The Heihe River is the second largest inland river in China,and plays vital roles in sustainable societal and economic development in northwestern China.The water conservation forest,located on Qilian Mountain where the source of the Heihe River is located,provides a clean water resource.When analyzing ecohydrology,the chemical characteristics of forests are important for understanding mechanisms of water purification.Therefore,in this study,we focus on the chemical effects of forests on water quality.We selected the Tianlaochi catchment,which is located in the upper reaches of the Heihe River on Qilian Mountain,as our study area.After rainfall events,we collected samples of rainfall,through fall,stemflow,and litter seepage.Ion mass concentrations and pH values were measured for each of these components.The 12 ionic species whose mass concentrations were measured were K+,Ca2+,Na+,Mg2+,NH4+,Cl-,SO42-,NO3-,Cu2+,Zn2+,Pb2+,and Cd2+.The results showed that the pH value of the rainfall was 7.74,and low absolute ionic mass concentrations in the precipitation were low,the most abundant ion being NO3-with a mass concentration of 1.1111 mg/L,and the least abundant being Na+with a mass concentration of 0.0108 mg/L.With respect to that of rainfall,the pH values of through-fall from Qinghai spruce (Picea crassifolia) and Qilian juniper (Sabina przewalskii) forests decreased to 7.34 and 7.50 respectively.The P.crassifolia forest canopy could increase the mass concentration of NH4+,while the S.przewalskii forest canopy showed the opposite effect.The canopies of both species could reduce NO3-and Cu2+ and increase concentrations of other ions.With respect to that of through-fall,the pH values of stemflow from P.crassifolia and S.przewalskii forests increased to 7.42 and 7.72 respectively,and anionic species increased in both types.All cationic species in the litter seepage from S.przewalskii forest decreased,but for P.crassifolia forest stemflow,the mass concentrations of Ca2+,K+,Mg2+,and Na+ decreased,and Cu2+ and NH4+ increased.With respect to that of through-fall,the pH values of litter seepage in P.crassifolia and S.przewalskii forests increased to 7.54 and 7.59 respectively,and all anionic species in the litter seepage from both types of forest increased.In litter seepage from P.crassifolia,all cationic species decreased.In litter seepage from S.przewalskii forests,the mass concentrations of Ca2+,K+,and Mg2+ increased,and NH4+,Na+,and Cu2+decreased.In addition,Pb2+ and Cd2+ were not detected in all the water samples,and Zn2+ was only detected in the stemflow of the P.crassifolia forest.%采集了黑河天涝池流域典型林分林外雨、穿透雨、树干径流和枯透水,并检测水体pH值和12种离子(K+、Ca2+、Na+、Mg2+、NH4+、Cu2+、Zn2+、Pb2+、Cd2+、Cl-、SO2-、NO3)的质量浓度.结果表明:天涝池流域大气降水pH均值为7.74,呈碱性,降水中离子绝对质量浓度较低,最高的是N3-,质量浓度为1.1111 mg/L,最低的为Na+,质量浓度为0.0108 mg/L;两种林分冠层有降低降雨pH值的作用,青海云杉林冠层对NH4+有升高作用,祁连圆柏林冠层对NH4+有降低作用,两种林冠层对NO3-和Cu2+质量浓度有降低作用,对其它离子质量浓度均表现为升高作用;两种林分树干径流有提高穿透雨pH值的作用,与穿透雨相比,两种林分树干径流中阴离子均有升高,圆柏树干径流中所有阳离子质量浓度均有下降,云杉树干径流中Ca2+、K+、Mg2+和Na+减少,NH:和Cu2+增加;典型林分枯透水有提升穿透雨pH值的作用,与穿透雨相比,两种林分枯透水中阴离子质量浓度均有升高,云杉枯透水各阳离子均有降低,圆柏枯透水中Ca2+、K+和Mg2+质量浓度升高,NH4+、Na+和Cu2+质量浓度下降;在采集的所有样本中,Pb2+和Cd2+均未检出,而Zn2+仅在云杉树干径流中检出.
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