The Long-term Variation Of Forest Water Quality And Its Trend In The Qinling Forest Region

This study took the Huodigou watershed on the southern slope and the Haoping watershed on the northern slope of the Qinling Mountains as the typical example.It analyzed the inter-annual,seasonal variations and trends of the water quality of small watersheds in the water conservation forest areas on the southern and northern slopes of the Qinling Mountains,and causes water quality changes,and discussed the characteristics of the annual and interannual changes in the water quality of forest ecosystems.The principal component analysis method was used to comprehensively evaluate the water quality of streams and selected the month of best water quality.The purpose was to provide the basis for the timing of the selection of quality water in urban and rural water supply reservoirs.The results showed that:?1?The monthly mean pH value of atmospheric precipitation and the monthly average concentrations of Cd,Zn and Pb in the southern slope of the Qinling Mountains were higher than those in the northern slope,and the NO₃^-,NH₄⁺and SO₄^2-concentrations were lower than those in the northern slope.During the period of 2008-2017,the pH value and Zn concentration of the precipitation on the southern slope of the Qinling Mountains showed a decreasing trend.The concentrations of SO₄^2-,PO₄^3-,Na⁺and Ca²⁺showed a increasing trend,and there was no significant change trend in the concentrations of NO₃^-,NH₄⁺,K⁺,Mg²⁺Cd and Pd.During the period of 2012-2017,the pH value of precipitation on the northern slope of the Qinling Mountains showed an increasing trend,and the concentrations of NO₃^-,NH₄⁺,SO₄^2-,Ca²⁺,Cd,Zn and Pd showed a decreasing trend,and the concentrations of PO₄^3-,K⁺,Na⁺and Mg²⁺showed no obvious trend.In the same year,the pH value of precipitation on the northern slope of the Qinling Mountains was lower than that on the south slope.The concentrations of NO₃^-,NH₄⁺,SO₄^2-,PO₄^3-,K⁺,Na⁺,Ca²⁺,Mg²⁺,Cd,Zn and Cd were all higher than those in the southern slope.Based on the characteristics of past changes and its influencing factors,it is estimated that the pH value of rainfall on the southern slope of the Qinling Mountains will decrease in the future and the SO₄^2-concentration will increase.The pH value of precipitation on the northern slope of the Qinling Mountains will increase,and the NO₃^-,NH₄⁺and SO₄^2-concentrations will decrease.?2?The pH value of the stream water on the southern slope of the Qinling Mountains was lower in autumn,the concentrations of NO₃^-,SO₄^2-,PO₄^3-,Cd and Pd were higher in the spring,the NH₄⁺,K⁺,Ca²⁺and Zn concentrations were higher in autumn,and Na⁺,Mg²⁺concentrations were higher in winter.The pH value of the stream water on the northern slope of the Qinling Mountains was lower in autumn,the concentrations of NO₃^-,PO₄^3-,Cd and Pd were higher in spring,Ca²⁺concentration was higher in summer,the concentrations of NH₄⁺,K⁺,Na⁺and Zn were higher in autumn,and the concentrations of SO₄^2-and Mg²⁺were higher in winter.The mean monthly pH value of water in the southern slope of the Qinling Mountains was higher than that in the northern slope.The NO₃^-,NH₄⁺,SO₄^2-,Cd,Zn and Pb concentrations in the streams on the northern slope of the Qinling Mountains from January to December were generally higher than those on the southern slope.?3?The inter-annual changes of pH and NO₃^-,K⁺,Zn and Pd concentrations in the stream water on the southern slope of the Qinling Mountains showed a decreasing trend,and the concentrations of SO₄^2-,PO₄^3-,Na⁺,Ca²⁺,Mg²⁺and Cd showed a increasing trend.There was no significant change in the NH₄⁺concentration.Based on the characteristics of past changes and its influencing factors,it is estimated that the pH and NO₃^-,K⁺,Zn and Pd concentrations in the streams of southern slope of the Qinling Mountains will decrease,and the concentrations of SO₄^2-,Na⁺,Ca²⁺,Mg²⁺and Cd will increase.During the period from 2012 to2017,the pH value and PO₄^3-concentration of the stream water on the northern slope of the Qinling Mountains showed an increasing trend,and the concentrations of NO₃^-,NH₄⁺,SO₄^2-,Ca²⁺,Mg²⁺,Zn and Pd showed a decreasing trend,and the K⁺,Na⁺and Cd concentrations showed no obvious change trend.?4?With the exception of K⁺,the pH values of forests in the south and north slopes of the Qinling Mountains were generally escalated Under the inter-annual and year scale,and the forests had an adsorption effect on NO₃^-,NH₄⁺,SO₄²,PO₄^3-,Cd,Zn and Pd concentration of rainfall,rainfall had a total rinsing effect on Na⁺,Ca²⁺and Mg²⁺in the forest.In 2012-2017,the upgrading effect of forest on the northern slope of the Qinling Mountains was less than that of the southern slope.?5?The principal component analysis method was used to evaluate the water quality of the streams.In the same year or month,the water quality of the southern slope of the Qinling Mountains was better than that of the northern slope.The water quality of streams on the south slope of the Qinling Mountains was the best in January,and the water quality of the streams on the northern slope was best in November.From 2015 to 2017,The stream water quality on the southern slope of the Qinling Mountains was at an excellent level.