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1.
This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (N–E France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio 87Sr/86Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the water–rock interaction kinetic code KINDIS. In the early stages of water–rock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The 87Sr/86Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified.  相似文献   

2.
《Applied Geochemistry》2006,21(8):1432-1454
Strontium-, Nd-, and rare-earth-element-isotope data are presented from rock, weathered rock (arene) and saprolite, sediment and soil, shallow and deep groundwater (e.g. mineral-water springs), and surface waters in the Margeride massif, located in the French Massif Central. Granitoid rock and gneiss are the main lithologies encountered in the Margeride, which corresponds to a large and 5-km-deep laccolith. Compared to bedrock, the Sr isotopes in arene, regolith, sediment and soil strongly diverge with a linear increase in the 87Sr/86Sr and Rb/Sr ratios. Neodymium isotopes fluctuate least between bedrock and the weathering products. In order to characterise the theoretical Sr isotopic signature IRf(Sr) of water interacting with granite, a dissolution model was applied, based on the hypothesis that most of the Sr comes from the dissolution of plagioclase, K-feldspar and biotite. Similar to the Sr model, an approach was developed for modelling the theoretical Nd isotopic signature IRf(Nd) of water interacting with a granite, assuming that most Nd originates from dissolution of the same minerals as those that yield Sr, plus apatite. The IRf(Sr) ratio of water after equilibration with the Sr derived from minerals was calculated for the Margeride granite and compared to values measured in surface- and groundwaters. Comparison of the results shows agreement between the calculated IRf(Sr) and the observed 87Sr/86Sr ratios. When calculating the IRf(Nd) ratio of water after equilibration with the Nd derived from minerals of the Margeride granite, the results indicated good agreement with surface-water values, whereas mineralised waters analysed within the Margeride hydrosystem could not be directly linked to weathering of the granite alone. Because the recharge area of deep groundwater is located on the Margeride massif, very deep circulation involving interaction with other rocks (e.g. shales) at depths of >5 km must be considered.  相似文献   

3.
《Applied Geochemistry》2000,15(3):311-325
Barium/Sr and Ca/Sr ratios have been used to model the relative importance of different sources of stream water. Major and trace element concentrations together with 87Sr/86Sr ratios were measured in precipitation, soil water, groundwater and stream water in a small (9.4 km2) catchment in northern Sweden. The study catchment is drained by a first order stream and mainly covered with podzolized Quaternary till of granitic composition. It is underlain by a 1.8 Ga granite. A model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components: soil water, shallow groundwater, and deep groundwater. Contributions from precipitation are thus not included in the model. This source may be significant for the stream water generation, but it does not interfere with the calculations of the relative contributions from the subsurface components. The results show that the deep groundwater constitutes between 5 and 20% of the subsurface water discharge into the stream water. The highest values of the deep groundwater fraction occur during base flow. Soil water dominates during snowmelt seasons, whereas during base flow it is the least important fraction. Soil water accounts for 10–100% of the subsurface water discharge into the stream water. Shallow groundwater accounts for up to 80% of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow. The validity of the model was tested by comparing the measured 87Sr/86Sr ratios in the stream water with the 87Sr/86Sr ratios predicted by the model. There was a systematic difference between the measured and modelled 87Sr/86Sr ratios which suggests that the fraction of soil water is overestimated by the model, especially during spring flood. As a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period. However, it is concluded that the differences between measured and predicted values are relatively small, and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments.  相似文献   

4.
This paper explores the influence of a fluorine-rich granite on fluoride concentration in a small boreal catchment in northern Europe. The materials include stream water and shallow groundwater sampled in spatial and temporal dimensions, and analytical data on fluoride and a number of ancillary variables. Fluoride increased strongly towards the lower reaches of the catchment—at the stream outlet the concentrations were up to 4.2 mg L−1 and 1.6–4.7 times higher than upstream. Additionally, fluoride concentrations were particularly high in groundwater and small surface-water bodies (including quarries) above or in direct contact with the granite and showed a strong inverse correlation with water discharge in the stream. Taken together, these data and patterns pin-point the granite intrusion as the ultimate source, explaining the abundance and distribution of dissolved fluoride within the catchment. The granite most likely deliver fluoride to the stream by three mechanisms: (1) weathering of the fine fraction of glacial deposits, derived from the granite and associated fluorine-rich greisen alterations, (2) large relative input of baseflow, partially originating in the granite and greisen, into the lower reaches during low flow in particular, and (3) water-conducting fractures or fracture zones running through the fluorine-rich granite and greisen.  相似文献   

5.
We have collected and analyzed a larger set of stream waters for major ions and strontium isotopes in Taylor Valley, McMurdo Dry Valleys, Antarctica. These new data substantiate the concept that the dissolution of carbonate minerals is a significant source of strontium, even in polar desert environments where liquid water is primarily limited to stream channels. In Taylor Valley, most of the carbonate minerals present are the result of secondary processes, such as mineral precipitation and/or eolian deposition, and not through primary geologic sources, such as bedrock or till sources. In Von Guerard Stream (Lake Fryxell basin) and Andersen Creek (Lake Hoare basin), water samples were collected during the austral summer to determine short-term 87Sr/86Sr patterns. The observed variability in both time and space may be dependent on the relative amounts of primary and secondary carbonates present in the streambeds and hyporheic zone as well as contingent on the relative proportions of carbonate and aluminosilicate weathering.  相似文献   

6.
广汉市平原区浅层地下水化学演化及其控制因素   总被引：4，自引：0，他引：4  
为在广汉市城乡规划过程中提供地下水资源开发利用的基础信息,采用矿物风化系统分析、相关性分析、主成分分析和PhreeQC反向水文地球化学模拟等方法对广汉市平原区的浅层地下水的地下水水化学组分进行分析,确定了浅层地下水的水化学演化及控制因素,完成了地下水资源的质量及时空分布特征分析。分析表明：Gibbs图显示岩石风化主导该区地下水水化学特征,风化过程产生离子和次生矿物又经历水解作用,在矿物风化系统稳定场图中显示水样中铝硅酸盐矿物逐渐趋于溶解,碳酸盐矿物处于饱和状态;PhreeQC反向水文地球化学模拟结果显示在水流模拟路径上主要发生了钙蒙脱石、钾长石溶解和高岭石、石英、钠长石的沉淀,以及Ca-Na2之间的阳离子交换吸附作用;离子相关性和主成分分析进一步的验证了溶滤作用、蒸发浓缩作用和阳离子交换吸附作用是引起浅层地下水水化学过程和矿物组成改变的主要原因。研究区地下水水质总体不会对人体健康造成不良影响。  相似文献   

7.
Hydrogeochemical processes controlling surface water chemistry were examined in five small (<1.5 km 2) forested catchments that have contrasting bedrock lithologies of granite, and conglomerate, and are distributed in the southeast of Seto district, central Japan. Watersheds developed on these two bedrocks differ in their ability to neutralize atmospheric acid (pH ~4.5) deposition. The study was conducted to (1) characterize the hydrogeochemical processes controlling surface water chemistry, and (2) to elucidate acidification of spring and stream waters using data from three sampling campaigns conducted from August to October 2000. Stream and spring water solutes fall into two general groups according to concentration: alkaline, relatively high pH (5.2–7.7) and high cation concentrations (HCO 3 -, Cl -, base cations), and dilute, low pH (4.2–5.5) waters. Concentrations of trace metals (Al, Ba, Sr) showed a strong negative correlation with pH, suggesting the mobility of these metals in the dissolved load of catchments underlain by Tokai conglomerate. The strontium isotope ratio ( 87Sr/ 86Sr) of rock and soil, plant, precipitation, and surface water samples was used to identify different reservoirs within the ecosystem. Low Si concentrations in stream and spring waters from the conglomerate area, with a relatively high pool of SiO 2, >90 (wt%), suggest slow chemical weathering. The dissolved solute concentrations are generally of similar magnitude in stream waters within the catchments of similar bedrock lithology. The high inverse correlation ( r 2=0.72) between pH and SO 4 – concentrations and the high positive correlation ( r 2 =0.90) between Ba and SO 4 – concentrations in waters draining Tokai conglomerate suggest that barite (BaSO 4) is being dissolved in an acidic environment. The three catchments were identified as being sensitive to acidic deposition because the bedrock conglomerate provided little capacity to buffer acidic inputs. The soils from the granite area have a high cation-exchange capacity (CEC an average of 868 µmol/kg), and are nearly ten times greater than the soils from the conglomerate area. Because ion exchange, besides weathering, is the main source that counteracts soil acidification, the sensitivity to further acidification may increase.  相似文献   

8.
In this study, the chemical and Sr isotopic compositions of shallow groundwater and rainwater in the Ordos Desert Plateau, North China, and river water from the nearby Yellow River, are investigated to determine the dissolved Sr source and water–rock interactions, and quantify the relative Sr contribution from each end-member. Three groundwater systems have been identified, namely, GWS-1, GWS-2 and GWS-3 according to the watershed distribution in the Ordos Desert Plateau. Ca2+ and Mg2+ are the most dominant cations in GWS-1, while Na+ is dominant in GWS-3. In addition, there is more SO42− and less Cl− in GWS-1 than in GWS-3. The shallow groundwater in GWS-2 seems to be geochemically between that in GWS-1 and GWS-3. The 87Sr/86Sr ratios of the shallow groundwater are high in GWS-1 and GWS-2 and are low in GWS-3. By geochemically comparing the nearby Yellow River, local precipitation and deep groundwater, the shallow groundwater is recharged only by local precipitation. The ionic and isotopic ratios indicate that carbonate dissolution is an important process controlling the chemistry of the shallow groundwater. The intensity of the water–rock interactions varies among the three groundwater systems and even within each groundwater system. Three end-members controlling the groundwater chemistry are isotopically identified: (1) precipitation infiltration, (2) carbonate dissolution and (3) silicate weathering. The relative Sr contributions of the three end-members show that precipitation infiltration and carbonate dissolution are the primary sources of the shallow groundwater Sr in GWS-3 whereas only carbonate dissolution is responsible for the shallow groundwater Sr in GWS-1 and GWS-2. Silicate weathering seems insignificant towards the shallow groundwater's chemistry in the Ordos Desert Plateau. This study is helpful for understanding groundwater chemistry and managing water resources.  相似文献   

9.
地壳风化速率研究综述   总被引：6，自引：1，他引：6  
地壳风化速率研究的理论基础是质量守恒原理和溶液与矿物反应动力学法则。元素在风化过程中的行为受多种因素控制，主要包括基岩风化量、大气沉降量、径流量、生物的输出数量和人为输入量（如施肥）。硅酸盐矿物化学风化过程中，矿物与溶液之间总的化学反应速率是单个反应速率之和，其中涉及到 3个关键参数，即：酸中和能力（ANC）、基本阳离子/无机铝（BC/Al无机）比值和临界负荷（CL）。风化速率的研究主要采用四种方法，即PROFILE模型、基本阳离子损耗、元素输入-输出指数和Sr同位素比值等。PROFILE模型是一个稳定态的综合土壤化学模型，矿物的分解速率、矿物的暴露表面积、土壤水饱和度和土壤层厚度决定着该矿物的风化速率，总的风化速率为各种矿物的风化速率之和。元素损耗，主要是基本阳离子（Ca、Na、K和Mg）的损耗，假设Ti、 Zr和Nb在成土过程中含量稳定并不参与风化反应，那么对于给定的土壤层，化学风化损耗的基本阳离子可以通过比较土层与成土母质之间元素组成的差异来计算。输入-输出指数的假设前提是研究的流域处于稳定状态，一般认为输入指数是大气沉降，输出指数是河流搬运溶解部分、悬浮的非岩屑成因部分和生物营养净吸收部分。Sr同位素在生物和化学作用过程中并不分馏，不同生态系统阳离子场中Sr同位素组成是大气和矿物风化来源的Sr的混合物。  相似文献   

10.
Filtered subglacial meltwater samples were collected daily during the onset of melt (May) and peak melt (July) over the 2011 melt season at the Athabasca Glacier (Alberta, Canada) and analyzed for strontium-87/strontium-86 (87Sr/86Sr) isotopic composition to infer the evolution of subglacial weathering processes. Both the underlying bedrock composition and subglacial water–rock interaction time are the primary influences on meltwater 87Sr/86Sr. The Athabasca Glacier is situated atop Middle Cambrian carbonate bedrock that also contains silicate minerals. The length of time that subglacial meltwater interacts with the underlying bedrock and substrate is a predominant determining factor in solute concentration. Over the course of the melt season, increasing trends in Ca/K and Ca/Mg correspond to overall decreasing trends in 87Sr/86Sr, which indicate a shift in weathering processes from the presence of silicate weathering to primarily carbonate weathering.Early in the melt season, rates of carbonate dissolution slow as meltwater approaches saturation with respect to calcite and dolomite, corresponding to an increase in silicate weathering that includes Sr-rich silicate minerals, and an increase in meltwater 87Sr/86Sr. However, carbonate minerals are preferentially weathered in unsaturated waters. During the warmest part of a melt season the discharged meltwater is under saturated, causing an increase in carbonate weathering and a decrease in the radiogenic Sr signal. Likewise, larger fraction contributions of meltwater from glacial ice corresponds to lower 87Sr/86Sr values, as the meltwater has lower water–rock interaction times in the subglacial system. These results indicate that although weathering of Sr-containing silicate minerals occurs in carbonate dominated glaciated terrains, the continual contribution of new meltwater permits the carbonate weathering signal to dominate.  相似文献   

11.
The groundwater chemistry of 14 shallow wells and 10 springs in Halland, southwest Sweden, and precipitation have been studied in trilinear diagrams. Ionic strength and saturation index (SI) for selected minerals have been calculated. Five springwaters have similar chemical composition to that of the precipitation, which indicates surficial and rapidly recharged water. The SI of the groundwaters is out of equilibrium (undersaturated) with respect to primary silicates such as mafic minerals, feldspar, K-mica and chlorite, but in equilibrium with solid SiO2 (quartz, cristobalite, or chalcedony). The SI shows oversaturation conditions for kaolinite, hydroxy-Al interlayered vermiculite, Na,K,Mg-beidellite, Mg-montmorillonite, and AB-montmorillonite. Concentrations of soluble Al and Si can be governed by Mg,Fe-beidellite, BF-montmorillonite, or Ca-montmorillonite at four springs, and by halloysite at two wells on the coastal plain. For these groundwaters, clay minerals may act as H+ buffers and thus have an influence on pH and toxic Al, i.e., parameters affecting the drinking water quality and environment. The study shows that the soil catena are intensily weathered at the investigated sites. It is further concluded that neither cation exchange nor primary silicate weathering will keep up with buffering the acidic loads into the soils. A general prediction of groundwater quality is presented.  相似文献   

12.
The relationship between subglacial chemical weathering processes and the Sr isotope composition of runoff from Robertson Glacier, Alberta, Canada, is investigated. This glacier rests on predominantly carbonate bedrock of Upper Devonian age, but silicate minerals are also present. The provenance of solute in meltwaters is found to vary systematically with solute concentration and, by inference, subglacial water residence time. In dilute waters, the principal process of solute acquisition is calcite dissolution fueled by protons derived from the dissolution of CO2 and subsequent dissociation of carbonic acid. At higher solute concentrations, dolomite dissolution coupled to sulfide oxidation is more important. Sr concentration is found to increase with total solute concentration in two separate meltwater streams draining from the glacier, but 87Sr/86Sr only increases in the eastern melt stream. Carbonate and K-feldspar sources are shown to dominate the Sr content of the western stream, irrespective of concentration. They also dominate the Sr content of the eastern stream at low and intermediate concentrations, but at higher concentrations, muscovite (with high 87Sr/86Sr) is also an important Sr source. This reflects the outcrop of muscovite-bearing lithologies in the catchment of the eastern stream and an increase in the rate of weathering of K-silicates relative to that of carbonates as more concentrated solutions approach saturation with respect to carbonates. Nonstoichiometric release of 87Sr/86Sr and preferential release of Sr over K from freshly ground K-silicate surfaces may also occur. This may help to explain the radiogenic nature of runoff from distributed subglacial drainage systems, which are characterized by long water:rock contact times and water flow through environments in which crushing and grinding of bedrock are active processes.Although the exchangeable Sr in tills has higher 87Sr/86Sr than local carbonate bedrock, only the more concentrated meltwaters from the eastern stream display similarly high values. The most dilute waters, which probably transport the bulk of the dissolved Sr flux from the glacier, have 87Sr/86Sr characteristic of local carbonate bedrock. Thus, the results suggest that although enhanced weathering of silicate minerals containing radiogenic Sr (such as muscovite) does occur in glaciated carbonate terrains, it is unlikely to contribute to any enhanced flux of radiogenic Sr from glaciated continental surfaces to the oceans.  相似文献   

13.
River water composition (major ion and 87Sr/86Sr ratio) was monitored on a monthly basis over a period of three years from a mountainous river (Nethravati River) of southwestern India. The total dissolved solid (TDS) concentration is relatively low (46 mg L−1) with silica being the dominant contributor. The basin is characterised by lower dissolved Sr concentration (avg. 150 nmol L−1), with radiogenic 87Sr/86Sr isotopic ratios (avg. 0.72041 at outlet). The composition of Sr and 87Sr/86Sr and their correlation with silicate derived cations in the river basin reveal that their dominant source is from the radiogenic silicate rock minerals. Their composition in the stream is controlled by a combination of physical and chemical weathering occurring in the basin. The molar ratio of SiO2/Ca and 87Sr/86Sr isotopic ratio show strong seasonal variation in the river water, i.e., low SiO2/Ca ratio with radiogenic isotopes during non-monsoon and higher SiO2/Ca with less radiogenic isotopes during monsoon season. Whereas, the seasonal variation of Rb/Sr ratio in the stream water is not significant suggesting that change in the mineral phase being involved in the weathering reaction could be unlikely for the observed molar SiO2/Ca and 87Sr/86Sr isotope variation in river water. Therefore, the shift in the stream water chemical composition could be attributed to contribution of ground water which is in contact with the bedrock (weathering front) during non-monsoon and weathering of secondary soil minerals in the regolith layer during monsoon. The secondary soil mineral weathering leads to limited silicate cation and enhanced silica fluxes in the Nethravati river basin.  相似文献   

14.
The Ballenera Creek has 160 km2 being a small catchment in the Pampa Plain in Argentina. This area has been deeply modified by human action through agricultural activities. From 2013 to 2017, electrical conductivity, stable isotopes of water and nitrate concentration monitoring program were conducted. The sampling included weekly and bimonthly samples in two sites along the stream, several groundwater wells and monthly precipitation. Chemical and isotopic tracers are used to discriminate the streamflow components and to evaluate their incidence in the nitrate concentration. The easiest conceptual model for gaining streams contemplates two main elements: direct runoff and groundwater (baseflow and pre-event water). The direct runoff has the lowest electrical conductivity and 18Ow variable content. The baseflow component is characterized by the highest electrical conductivity and isotope composition quite constant. Finally, pre-event water has an intermediate electrical conductivity and isotopic content close to the rainfall-weighted average composition. The nitrate concentration obtained was in general related to the different stream stages and was a useful indicator to evaluate the fertilization in agricultural zones.  相似文献   

15.
Hydrogeochemistry and isotopes were used to understand the origin and geochemical evolution in the Habor Lake Basin, northwestern China. Groundwater samples were taken, and the isotopic compositions δD, δ18O and major ions were analyzed. The groundwater can be divided into three types: the Quaternary groundwater, the shallow Cretaceous groundwater and the deep Cretaceous groundwater. The groundwater chemistry is mainly controlled by the feldspar weathering and dolomite weathering, the dissolution of Glauber’s salt, and cation exchange. Chemistry of lake water is mainly controlled by evaporation and precipitation. The stable isotopes of oxygen and hydrogen in groundwater cluster along the local meteoric water line, indicating that groundwater is of meteoric origin. Comparing with shallow groundwater, deep groundwater is depleted in heavy isotopes indicating that deep groundwater was recharged during late Pleistocene and Holocene, during which the climate was more wetter and colder than today.  相似文献   

16.
Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10?5 m/s. Discharge was estimated at 1.28×10?3 km3. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10?5–2.0×10?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10?9–2.0×10?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system.  相似文献   

17.
Determining the relative proportions of silicate vs. carbonate weathering in the Himalaya is important for understanding atmospheric CO2 consumption rates and the temporal evolution of seawater Sr. However, recent studies have shown that major element mass-balance equations attribute less CO2 consumption to silicate weathering than methods utilizing Ca/Sr and 87Sr/86Sr mixing equations. To investigate this problem, we compiled literature data providing elemental and 87Sr/86Sr analyses for stream waters and bedrock from tributary watersheds throughout the Himalaya Mountains. In addition, carbonate system parameters (PCO2, mineral saturation states) were evaluated for a selected suite of stream waters. The apparent discrepancy between the dominant weathering source of dissolved major elements vs. Sr can be reconciled in terms of carbonate mineral equilibria. Himalayan streams are predominantly Ca2+-Mg2+-HCO3− waters derived from calcite and dolomite dissolution, and mass-balance calculations demonstrate that carbonate weathering contributes ∼87% and ∼76% of the dissolved Ca2+ and Sr2+, respectively. However, calculated Ca/Sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock, suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and PCO2 gradients in the Himalaya.The state of calcite and dolomite saturation was evaluated across these gradients, and the data show that upon descending through the Himalaya, ∼50% of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas CO2. Stream water Ca/Mg and Ca/Sr ratios decrease as the degree of supersaturation with respect to calcite increases, and Mg2+, Ca2+, and HCO3− mass balances support interpretations of preferential Ca2+ removal by calcite precipitation. On the basis of patterns of saturation state and PCO2 changes, calcite precipitation was estimated to remove up to ∼70% of the Ca2+ originally derived from carbonate weathering. Accounting for the nonconservative behavior of Ca2+ during riverine transport brings the Ca/Sr and 87Sr/86Sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock, thereby permitting consistency between elemental and Sr isotope approaches to partitioning stream water solute sources. These results resolve the dissolved Sr2+ budget and suggest that the conventional application of two-component Ca/Sr and 87Sr/86Sr mixing equations has overestimated silicate-derived Sr2+ and HCO3− fluxes from the Himalaya. In addition, these findings demonstrate that integrating stream water carbonate mineral equilibria, divalent cation compositional trends, and Sr isotope inventories provides a powerful approach for examining weathering fluxes.  相似文献   

18.
Germanium-silicon (Ge/Si) ratios were determined on quartz diorite bedrock, saprolite, soil, primary and secondary minerals, phytolith, soil and saprolite pore waters, and spring water and stream waters in an effort to understand Ge/Si fractionation during weathering of quartz diorite in the Rio Icacos watershed, Puerto Rico. The Ge/Si ratio of the bedrock is 2 μmol/mol, with individual primary mineral phases ranging between 0.5 and 7 μmol/mol. The ratios in the bulk saprolite are higher (∼3 μmol/mol) than values measured in the bedrock. The major saprolite secondary mineral, kaolinite, has Ge/Si ratios ranging between 4.8 and 6.1 μmol/mol. The high Ge/Si ratios in the saprolite are consistent with preferential incorporation of Ge during the precipitation of kaolinite. Bulk shallow soils have lower ratios (1.1-1.6 μmol/mol) primarily due to the residual accumulation of Ge-poor quartz.Ge/Si ratios measured on saprolite and soil pore waters reflect reactions that take place during mineral transformations at discrete depths. Spring water and baseflow stream waters have the lowest Ge/Si ratios (0.27-0.47 μmol/mol), reflecting deep initial weathering reactions resulting in the precipitation of Ge-enriched kaolinite at the saprolite-bedrock interface. Mass-balance calculations on saprolite require significant loss of Si and Al even within 1 m above the saprolite-bedrock interface. Higher pore water Ge/Si ratios (∼1.2 μmol/mol) are consistent with partial dissolution of this Ge-enriched kaolinite. Pore water Ge/Si ratios increase up through the saprolite and into the overlying soil, but never reach the high values predicted by mass balance, perhaps reflecting the influence of phytolith recycling in the shallow soil.  相似文献   

19.
Evaluation of major ion chemistry and solute acquisition process controlling water chemical composition were studied by collecting a total of fifty-one groundwater samples in shallow (<25 m) and deep aquifer (>25 m) in the Varanasi area. Hydrochemical facies, Mg-HCO3 dominated in the largest part of shallow groundwater followed by Na-HCO3 and Ca-HCO3 whereas Ca-HCO3 is dominated in deep groundwater followed by Mg-HCO3 and Na-HCO3. High As concentration (>50 μg/l) is found in some of the villages situated in northeastern parts (i.e. adjacent to the concave part of the meandering Ganga river) of the Varanasi area. Arsenic contamination is confined mostly in tube wells (hand pump) within the Holocene newer alluvium deposits, whereas older alluvial aquifers are having arsenic free groundwater. Geochemical modeling using WATEQ4F enabled prediction of saturation state of minerals and indicated dissolution and precipitation reactions occurring in groundwater. Majority of shallow and deep groundwater samples of the study area are oversaturated with carbonate bearing minerals and under-saturated with respect to sulfur and amorphous silica bearing minerals. Sluggish hydraulic conductivity in shallow aquifer results in higher mineralization of groundwater than in deep aquifer. But the major processes in deep aquifer are leakage of shallow aquifer followed by dominant ion-exchange and weathering of silicate minerals.  相似文献   

20.
《Applied Geochemistry》1999,14(7):939-951
Strontium isotope ratios are used to identify end-member ground-water compositions at Äspö in southeastern Sweden where the Hard Rock Laboratory (HRL) has been constructed to evaluate the suitability of crystalline rock for the geologic disposal of nuclear waste. The Hard Rock Laboratory is a decline (tunnel) constructed in 1.8 Ga-old granitic rock that forms islands in an archipelago along the Swedish coast. Ground-water samples were obtained for isotopic analyses from boreholes drilled from the surface and from side boreholes drilled within the HRL. Infiltration at Äspö occurs primarily through fractures zones in the granitic bedrock beneath thin soils throughout the area. Because of extremely low Sr concentrations, rain and snow are not important contributors to the Sr isotope budget of the ground-water system. At shallow levels, water percolating downward along fractures and fracture zones acquires a δ87Sr between +9.5 and +10.0‰ and maintains this value downward while Sr concentrations increase by two orders of magnitude. Ground-water samples from both boreholes and from in the HRL show the effects of mixing with saline waters containing as much as 59 mg/L Sr and δ87Sr values as large as +13.9‰. Baltic Sea water is a potential component of the groundwater system with δ87Sr values only slightly larger than modern marine values (+0.3‰) but with much lower concentrations (1.5 mg/L) than ocean water (8 mg/L). However, because of large Sr concentration differences between the saline groundwater (59 mg/L) and Baltic Sea water (1.5 mg/L), δ87Sr values are not particularly sensitive indicators of sea-water intrusion even though their δ87Sr values differ substantially.  相似文献   

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