黄土高原典型山地-沟壑区地下水水化学特征及成因——以六盘山地区为例

Hydrochemical Property and Origin of Groundwater in Hilly-gully Areas of Loess Plateau

为了揭示黄土高原山地-沟壑区黄土地下水水化学特征及成因,对六盘山东西两侧山区及其西部典型黄土高原山地-沟壑区进行了多次实地考察,合理选择采样点,采集了浅层地下水监测水样。对采集的样品水化学数据进行了分析,结果表明:六盘山地区浅层地下水以低TDS重碳酸盐型为主,径流途径较短,循环条件较好,保持了较好的天然淡水资源状态;而在山地-沟壑区水化学类型则复杂多样,TDS平均值达1 870mg/L,淡水资源相对匮乏。结合各类水化学图可以看出,浅层地下水和地表水的离子来源优势机制以岩石风化为主,并且在山地-沟壑区受到不同程度蒸发作用控制。通过分析地下水中的离子浓度比以及锶元素,发现六盘山区主要为补给区和径流区,山地-沟壑区则是补给区、径流区和径流滞缓区,黄土地下水可能有来自六盘山岩溶水的补给。氟离子浓度和硬度超标是影响区域内水质的最主要因素,在受蒸发作用影响较大的地区尤为突出。黄土高原地下水资源的分布状况和质量参差不齐,保护好区域内较好的淡水资源并且按照地下水分布规律进行合理的开发与宏观调控,是缓解黄土高原水资源问题的关键。

The shallow groundwater that exists in the loess is the basic and precious source of water to the people who live in the Loess Plateau. But there are little scholars who studied hydrochemical characteristics of the groundwater there. The west Liupan Mountain is the model loess hilly-gully area. The Liupan Mount Liupan area and the model loess hilly-gully area were taken as the crucial study areas in this paper. We studied the hydrochemical property and origin of groundwater by making some field visits, monitoring and sampling through several years. We chose 29 sampling sites and collected 58 samples including 26 spring water samples, 26 well water samples, 5 river water samples and 1 reservoir water sample. The shallow groundwater which exists in the Liupan Mountain area has a low TDS and a high number of bicarbonate ions, so the groundwater has a short flow route and a good circulation condition, and this area keeps a natural state of freshwater resources. There are many different hydrochemical types of the groundwater in the model loess hilly-gully area, and the average TDS of the groundwater is 1870mg/L. Rock weathering is an influencing factor on the shallow groundwater and river water, specially in the loess hilly-gully area. Evaporation is another crucial influencing factor. The Liupan Mountain area is both a recharge area and runoff area, and the model loess hilly-gully area is not only a recharge area but also a runoff area and runoff-stay area. The loess groundwater is likely to accept the Liupan Mountain karst water. The calcite and dolomite saturation index of the groundwater stay the equilibrium state or supersaturated state, and there is hardly any water in the unsaturated state. The fluorine ion concentration and hardness exceed permissible standard that are most fearful factors to water quality. In the areas that have a strong impact on evaporation, the problems about exceeded permissible standard stand out. The distribution and quality of the groundwater are different in various parts of the Loess Plateau. The valuable and high quality fresh groundwater resource should be protected well, reasonably developed and utilized in macroeconomic regulation and control, which is the key to alleviate the shortage of water resources in the Loess Plateau.