The groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks: an application of natural environmental tracers          下载免费PDF全文

Sandow Mark Yidana  Eric Koffie 《水文研究》2014,28(7):3104-3117

Isotope data of precipitation and groundwater in parts of the Voltaian Basin in Northern Ghana were used to explain the groundwater recharge regime in the area. Groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area. It is therefore important to establish the processes and sources of groundwater recharge. δ¹⁸O and δ²H data for local precipitation suggest enrichment relative to the Global Meteoric Water Line (GMWL) and indicate that precipitation takes place at a relative humidity less than 100%. The groundwater data plot on an evaporation line with a slope of 5, suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone. This finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates. Groundwater recharge estimates from the chloride mass balance, CMB, method suggest recharge in the range of 1.8–32% of the annual average precipitation in the form of rainfall. The highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area. In the northern parts of the study area, groundwater recharge is lower than 12%. The recharge so computed through the application of the CMB methodology takes on a spatial distribution akin to the converse of the spatial pattern of both δ¹⁸O and δ²H in the area. As such, the locations of the highest recharge are associated with the most depleted values of the two isotopes. This observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water. The percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates. At the same time, the amount of water that finally reaches the water table is considerably reduced. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers          下载免费PDF全文

Tianming Huang  Zhonghe Pang  Jilai Liu  Lihe Yin  W. Mike Edmunds 《水文研究》2017,31(5):1047-1057

Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (²H, ¹⁸O, ¹³C, ¹⁴C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected ¹⁴C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years.  相似文献   

土壤样品镉同位素分析中Cd与Sn有效分离方法的改进     

段桂玲  段瑞春  谭娟娟  顾涛  邵长生  路韬 《岩矿测试》2016,35(1):10-16

保证Cd的高回收率以及彻底的Sn干扰去除是获得精确镉同位素组成的前提,目前报道的多种Cd分离与纯化方法获得的Cd回收率有较大差异(42.6%~99.8%),且去除Sn干扰的效果也不同(去除率在87.8%~97.4%之间),Cd回收率和Sn去除率均不理想。本文对前人报道的分离方法进行对比实验,发现0.1 mol/L氢溴酸-0.5 mol/L硝酸是分离Cd和Sn的有效试剂,增加该组混合酸的用量可淋洗出样品中更多的Sn且不会损失Cd,当混合酸的淋洗用量增加至30 mL时,Sn的淋洗率达到99.8%以上,Cd的回收率亦达到99.0%±0.5%,可满足土壤样品镉同位素的测定要求。本工作为获得高精度的镉同位素组成奠定了基础,为研究土壤环境中镉的污染来源提供了技术手段。  相似文献   

2010—2020年黄河下游河南典型灌区浅层地下水中砷和氟的演化特征及变化机制     

任宇  曹文庚  潘登  王帅  李泽岩  李谨丞 《岩矿测试》2021,(6):846-859

黄河下游典型灌区河南段是豫北平原重要的农业种植区。该地区浅层水质整体较差,因常用于作物灌溉或家畜饮用,会对人体健康产生风险,因此对该地区地下水中砷与氟浓度变化特征和机制的研究将有助于提高对该地区地下水污染的认识水平。本文基于2010年和2020年在灌区范围内采集的327组浅层地下水样品,研究区内地下水砷和氟分布情况,并在此基础上对比研究十年间灌区浅层地下水中砷、氟的演化特征,探索分析砷与氟浓度及空间变化机制。研究结果表明：该地区浅层地下水中存在砷与氟超标问题,2020年浅层地下水中高砷（砷浓度大于10μg/L）和高氟（氟浓度大于1mg/L）的样品数量分别占总数的26.1%和26.06%。高砷水分布在太行山前洼地与黄河冲积平原等泥沙互层结构的沉积环境中,还原性较强,同时地下水径流不畅,较强的阳离子交换作用使得其所处环境中Ca²⁺浓度较高。近十年间砷浓度增加的水样占总数31.8%,砷浓度减少的水样占36.7%。砷浓度的增长（减少）是地下水还原性增强（减弱）使得锰氧化物溶解释放（吸附）导致。近十年间不同地区农业灌溉和水源置换等用水方式导致水位变化是引起砷浓度变化的潜在因素。高氟水主要分布在河南新乡与濮阳的黄河沿线,氟离子浓度受到沉积物中萤石等钙质矿物溶解影响,使得高氟地下水出现在低钙环境中。近十年间研究区中氟离子浓度减少的占总数60.2%,氟离子浓度增加的占32.1%,整体变化趋势向好,但是高氟区中氟离子浓度继续增加。氟浓度的变化同样受到Ca²⁺变化影响,在Ca²⁺浓度降低（升高）时氟浓度进一步升高（降低）。地下水中氟升高地区分布在黄河沿线,因此受到黄河水补给影响较大,地下水径流条件较好,阳离子交换作用减弱,使得Ca²⁺浓度降低,此时地下水中砷浓度受到环境影响而降低,因此研究区氟增加地区中砷与氟的分布和演化呈现反向关系。  相似文献   

Inter‐laboratory Characterisation of Apatite Reference Materials for Chlorine Isotope Analysis     

Alicja Wudarska  Ewa S&#x;aby  Michael Wiedenbeck  Jaime D. Barnes  Magali Bonifacie  Neil C. Sturchio  Grard Bardoux  Frdric Couffignal  Johannes Glodny  Linnea Heraty  Timm John  Christof Kusebauch  Sathish Mayanna  Franziska D. H. Wilke  Ewa Deput 《Geostandards and Geoanalytical Research》2021,45(1):121-142

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca₁₀(PO₄)₆(F,Cl,OH)₂ solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for ³⁷Cl/³⁵Cl homogeneity using SIMS followed by δ³⁷Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with > 0.5 % m/m Cl and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean ³⁷Cl/³⁵Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ³⁷Cl_SMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 10³δ³⁷Cl_SMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.  相似文献   

塔城盆地地下水氟分布特征及富集机理   总被引：2，自引：0，他引：2  

吕晓立  刘景涛  周冰  朱亮  张玉玺 《地学前缘》2021,28(2):426-436

塔城盆地位于新疆维吾尔自治区西北部,干旱少雨,蒸发强烈。但相对于新疆其他盆地,塔城盆地地下水水质相对较好,溶解性总固体和F^-含量相对较低。为解译这种差异及盆地内高氟地下水的成因,本文在对盆地地下水样品水化学组分系统分析的基础上,结合多种水文地质调查数据,利用数理统计、离子比及主成分分析等手段,研究高氟水的成因及其分布规律。结果表明:受气候以及地质等因素控制,研究区地下水氟浓度总体较低,高氟水主要分布于扇前洼地及盆地中部的低洼地带;受承压含水层的顶托补给,地下水氟浓度呈现出上高下低的垂向分带特征。研究区地下水径流途径短,水循环快,水岩相互作用时间较短,且山区地下水以深径流形式循环补给平原区深层承压含水层,再顶托补给潜水,避免了强烈的蒸发浓缩作用。山前洪积扇地下水氟富集主要受控于沉积地层中含氟矿物的风化溶解,而岩石风化、蒸发浓缩、阳离子交换、竞争吸附为平原区地下水氟浓度的主要影响因素。  相似文献   

方解石负载羟基磷灰石复合材料去除水中铀离子的PRB活性介质研究     

张卫民  王振  钱程  郭亚丹  刘海燕 《地学前缘》2021,28(5):175-185

铀污染地下水分布于世界多国,其危害备受关注。本文基于溶胶-凝胶法制备方解石负载羟基磷灰石复合材料(CLHC),通过静态与动态对比试验,探讨了PRB活性介质对水中铀离子的吸附机理和去除效果。试验结果表明,制备的CLHC表面被羟基磷灰石覆盖,对铀离子具有较强的吸附能力。当U的初浓度为5.0 mg/L、试验周期为2 h、溶液pH值为4、CLHC用量为0.5 g/L时,CLHC可以吸附水中所有的铀离子。CLHC对铀离子的吸附过程可以用Langmuir等温吸附模型、粒子内扩散吸附动力学模型和准二级吸附动力学模型较好地进行描述。石英砂负载羟基磷灰石与CLHC相比,后者具有更强的吸附能力,而且具有更长的使用寿命。CLHC在吸附铀的过程中没有价态变化,其对铀离子的吸附主要为离子交换的化学吸附。本研究的成果可为可渗透反应墙被应用于铀污染地下水修复提供试验依据。  相似文献   

济南市新旧动能转换区浅层地下水硝酸盐污染特征     

成世才 《中国煤炭地质》2021,(2)

为查清济南市新旧动能转换先行区浅层地下水NO₃^-污染问题,对研究区7种污染源类型64件浅层地下水样品水质结果进行统计分析后认为:受人类活动影响,地下水中NO₃^-含量的高低往往与几种特定的水化学类型存在对应关系。4类主要污染源类型浅层地下水NO₃^-含量一般顺序为:垃圾渗滤液>禽畜养殖>生活污水>农业种植。垃圾渗滤液下渗导致的NO₃^-污染对应的主要地下水化学类型为HCO₃·Cl^-Na·Mg型,粪便渗滤液及尿液下渗主要对应产生HCO₃·SO₄-Na·Mg型、生活污水入渗对应产生HCO₃·Cl^-Na·Ca型,农业种植区主要对应HCO₃-Na·Ca型。离子相关性分析表明,NO₃^-含量与Ca²⁺、Cl^-存在相关关系。研究区以农业种植为主,大量氮素化肥和石灰等土壤改良剂的使用是导致浅层地下水NO₃^-与Ca²⁺相关的主要因素。NO₃^-与Cl^-在地下水中同属较稳定离子,由长期的人类活动排放、入渗积累或蒸发浓缩富集,是一个地区人类活动密集程度和历史长度的综合反映,提出了NO₃^-与Cl^-质量浓度联合评价地下水污染的基本方法。  相似文献   

Spatial patterns of groundwater‐lake exchange – implications for acid neutralization processes in an acid mine lake     

Christiane Neumann  Julia Beer  Christian Blodau  Stefan Peiffer  Jan H. Fleckenstein 《水文研究》2013,27(22):3240-3253

Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m^‐2 d^‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m^‐2 d^‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g^‐1 d^‐1) compared to alternating sites (<220 nmol g^‐1 d^‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen‐18 in dry river bed of North China Plain     

Ruiqiang Yuan  Xianfang Song  Dongmei Han  Yinghua Zhang  Liang Zhang  Bing Zhang  Xiting Long  Yilei Yu 《水文研究》2012,26(9):1291-1301

Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well‐irrigated agriculture. In the North China Plain, the land use is dominated by groundwater‐irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ¹⁸O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ¹⁸O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year^?1, which accounts for about 0·7% of the long‐term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year^?1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ¹⁸O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献