runoff process were investigated. The results showed that:①Rainfall was acidic. The pH of the water increased as it moved through all components of four typical forests except canopy. All elements from rainfall were increased after moving through canopy except Na+.②All elements from rainfall were reduced except Ca2+. The curtailment of SO42-, NH4+, Mg2+, Mn and Al3+ was mainly occurred in runoff generation and confluence period. Soil under typical forest played vital role in the reduction of NO3-, K+, Na+ and Fe.③Surface runoff element contents had little correlationship with litter and soil element contents. But interflow ion content had correlationship with soil element contents. Almost every element in interflow had correlationship with soil element content except Mg2+ and Mn.(4)Result of acid buffer ability evaluation of litter was:P3(-82.01)>P7(-93.85)>P8(-94.98) >P6(-95.90)>P,(-97.58)>P4(-100.08)>P2(-103.16). Litter in I3 had the best acid buffer ability, I2 was the worst. Result of acid buffer ability evaluation of soil was:P6(29.37)>P4(23.23)>P8(22.71) >P7(18.50)>P1(15.39)>P2(13.61)>P3(13.22)>P5(11.31). Acid buffer ability of forest soil was better than bareland.16 was the best among forest stands, and I1 was the worst.(5)The the hydro-chemical properties of litter layers in I1, I2, I3, I4, I6 and I8 were studied by the simulated acid rain experiment. The results showed:The acid buffer ability of litter layer in I8 was best under the leaching of acid rain whose pH=4.5,3.5 or 2.7. Base cation(Ca2+,Mg2+,K+,Na+,NH4+), Al3+, Fe and Mn concentrations of all 6 typical forest litter leachings increased with the decrease of pH of simulated acid rain. The fact that Ca/Al molar ratio of I8 is always at a low level indicated that I8 was more susceptible to aluminum toxicity hazards. Under the eluviation of pH2.7 simulated acid rain, the concentrations of Fe (4.4μmol/L) and Mn (10.7μmmol/L) in I8 litter leaching were larger than that of the others. It indicated that I8 was more vulnerable to these toxic elements.(6)I1(Pinus massonianaX Gordonia acuminate mixed forest) had better water quality situation by water quality evaluation analysis.