【作者】 魏国孝；

【导师】 陈发虎；

【作者基本信息】 兰州大学 ， 自然地理学， 2011， 博士

【摘要】 首先以吉兰泰盆地地下水为研究对象,深入分析现代吉兰泰盐湖地下水的补给与演化规律以及地下水水化学的演化规律；其次,论文以“吉兰泰—河套”古大湖的水源为研究对象,依据古大湖沉积物的相关信息,研究古大湖存在的可能性,探索通过古大湖水量平衡和锶平衡及流域水文模型SWAT相耦合的计算古降水量的更为科学的方法,并利用该方法定量研究了古大湖期的古气候,同时结合地下水同位素的定量分析地下水的补给环境。论文的主要结论如下：1、贺兰山山区地下水既有碳酸盐矿物的溶解又有硅酸盐矿物的溶解,也有石盐的溶解,但浅层地下水中硅酸盐溶解较小,而深层地下水中的Na+被含水层中粘性矿物吸附；巴彦乌拉山和排泄区地下水中的Na++K+和Cl-都主要来源于岩盐,但也有芒硝的溶解；排泄区地下水受到一定程度的人类活动影响。2、从总体来看,地下水的SO42-的变化主要受蒸发作用控制,沿着地下水流动方向,有些区域发生了硫酸盐的溶解,但有些区域存在其还原作用；研究区浅层地下水中富含碳酸盐矿物,且主要源于贺兰山山区碳酸盐溶解,而白云石主要受贺兰山山区和湖区沙漠区的白云石溶解控制,浅层地下水水流过程中发生了CaCO3沉淀和C02(g)析出,但白云石、石膏、岩盐均发生了溶解作用；蒸发岩类矿物处于不饱和状态,并且主要受巴彦乌拉山的蒸发岩类矿物溶解控制；深层地下水阳离子交换大于浅层地下水,而地下水排泄区离子交换作用不是很明显,大部分深层地下水都经历了长期的阳离子交换作用以及碳酸盐溶解的作用,地下水的另一个重要特点是研究区钠长石对地下水的作用明显大于钾长石。3、吉兰泰盆地的地下水主要来源于贺兰山降水,仅有2%来源于巴彦乌拉山。贺兰山的基岩裂隙水在侧向补给了贺兰山前的单一第四系潜水和位于吉兰泰南端的碎屑岩类孔隙裂隙水,而且较浅的潜水存在由上向下的越流补给；在盆地内,由山前的单一潜水逐渐发展为上覆潜水,第一、第二承压含水层,盆地的盐湖区及周边区域是地下水的主要排泄区,在排泄区深层的第二承压水与较浅的第一承压水和潜水之间存在明显的越流补给关系,补给方向为从下向上4、校正后的地下水14C年龄表明盆地地下水既有全新世以来的地下水,也有10-20ka的古地下水,而现代降水与古地下水的混合比例为现代降水占43.89%。从补给环境来看,古地下水的δ18O和δ2H比]0ka以来地下水的值低,表明距今10-20ka的气温较10ka以来的气温低,根据同位素值可得晚更新世的年均气温大约为2.4℃-4.5℃。从地下水年龄、古大湖的时空分布,并结合氢氧同位素来看,这些地下水并不是来源于古主湖水体的补给,而是来源于当时的大气降水补给。5、根据现代气象资料,从Sr平衡和水量平衡来看,在考虑各补给源对古湖Sr的贡献量后,黄河所需的补给量为371.19亿m3。而从天然径流量的长系列来看,在1965-2000年期间有多年的天然径流量大于补给量。因此从天然径流量来看,黄河的天然径流量完全可以满足古大湖水量的要求,也就是在现代气候条件下,古大湖完全有存在的可能性。6、古大湖期“吉兰泰-河套”古湖范围降水量大约为334mm,比现代多年平均降水量增加104mm,而蒸发量比现代增加246mm。干旱指数表明总体上古大湖期比现在湿润,但区域仍属半干旱区。更多还原

【Abstract】 Firstly this thesis attempts to characterize the groundwater circulation and hydrochemical evolution in the modern Jilantai basin, and then the recharge sources of the Jilantai-Hetao Megalake is studied to explain the possibility of the paleolake based on Megalake sediments information. The more scientific method through coupling the strontium balance, paleolake water balance and SWAT hydrological model is explored to estimate the paleoprecipitaton and the paleoclimate. In the meantime, the groundwater recharge environment is studied through above model and groundwater isotopes composition. The main conclusions are as follows:1. The Helan Mountains’groundwater composition derived from the dissolution of silicate and carbonate minerals and also the dissolution of halite, but the shallow groundwater dissolved less silicate and Na+is more likely to be absorbed by clays in deep groundwater. In the groundwater of Bayan U1 Mountain and discharge area, the Na+, K+and Cl" are mainly derived from halite but some of Na+may be provided by Glauber’s salt. Some samples composition suggests that the groundwater in discharge area is impacted by human activities to some extent.2. In general, SO42- in all samples is principally controlled by evaporation and along the groundwater flow direction in some areas the sulfate dissolved and some reduced. All the shallow groundwater is rich in carbonate minerals, which is primarily derived from carbonate dissolution from Helan Mountain, but the dolomite is mainly controlled by the dolomite dissolution from Helan Mountain, Jilantai salt lake and sands. Along the shallow groundwater flow path, the CaCO3 precipitated and the dolomite, gypsum, halite dissolved. The shallow groundwater is unsaturated with respect to evaporate which is mainly from Bayan U1 Mountain. Ion exchange occurring in the deep groundwater is much more evident than that in the shallow groundwater, but the ion exchange in discharge area is not very obvious. Ion exchange occurred and carbonate dissolved in all deep groundwater for a long time.3. The Jilantai groundwater comes mainly from Helan Mountain rainfall and only 2%from the Bayan Ul Mountain. The single Quaternary phreatic water of the Helan piedmont and the clastic rock crevice water of the southern Jilantai is recharged by Helan mountains bedrock crevice water laterally. The groundwater in the basin becomes to the phreatic water, the first and second confined water evolved from single Quaternary phreatic water of the Helan piedmont. The groundwater discharges in the basin and surrounding areas. In this areas, the second deep confined groundwater recharges the first shallow phreatic groundwater. 4. The corrected 14C age of the groundwater indicates that the groundwater occurred in the Holocene and late Pleistocene in the range of 10-20 ka and the groundwater recharged from modern rainfall accounts for only 43.89%. Theδ18O andδ2H of the paleo-groundwater is lower than the Holocene groundwater. This indicates that the Pleistocene temperature is lower than the Holocene and according to theδ18O andδ2H, the Pleistocene temperature is about 2.4℃-4.5℃From the groundwater age, temporal and spatial distribution of paleolake, combined withδ18O and 82H data, it can be inferred that the modern groundwater is recharged by the pale-rainfall not the paleolake water recharged in past.5. Using the modern weather information, the results of Sr-isotope simulation and water balance model show that when the paleolake was at 1080m level, the annual recharged volume from the Yellow River was about 371.19×108m3. The corrected natural runoff from 1965 to 2000 is greater than the needed volume. Therefore, the natural runoff of the Yellow River can meet the requirements of the paleolake water. That is to say. it is possible for the formation of the Jilantai-Hetao Megalake under the modern weather conditions.6. Using SWAT distribute hydrological model for upstream basin of Shizuishan gauge, the landuse and other spatial and attribute database is recovered for the palebasin. Based on paleoclime with different assumptions the SWAT model is used to estimate the precipitation and temperature. The results indicate that the paleoprecipitaton is about 334mm which 104mm is more than the modern mean annual precipitation, while the paleoevaporation is 246mm more than modern evaporation. Drought index shows that the period of paleolake is more humid than present, but still belongs to the semi-arid region.更多还原