内蒙古河套盆地含氟地下水分布特点及成因

内蒙古河套盆地不仅存在高砷地下水,还存在高氟地下水,严重影响居民的身体健康。尽管高砷地下水开展了大量的研究工作,但对高氟地下水的分布及形成机理却认识不足。在资料检索和和水文地质条件的分析的基础上,通过对406个地下水水样的采集和分析,研究了高氟地下水的化学特征和分布规律,并从矿物溶解与沉淀、蒸发浓缩、解吸与竞争吸附及阳离子交换4个方面探讨了河套盆地山前与平原两种不同水文地质条件下地下水的主要富氟机理。结果显示,406个水样中,超过59%的水样含氟量超过我国饮用水1.0mg/L的标准,其中山前地下水氟的超标率高于平原地区。高氟地下水表现出富钠、贫钙、弱碱性的特点。平原区高氟地下水的pH、HCO-3、δ18 O、δD和TDS普遍高于山前,Ca2+、NO-3普遍低于山前。萤石溶解与方解石沉淀为山前地区氟含量主要控制因素;而蒸发作用、阳离子交换作用、OH-、HCO-3与F-的竞争吸附成为平原地区氟含量的主要控制因素。     

内蒙古河套平原地下水砷异常分布规律研究

通过对内蒙古河套平原砷异常区的实际调查、现场取样、测试、室内实验以及数据分析,得出本区高砷地下水的分布具有明显的地带性,其中双庙和三道桥、沙海和蛮会、白脑包和狼山、塔尔湖及胜丰5片为高砷水地带,从西向东呈不连续的条带状展布,而且与盆地沉降中心带相一致。同时分析了高砷地下水的分布规律及其与古地理环境特征、地下水环境演化的关系。通过研究,可以看出以还原环境为主的富含有机质的湖沼相沉积环境、特定的地质、地形条件为地下水砷异常的原因。     

Principal component analysis and hierarchical cluster analyses of arsenic groundwater geochemistry in the Hetao basin,Inner Mongolia

Although high As groundwater has been observed in shallow groundwater of the Hetao basin, little is known about As distribution in deep groundwater. Quantitative investigations into relationships among chemical properties and among samples in different areas were carried out. Ninety groundwater samples were collected from deep aquifers of the northwest of the basin. Twenty-two physicochemical parameters were obtained for each sample. Statistical methods, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), were used to analyze those data. Results show that As species were highly correlated with Fe species, NH₄-N and pH. Furthermore, result of PCA indicates that high As groundwater was controlled by geological, reducing and oxic factors. The samples are classified into three clusters in HCA, which corresponded to the alluvial fans, the distal zone and the flat plain. Moreover, the combination of PCA with HCA shows the different dominant factors in different areas. In the alluvial fans, groundwater is influenced by oxic factors, and low As concentrations are observed. In the distal zone, groundwater is under suboxic conditions, which is dominated by reducing and geological factors. In the flat plain, groundwater is characterized by reducing conditions and high As concentrations, which is dominated by the reducing factor. This investigations indicate that deep groundwater in the alluvial fans mostly contains low As concentrations but high NO₃ and U concentrations, and needs to be carefully checked prior to being used for drinking water sources.     

Environmental geochemistry of high arsenic groundwater at western Hetao plain, Inner Mongolia

Environmental geochemistry of high arsenic groundwater at Hetao plain was studied on the basis of geochemical survey of the groundwater and a core sediment. Arsenic concentration in groundwater samples varies from 76 to 1093 μg/L. The high arsenic groundwater mostly appears to be weakly alkaline. The concentrations of NO₃⁻ and SO₄²⁻ are relatively low, while the concentrations of DOC, NH₄⁺, dissolved Fe and sulfide are relatively great. Analysis of arsenic speciation in 21 samples shows that arsenic is present in the solution predominantly as As(III), while particulate arsenic constitutes about 10% of the total arsenic. Methane is detected in five samples with the greatest content being 5107 μg/L. The shallow aquifer in Hangjinhouqi of western Hetao plain is of strongly reducing condition. The arsenic content in 23 core sediment samples varies from 7.7 to 34.6 mg/kg, with great value in clay and mild clay layer. The obvious positive relationship in content between Fe₂O₃, Mn, Sb, B, V and As indicates that the distribution of arsenic in the sediments may be related to Fe and Mn oxides, and the mobilization of Sb, B and V may be affected by similar geochemical processes as that of As.     

Techniques and methods of arsenic contaminated groundwater exploration in the Hetao plain of Inner Mongolia,China

1990年报道了在中国内蒙古河套平原由于饮用污染的地下水而患砷中毒的病例.估计目前内蒙受到砷中毒影响的居民已超过41万人.从1997年至2004年,在长达8年的时间里,我们进行了水文地质调查、地质调查和医学调查,并装置了管道输送的供水系统.这些调查揭示了河套平原地下水受砷污染的机理:由于被吸收的砷释放进入地下水,蓄水层中不断加强的还原环境造成铁氢氧化物的溶解.为了防止砷中毒病人数量的进一步增加,停止饮用污染过的水和供应安全的饮用水是重要的.我们需要根据当地的地质和水文地质条件来了解砷污染的机理.     

内蒙古河套平原典型高砷区地下水中砷的演化规律

通过对高砷地下水典型区完整地质单元不同深度含水层地下水进行监测,分析了与砷释放、迁移和富集有关的敏感因素（水位、Eh、总铁、亚铁等）的时间和空间变化规律,探讨了高砷地下水的形成机理。结果发现,地下水灌溉区和黄河水灌溉区,地下水水位均受人为灌溉活动的影响。地下水砷含量在空间和时间尺度上发生有规律的变化。在空间尺度上,地下水中砷含量随着深度的增加而升高,井深小于10 m的地下水砷含量在1.88～2.58 μg/L;井深在10~15 m之间的地下水中砷含量在18.2～217 μg/L;井深在15~25 m之间的地下水中砷含量在38.3～226 μg/L。受人为灌溉影响,地下水中砷的含量会随着地下水位的抬升而升高。地下水砷含量随时间变化的原因是水位抬升使水位变化造成氧化还原环境改变。地下水系统中含砷铁氧化物矿物的还原性溶解、脱硫酸作用等是控制地下水砷含量的主要水文地球化学过程。     

Arsenic movement and traces in the groundwater from the Hetao area, Inner Mongolia

In the Hetao area of Inner Mongolia, Quaternary alluvial aquifers used for the water supply are contaminated by naturally occurring arsenic, which heavily affects the health of 200,000 local residents. This study on the isotopes of strontium and relevant elements contained in the groundwater as well as the arsenic in the groundwater and residents’ hair indicates that the arsenic originally derives from the upper reaches of this area where arsenic levels are high in groundwater, rock, and soil. Over, respectively, 44 km (work-line AA′) and 36 km (work-line BB′) away from there, the levels of arsenic in the water, corresponding to the trend of the residents’ arseniasis, decrease along the direction of the flow from 0.251 to 0.05 mg/L and 0.232 to 0.036 mg/L. The result of this research suggests that long-term strategies to deal with this arseniasis should involve finding hydrous terrains uncontaminated by water from the upper reaches and developing routes to prevent water from taking arsenic.     

Control of organic and iron colloids on arsenic partition and transport in high arsenic groundwaters in the Hetao basin, Inner Mongolia

Due to the importance of colloids in regulating element transport and mobility in aquifers, As distribution in the colloidal fraction needs to be identified in high As groundwaters. Groundwater samples were filtered in the field through a progressively decreasing pore size (0.45 μm, 100, 30, 10, 5 kDa) using a filtration technique under a N₂ atmosphere. Major and trace elements and organic C (OC) were measured in (ultra)filtrates. The studied groundwater samples have typical physio-chemical characteristics of the basin waters. Declines in concentrations of alkali (Na, K), alkaline-earth (Mg, Ca, Sr, Ba) elements, Mo, Si and Se during ultrafiltration are smaller relative to other elements. Arsenic, Cu, Cr, U and V are generally about 30% lower in 5 kDa ultrafiltrates in comparison with 0.45 μm filtrates. Around 50% of Fe, OC and Al are bound to colloids with grain size between 5 kDa and 0.45 μm. Two types of colloids, including large-size Fe colloids and small-size organic colloids, have been identified. Results indicate that As would be more likely to be associated with small-size organic colloids than Fe colloids. SEM images and EDS analysis and synchrotron XRF analyses confirm the association of As with NOM with molecular weights of 5-10 kDa. The better correlation between As(V) and OC in the 5-10 kDa fraction indicates that the small-size organic colloids have a greater affinity for As(V) than As(III). Arsenic associated with organic complexes may not be immobilized by adsorption, and, therefore, easily transported in the aquifer. Thus, the presence of As-containing colloidal complexes in high As groundwaters must be considered in the modeling of As transport in the aquifers.     

Influences of groundwater extraction on flow dynamics and arsenic levels in the western Hetao Basin,Inner Mongolia,China

Data on spatiotemporal variations in groundwater levels are crucial for understanding arsenic (As) behavior and dynamics in groundwater systems. Little is known about the influences of groundwater extraction on the transport and mobilization of As in the Hetao Basin, Inner Mongolia (China), so groundwater levels were recorded in five monitoring wells from 2011 to 2016 and in 57 irrigation wells and two multilevel wells in 2016. Results showed that groundwater level in the groundwater irrigation area had two troughs each year, induced by extensive groundwater extraction, while groundwater levels in the river-diverted (Yellow River) water irrigation area had two peaks each year, resulting from surface-water irrigation. From 2011 to 2016, groundwater levels in the groundwater irrigation area presented a decreasing trend due to the overextraction. Groundwater samples were taken for geochemical analysis each year in July from 2011 to 2016. Increasing trends were observed in groundwater total dissolved solids (TDS) and As. Owing to the reverse groundwater flow direction, the Shahai Lake acts as a new groundwater recharge source. Lake water had flushed the near-surface sediments, which contain abundant soluble components, and increased groundwater salinity. In addition, groundwater extraction induced strong downward hydraulic gradients, which led to leakage recharge from shallow high-TDS groundwater to the deep semiconfined aquifer. The most plausible explanation for similar variations among As, Fe(II) and total organic carbon (TOC) concentrations is the expected dissimilatory reduction of Fe(III) oxyhydroxides.     

Arsenic associations in sediments from shallow aquifers of northwestern Hetao Basin,Inner Mongolia

Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry analysis of sediment samples indicated that total As concentrations have a range of 6.8–58.5 mg/kg, with a median of 14.4 mg/kg. The highest As concentrations were found at 15–25 m depth. In the meanwhile, the range of As concentration in the sediments from background borehole is 3–21.8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively, of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur in the reductive sediments.     

内蒙古河套平原高碘地下水的水文地球化学特征

以内蒙古河套平原西北部的高砷地下水分布区为研究区,通过对区内22组地下水和2组地表水中碘含量的测试和分析可知,研究区地下水中碘含量在27.30～1 638.00μg/L,其中,约50%的地下水样品中碘含量超过我国饮用水的标准限定值150μg/L,约84.6%的高碘地下水为高砷地下水。高碘地下水主要分布于研究区北部地下水水流相对滞缓的平原中心地带,以Cl-Na、Cl·HCO₃-Na和HCO₃·Cl-Na型水为主。研究区地下水中碘的富集有两种机制:浅层地下水的蒸发作用和深部富含有机质的、偏还原的地下水环境中的微生物作用。两种机制相比,后者对地下水中碘的贡献更大些,但前者更普遍些。     

内蒙古河套平原高砷地下水中稀土元素含量及分异特征

高砷地下水是世界范围内的一个重大环境问题。尽管已有工作在高砷地下水的地球化学特征、形成条件和富砷机理等方面取得了很大进展,但其稀土元素(REE)含量及分异特征却一直不清楚,这就限制了稀土方法在评价此类地下水中的应用。在对内蒙古河套盆地地下水样品进行现场测试、实验室分析检测的基础上,我们发现高砷地下水的REE浓度较低。对地下水REE浓度依照北美页岩平均组分(NASC)进行归一化处理后,我们发现大部分水样富集重稀土元素(HREEs),而贫化轻稀土元素(LREEs)。HREEs的富集与地下水中碳酸根对于REE的络合作用密切相关,而弱碱性环境下REE的再吸附可导致LREEs的贫化。所有地下水样表现为Eu正异常,其中大部分表现为Ce负异常。Eu正异常似乎与铁锰氧化物的还原性溶解和解吸附有关,地下水As浓度随[Eu]NASC的升高而升高。从某种意义上说,还原性含水系统中Eu正异常的程度也许可以反映地下水As的富集程度。     

Vertical distribution of bacterial populations associated with arsenic mobilization in aquifer sediments from the Hetao plain, Inner Mongolia

To understand the mechanism of arsenic mobilization from sediment to groundwater mediated by microorganism, vertical distribution of bacterial populations in aquifer sediments of the Hetao plain, Inner Mongolia was investigated by a two-step nested PCR-DGGE and 16S rRNA gene clone libraries, combined with sediment geochemistry. A borehole to 30 m depth was drilled and 11 sediment samples were collected. Lithological profile and different geochemical characteristics of sediments indicated a distinct transition of oxidizing–reducing environment along the depth of the sediment core. As(III) and Fe(II) concentrations elevated progressively from 10 m, simultaneously coupling with decrease of As(V) and Fe(III) concentrations, implying that reductive dissolution of arsenic-rich Fe(III) oxyhydroxides led to arsenic release. Results of DGGE displayed that sediment samples with higher concentrations of total arsenic and total organic carbon had lower population diversity, which suggested total arsenic concentrations were important to determine the population diversity of sediments. Bacterial communities of a sediment sample with the highest diversity and ratio of As(III) to total As were dominated by aerobic and facultative anaerobic bacteria and belonged to Alpha-, Beta-, and Gammaproteobacteria and Firmicutes group. Most of the retrieved sequences were closely related to high arsenic-resistance organisms, sulfide/thiosulfate oxidizers, denitrifiers, and aromatic hydrocarbon degraders. Thiobacillus distinctly predominated in clone library, which suggested that arsenic might be released by oxidized dissolution of sulfide minerals coupled to arsenate reduction or nitrate reduction in anaerobic condition. These data have important implications for understanding the microbially mediated arsenic mobilization in aquifers.     

Chemical evolution in the high arsenic groundwater of the Huhhot basin (Inner Mongolia,PR China) and its difference from the western Bengal basin (India)

Elevated As concentrations in groundwater of the Huhhot basin (HB), Inner Mongolia, China, and the western Bengal basin (WBB), India, have been known for decades. However, few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the HB. In this study, the controls on solute chemistry in the HB have been interpreted and compared with the well-studied WBB, which has a very different climate, physiography, lithology, and aquifer characteristics than the HB. In general, there are marked differences in solute chemistry between HB and WBB groundwaters. Stable isotopic signatures indicate meteoric recharge in the HB in a colder climate, distant from the source of moisture, in comparison to the warm, humid WBB. The major-ion composition of the moderately reducing HB groundwater is dominated by a mixed-ion (Ca–Na–HCO₃–Cl) hydrochemical facies with an evolutionary trend along the regional hydraulic gradient. Molar ratios and thermodynamic calculations show that HB groundwater has not been affected by cation exchange, but is dominated by weathering of feldspars (allitization) and equilibrium with gibbsite and anorthite. Mineral weathering and mobilization of As could occur as recharging water flows through fractured, argillaceous, metamorphic or volcanic rocks in the adjoining mountain-front areas, and deposits solutes near the center of the basin. In contrast, WBB groundwater is Ca–HCO₃-dominated, indicative of calcite weathering, with some cation exchange and silicate weathering (monosiallitization).     

内蒙古苏尼特地下水氟污染形成机理研究

为了研究内蒙古苏尼特地区地下水氟污染机理,本文运用水文地球化学分类方法,从水文地质、水化学特征两方面研究其地下水的水质特征、氟的起源、分布规律及污染形成机理。研究结果发现:高氟地下水的主要水质类型为HCO3—Na型,pH值在7.08～9.38之间,氟浓度与井深有关,即井越浅,氟浓度越高;地下水中氟浓度最高达14.78mg/L,5～9月地下水氟浓度相对增长率在7.8～23.1之间;F-浓度与Li+、Br-相关系数达0.89和0.82,受断层影响的深层地下水中F-浓度几乎与Li+、Br-没有相关关系,这暗示着氟来源于浅部,并受到强烈的蒸发作用影响而使水中的氟浓缩;地质调查发现该地区还有数个萤石矿存在,显微镜分析结果证实表层土壤中普遍存在CaF2,地下水中的氟来自CaF2。高氟地下水存在于潜水层,深部含水层的地下水可供开采。从断层带涌出的水对潜水层有稀释作用。     

Arsenic pollution of groundwater and its release mechanism in the central part of the Hetao Plain, Inner Mongolia, China

Arsenic pollution of groundwater has become a serious health problem in several regions of the world. Wuyuan County located in the central part of the Hetao Plain, Inner Mongolia, is one of the most severely arsenic polluted areas. Peoples of the county have used groundwater of shallow （12-25 m） tube-well as drinking water. The groundwater is Na-HCO3 and Na-Cl type on the piper plots and aligns with steady Ca ： Mg ratio on cation diagram. The arsenic content in the water is more than 0.2 mg/L and the highest value reaches up to 0.52 mg/L. Drilling data show that Holocene sediments are divided into three zones on the basis of their color appearances; brown, grey and dark gray zones. The strata from 2m to 9-14m under the surface are mainly composed of clay and silt which are impermeable layers. The grey and dark grey zones composed of sand underlie the impermeable bed and the condition of their zones is reductive. At the depth of 30 m near the bottom of drilling, ORP of the groundwater is -300- -400 mV. The dark grey sand changes to yellow in color under the atmosphere. Under reducing environment, the color returns to its original dark grey. The characteristic color is due to amorphous or low-crystalline Fe sulfide coating sand grains. The sediments are of fluvial origin by the Yellow River. The arsenic content in the sediments is rich in fine-grained part and its values are more than 20 mg/kg in clay layer. The highest is 38 mg/kg. X-ray diffraction and macroscopic observation show that the clay layer is made of minerals such as chlorite and illite and contains high quantities of organic matter.     

干旱、半干旱地区高砷地下水形成机理研究:以中国内蒙古河套平原为例

干旱、半干旱地区高砷地下水形成机理,是一较为复杂的地球化学和环境水文地球化学过程。通过多年来的实地调查、资料分析和试验测试等方法手段,详细研究了中国西部地区,特别是中国内蒙古河套平原,高砷地下水的分布特征及地质环境背景。研究并阐述了地下水中砷的来源,地层中砷的来源、聚集、溶出的地球物理、地球化学过程,提出了河套平原地层中砷聚集的3种模式,即断裂运移聚集模式,河、湖水胶体作用聚积模式和蒸发浓缩再聚集模式。研究表明：河套平原地下水中的砷,主要来源于地层,而地层中的砷主要来源于3个方面：周边的山区特别是存在高矿化带的西部山区、黄河上游和构造运移深部地下水;地层中砷的溶出主要与3个因素有关：地下封闭的还原环境、脱硫酸作用和大量灌溉水的入渗。