Strontium isotope geochemistry of groundwaters and streams affected by agriculture,Locust Grove,MD

The effects of agriculture on the isotope geochemistry of Sr were investigated in two small watersheds in the Atlantic coastal plain of Maryland. Stratified shallow oxic groundwaters in both watersheds contained a retrievable record of increasing recharge rates of chemicals including NO₃⁻, Cl, Mg, Ca and Sr that were correlated with increasing fertilizer use between about 1940 and 1990. The component of Sr associated with recent agricultural recharge was relatively radiogenic (⁸⁷Sr/⁸⁶Sr=0.715) and it was overwhelming with respect to Sr acquired naturally by water–rock interactions in the oxidized, non-calcareous portion of the saturated zone. Agricultural groundwaters that penetrated relatively unoxidized calcareous glauconitic sediments at depth acquired an additional component of Sr from dissolution of early Tertiary marine CaCO₃ (⁸⁷Sr/⁸⁶Sr=0.708) while undergoing O₂ reduction and denitrification. Ground-water discharge contained mixtures of waters of various ages and redox states. Two streams draining the area are considered to have higher ⁸⁷Sr/⁸⁶Sr ratios and NO₃⁻ concentrations than they would in the absence of agriculture; however, the streams have consistently different ⁸⁷Sr/⁸⁶Sr ratios and NO₃⁻ concentrations because the average depth to calcareous reducing (denitrifying) sediments in the local groundwater flow system was different in the two watersheds. The results of this study indicate that agriculture can alter significantly the isotope geochemistry of Sr in aquifers and streams and that the effects could vary depending on the types, sources and amounts of fertilizers added, the history of fertilizer use and groundwater residence times.     

滇东南南洞地下河系统源区洞穴特征及其成因演化机制

滇东南岩溶地貌发育,岩溶洞穴是该区典型空洞体系。文章以滇东南南洞地下河系统源区典型岩溶洞穴为研究对象,基于地学理论和地球化学分析,对该区地貌特征、成因及演化机制开展科学研究。研究表明,NW向的张性断裂、区内可溶部分最高个旧组碳酸盐岩以及杨柳河向西流动的水动力作用是南洞地下河系统源区洞穴发育的主要成因;全新世中期6 kaBP以来,该地区洞穴演化过程经历了三个阶段,其中,主体形成时间为6~4 kaBP;此外,建立石洞洞穴与地下河发育模式。本次研究对南洞地区地下水资源评价具有实际意义。      

云南南洞地下河系统边界及性质研究

地下河系统具有固定补给范围和资源要素,是岩溶地下水进行独立循环的基本单元,控制了岩溶水的运移富集、水化学演化特征、资源构成以及环境地质问题。开展地下河系统研究首要任务是确定系统边界位置及其水文地质性质。以南洞地下河系统为研究对象,据野外调查、勘探、试验资料,以地球系统科学理论为指导,运用现代岩溶学、地质学及水文地质学的分析方法,确定南洞地下河系统是由1号暗河和2号暗河系统组成的,其中2号暗河还有叠置于其上的平石板和黑龙潭两个全排型暗河子系统;其含水岩层主要为三叠系个旧组（T2g）灰岩、灰质白云岩、白云质灰岩;根据边界的水文地质性质可以划分为地表分水岭边界、地下分水岭边界、隔水边界、岩溶含水层深埋滞留型边界。      

云南开远南洞地下河水质演变特征

在云南开远南洞地下河出口,连续19年采取旱、雨季水样进行水质变化监测,结果表明: ( 1)整体上地下水水质旱季好于雨季,历年旱季水质类型以良好为主,雨季则以较差为主; ( 2)水质变化阶段性明显: 1987— 1993年,离子浓度普遍较低,旱、雨季波动不大,水质多属Ⅰ 、Ⅱ 类,有机污染以NH+4 、NO-3 等为主; 1994—2000年,旱、雨季离子浓度均普遍升高且变化加剧, N H+4 、As、Cd、Cr、Mn出现历年最大值,金属离子污染日趋加剧,水质以Ⅱ 、Ⅲ 类为主; 2001— 2005年,旱、雨季离子浓度有升有降,以升为主, Pb、Zn、Cl- 、SO2-4 出现历年最大值,水质以Ⅱ 、Ⅲ 类为主。南洞地下河水质19年来发生了较大的变化,污染日趋严重。分析认为该地下河水质逐步变差与上游补给区盆地内经济发展状况密切相关。为此,提出了采用自动监测等方法加强地下河动态变化监测研究以及实行分区、分级管理等水质保护的具体对策建议。      

Strontium isotope geochemistry of groundwater in the central part of the Dakota (Great Plains) aquifer,USA

The Dakota aquifer of the central and eastern Great Plains of the United States is an important source of water for municipal supplies, irrigation and industrial use. Although the regional flow system can be characterized generally as east to northeasterly from the Rocky Mountains towards the Missouri River, locally the flow systems are hydrologically complex. This study uses Sr isotopic data from groundwater and leached aquifer samples to document the complex subsystems within the Dakota aquifer in Nebraska and Kansas. The interaction of groundwater with the geologic material through which it flows has created spatial patterns in the isotopic measurements that are related to: long-term water–rock interaction, during which varying degrees of isotopic equilibrium between water and rock has been achieved; and the alteration of NaCl fluids by water-rock interaction. Specifically, Sr isotopic data distinguish brines from Kansas and western Nebraska from those in eastern Nebraska: the former are interpreted to reflect interaction with Permian rocks, whereas the latter record interaction with Pennsylvanian rocks. The Sr isotopic composition of groundwater from other parts of Nebraska and Kansas are a function of the dynamic interaction between groundwater and unlithified sediments (e.g., glacial till and loess), followed by interaction with oxidized and unoxidized sediments within the Dakota Formation. This study illustrates the power of combining Sr chemistry with more conventional geochemical data to obtain a more complete understanding of groundwater flow systems within regional aquifer systems where extensive monitoring networks do not exist.     

湘中锡矿山锑矿床的Sr同位素地球化学

对湘中锡矿山锑矿床围岩灰岩、硅化灰岩、煌斑岩和脉石矿物进行了系统的Sr同位素研究。结果表明，矿区围岩发生了隐性蚀变，灰岩中Sr亏损，而^87Sr/^86Sr高于同时代的海相碳酸盐，这种隐性蚀变很可能是水／岩反应所致。矿体附近的硅化灰岩中Sr更加亏损，而^87Sr/^86Sr明显增加。成矿期方解石的^87Sr/^86Sr较高，成矿体系中变化的W／R比造成了方解石中^87Sr/^86Sr值的明显波动。成矿流体为一富放射成因^87Sr的溶液。成矿流体来自或流经基底地层，流体中的Sr由基底碎屑岩提供，矿质Sb也可能主要来自富Sb的元古宇基底。水／岩反应的理论模拟显示，锡矿山成矿流体中的Sr约为3．0μg/g，^87Sr/^86Sr为０．７１７；蚀变－成矿体系为一开放体系，矿石的沉淀机制主要为水／岩反应，成矿体系中W／R 比较高。     

南洞地下河流域南部岩溶石漠化空间分布特征分析

基于2013年9月29日GF-1号WFV遥感数据对南洞地下河流域蒙自幅、个旧幅、新安幅和鸣鹫幅进行岩溶石漠化遥感解译,通过归一化植被指数（NDVI）和植被覆盖度（FVC）提取研究区域内石漠化信息,得到其空间分布规律。研究区岩溶石漠化发生率74.55%,属石漠化高发地区,其中中度石漠化最为发育,占全区石漠化的32.63%,重度石漠化最少,占17.59%。基于岩性、高程、坡向和坡度等4个影响因素与岩溶石漠化进行相关性分析,对不同因素中石漠化发生率的变化规律进行分析,结果表明南洞地下河流域南部区域岩溶石漠化在低海拔、缓坡度和纯碳酸盐岩中较为发育,在不同坡向中岩溶石漠化发育程度则较为相似。     

The geochemistry of the Dunedin Volcano: Strontium isotope chemistry

The isotopic composition of strontium has been determined for samples from the alkaline lavas of the Dunedin Volcano covering the range basalt, basanite, intermediate compositions, phonolite and quartz normative trachyte. The basaltic, intermediate and phonolitic rocks appear to be comagmatic and have similar low initial Sr⁸⁷/Sr⁸⁶ ratios around 0.7030, comparable with those of other alkaline provinces. The quartz normative trachytes have initial ratios significantly higher than those of the other rocks (0.7040) although their age is comparable. Contamination by sea water or crustal material could explain the higher initial ratios of the trachytes but it does not account for important features of their chemistry. It is suggested that the trachytes formed by partial melting involving an alkali feldspar-rich portion of older igneous rocks. Rb-Sr ages obtained are comparable with published K-Ar dates. The Rb-Sr age for the trachytes is 14.± 7 m.y. and the other alkali-enriched rocks give ages ranging within the limits of 14.4 to 12.0 m.y.     

南洞地下河岩溶管道展布及结构特征的示踪试验解析

运用高精度的示踪试验研究了南洞地下河流域部分岩溶管道的展布状况,并对暗河管道的结构特征进行了分析。试验结果表明:一号暗河有一独立的含水系统,补给区为瓦白白一带,二号暗河主管道总体通往永宁和石洞方向,三号暗河通往城红寨方向,二号暗河和三号暗河在南洞口附近有连通,枯季时二号暗河补给三号暗河。此外,一号暗河和二号暗河分别呈老年期和壮年期地下河形态,较为畅通;三号暗河则发育较晚,出口处有较多的裂隙。最后,结合现有的资料及流域内的水文地质条件,对流域内岩溶管道的大体分布位置进行了推断,绘制了岩溶管道的展布图,以期为南洞地下河流域的岩溶水文地质调查、物探、钻探及地下水开发利用等提供理论依据。      

Strontium isotope geochemistry of megacrysts and host basalts from southeastern Australia

Strontium isotopic data for megacrysts and lavas from six eruptive centers within the Newer Basalts province of southeastern Australia show that megacrysts of clinopyroxene are in isotopic equilibrium with associated basalts, but that megacrysts of kaersutite, ferrokaersutite, orthopyroxene and anorthoclase may exhibit slight disequilibrium with their host basalts. Furthermore, the anorthoclase megacrysts may be either more or less radiogenic than their hosts. The ⁸⁷Sr/⁸⁶Sr ratios for 14 basalts from throughout the province vary from 0.7035 to 0.7045 and it is proposed that anorthoclase, amphibole and orthopyroxene megacrysts which crystallized in isotopic equilibrium with one magma may have been caught up in a pulse of a later magma of a different isotopic composition. The variations in the ⁸⁷Sr/⁸⁶Sr ratios for the basalts are attributed to variations in the isotopic composition of their source regions. Such isotopic heterogeneity is supported by published data for ultramafic xenoliths which occur in the Newer Basalts lavas.     

Strontium isotopic geochemistry of Tianqiao Pb-Zn deposit,Southwest China

Tianqiao carbonate-hosted Pb-Zn deposit, controlled by NW-trending F37 thrust fault and NW-trending Tianqiao anticline, is located in the eastern part of Sichuan-Yunnan-Guizhou （SYG） Pb-Zn metallogenic province, southwestern Yangtze Block, southwest China. Ore bodies in this deposit are hosted in the Devonian-Carboniferous carbonate rocks, and ore minerals include sphalerite, galena and pyrite, while the gangue minerals are dominated by calcite and dolomite. Using high-precision solid thermal ionization mass spectrometry （TIMS）, this paper reports the strontium isotopic compositions （0.7119 to 0.7167） of sulfide samples from the Tianqiao deposit in order to trace the origin of hydrothermal fluids. Compared with the country rocks, the calculated 87Sr/86Sr200 Ma values of sulfide range from 0.7118 to 0.7130, higher than those of the age-corrected Devonian to Permian sedimentary rocks （0.7073 to 0.7101） and the Middle Permian Emeishan flood basalts （0.7078 to 0.7039）, but lower than those of the age-corrected Proterozoic basement rocks （such as the Kunyang and Huili Groups, 87Sr/86Sr200 Ma=0.7243 to 0.7288）. This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Together with geologic and previous isotopic evidences, we considered that the fluids＇ mixing is a possible mechanism for sulfide precipitation in the Tianqiao deposit.     

Impact of human activities on quality and geochemistry of groundwater in the Merdja area,Tebessa, Algeria

Chemical data are used to clarify the hydrogeological regime in the Merdja area in Tébessa, as well as to determine the status of water quality in this area. Groundwater from the aquifer in the Merdja area can be divided into two major groups according to geographical locations and chemical compositions. Water in the center part of the area of study is characterized by the dominance of chloride, sulfate, sodium, and potassium; whereas waters in the limestone aquifers in the west are dominated by the same cations but have higher concentrations of bicarbonate. Stable isotopes show that the Tébessa aquifers contain a single water type, which originated in a distinct climatic regime. This water type deviates from the Global Meteoric Water Line (MWL), as well as from the Mediterranean meteoric water line. The water is poor in tritium, and thus can be considered generally older than 50 years. Piezometric map suggests that water is moving from the west towards the center of the studied area, and from east towards center. Degradation of water quality can be attributed to agricultural fertilizers in most cases, although the wadi El Kebir River is a contributor to pollution in the middle part of the studied area.     

旅游活动输入岩溶地下河系统的水化学指纹记录

地下河系统是岩溶地质景观的重要组成部分,利用特殊岩溶地形地貌建立的国家重大科技基础设施成为科研和旅游的胜地。为了解旅游活动对岩溶地下河系统水化学的影响,文章分析了大小井地下河系统入口和出口在不同旅游时段的水化学特征。结果表明：受旅游人数影响,污水水化学变化较大;大小井水化学类型为Ca-HCO3型,水岩相互作用产生的Ca2+、Mg2+和${\rm{HCO}}_3^{-}$从入口到出口逐渐增加,而人类活动输入的K+、Na+、Cl−、${\rm{NO}}_3^{-}$和${\rm{SO}}_4^{2-}$则表现出差异性特征。小井地下河系统因受沿途城镇生活排放污水和农业活动影响,水化学波动较大,出口K+、Na+、Cl−和${\rm{NO}}_3^{-}$升高;大井地下河虽受旅游活动输入影响,但K+、Na+、Cl−、${\rm{NO}}_3^{-}$和${\rm{SO}}_4^{2-}$随着地下径流长度增加而降低。HFE−D和Gibbs模型以及离子比例系数分析显示,地下河系统受到了城镇生活排放、旅游和农业等人类活动输入的影响,这一现象应引起足够的重视。     

典型岩溶区地下水系统重金属元素分布特征浅析——以广西坡月地下河为例

地下河为岩溶地下水系统的重要组成部分,为查清典型岩溶区地下水系统中重金属指标的含量变化及空间分布特征,文章以广西坡月地下河系统为例,通过不同断面两次采样分析,重点剖析地下河系统在水文地球化学作用下,地下水中以“五毒”元素及Zn、Al和Mn为代表的重金属元素含量。分析结果表明:坡月地下河水体pH值在7.34～8.10 之间,水体中“五毒”元素、Zn、 Al和Mn的检出含量极低或未检出,质量浓度均远小于国家地下水环境质量标准中的Ⅲ类水质标准,适合各种用途。检出含量较高的点主要为地下河明流段或补给区地表水,含量最高分布在坡心地下河出口水体,其原因是坡心地下河系统区内工矿企业和其它经济活动干扰相对较强,特别是工矿企业的矿石和尾矿渣的露天堆放（如金矿）是引起地下水中重金属元素的检出或超标的重要因素。      

Strontium isotope geochemistry of Icelandic geothermal systems and implications for sea water chemistry

Chemical and Sr isotopic analyses have been made of waters from 16 geothermal sites in Iceland with particular reference to the systems at Reykjanes and Svartsengi for which compositions of geothermal sea water and fresh and hydrothermally-altered rocks have been compared. The alkalies display mixing relationships indicating a hydrothermal input of Rb and K to local meteoric and sea waters as do results for Sr and Ca involving high-temperature fluids. ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the geothermal waters of meteoric origin parallel those of associated rocks but are higher. Ratios for geothermal sea waters are 0.7042 (Reykjanes) and 0.7040 (Svartsengi), lower than for normal sea water (0.7092) because of leaching of Sr from rocks followed by partial removal into alteration minerals, of which epidote and chlorite may be most important. Consequently, associated hydrothermally-altered rocks have been subject to significant Sr isotopic contamination by sea water Sr raising ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios from 0.7032 for fresh rock to 0.7038–0.7042 (Reykjanes) and to 0.7039–0.7041 (Svartsengi). Altered basalt is only ~50% equilibrated isotopically with geothermal sea water, at a water/rock ratio of ~2, but is internally equilibrated whereas palagonitized rocks (water/rock ratio of 3 to 4) are close to Sr isotopic equilibrium with associated sea water but show significant internal Sr disequilibrium. Hydrothermal input is unlikely to be important in the oceanic mass balance of Sr but is likely to be highly significant in controlling the strontium isotopic composition of sea water.     

Boron isotopic geochemistry of karst groundwater in Guiyang City, China

Boron has two stable isotopes （^10B and ^11B） with relative abundances of about 20% and 80%, respectively. Boron isotopic ratios in natural materials show a huge range of variations, from -70‰ to ＋60‰, when expressed with the classical δ^11B notation. Most of these isotopic variations occur at the surface of the Earth. Hence, boron isotopic composition can be used as a sensitive tracer in geochemical study, for instance, to identify the different sources of contamination and factors controlling the salinity of groundwater. During the last decade, boron isotopes have been used to discriminate between the influences of seawater intrusion and anthropogenic discharge. But few of those researches can precisely identify the different sources of contamination. We measured the boron concentrations and boron isotopic ratios of groundwater samples collected in Guiyang City, as well as the major ions. The results indicate that the major ion composition of the groundwater in the investigated area is mainly controlled by the interactions between water and the dominant rock i.e. carbonates. All the water compositions are characterized by high concentrations of Ca^2＋, Mg^2＋, HCO3^-, SO4^2-, and NO3^-, which are the dominant contaminants. Both dissolved boron concentrations and isotopic ratios show large variations among the ground waters, from 2 μg/L to 90 μg/L and from -6‰ to ＋26‰, respectively. The boron concentrations and isotopic ratios indicate that the river across the studied city has been seriously contaminated by urban discharge. Boron concentrations of fiver water samples varied from 20 μg/L to 140 μg/L, with an average δ^11B value of ＋2.0‰. Using boron isotopic compositions and different geochemical indices allowed us to clearly identify and distinguish the two major sources of contamination, agricultural activity and urban wastewater. Both of the two sources are characterized by high boron concentrations but their boron isotopic compositions significantly differ.     

Strontium isotope systematics of mixing groundwater and oil-field brine at Goose Lake in northeastern Montana,USA

Groundwater, surface water, and soil in the Goose Lake oil field in northeastern Montana have been affected by Cl⁻-rich oil-field brines during long-term petroleum production. Ongoing multidisciplinary geochemical and geophysical studies have identified the degree and local extent of interaction between brine and groundwater. Fourteen samples representing groundwater, surface water, and brine were collected for Sr isotope analyses to evaluate the usefulness of ⁸⁷Sr/⁸⁶Sr in detecting small amounts of brine. Differences in Sr concentrations and ⁸⁷Sr/⁸⁶Sr are optimal at this site for the experiment. Strontium concentrations range from 0.13 to 36.9 mg/L, and corresponding ⁸⁷Sr/⁸⁶Sr values range from 0.71097 to 0.70828. The local brine has 168 mg/L Sr and a ⁸⁷Sr/⁸⁶Sr value of 0.70802. Mixing relationships are evident in the data set and illustrate the sensitivity of Sr in detecting small amounts of brine in groundwater. The location of data points on a Sr isotope-concentration plot is readily explained by an evaporation-mixing model. The model is supported by the variation in concentrations of most of the other solutes.