内蒙古鄂尔多斯西北土壤水流动示踪实验及自流井群补给源讨论

降水模拟实验证明,鄂尔多斯北部沙土层单次降水入渗最大深度小于1 m,降水在土壤中受到蒸发后排泄到大气中。实验证实,只有当土壤含水率达到最大田间持水率,吸附在土颗粒表面的薄膜水才能克服电磁引力转化为重力水,在重力的作用下继续下渗。鄂尔多斯北部的年降水量小而蒸发量大,降水入渗土壤不能形成累积效应,无法形成连续下渗的重力水流。同位素示踪分析表明,土壤水主要来源于地下潜水,结合土壤含水率与TDS分析证实,地下水是通过薄膜水与蒸发-凝结方式补给到土壤水中,薄膜水从高温区向低温区流动,对于等温的薄膜水而言,薄膜水从厚层向薄层流动。同位素分析表明,都思兔河流域的河水、泉水、井水、湖泊、土壤水接受相同的外源水补给。鄂尔多斯盆地降水比地表水与地下水明显富集重同位素,不符合补给区降水同位素特征。鄂尔多斯盆地地下水分水岭与基底断裂带重合,据此推断,外源水以深循环方式通过基底断裂带补给鄂尔多斯盆地,在干旱地区形成自流井群。

Soil Water Flow Tracer Test in Northwest Ordos Basin, Inner Mongolia and Discussion on Recharge Resources of Artesian Wells

Precipitation simulation tests prove that, maximum depth of single rainfall infiltration in northern Ordos sandy stratum is less than 1 m. Precipitation discharges to the atmosphere in the soil by evaporation. Tests confirm that only when the soil moisture content is greater than the maximum field moisture capacity, can film water on the surface of the soil particles overcome electromagnetic attraction and turn into gravitational water to infiltrate under gravity. Annual rainfall in northern Ordos is small but evaporation is large, rainfall infiltration water does not form a cumulative effect or continuous gravity water flow in the soil. Isotopic tracing analysis shows that soil water mainly comes from phreatic water. Combined with the analysis of soil moisture content and TDS, confirm that groundwater supply to the soil water through the way of film water and evaporation-condensation mode. Film water flows from high to low temperature area. For isothermal film water, it flows from thick to thin layer. Isotope analysis suggests that rivers, springs, wells, lakes, soil water in Dusitu River basin receive the same allogenic water supply. Precipitation of Ordos Basin enriches of heavier isotopes than surface water and groundwater. This does not conform to the precipitation isotope characteristics of recharge area. Groundwater watershed of Ordos Basin coincides with the basement fault zone. According to this, allogenic water supplies to the Ordos Basin through the basement fault zone and forms the artesian well group in dry areas.