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1.
The geochemical and isotopic compositions of river water are controlled by different factors. The seasonal and spatial variations in the geochemical composition, δD, δ18O, and δ15N–NO3 of the Kumho River were investigated to reveal the geochemical processes occurring at different seasons. The Kumho River, which runs through different geologic terrains with different land use characteristics, is the largest tributary of the Nakdong River, the longest river in South Korea. The data varied significantly according to the land use and the season. Each monitoring station showed the lowest concentrations of various ions during July, the rainy season, due to the increase of precipitation rate. The ionic concentrations gradually increased downstream by the mineral weathering and anthropogenic activity. At the upper regions of the river, Ca and HCO3, which are closely associated with mineral weathering, were the most dominant cation and anion, respectively. The relatively high Si concentration of the headwater samples, caused by the weathering of volcanic rocks, also showed the importance of weathering in the upper regions mainly composed of volcanic rocks. The downstream regions of the Kumho River are mainly influenced by sedimentary rocks. At the lower reaches of the river, especially near the industrial complexes in Daegu, the third largest city in Korea, Na, Cl, and SO4 became the dominant ions, indicating that the anthropogenic pollution became more important in regulating the chemical composition of the river. The increasing (Ca + Mg + Na + K)/HCO3 ratio downstream also indicates that the anthropogenic effects became more important as the river flows downstream. The isotopic compositions of δD and δ18O indicate that the river waters were significantly affected by evaporation during May and July, but the evaporation effect was relatively low during October. The isotopic composition of δ15N–NO3 increased downstream, also confirming that anthropogenic effects became more significant at the lower reach of the river and near Daegu.  相似文献   

2.
River waters play a significant role in supplying naturally- and anthropogenically-derived materials to Lake Qinghai, northeastern Tibetan Plateau. To define the sources and controlling processes for river water chemistry within the Lake Qinghai catchment, high precision ICP-MS trace element concentrations were measured in water samples collected from the Buha River weekly in 2007, and from other major rivers in the post-monsoon (late October 2006) and monsoon (late July 2007) seasons. The distributions of trace elements vary in time and space with distinct seasonal patterns. The primary flux in the Buha River is higher TDS and dissolved Al, B, Cr, Li, Mo, Rb, Sr and U during springtime than those during other seasons and is attributed to the inputs derived from both rock weathering and atmospheric processes. Among these elements, the fluxes of dissolved Cr, B and Rb are strongly influenced by eolian dust input. The fluxes of dissolved Li, Mo, Sr and U are also influenced by weathering processes, reflecting the sensitivity of chemical weathering to monsoon conditions. The anthropogenic sources appear to be the dominant contribution to potentially harmful metals (Ni, Cu, Co, Zn and Pb), with high fluxes at onset of the main discharge pulses due, at least partially, to a runoff washout effect. For other major rivers, except for Ba, concentrations of trace elements are higher in the monsoon than in the post-monsoon season. A total of 38.5 ± 3.1 tons of potentially harmful elements are transported into the lake annually, despite human activities within the catchment being limited. Nearly all river water samples contain dissolved trace elements below the World Health Organization guidelines for drinking water, with the exception of As and B in the Daotang River water samples collected in late July probably mobilized from underlying lacustrine sediments.  相似文献   

3.
Shoreline carbonate deposits of Pleistocene Lake Bonneville record the conditions and processes within the lake, including the evaporative balance as well as vertical and lateral chemical and isotopic gradients. Tufas (swash‐zone) and tufaglomerates (cemented, subaqueous colluvium or beachrock) on multiple, well‐developed shorelines near the Silver Island Range, Utah, also present an opportunity to examine physicochemical lake processes through time. Three shorelines are represented by carbonate deposits, including the 23–20 ka Stansbury stage, 15–14.5 ka Bonneville stage, and 14.5–14 ka Provo stage. Mean δ18OVSMOW values of all three shorelines are statistically indistinguishable ( ～ 27 ± 1‰), when a few Bonneville samples of unusual composition are neglected. However, differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water. Second, in order to sustain a much smaller, shallower lake during the colder Stansbury stage, the climate must have also been relatively dry. Third, δ18O values in tufa are higher than tufaglomerate by ～ 0.5‰, consistent with greater evaporative enrichment of lake water in the swash zone. Fourth, mean δ13C values for the Provo, Stansbury and Bonneville shorelines (4.4, 5.0 and 5.2‰, respectively) show that carbon species were dominated by atmospheric exchange, with the variations produced by differences in the oxidation of organic matter. Comparisons of shoreline carbonates with deep‐lake marls of the same approximate age indicate that shoreline carbonate was much higher in δ13C and δ18O values (both ～ 2.5‰) during Bonneville time, whereas isotopic differences were minor (both ～ 1‰) in Stansbury time. In particular, the Bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on δ18O values. In contrast, the lake during the much shallower Stansbury stage may have been well mixed. Differences in the primary mineralogy (Stansbury and Bonneville, aragonite > calcite; Provo, calcite > aragonite) reflect profound differences in lake chemistry in terms of open versus closed‐basin lakes. The establishment of a continuous outlet during Provo time probably reduced the Mg2+/Ca2+ ratio of lake water. Curiously, regardless of primary mineralogy, tufaglomerate cements are enriched in Na+ and Cl? and depleted in Mg2+ relative to capping tufa of the same age. This probably reflects vital or kinetic effects in the swash zone (tufa). We suspect that ‘abiotic’ effects may have been important in the dark pore space of developing tufaglomerate, where the absence of light suppressed photosynthesis. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

4.
Zn and Pb smelters are the major contributors to Zn and Pb emissions among all anthropogenic sources, thus, it is essential to understand Zn isotopic variations within the context of metallurgical industries, as well as its fractionation in different environments impacted by smelting activities. This mini review outlines the current state of knowledge on Zn isotopic fractionation during the high-temperature roasting process in Zn and Pb refineries; δ66Zn values variations in air emissions, slags and effluents from the smelters in comparison to the geogenic Zn isotopic signature of ores formation and weathering. In order to assess the environmental impact of these smelters, the available and measured δ66Zn values are compiled for smelter impacted natural water bodies (groundwater, stream and river water), sediments (lake and reservoir) and soils (peat bog soil, inland soil). Finally, the discussion is extended to the fractionation induced during numerous physicochemical reactions and transformations, i.e. adsorption, precipitation as well as both inorganic and organic surface complexation.  相似文献   

5.
The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the Ganga River, draining nearly 30,500 km2 area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about 335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the alluvial plain rivers. This study establishes that elevated 87Sr/86Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain.  相似文献   

6.
Natural and anthropogenic impacts on dissolved inorganic carbon (DIC) within an urban river, Nanming River in southwestern China, were investigated using hydrochemistry and carbon isotopic compositions of dissolved inorganic carbon (δ13CDIC). Because of the anthropogenic inputs, generally, the TDS values and major ionic compositions showed an increasing trend along the mainstream. The TDS values and most of the dissolved solutes compositions showed a dilution effect during storms, but the dilution effect did not strictly follow the theoretical dilution curve. Lighter δ13CDIC values in the river after a rainstorm reflected the influx of rain water with biological CO2 during the rain event. Meanwhile, the negative relationship between δ13CDIC values and dissolved inorganic carbon concentrations in the mainstream at different sampling campaigns suggested significant degradation of organic matter in the riverine channels. The variabilities of DIC in an urban river were mainly impacted by biological activities and infiltration of soil carbon dioxide. This study demonstrated that hydrological events and anthropogenic inputs are the main controls on the variations of dissolved solutes compositions and the DIC dynamics for an urban river.  相似文献   

7.
《Applied Geochemistry》1997,12(5):607-623
The aim of this study is to characterize the processes and phases which control migration and retention of rare earth elements (REE) in a heavy metal contaminated soil. In addition to concentration data, we used Pb, Sr and Nd isotopic compositions in order to distinguish between natural and anthropogenic trace metals and to characterize the phases leached away during the sequential extraction procedure.The samples were sequentially extracted in 3 steps with 1 N acetic acid (HAc), 1 N HCl and 1 N HNO3. The Pb isotope data showed that anthropogenic Pb had mainly been retained in the uppermost 10 cm by the organic matter of the topsoil. The87Sr/86Sr ratios of the HAc extracts are almost constant and indicate that soil carbonate is derived from regionally outcropping carbonate-rich sediments. Most HCl and HNO3 extracts have more radiogenic Sr isotopic compositions, but it is unclear whether this reflects a growing influence of anthropogenic or silicate-derived Sr.The depth distribution of the REE is mainly controlled by two different parameters: soil pH for the HAc extractable REE and FeMn oxides for the REE in the HCl and HNO3 extracts. A part of the HNO3 extractable REE was also bound to the organic matter of the topsoil. The REE concentrations in the HAc extractable phase increase with depth and increasing soil pH, which indicates that they are derived from the surface and hence are of anthropogenic origin. This is confirmed by143Nd/144Nd isotope ratios which show a mixing between a natural end-member at the top and an anthropogenic end-member at the base of the profile. We assume that the anthropogenic REE were transported in dissolved form as carbonate complexes and then precipitated during downward migration as soil pH increased.  相似文献   

8.
Sr and Nd isotopes were applied to 5 soil profiles from the Muravera area, in south-eastern Sardinia.All the soils, which have developed during the Quaternary on the Lower Paleozoic metamorphic basement except for one on Eocene carbonates, are located far from major sources of pollution. Therefore, they are suitable for testing pedogenic processes and geochemical evolution to benefit for environmental studies.The Sr isotopic ratios range largely (δ87Sr = 1.7–65.9‰), even in each soil profile. In particular, the observed increase of δ87Sr with depth in the most of the metamorphic rock-based soils can be accounted for by the downward decrease of Sr contributions from organic matter and Saharan dust, both displaying lower isotopic ratios than the soil bedrocks. The carbonate rock-based soil exhibits δ87Sr higher (1.7–18.1‰) than the bedrock, indicating a significant contribution of radiogenic Sr from the siliciclastic fraction of the soil, and probably from dust input. The Nd isotopic ratios are slightly variable through the profiles (ɛNd from −7.8 to −14.5), confirming little mobility of Nd and Sm during the pedogenesis. Among the minerals present in the soils, phosphates, albite, and calcite are those important in providing low radiogenic Sr and Nd to organic matter of the soils.Lastly, this isotopic study has in particular allowed for evaluating the potential proportion of contribution of Saharan dust to south-eastern Sardinia, thus corroborating the findings of other studies related to soils from the central-western Mediterranean.  相似文献   

9.
In order to better understand the relative importance of hydrologic variation and anthropogenic disturbance and their complex interactions within the trace elemental geochemical cycle, water samples were collected monthly over 1 year in the Min River, eastern Tibetan Plateau, and analyzed for trace element composition. The dissolved trace elements exhibited different relationships with increasing discharge compared with major elements. The elements analyzed can be divided into three groups according to their behavior in response to changing discharge: (1) elements that showed weak positive correlation with discharge, e.g. Cu, V, and Ba; (2) elements that exhibited weak negative correlation with discharge, including Rb, Sr, Pb, Sb, Zn, Cr, Cd, and U; and (3) elements that displayed no significant correlation with variation in discharge, e.g. Ti, Fe, Co, Ni, and As. Cu was strongly affected by anthropogenic activities and flushed into the river with increasing discharge. Ba has a strong solubility in the terrestrial environment, dissolved quickly, and was released into the river. The positive relationship between V concentration and discharge may be attributed to secondary reactions, such as precipitation and adsorption on oxides and aluminosilicate clays. Conservative behavior had an impact on the geochemical behavior of Sr and Rb across hydrologic variation. Pb, Zn, Sb, Cd, and Cr underwent a mild dilution effect connected with anthropogenic activities. The chemostatic behavior of U was regulated by carbonate dissolution and biological uptake. In addition, higher temperatures enhanced biotic activities, affecting the concentrations of Fe and Ni. The relationship between power law slopes and coefficient of variation for discharge and solute concentration suggests that concentrations of trace elements vary significantly with increasing discharge compared with major elements. Silicate mineral weathering had less effect on the fluvial solutes with increasing discharge. Mining activity may exert an additional control on concentration–discharge dynamics of anthropogenic trace elements.  相似文献   

10.
The chemical and isotopic (87Sr/86Sr, δ11B, δ34Ssulfate, δ18Owater, δ15Nnitrate) compositions of water from the Lower Jordan River and its major tributaries between the Sea of Galilee and the Dead Sea were determined in order to reveal the origin of the salinity of the Jordan River. We identified three separate hydrological zones along the flow of the river:
(1)
A northern section (20 km downstream of its source) where the base flow composed of diverted saline and wastewaters is modified due to discharge of shallow sulfate-rich groundwater, characterized by low 87Sr/86Sr (0.7072), δ34Ssulfate (−2‰), high δ11B (∼36‰), δ15Nnitrate (∼15‰) and high δ18Owater (−2 to-3‰) values. The shallow groundwater is derived from agricultural drainage water mixed with natural saline groundwater and discharges to both the Jordan and Yarmouk rivers. The contribution of the groundwater component in the Jordan River flow, deduced from mixing relationships of solutes and strontium isotopes, varies from 20 to 50% of the total flow.
(2)
A central zone (20-50 km downstream from its source) where salt variations are minimal and the rise of 87Sr/86Sr and SO4/Cl ratios reflects predominance of eastern surface water flows.
(3)
A southern section (50-100 km downstream of its source) where the total dissolved solids of the Jordan River increase, particularly during the spring (70-80 km) and summer (80-100 km) to values as high as 11.1 g/L. Variations in the chemical and isotopic compositions of river water along the southern section suggest that the Zarqa River (87Sr/86Sr∼0.70865; δ11B∼25‰) has a negligible affect on the Jordan River. Instead, the river quality is influenced primarily by groundwater discharge composed of sulfate-rich saline groundwater (Cl-=31-180 mM; SO4/Cl∼0.2-0.5; Br/Cl∼2-3×10-3; 87Sr/86Sr∼0.70805; δ11B∼30‰; δ15Nnitrate ∼17‰, δ34Ssulfate=4-10‰), and Ca-chloride Rift valley brines (Cl-=846-1500 mM; Br/Cl∼6-8×10-3; 87Sr/86Sr∼0.7080; δ11B>40‰; δ34Ssulfate=4-10‰). Mixing calculations indicate that the groundwater discharged to the river is composed of varying proportions of brines and sulfate-rich saline groundwater. Solute mass balance calculations point to a ∼10% contribution of saline groundwater (Cl−=282 to 564 mM) to the river. A high nitrate level (up to 2.5 mM) in the groundwater suggests that drainage of wastewater derived irrigation water is an important source for the groundwater. This irrigation water appears to leach Pleistocene sediments of the Jordan Valley resulting in elevated sulfate contents and altered strontium and boron isotopic compositions of the groundwater that in turn impacts the water quality of the lower Jordan River.
  相似文献   

11.
 Heavy metal and metalloid concentrations within stream-estuary sediments (<180-μm size fraction) in north-eastern New South Wales largely represent natural background values. However, element concentrations (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Zn) of Hunter River sediments within the heavily industrialized and urbanized Newcastle region exceed upstream background values by up to one order of magnitude. High element concentrations have been found within sediments of the Newcastle Harbour and Throsby Creek which drains into urbanized and light industry areas. Observed Pb enrichments and low 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb ratios are likely caused by atmospheric deposition of Pb additives from petrol and subsequent Pb transport by road run-off waters into the local drainage system. Sediments of the Richmond River and lower Manning, Macleay, Clarence, Brunswick and Tweed River generally display no evidence for anthropogenic heavy metal and metalloid contamination (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Zn). However, the rivers and their tributaries possess localized sedimentary traps with elevated heavy metal concentrations (Cu, Pb, Zn). Lead isotope data indicate that anthropogenic Pb provides a detectable contribution to investigated sediments. Such contributions are evident at sample sites close to sewage outlets and in the vicinity of the Pacific Highway. In addition, As concentrations of Richmond River sediments gradually increase downstream. This geochemical trend may be the result of As mobilization from numerous cattle-dip sites within the region into the drainage system and subsequent accumulation of As in downstream river and estuary sediments. Received: 5 September 1997 · Accepted: 4 November 1997  相似文献   

12.
We report Zn isotopic ratios (δ66Zn) of river suspended particulate matter (SPM) and floodplain deposits (FD) from the Seine basin, France, with a precision ?0.05‰. A decrease in δ66Zn from 0.30‰ to 0.08‰ is observed in SPM from the upstream to downstream parts of the fluvial system, associated with an increase in Zn concentration from 100 ppm to 400 ppm. The Zn/Al of SPM at the river mouth is up to five times greater than the Zn/Al of the natural background, and by normalizing to the later value we define a Zn enrichment factor. Suspended sediments from a temporal series of samples collected in Paris display a similar variation in δ66Zn of between 0.08‰ and 0.26‰, while showing an inverse relationship between the Zn enrichment factor and δ66Zn. The amount of Zn transported as suspended load varies from 10% to 90%, as a function of increasing discharge. The δ66Zn of SPM and the dissolved load are correlated, suggesting that adsorption processes are probably not the dominant process by which the Zn enrichment of SPM takes place. Instead, we interpret our data as reflecting the mixture of two main populations of suspended particles with distinct δ66Zn. The first is characteristic of natural silicate particles transported by erosion processes to the river, while the second likely represents anthropogenic particles derived from wastewater treatment plants or combined sewer overflows. Based on isotopic ratios, we calculate that 70% of Zn in SPM of the Seine River in Paris is of anthropogenic origin.  相似文献   

13.
Sequential leaching experiments were made on Recent glauconies and clay fractions of the associated mud from off-shore Africa near the estuary of the Congo River. Analyses of major/rare earth elements (REE) and Nd isotopic compositions on the resulting leachate and residue pairs allow identification of at least three important and isotopically distinct components which contributed to the glauconitization process: (1) a detrital component with relatively high 87Sr/86Sr and relatively low 143Nd/144Nd isotopic ratios; (2) a phosphate phase rich in REE and Sr with sea water Sr and Nd isotopic characteristics; (3) a component rich in organic matter and Ca with a sea water Sr isotopic signature, a relatively low Nd isotopic composition and elevated Sm/Nd ratios. This latter component probably represents the suspended organic and carbonate-rich river load. The detrital and the river components were mixed up in the muddy off-shore sediment, ingested by worms, and integrated into faecal pellets. The resulting material has Sr and Nd isotopic signatures intermediate between those of the detrital and river components, and represents the precursor of the glaucony minerals. During the subsequent dissolution-crystallization process, the glauconitic pellets remain isotopically closed to any external supply, but expulsion of Sr and Nd with increasing degree of maturation is observed without any effect on the Sr and Nd isotopic compositions. At a higher maturation stage (K2O>4.5%), the Sr and Nd isotopic compositions tend to decrease and increase, respectively, approximating the isotopic composition values of the phosphate-rich phase. Because the Sr and Nd concentrations decrease, the evolution of the glauconies toward lower Sr and higher Nd isotopic compositions can only be explained by expulsion of Sr and Nd of the detrital component with high Sr and low Nd isotopic signatures. Dissolution of the chemically unstable, wormdigested clay material from mud may be responsible for the liberation of these elements. Consequently, the phosphate-rich phase with sea water Sr and Nd isotopic signatures becomes increasingly important for the isotopic characteristics of the maturing glauconite grains, and sea water isotopic signatures can be reached during the stage of mature glauconite (K2O>6.5%), without chemical exchange with the depositional environment.  相似文献   

14.
阿坝州位于四川西北部,与青海、甘肃交界,处于高海拔地区;该地区地表水资源丰富,长江与黄河上游水系均流经该区域。通过系统性采集区内河水(76件)、井水(7件)、溪水(8件)等样品,测试水体中D与18O的丰度与微量元素含量。结果表明:①受大气降水与流经地层的影响,阿坝地区河水中D与18O的丰度均显著高于溪水、井水与自来水等介质,线性相关性表明,河水中18O的富集与硫酸盐矿物的溶解密切相关;②阿坝地区井水、自来水、溪水之间存在明显的水力联系;③对于阿坝地区而言,黄河上游河流中δD与δ18O值均高于长江上游水系河流,但两者之间差别较小,这由于同一地区水系具有相同的大气降水来源;④河水、井水、溪水等表水中微量元素呈高Ba、Zn、Cr,低As、Pb、Cd的特点,与该地区岩石样品中微量元素特征基本一致,表明该地区表水中微量元素含量主要受地质背景因素控制。  相似文献   

15.
The chemical and isotopic characteristics of the water and suspended particulate materials（SPM） in the Yangtze River were investigated on the samples collected from 25 hydrological monitoring stations in the mainsteam and 13 hydrological monitoring stations in the major tributaries during 2003 to 2007. The water samples show a large variation in both δD（ 30‰ to 112‰） and δ18O（ 3.8‰ to 15.4‰） values. Both δD and δ18O values show a decrease from the river head to the Jinsha Jiang section and then increase downstream to the river mouth. It is found that the oxygen and hydrogen isotopic compositions of the Yangtze water are controlled by meteoric precipitation, evaporation, ice（and snow） melting and dam building. The Yangtze SPM concentrations show a large variation and are well corresponded to the spatial and temporal changes of flow speed, runoff and SPM supply, which are affected by the slope of the river bed, local precipitation rate, weathering intensity, erosion condition and anthropogenic activity. The Yangtze SPM consists of clay minerals, clastic silicate and carbonate minerals, heavy minerals, iron hydroxide and organic compounds. From the upper to lower reaches, the clay and clastic silicate components in SPM increase gradually, but the carbonate components decrease gradually, which may reflect changes of climate and weathering intensity in the drainage area. Compared to those of the upper crust rocks, the Yangtze SPM has lower contents of SiO2, CaO, K2 O and Na2 O and higher contents of TFe2 O3 and trace metals of Co, Ni, Cu, Zn, Pb and Cd. The ΣREE in the Yangtze SPM is also slightly higher than that of the upper crust. From the upper to lower reaches, the CaO and MgO contents in SPM decrease gradually, but the SiO2 content increases gradually, corresponding to the increase of clay minerals and decrease of the carbonates. The δ30SiSPM values（ 1.1‰ to 0.3‰） of the Yangtze SPM are similar to those of the average shale, but lower than those of the granite rocks（ 0.3‰ to 0.3‰）, reflecting the effect of silicon isotope fractionation in silicate weathering process. The δ30SiSPM values of the Yangtze SPM show a decreasing trend from the upper to the middle and lower reaches, responding to the variation of the clay content. The major anions of the river water are HCO 3, SO 4 2, Cl, NO 3, SiO 4 4 and F and the major cations include Ca2＋, Na＋, Mg2＋, K＋ and Sr2＋. The good correlation between HCO3-content and the content of Ca2＋may suggest that carbonate dissolution is the dominate contributor to the total dissolved solid（TDS） of the Yangtze River. Very good correlations are also found among contents of Cl, SO4 2, Na＋, Mg2＋, K＋and Sr2＋, indicating the important contribution of evaporite dissolution to the TDS of the Yangtze River. High TDS contents are generally found in the head water, reflecting a strong effect of evaporation in the Qinghai-Tibet Plateau. A small increase of the TDS is generally observed in the river mouth, indicating the influence of tidal intrusion. The F and NO3 contents show a clear increase trend from the upstream to downstream, reflecting the contribution of pesticides and fertilizers in the Chuan Jiang section and the middle and lower reaches. The DSi shows a decrease trend from the upstream to downstream, reflecting the effect of rice and grass growth along the Chuan Jiang section and the middle and lower reaches. The dissolved Cu, Zn and Cd in the Yangtze water are all higher than those in world large rivers, reflecting the effect of intensive mining activity along the Yangtze drainage area. The Yangtze water generally shows similar REE distribution pattern to the global shale. The δ30SiDiss values of the dissolved silicon vary from 0.5‰ to 3.7‰, which is the highest among those of the rivers studied. The δ30SiDiss values of the water in the Yangtze mainsteam show an increase trend from the upper stream to downstream. Its DSi and δ30SiDiss are influenced by multiple processes, such as weathering process, phytolith growth in plants, evaporation, phytolith dissolution, growth of fresh water diatom, adsorption and desorption of aqueous monosilicic acid on iron oxide, precipitation of silcretes and formation of clays coatings in aquifers, and human activity. The δ34SSO4 values of the Yangtze water range from 1.7‰ to 9.0‰. The SO4 in the Yangtze water are mainly from the SO4 in meteoric water, the dissolved sulfate from evaporite, and oxidation of sulfide in rocks, coal and ore deposits. The sulfate reduction and precipitation process can also affect the sulfur isotope composition of the Yangtze water. The87Sr/86Sr ratios of the Yangtze water range from 0.70823 to 0.71590, with an average value of 0.71084. The87Sr/86Sr ratio and Sr concentration are primary controlled by mixing of various sources with different87Sr/86Sr ratios and Sr contents, including the limestone, evaporite and the silicate rocks. The atmospheric precipitation and anthropogenic inputs can also contribute some Sr to the river. The δ11B values of the dissolved B in the Yangtze water range from 2.0‰ to 18.3‰, which is affected by multifactors, such as silicate weathering, carbonate weathering, evaporite dissolution, atmospheric deposition, and anthropogenic inputs.  相似文献   

16.
This paper presents a study of the petrography, mineral chemistry, geochemistry, and Sr–Nd–Pb–C–O isotope systematics of carbonatite dykes and associated rocks from the northeastern part of the Song Da intracontinental rift in South Nam Xe (northwest Vietnam) aimed at constraining the origin of the carbonatite magmas. The carbonatites are characterized by SiO2 < 12.18 wt.% and by wide ranges in FeO, MgO and CaO content that define them as calciocarbonatite and ferrocarbonatite. On U–Th–Pb isochron diagrams, whole rocks and mineral separates from the ferrocarbonatites form linear arrays corresponding to ages of 30.2–31.6 Ma (Rupelian, Oligocene). The South Nam Xe carbonatites are extremely enriched in Sr, Ba, and light rare earth elements (LREE), and depleted in high field strength elements (HFSE) (e.g. Ti, Nb, Ta, Zr and Hf). The age–corrected Sr–Nd–Pb isotope ratios and C isotope data are relatively uniform (87Sr/86Sr(t) = 0.708193–0.708349; 143Nd/144Nd(t) = 0.512250–0.512267; εNd(t) = ?6.46 to ?6.80; 206Pb/204Pb(t) = 18.26–18.79; 207Pb/204Pb(t) = 15.62–15.64; 208Pb/204Pb(t) = 38.80–39.38; δ13CV-PDB = –2.7?‰ to ?4.1?‰). These isotopic compositions indicate source contamination that occurred before the production of the carbonatite magmas, and did not change noticeably during or after emplacement. The variation in oxygen isotopes is consistent with the change in mineral compositions and trace element abundances: the lower δ18O values (9.1–11.0?‰) coupled with Sr-rich, Mn-poor calcite, and igneous textures such as triple junctions among calcite grain boundaries, define a magmatic origin. However, the elevated δ18O values of the ferrocarbonatites (12.0–13.3?‰) coupled with a volatile-bearing mineral assemblages (including REE fluorcarbonates, sulfates, sulfides and fluorite) may be due to interaction with meteoric water during low-temperature alteration. High δ13C values and Sr–Pb ratios, and low Rb/Sr (0.00014–0.00301), Sm/Nd (0.089–0.141) and 143Nd/144Nd ratios, coupled with very high Sr-Nd concentrations, suggest the involvement of an enriched mantle component, which probably resulted from metasomatism due to the migration of subducted material. Because of the lack of tectonic data and the limited number of samples studied, this conclusion is still ambiguous and requires further study.  相似文献   

17.
Calcite is a common fracture inflilling mineral in the Grenville gneisses of the Chalk River area, Ontario, Canada. It exhibits a variety of occurrences and textures which suggests calcite has precipitated under different hydrogeochemical conditions that may be identified through a detailed chemical and isotopic investigation of the calcite and associated infilling minerals.The δ18O of these calcites range over 20%. but the δ13C varies over a narrow range of 5%.. None of the calcites analyzed is in isotopic equilibrium with both the δ18O and δ13C of the present day ground water. The lightest δ18O calcites (near 0%. SMOW) are present in sealed fractures and are sometimes associated with laumontite. This suggests that these light calcites formed from hydrothermal solutions (at temperatures less than about 300°C) shortly after the period of metamorphism that formed the gneisses. This interpretation is supported by relatively unradiogenic87Sr/86Sr ratios near 0.709 and δ13C values of −5 to −6%..Most of the Chalk River calcites, however, are considerably heavier in18O and lighter in13C than the hydrothermal end member. This may be the result of low temperature recrystallization of the hydrothermal calcites by meteoric waters under variable water/rock ratios. The13C contents and87Sr/86Sr ratios of these younger, low temperature calcites appear to be partially buffered by the isotopic composition of the original hydrothermal calcite.Pyrite is often associated with the fracture calcites. These pyrites display a wide range in δ34S values of about 70%., which suggests that sulphide precipitation occurred under semi-closed conditions. These data indicate that fracture permeability has been a major control on the isotopic composition of fracture minerals since formation of the gneiss.  相似文献   

18.
Magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the Moselle basin, northeastern France. This small basin is remarkable for its well-constrained and varied lithology on a small distance scale, and this is reflected in river water Sr isotope compositions. Upstream, where the Moselle River drains silicate rocks of the Vosges mountains, waters are characterized by relatively high 87Sr/86Sr ratios (0.7128-0.7174). In contrast, downstream of the city of Epinal where the Moselle River flows through carbonates and evaporites of the Lorraine plateau, 87Sr/86Sr ratios are lower, down to 0.70824.Magnesium in river waters draining silicates is systematically depleted in heavy isotopes (δ26Mg values range from −1.2 to −0.7‰) relative to the value presently estimated for the continental crust and a local diorite (−0.5‰). In comparison, δ26Mg values measured in soil samples are higher (∼0.0‰). This suggests that Mg isotope fractionation occurs during mineral leaching and/or formation of secondary clay minerals. On the Lorraine plateau, tributaries draining marls, carbonates and evaporites are characterized by low Ca/Mg (1.5-3.2) and low Ca/Sr (80-400) when compared to local carbonate rocks (Ca/Mg = 29-59; Ca/Sr = 370-2200), similar to other rivers draining carbonates. The most likely cause of the Mg and Sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer. δ26Mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year (from −1.4‰ to −1.6‰ and from −1.2‰ to −1.4‰, respectively), within the range defined for the underlying rocks. Downstream of Epinal, the compositions of the Moselle River samples in a δ26Mg vs. 87Sr/86Sr diagram can be explained by mixing curves between silicate, carbonate and evaporite waters, with a significant contribution from the Vosgian silicate lithologies (>70%). Temporal co-variation between δ26Mg and 87Sr/86Sr for the Moselle River throughout year is also observed, and is consistent with a higher contribution from the Vosges mountains in winter, in terms of runoff and dissolved element flux. Overall, this study shows that Mg isotopes measured in waters, rocks and soils, coupled with other tracers such as Sr isotopes, could be used to better constrain riverine Mg sources, particularly if analytical uncertainties in Mg isotope measurements can be improved in order to perform more precise quantifications.  相似文献   

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20.
The Pb, Sr and Nd isotopic compositions of biomonitors (lichen, moss, bark) and soil litter from different regions in the Rhine valley, as well as of <0.45 μm particles separated out of ice of the Rhône and Oberaar glaciers and lichens from the Swiss Central Alps, have been determined in order to deduce the natural baseline of the atmospheric isotopic compositions of these regions, which are suggested to be close to the isotopic compositions of the corresponding basement rocks or soils at the same sites. 206Pb/207Pb and 87Sr/86Sr isotope ratios are positively correlated. Most polluted samples from traffic-rich urban environments have the least radiogenic Pb and Sr isotopic compositions with 206Pb/207Pb and 87Sr/86Sr ratios of 1.11 and 0.7094, respectively. These ratios are very different from those of the atmospheric baseline for the Vosges mountains and the Rhine valley (206Pb/207Pb: 1.158–1.167; 87Sr/86Sr: 0.719–0.725; εNd: −7.5 to −10.1). However, this study indicates that the baseline of the atmospheric natural Pb and Sr isotopic compositions is affected by anthropogenic (traffic, industrial and urban) emissions even in remote areas. Lichen samples from below the Rhône and Oberaar glaciers reflect the baseline composition close to the Grimsel pass in the Central Swiss Alps (87Sr/86Sr: 0.714 − 0.716; εNd: −3.6 to −8.1). The 143Nd/144Nd isotope ratios are highly variable (8ε units) and it is suggested that the variation of the 143Nd/144Nd is controlled by wet deposition and aerosols originating from the regional natural and industrial urban environments and from more distant regions like the Sahara in North Africa. The least anthropogenetically affected samples collected in remote areas have isotopic compositions closest to those of the corresponding granitoid basement rocks.  相似文献   

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