The Characteristics Of Hydrochemistry Of Precipitation In Subtropical Urban And Rural Forest Ecosystems In Anhui

Rainfall plays an important role in the water and nutrient cyclings in forest ecosystems. Onepart of rainfall falls down directly to the soil surface which affects the soil in the form of surfacerunoff and infiltration, the other part of rainfall first passes through the canopy called throughfallthen falls down to the surface and the soil. The variety of chemical elements carried by rainfall is themain input of the forest nutrient. The rainfall passing through the canopy could cause the elutingeluviation, adsorption and absorption effect. The nutrient leaching down with throughfall directlyinto the soil can cause important effect on the nutient availability in the forest soil. The effect ofrainfall timing, environment condition and forest type on the rainfall nutirent are generally different.In order to investigate the characteristic of quantity and chemistry of rainfall and throughfall indifferent forest types, and the effect of different sites on rainfall quantity and chemistry, acomparative study on the quantity, pH, EC value of rainfall and throughfall, and their chemicalcomposition (including NH₄⁺-N, NO3N, SO₄^2-, Cl^-, PO₄^3-P, TOC, K⁺, Ca²⁺, Mg²⁺) were carried outin an urban Metasequoia glyptostroboides forest in Hefei and evergreen broadleaved forests in Shitaiand Qimen. Results obtained are as follows.（1） Gross rainfallIn Hefei, a total of38periods of rainfall was recorded from March2010to December2011,which concentrated in summer. The total rainfall was1654.08mm. The total throughfall was1326.34mm in the Metasequoia glyptostroboides forest, and the throughfall rate was80.19%.In the evergreen broad-leaved forest in Shitai and Qimen, the total rainfall were, respectively,853.00mm and1976.22mm from May to December2012. The total throughfall were, respectively,832.26mm and1658.20mm, and the throughfall rate were93.58%and83.91%, respectively. Therainfalls at both sites were also concentrated in summer.The order of annual mean rainfall was Hefei <Shitai <Qimen, and for the throughfall rate wasranked by Hefei <Qimen <Shitai. The quantity of throughfall has a great relationship to the quantityof rainfall, and to the tree conditions and rainfall intensity as well.（2） pH valueThe pH values of rainfall and throughfall were neutral at all three sites （Hefei, Shitai and Qimen）.The order of pH value was ranked by throughfall <rainfall. The order of pH value of rainfall wasQimen <Shitai <Hefei. The order of pH value of throughfall was Qimen=Shitai <Hefei. Theseasonal pattern of pH value for the rainfall and throughfall were both high in autumn and low insummer. （3） EC valueThe order of EC values for the three sites was rainfall <throughfall. the order of EC value ofrainfall was Qimen <Shitai <Hefei and for the throughfall was Qimen <Shitai <Hefei. Theseasonal pattern of EC value for the rainfall and throughfall were both high in autumn and low insummer.（4） Chemical compositionThe order of the nutrient concentrations of rainfall in the urban Hefei was ordered bySO₄^2->TOC>K⁺> Cl^-> Ca²⁺> NH₄⁺-N+NO₃^-N> NH₄⁺-N> NO₃^--N> Mg²⁺> PO₄^3--P. The order ofthe nutrient concentration of the throughfall in the urban Metasequoia glyptostroboides forest wasSO2-++4> Cl^-> K⁺> TOC> Ca²⁺> NH₄^-N+NO₃^--N> NO₃^--N>Mg²⁺>NH₃--N> PO₄^3-P. In Hefei, theorder of NH₄⁺-N and TOC concentration was rainfall <throughfall, and the other nutrientconcentration was throughfall <rainfall.In Shitai, the order of the nutrient concentration in rainfall was TOC> SO₄^2-> Ca²⁺>NO₃^--N+NH₄⁺-N>Cl^->K⁺> NO₃^--N> NH₄⁺-N> Mg²⁺> PO₄^3--P, and in the throughfall was TOC>SO₄^2-> K⁺> Ca²⁺> NH₄⁺-N+NO₃^--N> Cl^-> NO₃^--N> NH₄⁺-N> Mg²⁺> PO₄^3--P. The order of thenutrient concentration was rainfall <throughfall.In Qimen, the order of the nutrient concentration in rainfall was TOC> SO₄^2-> K⁺> Cl^->NH₄⁺-N+NO₃^--N> Ca²⁺> NO₃^--N> NH+²⁺4-N> Mg> PO₄^3--P and in the throughfall was TOC>SO2-+-4> K⁺>Cl^-> Ca²⁺> NH₄^-N+NO₃^-N> NO₃^--N> NH₄⁺-N> Mg²⁺> PO₄^3--P. The order of thenutrient concentration was rainfall <throughfall.In the three sites, the order of the nutrient concentration was Shitai<Hefei, Qimen<Hefei.