Changes of water cycle structure and its effect on water resource development in fans

世界上大多数城市都是在山前或沿河的冲积扇上发展起来的。随着经济、工业的发展和人口的增加，这些地区地下水的质量和数量受到了严重的损害。为了解决地下水资源潜力及其可持续性的现实评价问题，了解冲积扇地下水的补给来源、流动系统、水文地球化学演化和地下水年龄至关重要。作为主要的经济中心，华北平原西部和南部有两个主要的冲积扇。一个是太行山冲积扇，另一个是黄河冲积扇，以黄河为界可分为南北两翼。然而，很少有研究关注这些风机中的水循环。本文的研究目标是了解地下水的补给源和地表水与地下水的相互作用；更明确地下水流经扇区的水文地球化学演化，特别是硝酸盐的命运和运移；并使用新的方法——氯氟烃（氯氟烃）与氚结合来测定地下水年龄。还进行了几个案例研究，以介绍山区的降雨入渗过程，以及灌溉引水对当地地下水系统的长期影响。收集了这些冲积扇附近当地河流的地下水和地表水，分析了研究期间主要离子、硝酸盐浓度、稳定同位素（氧-18和氘）组成、氮同位素（^<15>N）、氚和CFC-12的测量值。主要结论是：1)太行山冲积扇地下水经降水补给，具有Ca-HCO_3水型特征；黄河冲积扇地下水演化过程中存在离子交换和吸收效应。从山区到太行山冲积扇，到黄河冲积扇北部，地下水经历了从Ca-HCO_3、Na-HCO_3到na - so_2的演化过程。黄河冲积扇南部地下水年龄在23 ~ 50年之间。3)在<15>^N范围内，浅层地下水中硝酸盐的主要来源是氮肥和粪肥的使用。复杂冲积扇中硝酸盐浓度超过饮用水标准。而在黄河南部冲积区，反硝化作用存在于河水对地下水的补给过程中。4)引黄灌溉对当地地下水的净化作用显著。浅层地下水的淡水锋面估计以200m/年的速度推进。这意味着整个研究区地下水组成由Na-SO_4水型向Ca-Na-HCO_3水型转变至少还需要45年的时间。少

Most of cities in the world are developed at alluvial fans in piedmont or along the river. With the developing of economy and industry and the increasing of population, quality and quantity of groundwater are aggrieved by over-exploitation in these areas. In order to address the problem of realistic assessment of groundwater resources potential and its sustainability, it is vital to understand the recharge sources, flow system, hydro-geochemical evolution and the age of groundwater in the alluvial fan. As a main economic center, there are two main alluvial fans in west and south of the North China Plain (NCP). One is the Taihang Mts. alluvial fan, the another is the Yellow River alluvial fan, which can be divided into north and south wings by the Yellow River. However, few studies have paid attentions to water cycle in these fans. The objectives in this dissertation are to understand the water cycle concerning recharge sources, and interaction between surface water and groundwater; to … More make clear hydro-geochemical evolution in fans through which groundwater flows, especially, the fate and transport of nitrate; and to date groundwater age using new method-CFCs (Chlorofluorocarbons) combining with tritium. Several case studies also have been carried out to present rainfall-infiltration processes inmountain area, as well as the long-term effects of irrigation diversion water on the local groundwater system. Groundwater and surface water from local rivers, located at these alluvial fans, were collected for analyzing major ions, nitrate concentration, stable isotope (oxygen-18 and deuterium) compositions, nitrogen isotope (^<15>N), tritium and CFC-12 measurements in the study period. The main conclusions are:1) Recharged by precipitation, groundwater in the Taihang Mts.alluvial fan is characterized by Ca-HCO_3 water type. Ion exchange and absorption effect are expected to the groundwater evolution in the Yellow River alluvial fan. From the mountainous area, to Taihang Mts.alluvial fan, and to the north Yellow River alluvial fan, the groundwater undergoes the evolution from Ca-HCO_3, Na-HCO_3, to Na-SO_4.2) The groundwater age in the south Yellow River alluvial fan ranged from 23 to 50 years dating by the CFC-12 and tritium.3) Identified by <15>^N, the main sources of nitrate in the shallow groundwater came from nitrogen chemical fertilizer and manure use. The nitrate concentrations in the complex alluvial fan were over the drinking water standard. In the south Yellow River alluvial, however, denitrification exists in the recharge process of river water to groundwater.4) The diversion water for irrigation from the Yellow River is freshening the local groundwater remarkably. The freshening front in the shallow groundwater can be estimated to advance at a rate of 200m/year. This means that it will take, at least, another 45 years to change the groundwater composition in the entire study area from Na-SO_4 water type to Ca-Na-HCO_3 water type. Less