渭河沉积物浸出的水文地球化学效应研究

Hydrogeochemical effects during leaching of sediments in Wei River basin:an experimental analysis

基于渭河咸阳段(中游)和渭南段(下游)沉积物在水更新条件下的浸出实验及水文地球化学模拟,分析了浸出液中3个特征值和8个水化学组分的变化规律及5种矿物质饱和指数的变化特征.结果表明:浸出液中电导率、Eh值和p H值均随着换水量的增加呈现出波动式上升的变化趋势,电导率增加趋势中咸阳段高于渭南段,Eh值增加趋势中渭南段高于咸阳段,说明渭河下游沉积物的颗粒更细,物质还原性更强,浸出液由弱酸性逐步向弱碱性转变;浸出液的HCO^-_3、Cl^-、SO^(2-)_4含量均表现出随着换水量的增加呈现出先迅速增加,而后逐步减少直至趋于稳定的变化过程,且咸阳段的变化幅度明显高于渭南段,而CO^(2-)_3含量则呈现不断减少的趋势;Ca^(2+)、Mg^(2+)、Na^+、K^+含量均表现出随着换水量的增加呈现出先迅速增加,而后趋于稳定的变化过程,且咸阳段的起始含量和增加幅度均高于渭南段;浸出液中无水石膏、石膏的饱和指数随换水量的增加呈现相同的变化规律,且饱和指数都小于0,咸阳段饱和指数在换水量小于22.5%时溶解能力强,换水量大于22.5%后趋于饱和并开始沉淀的特征,渭南段换水量为12.5%时饱和指数最小,换水量大于或小于12.5%后饱和指数均呈缓慢增加的趋势;方解石、白云石的饱和指数随换水量的增加也呈现相同的变化规律,且饱和指数都大于0,咸阳段在换水量小于12.5%时溶解能力较强,换水量大于12.5%后处于饱和状态并开始沉淀,渭南段在换水量小于5%时溶解能力较强,换水量大于5%后处于饱和状态并开始沉淀;Na Cl饱和指数在换水量小于10%时溶解能力较强,换水量大于15%后开始沉淀.咸阳段沉积物中五种矿物质的饱和指数均要大于渭南段,说明渭河中游咸阳段沉积物在水不断更新条件下矿物质溶解能力低于下游渭南段,且沉淀能力较强、沉淀量较大.

Based on the leaching experiment of the sediments in Weihe River at Xianyang section（midstream） and Weinan section（downstream）under the condition of water renewal and the hydrogeochemical simulation, three eigenvalues,the change rule of eight water chemical constitutes and the change characteristics of the satura-tion indexes of five mineral substances were analyzed in this research. The results showed that the conductivity, Eh and Ph of the lixivium presented fluctuant ascending trend with the increase of water renewal volume. Con-cerning the change trend of the conductivity,Xianyang section was more significant than that of Weinan section, and the change trend of Eh,Weinan section was more significant than that of Xianyang section,indicating that the sediments at the downstream of Weihe River have finer grains and higher reducibility. The lixivium gradually transformed from weakly acid to weakly alkaline. The concentrations of HCO-3 ,Cl-,SO2-4 presented a changing process from fast increase and gradual decrease and then to the stable state with the increase of water renewal vol-ume,and the rangeability at Xianyang section was much higher. The concentrations of CO2-3 showed a decreas-ing trend. With the increase of water renewal volume,the concentrations of Ca2＋;Mg2＋,Na＋and K＋quickly in-creased firstly and then to the stable state,and the initial concentrations and the rangeability of these substance at Xianyang section were higher than those at Weinan section. The saturation indexes of anhydride and gypsum in the lixivium presented the same change trend with the increase of water renewal volume,and the saturation in-dexes were less than zero. When the water renewal volume was less than 22. 5%,Xianyang section had the stron-gest dissolving capacity;when the water renewal volume was more than 22. 5%,it began to saturate and precipi-tate. When the water renewal volume was by 12. 5%,Weinan section presented the lowest saturation index;when it got to more or less than 12. 5%,the saturation index presented the slow increasing trend. The saturation indexes of calcite and dolomite also presented the same change trend with the increase of water renewal volume, and the saturation indexes were more than 0. When the water renewal volume was less than 12. 5%,Xianyang section had the stronger dissolving capacity;when the water renewal volume was more than 12. 5%,it began to saturate and precipitate. When the water renewal volume was less than 5%,Weinan section had the stronger dis-solving capacity;when the water renewal volume was more than 5%,it began to saturate and precipitate. When the water renewal volume was more than 10%,the saturation index of NaCl got to the maximum;and when the water renewal volume was more than 15%,it began to precipitate. The saturation indexes of the five mineral sub-stances in the sediments of Xianyang section were higher than those of Weinan section respectively,indicating that the dissolving capacity of the mineral substances at the midstream of Xianyang section in Weihe River was lower than that of the downstream Weinan section under the condition of water renewal,and the precipitation ca-pacity and volume of Xianyang section were much higher.