Hydrogeochemistry and environmental impact of geothermal waters from Yangyi of Tibet,China

The Yangyi geothermal field, located 72 km northwest to Lhasa City, capital of Tibet, has a high reservoir temperature up to at least 207.2 °C. The geothermal waters from both geothermal wells and hot springs belong to the HCO₃ (+CO₃)–Na type. Factor analysis of all the chemical constituents shows that they can be divided into two factors: F₁ factor receives the contributions of SO₄²⁻, Cl⁻, SiO₂, As, B, Na⁺, K⁺, and Li⁺; whereas F₂ factor is explained by HCO₃⁻, F⁻, CO₃²⁻, Ca²⁺, and Sr²⁺. The F₁ factor can be regarded as an indicator of the reservoir temperature distribution at Yangyi, but its variable correlation with the results of different geothermometers (Na–K, quartz and K–Mg) does not allow one to draw further inferences. Different from F₁, the F₂ factor is an indicator of a group of hydrogeochemical processes resulting from the CO₂ pressure decrease in geothermal water during its ascent from the deep underground, including transformation of HCO₃⁻ to CO₃²⁻, precipitation of Ca²⁺ and Sr²⁺, and release of F⁻ from some fluoride-bearing minerals of reservoir rocks. The plot of enthalpy vs. chloride, prepared on the basis of Na–K equilibrium temperatures, suggests that a parent geothermal liquid (PGL) with Cl⁻ concentration of 185 mg/L (that of sample YYT-8) and enthalpy of 1020 J/g (corresponding to a temperature of 236–237 °C, i.e., somewhat higher than that of sample YYT-6) is present in the geothermal reservoir of the Yangyi area, below both the Qialagai valley and the Bujiemu valley, although the samples less affected by mixing and cooling (YYT-6 and YYT-7) come from the second site. The discharge of geothermal waters with high contents of toxic elements such as B, As and F into the Luolang River, the only drinking water source for local residents, has caused slight pollution of the river water. Great care should therefore be taken in the geothermal water resource management at Yangyi.     

Hydrogeological and hydrogeochemical control of groundwater salinity in an arid inland basin: Dunhuang Basin,northwestern China

High groundwater salinity has become a major concern in the arid alluvial plain of the Dunhuang Basin in northwestern China because it poses a significant challenge to water resource management. Isotopic and geochemical analyses were conducted on 55 water samples from springs, boreholes and surface water to identify potential sources of groundwater salinity and analyse the processes that control increasing salinity. The total dissolved solid (TDS) content in the groundwater ranged from 400 to 41 000 mg/l, and high TDS values were commonly associated with shallow water tables and flow‐through and discharge zones in unconfined aquifers. Various groundwater contributions from rainwater, agricultural irrigation, river water infiltration and lateral inflows from mountains were identified by major ions and δD and δ¹⁸O. In general, HCO₃^? and SO₄^2? were the dominant anions in groundwater with a salinity of <2500 mg/l, whereas Cl^? and SO₄^2? were the dominant anions in groundwater with a salinity of >2500 mg/l. The major ion concentrations indicated that mineral weathering, including carbonate and evaporite dissolution, primarily affected groundwater salinity in recharge areas. Evapotranspiration controlled the major ion concentration evolution and salinity distribution in the unconfined groundwaters in the flow‐through and discharge areas, although it had a limited effect on groundwater in the recharge areas and confined aquifers. Agricultural irrigation increased the water table and enhanced evapotranspiration in the oasis areas of the basin. TDS and Cl became more concentrated, but H and O isotopes were not enriched in the irrigation district, indicating that transpiration dominated the increasing salinity. For other places in the basin, as indicated by TDS, Cl, δD and δ¹⁸O characteristics, evaporation, transpiration and water–rock interactions dominated at different hydrogeological zones, depending on the plant coverage and hydrogeological conditions. Groundwater ages of ³H, and δD and δ¹⁸O compositions and distributions suggest that most of the groundwaters in Dunhuang Basin have a paleometeoric origin and experienced a long residence time. These results can contribute to groundwater management and future water allocation programmes in the Dunhuang Basin. Copyright © 2015 John Wiley & Sons, Ltd.     

Denitrifying bacteria and hydrogeochemistry in a natural wetland adjacent to farmlands in Chiba,Japan

This study combined bacterial incubation and hydrogeochemical methods to investigate denitrification in the surface water, top soil (0–20 cm), and shallow groundwater of the Ochi wetland in Japan. Surface water was rich in nitrate (40 mg/l) and denitrifying bacteria (700 per ml). Three functional zones in the wetland were identified in the top soil and shallow groundwater. In the upstream portion of the wetland (Zone I), the counts of denitrifying bacteria in top soil increased from 5200 to 14 970 per ml and nitrate decreased from 25·4 to 1·8 mg/l. Organic carbon concentrations decreased as sulfate increased from 4·0 to 9·6 mg/l in this zone. In the middle‐stream of the wetland (Zone II), all concentrations of major anions, iron, organic carbon, and total nitrogen content in top soil were relatively constant, but the counts of denitrifying bacteria increased up to 70 200 per ml. In the downstream portion of the wetland (Zone III), complete removal of nitrate resulted in sharp reduction of counts of denitrifying bacteria. Correspondingly, dissolved oxygen (DO), organic carbon, and total nitrogen increased in this zone. Counts of denitrifying bacteria were lower in shallow groundwater than in top soil; nitrate concentrations in shallow groundwater were also very low in this zone. DO and the oxidation/reduction potential data suggest that groundwater flows to the surface along an extended flow path, thus providing nitrate for the denitrifying community. Copyright © 2011 John Wiley & Sons, Ltd.     

昆明吴家营岩溶水系统边界的水文地球化学分析

西南岩溶水系统边界条件复杂,其中水头隔水边界在水动力条件改变的情况下具有不稳定的隔水特性。文章以昆明吴家营岩溶地下水系统为例,通过水化学组分动态序列图解法、数理统计法及水文地球化学模拟等方法对研究区边界特性进行了研究。研究结果表明该岩溶水系统水动力条件丰水季优于枯水季,并存在与边界外发生水力联系的越流通道;丰水季时岩溶槽谷区地下水在高水力梯度的驱动下向下绕过玄武岩隔水层,通过下部阳新灰岩对系统内岩溶水进行越流补给,枯水季受深部滞流阻水影响,越流补给现象不明显;由此得出此类水头边界的隔水特性会随水动力条件的改变而具有动态响应特征。研究成果对当地岩溶水资源量的评价和合理开发利用提供科学依据。      

黔西南Au-As-Hg-Tl矿化区毒害金属元素的水地球化学

研究了黔西南典型Ａｕ－Ａｓ－Ｈｇ－Ｔｌ矿化区内毒害金属元素在采矿活动和自然状态影响下的水地球化学特征及其环境效应。结果表明,已开采的Ｈｇ－Ｔｌ矿区地下水和地表水中均有很高的毒害金属元素,煤采区地下水中亦表现出类似的特征,而Ｈｇ－Ｔｌ矿区外围地下水中金属元素保持在较低的水平。Ｈｇ－Ｔｌ矿区地素水中Ａｓ和Ｔｌ的分布模式表明,其含量的变化受矿区地下水排泄和尾矿淋滤作用的控制。在尚未开采的金矿区,浅层地下     

川滇高原斜坡地带峡谷区岩溶水化学特征及演化规律

岩溶地下水不仅作为重要的生活和生产用水水源,而且作为一种重要的地质营力,对于岩溶演化史具有重要影响,对其进行水化学特征分析及演化规律研究,能够为岩溶水资源及岩溶生态环境保护提供科学依据。以川滇高原斜坡地带峡谷区岩溶地下水为研究对象,结合研究区水文地质条件,对比分析了龙爪坝河岩溶水系统和洛泽河岩溶水系统内地下水化学特征。通过常规地下水化学组分、氢氧同位素分析和水文地球化学反向模拟,识别了地下水化学类型,确定了岩溶水的主要离子来源和补给特征,判别了发生的水岩相互作用过程。研究表明：岩溶地下水以大气降水为补给来源,离子源于岩石风化作用,物质来源为灰岩、白云岩夹灰岩,水岩相互作用均受方解石、白云石和石膏沉淀及溶解作用控制,且龙爪坝河岩溶水系统内矿物饱和指数趋近饱和,岩溶发育趋于停滞,而洛泽河岩溶水系统内矿物饱和指数处于不饱和或饱和的波动态,岩溶仍然发育。     

地浸过程中溶质(铀)迁移特征研究

本通过室内溶质迁移试验，运用化学热力学计算，对地浸过程中的溶质迁移规律进行了研究。溶质（铀）迁移研究表明：随着水地球化学条件的改变，溶质（铀）经历了溶解迁移、水解沉淀、再溶解迁移的多次旋回，章还根据铀浓度和水地球化学指标，在整个渗透途径中划分出不同特征的浸出带。     

对公婆泉盆地铀成矿水文地球化学条件的认识

通过对公婆泉盆地地质、水动力、水文地球化学条件的分析和地球化学模式计算 ,确定了盆地下白垩统层间水水化学类型主要为SO4 ·Cl Na型或Cl·SO4 Na型 ;水中铀存在形式以UO2(CO3) 4- 3占优势 ;盆地内存在有利于铀还原沉淀的水文地球化学环境的可能性、及具备满足铀沉淀条件的矿化远景有利地段     

桂西大型岩溶地下河系统离子来源及碳稳定同位素信息——以坡心地下河流域为例

为探讨坡心地下河系统内地表和地下水体的水化学离子特征、来源及其控制因素,无机碳来源及其稳定性。运用水化学计量法和同位素法对采自坡心地下河流域的38个采样点的水化学和碳稳定同位素样品数据进行分析。结果表明,地下河干流沿程受到局部岩性和支流稀释作用的影响明显,各水化学离子均有所变化。化学离子比例分析发现:大气降水对部分泉水的Cl~-和Na~+影响较大;碳酸盐岩溶解类型主要以灰岩溶解为主,地表水和地下河天窗的Mg~(2+)/Ca~(2+)摩尔比值与HCO_3~-呈负相关,说明在宏观上灰岩溶解程度越强烈,HCO_3~-值就越高,并且H_2SO_4和HNO_3积极参与流域内碳酸盐岩风化。硅酸盐岩的风化对地表和地下水体的Ca~(2+)、Mg~(2+)、Na~+、K~+有一定的贡献。此外,人为采矿活动和农业活动对SO_4~(2-)和NO_3~-的产生有较大的影响。质量平衡正推模型结果显示:受到区域岩性和水文条件的影响,地表和地下河天窗水体主要受碳酸盐岩溶解影响,硅酸盐岩溶解和大气输入也有一定的贡献,三大来源的相对比例在空间上变化较大。水体内的可溶性无机碳(DIC)主要来源于碳酸盐岩的溶解和土壤内CO_2的贡献。地表水和地下水的DIC浓度和δ~(13)C_(DIC)值差别较大,DIC值与δ~(13)C_(DIC)呈反相关关系,这说明来自土壤CO_2贡献的DIC越多,其对碳酸盐岩矿物的溶解能力越强。根据本研究区的数据与前人在西江干流的上、中、下游进行对比,结果表明碳酸盐岩风化产生的DIC可以被西江干流的水生植物利用,从而形成稳定的碳汇。     

伯特兰德定律和温伯格原理及推广

将温伯格原理和伯特兰德定律推广到水文地质单元内不同水文地球化学区，在元素被溶（淋）滤，强烈迁移的水文地球化学区段造成某些元素缺乏，生物生理负效应与元素质量浓度成负相关关系，在元素聚（富）集，溶滤，蒸发浓缩水文地球化学环境区，以及某些元素污染环境造成过量，生物生理负效应与元素质量浓度成正相关关系，在此两者之间为元素质量浓度适宜区，根据山西离柳水文地质单元内研究获得：在元素淋滤，流失水文地球化学区水（土）中缺Se,I,F引起的KBD，IDD，龋齿病证实，其患病率与相应元素质量浓度成负相关关系，在聚（富0集，溶淋区因水（土）中F过量而患的地氟病，患病率与F质量浓度正相关关系。