疏勒河流域及周边地区地下水补给演化规律与古气候记录研究

The Shule River Basin and adjoining Kumtag Desert has recently been the focus of attention due to increasing stress on its water resources and environmental degradation and the centre government has indicated a national priority to rehabilitate this important and historic area. The environmental challenges have also become apparent from high rates of desertification, falling water tables and soil salinization. Instrumental records of climate change are only available for the past 150 years and it is difficult to find reliable proxy records. At present, few data are available for the hydrogeology of the Kumtag Desert, and much about the sources and characteristics of shallow groundwaters remain poorly understood owing to the area's isolation and relatively low water demand. The project considers a wide selection of geochemical indicators to aid understanding of the groundwater recharge and evolution. Specific targets are the recharge sources, timing of recharge and recharge history, especially since much of the water being exploited may have been recharged under different climatic conditions to the present day. The research investigates age of groundwater using tritium, CFCs,radiocarbon and clorine-36, provenance of groundwater using stable isotopes and Sr, palaeo-recharge temperatures using noble gases and also multi-element approaches linked with simulation modeling to resolving some of the key questions in hydrogeology such as surface water and groundwater intraction and renewable periods of groundwater in this arid basin. We plan to use a novel medium - the moisture percolating through dune sands - containing in its chemistry, the record of wetter and drier years with a resolution of about 5-10 years. Sand samples are recovered by augur to approx. 50m. Moisture content, geological and physical properties are logged, then samples are eluted with high purity deionised water for Cl analysis and other inert tracers such as NO3. Radioisotopes- tritium and chlorine-36 will also be applied to investigation of modern recharge. Geochemical and isotope results are interpreted in relation to the regional hydrogeology and water quality to validate the results in terms of modern and palaeowaters. We plan to compare the groundwater results with the palaeoenvironmental records from lake sediment, ice core and historic documents to reveal the impact of climate change on groundwater system. The results are then discussed in terms of their application to the improved water resources management in the region by providing a deeper understanding on the slow accumulation of water resources and raising a greater appreciation of the value and the fragility of the resource.

针对干旱区地下水补给循环与可更新能力研究的重要性与气候环境信息直接提取的难度，以疏勒河流域为重点研究区域结合毗邻的库姆塔格沙漠，通过对大气降水、冰雪融水、河水、地下水等水体的水化学、同位素时空分布与组成特征结构研究，利用Sr及其同位素示踪地下水的补给来源与路径，以惰性气体重建古补给环境；采用高精度氚、CFCs、C-14 与Cl-36等定年方法研究地下水循环年代学与动力学；以包气带氯质量平衡重建地下水补给量、补给历史与主要补给期。将多元示踪与定量数值模拟计算相结合，研究山前来水总量与构成、不同区域大气降水、地表水与地下水之间的转换关系、地下水各子系统间循环演化模式与周期性。通过与典型湖泊沉积记录、史料等相互印证，全面揭示该地区过去的气候环境变化及其对地下水补给的影响，为认识地下水资源属性和实现可持续开发战略提供依据，为恢复干旱化环境形成的自然过程与预测未来发展趋势提供相关基础数据。

疏勒河流域地下水从山前隔壁带到中游细土平原区再到下游荒漠区，地下水以碱土金属离子、弱酸根离子为优势成分逐渐演替为以碱金属、强酸根离子为主。阳离子由无明显离子特征过渡到以Na++K+为主，阴离子则从HCO3-过渡到无明显特征，最后向SO42-型水演化。地下水87Sr/86Sr介于0.711041到0.714029，与蒸发岩特征值很接近，Sr2+分别于Ca2+和SO42-具有很好的相互关系，说明研究区地下水发生了明显的蒸发岩溶解反应。第四纪地下水年龄分布范围较大，从现代到数万年，大多数承压水年龄分布在3000-7000年间，反映了中全新世大暖期暖湿的气候对地下水补给的重要作用。瓜州盆地东部补给区潜水很年轻，循环速率为16.2-17.5 m/a。各盆地细土平原区深层潜水从现代到2000年不等，说明深部地下水循环交替也比较迟缓。研究区承压水普遍年龄很老，从3000年到1.6万年，地下水的循环速度介于2.4-3.7 m/a，更新能力较差。.浅层包气带降水入渗与蒸发范围局限在表层30cm范围内，是土壤水热变化的剧烈层位。雨后土壤表层发散型零通量面的形成于下移是驱动土壤水分运移的根本动力。凝结水量并不能完全补充蒸发消耗水量，蒸发的持续进行将会消耗蒸发面下土壤水分，而该部分水分来源往往为前期强降水事件后存储的土壤水。.干旱区包气带硝态氮的主要来源是大气沉降，无植被生长的戈壁和荒滩中较高的NO3-/ Cl-伴随较低的Cl-含量说明硝态氮的富集主要发生在干旱阶段，蓝藻菌的固氮作用活跃，而农田土壤中硝态氮的大量富集受人为源影响显著，如大量氮肥的施用和生活污水的灌溉。硝态氮主要累积在土壤表层，在0～40 cm土层中的累积量占总累积量的80%以上，这与土壤性质和植被覆盖度关系密切。NO3-和Cl-在沙漠中呈活塞式迁移规律，二者显著正相关并与含水率负相关，短暂的降雨和强烈的蒸发使硝态氮在地表大量聚集，深层土壤的含量高表明了硝态氮的淋吸效应，较高的NO3-/Cl-进一步说明了硝态氮在干旱时富集度高。