Comparative Analysis Of Main Stands’ Effects On The Water Quality In The Huoditang Forest Region,Qinling Mountains

Based on the spacial order of the interaction between rainfall and forest ecosystem,this thesis studied pH of rainwater and the change of the chemical elements in the water,during the move process in Pinus armandi,Pinus tabulaeformis carr,Quercus aliena var.Acuteserrata and Pine-oak mixed forest in the Huoditang forest region,so as to check the key layers where different forest ecosystems influenced the chemical elements in the water and explore their influences on atmospheric rainwater quality.Later,adopting the method of principal component analysis,comprehensive evaluation about the quality of the water collected in these stands was carried out to screen out the stands and layers which had the best effects on the rainwater quality.Then,via simulating the rainfall leaching soil indoors,the influences which rainwater of different concentration of heavy metals and pH had on soil pH and adsorption-desorption of Pb,Zn and Cd were studied,laying a scientific foundation for managing headwaters forest in Qinling Mountains.The results showed that:（1）The average pH value of the atmospheric rainwater in the Huoditang forest region was 6.03,which was sightly acidic.All the four stands could raise the pH of slightly acidic rainwater and the whole sequence was Pine-oak mixed forest > Pinus tabulaeformis carr > Pinus armandi > Quercus aliena var.Acuteserrata,in which the effect of Pine-oak mixed forest was the best.The key layer of Pinus armandi and Quercus aliena var.Acuteserrata was canopy,while the key layer of Pine-oak mixed forest and Pinus tabulaeformis carr was soil.The soil of all the four stands could regulate the pH value of the rainwater.With the same pH,the more heavy metals,the more soil could raise pH of the rain.（2）All the four forest ecosystems could absorb Pb,Cd,Cr and NH₄⁺ in the atmospheric rainwater.The absorption of NH₄⁺ in canopy and soil was the main means,and the effect of Quercus aliena var.Acuteserrata among the four was the best,in which the purification rate of NH₄⁺ was 71.15%.Canopy was the key layer to absorb Pb,Cd and Cr.For Pb,Pinus armandi was the best,in which it decreased by 73.31%;for Cd,Pinus tabulaeformis carr was the best,in which it dropped by 84.09%.Quercus aliena var.Acuteserrata and Pine-oak mixed forest had strong ability of absorbing SO₄^2-,Zn²⁺ and Cr,of which Pine-oak mixed forest was better.And the content decreased by 60.28%,79.76% and 19.00% respectively.（3）Rainwater had an effect of leaching on NO₃^-,PO₄^3-,K⁺,Ca²⁺,Mg²⁺ and Al³⁺ in the four forest ecosystems.NO₃^-,K⁺,Ca²⁺,Mg²⁺ and Al³⁺ in the output water mainly came from soil.Canopy and litter were the key layers to leach NO₃^-and PO₄^3-,which increased by 3.41 mg·L^-1 and 0.48 mg·L^-1 when they passed through Pinus armandi.K⁺ and Ca²⁺ increased largely when they moved through Quercus aliena var.Acuteserrata and canopy and litter were key layers.Mg²⁺ increased most as it passed through Pine-oak mixed forest,whose content went up by 2.21 mg·L^-1.What’s more,SO₄^2-and Zn²⁺ increased with rainwater leaching canopy and litter of Pinus armandi.（4）The atmospheric rainwater could be improved after being purified by the four forest ecosystems.No matter which layer the rainwater passed by,the quality was the best when in Pine-oak mixed forest,which showed that the Pine-oak mixed forest ecosystem was better to purify the rainwater than other single stand.（5）With the same concentration of the heavy metals in the simulated rainfall,as the pH went up,the four stands had different effects on the adsorption-desorption of Pb,Zn and Cd.For Pb,the absorption capacity of the soil in Pinus armandi and the Pine-oak mixed forest would weaken,while the absorption capacity of the soil in Pinus tabulaeformis carr and Quercus aliena var.Acuteserrata would strengthen.For Zn,the absorption capacity of the soil of Pinus armandi and the Pine-oak mixed forest would strengthen,while the absorption capacity of the soil of Pinus tabulaeformis carr and Quercus aliena var.Acuteserrata would weaken.For Cd,the absorption capacity of all the four stands soil weaken,while the desorption capacity would strengthen.（6）With the same pH,when the concentration of the heavy metals in the simulated rainfall was lower（under the conditions of M0,Min and Mv）,the soil of all the four stands had an effect of leaching on Pb,Zn and Cd.While the concentration of the heavy metals was higher（under the condition of Max）,Pb,Zn and Cd would be absorbed and purified by the soil of the four stands.