geochemistry of eolian dust and its elemental contribution to lake qinghai sediment abstract located at the midpoint of the asian airborne dust corridor lake qinghai receives substantial dust annually which may impact the biogeochemical cycles of the system in order to determine quantitatively the flux and chemical contributions of dust to lake qinghai sediment dust samples were collected monthly at two sites surrounding the lake from june 2009 to may 2011 the results demonstrate similar chemical compositions of dust samples to the local loess implying strong representativeness of regional dust the average dust deposition flux is 265 7 55 0 g m 2 a constituting 56 6 11 7 of the modern sediment approximating to previous estimates 65 contributions of dust derived elements in the sediment differ substantially with a minimum of 16 7 for sr and a maximum of 83 9 for cu among these elements the contribution of lithophile elements na al k ti mn fe and rb is close to that of the bulk dust the contributions of mobile elements mg ca and sr are low only 16 7 sr 26 1 mg whereas potentially harmful metals cu zn and pb have high contributions 70 3 83 9 seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment in agreement with the high dust flux in spring these observations not only quantify the contribution of dust to the sediment of lake qinghai but also highlight the important role of dust in the accumulation of various elements in the sediment especially for potentially harmful metals

hydrological and solute budgets of lake qinghai the largest lake on the tibetan plateau abstract water level and chemistry of lake qinghai are sensitive to climate changes and are important for paleoclimatic implications an accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle published results of water budget are firstly reviewed in this paper chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry the results indicate that carbonate weathering is the most important riverine process resulting in dominance of ca2 and dic for river waters and groundwater groundwater contribution to major dissolved constituents is relatively small 4 2 0 5 wet atmospheric deposition contributes annually 7 4 44 0 soluble flux to the lake resulting from eolian dust throughout the seasons estimates of chemical budget further suggest that 1 the buha type water dominates the chemical components of the lake water 2 na cl mg2 and k in lake water are enriched owing to their conservative behaviors and 3 precipitation of authigenic carbonates low mg calcite aragonite and dolomite transits quickly dissolved ca2 into the bottom sediments of the lake resulting in very low ca2 in the lake water therefore authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past

surface water groundwater interactions in an alluvial plain chemical and isotopic systematics our work on the loire river forms part of a french national research program dedicated to wetlands and aims to better understand the global functioning of the system from the hydrological geochemical ecological and sociological aspects the present study using a coupled hydrological and geochemical stable and sr isotopes approach focuses on the soulangy site with its secondary anastomosing channels just below the confluence of the loire and allier rivers and also on the dorna nt site with two unconnected oxbow lakes 50 km upstream of the confluence the stable isotopes of water 18o 2h show that the alluvial or riverbank aquifer feeds the loire river during the summer but is not recharged by the river during flood periods in the winter the alluvial groundwater thus has a purely local origin from precipitation the major elements reveal an anthropogenic input of cl and more importantly of no3 especially near farms the 87sr 86sr isotopes identify different groundwater layers in the alluvium i e an upper and a lower alluvial aquifer and a perched aquifer at dornant that have relatively complex relationships with the surface water the two main rivers loire and allier present distinct geochemical characteristics reflecting the different lithologies that they drain upstream in addition the secondary channels lying parallel to the loire main stream at the soulangy site give different geochemical signatures which shows that they are not fed by the same overflows of the loire they are more or less well connected to the upper level of the alluvial plain and a longitudinal study of one of these channels has revealed a loire river influence progressively replaced by a water contribution from the upper alluvial aquifer similarly the two oxbow lakes at the dornant site are not supplied by the same water during the summer months a conceptual scheme of the loire hydrosystem based on 18o and 87sr 86sr suggests that the isotopic variations of the loire river can be related to a massif central surface water supply for the loire and allier main streams and to a groundwater supply from the alluvial plains

strontium isotopes and major ion chemistry in the chambal river system india implications to silicate erosion rates of the ganga article i nfo much higher than the global mean river water a significant fraction of solute abundance in the chambal river is derived from sodium salts unlike the himalayan rivers which exhibit dominance of ca mg salts it is estimated that the chambal river supplies about one third of sodium via the yamuna to the ganga at rajshahi bangladesh with only 6 5 of water discharge the presence of na salts not associated with chloride in the chambal headwaters constraints the application of na na corrected for cl as an index of silicate derived component this finding brings out the need to revisit the estimates of silicate erosion rate ser and associated co2 consumption in the ganga basin downstream allahabad based on na as an index the sr concentration in the chambal tributaries varied from 1 9 m to 5 9 m and 87 sr

strontium isotope geochemistry of groundwater affected by human activities in nandong underground river system china abstract the nandong underground river system nurs is located in a typical karst area dominated by agriculture in se yunnan province china groundwater plays an important role in the social and economical development in the area the effects of human activities agriculture and sewage effluents on the sr isotope geochemistry were investigated in the nurs seventy two representative groundwater samples which were collected from different aquifers calcite and dolomite under varying land use types both in summer and winter showed significant spatial differences and slight seasonal variations in sr concentrations and 87sr 86sr ratios agricultural fertilizers and sewage effluents significantly modified the natural 87sr 86sr ratios signature of groundwater that was otherwise dominated by water rock interaction three major sources of sr could be distinguished by 87sr 86sr ratios and sr concentrations in karst groundwater two sources of sr are the triassic calcite and dolomite aquifers where waters have low sr concentrations 0 1 0 2 mg l and low 87sr 86sr ratios 0 7075 0 7080 and 0 7080 0 7100 respectively the third source is anthropogenic sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87sr 86sr ratios 0 7080 0 8352 for agricultural fertilizers and 0 7080 0 7200 for sewage effluents respectively with higher sr concentrations 0 24 0 51 mg l due to the overlapping 87sr 86sr ratios it is difficult to distinguish the sources of sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87sr 86sr ratios however 87sr 86sr ratios do provide key information for natural and anthropogenic sources in karst groundwater

geochemistry of surface and ground water in guiyang china water rock interaction and pollution in a karst hydrological system the chemical compositions of the surface ground water of guiyang the capital city of guizhou province china are dominated by ca2 mg2 hco3 andso42 which have been derived largely from chemical weathering of carbonate rocks limestone and dolomite the production of so42 has multiple origins mainly from dissolution of sulfate evaporites oxidation of sulfide minerals and organic s in the strata and anthropogenic sources most ground water is exposed to soil co2 and therefore the h2co3 which attacks minerals contains much soil c in addition the h2so4 produced as a result of the oxidation of sulfides in s rich coal seams and or organic s is believed to be associated with the chemical weathering of rocks the major anthropogenic components in the surface and ground water include k na cl so42 andno3 with cl and no3 being the main contributors to ground water pollution in guiyang and its adjacent areas the seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities the higher content of no3 in ground water compared to surface water during the summer and winter seasons indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

the dynamics of central main ethiopian rift waters evidence from δd δ18o and 87sr 86sr ratios abstract water samples from cold and geothermal boreholes hot springs lakes and rivers were analyzed for d 18o and 87sr 86sr compositions in order to investigate lake water groundwater mixing processes water rock interactions and to evaluate groundwater flow paths in the central main ethiopian rift mer of the ziway shala basin different ranges of isotopic values were recorded for different water types hot springs show 18o 3 36 to 3 69 and d 15 85 to 24 23 deep aluto langano geothermal wells show 18o 4 65 to 1 24 and d 12 39 to 9 31 groundwater wells show 18o 3 99 to 5 14 and d 19 69 to 32 27 whereas the lakes show 18o and d in the range 3 98 to 7 92 and 26 19 to 45 71 respectively the intersection of the local meteoric water line lmwl d 7 18o 11 2 r2 0 94 n 42 and the local evaporation line lel d 5 63 18o 8 n 14 r2 0 82 was used to estimate the average isotopic composition of recharge water into the basin d 5 15 and 18o 2 34 these values are depleted if compared with the modern day average precipitation presumably indicating paleo groundwater components recharged during previous humid climatic phases the measured stable isotope values indicate that the geothermal wells some of the hot springs and groundwater wells mainly consist of meteoric water the sr isotopic signatures in all waters are within the range of the sr isotopic composition of the rift basalts and rhyolites the variability of sr isotopic data also pinpoints complex water rock interaction and mixing processes in groundwater and surface water the 87sr 86sr ratio ranges from 0 70445 to 0 70756 in the hot springs from 0 70426 to 0 70537 in two deep geothermal wells and from 0 70673 to 0 70721 in the rift lakes ziway langano shala and awasa the radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments there is a change in mer water composition between the recharge infiltration zone surrounding highlands and the discharge areas from depleted d 18o and less radiogenic sr isotope compositions to enriched d 18o and more radiogenic sr isotope compositions isotope analyses are therefore useful in providing further understanding of the hydrologeological processes occurring within a productive aquifer and the surface water system

sources and flux of trace elements in river water collected from the lake qinghai catchment ne tibetan plateau 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

the northwest africa 8159 martian meteorite expanding the martian sample suite to the early amazonian abstract northwest africa nwa 8159 is an augite rich shergottite with a mineralogy dominated by ca fe rich pyroxene plagioclase olivine and magnetite nwa 8159 crystallized from an evolved melt of basaltic composition under relatively rapid conditions of cooling likely in a surface lava flow or shallow sill redox conditions experienced by the melt shifted from relatively oxidizing with respect to known martian lithologies qfm on the liquidus to higher oxygen fugacity qfm 2 during crystallization of the groundmass and under subsolidus conditions this shift resulted in the production of orthopyroxene and magnetite replacing olivine phenocryst rims nwa 8159 contains both crystalline and shock amorphized plagioclase an50 62 often observed within a single grain based on known calibrations we bracket the peak shock pressure experienced by nwa 8159 to between 15 and 23 gpa the bulk composition of nwa 8159 is depleted in lree as observed for tissint and other depleted shergottites however nwa 8159 is distinct from all other martian lithologies in its bulk composition and oxygen fugacity we obtain a sm nd formation age of 2 37 0 25 ga for nwa 8159 which represents an interval in mars geologic time which until recently was not represented in the other martian meteorite types the bulk rock 147sm 144nd value of 0 37 0 02 is consistent with it being derived directly from its source and the high initial e143nd value indicates this source was geochemically highly depleted cr nd and w isotopic compositions further support a unique mantle source while the rock shares similarities with the 2 4 ga nwa 7635 meteorite there are notable distinctions between the two meteorites that suggest differences in mantle source compositions and conditions of crystallization nevertheless the two samples may be launch paired nwa 8159 expands the known basalt types ages and mantle sources within the mars sample suite to include a second igneous unit from the early amazonian

implications of radiolarian research for analysis of subduction complex terranes in the new england orogen nsw australia radiolarians provide important age constraints on geologically complex strata in the new england orogen of eastern australia several terranes interpreted as subduction complexes were undated prior to radiolarian studies radiolarian faunas indicate that the djungati terrane is significantly younger than the previously inferred ordovician to sulurian age range basalt chert successions in the djungati terrane developed during the silurian to late devonian in an environment which was far from the influence of terrigenous sedimentation radiolarians from tuffs within overlying arc derived volcaniclastic sequences constrain the timing of tectonic assembly of the terrane at a convergent margin to the latest devonian early carboniferous the extensive but previously undated anaiwan terrane also contains radiolarians which indicate a latest devonian to early carboniferous age for siliceous oceanic sediments these sediments were accreted into a subduction complex volcaniclastic sediments within this subduction complex contain radiolarians which indicate that it developed during the early carboniferous radiolarians in the willowie creek beds provide the first age constraints late devonian for another lithotectonic entity the yugambal terrane which is located along the eastern edge of the southern new england orogen many of the recently determined radiolarian ages are at variance with age estimates used to develop models for the tectonic development of the orogen these new age data require major reappraisal of models detailed analysis of the geological evolution of individual terranes is required before an integrated model for the entire orogen can be developed

toward a geochemical mass balance of major elements in lake qinghai ne tibetan plateau a significant role of atmospheric deposition abstract sediments in lake qinghai archive important information about past environmental changes in order to faithfully interpret the sediment records and constrain the elemental cycles it is critical to trace various sources of sediments in the lake the results show that the elemental input output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate mar of lake qinghai sediments a realistic model must include contributions of dry wet atmospheric deposition that allow the major element mass balance for the lake to be defined the budget estimation is based on mass balances of si and al which are relatively immobile and carried to the lake via particulate forms estimated annual budget of dry atmospheric deposition is 1 3 0 3 103 kt a accounting for 65 of the total inputs to the lake sediments assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake the resultant flux of 300 45 g m2 a falls within the flux average of the desert area 400 g m2 a and the loess plateau 250 g m2 a consistent with the geographical setting of lake qinghai the role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account this highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide the results also indicate that nearly all ca input was preserved in the lake sediments under modern conditions consistent with ca2 supersaturation of the lake water

earth surface evaporative process a case study from the great lakes region of the united states based on deuterium excess in precipitation abstract the deuterium excess parameter in rain defined as d d 8 18o is a powerful geophysical tool which can be used to estimate secondary processes that influence atmospheric vapor content in the evaporation condensation cycle in nature the d excess has been calculated based on the systematic analysis of the stable oxygen and hydrogen isotope ratios in precipitation samples from kalamazoo southwest michigan the results show that moisture derived from the evaporation of lake michigan contributes between 9 16 during the summer months to the atmospheric vapor load in the region admittedly this estimate is an upper value since in our model we have assumed that transpiration from leaf surfaces is minimal compared to the evaporation from lake michigan it is therefore obvious that large freshwater systems need to be regarded as a potentially significant source of atmospheric vapor load isotopic investigations such as this will enable to attain quantitative estimates of this important aspect a knowledge of which will enhance the usefulness of or perhaps even be essential in calculations based on many atmospheric circulation models

sr isotopes in natural waters applications to source characterisation and water rock interaction in contrasting landscapes strontium isotopes 87sr 86sr are routinely measured in hydrochemical studies to determine sources and mixing relationships they have proved particularly useful in determining weathering processes and quantifying end member mixing processes a number of routine case studies are presented which highlight that sr isotopes represent a powerful tool in the geochemists toolbox helping to constrain weathering reactions weathering rates flow pathways and mixing scenarios differences in methodologies for determining the weathering component in natural environments inherent differences in weathering rates of different minerals and mineral heterogeneity often cause difficulties in defining the weathering component of different catchments or aquifer systems nevertheless sr isotopes are useful when combined with other hydrochemical data to constrain models of water rock interaction and mixing as well as geochemical processes such as ion exchange this paper presents a summary of recent work by the authors in constraining the sources of waters and weathering processes in surface catchments and aquifers and indicates cases where sr isotopes alone are insufficient to solve hydrological problems

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

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

the significance of mid latitude rivers for weathering rates and chemical fluxes evidence from northern xinjiang rivers rivers draining the sedimentary platform of northern xinjiang the center of asian continent are characterized by low discharge under a temperate and arid climate the influence of rock mineralogy climate relief and human activity on natural water composition and export as a result of weathering is a major scientific concern both at the local and the global scale while comprehensive work on the controlling mechanism of chemical weathering has been less carried out in the sedimentary platform of northern xinjiang thus the effects of climate and rock weathering on the inorganic hydrogeochemical processes are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large pristine rivers in northern xinjiang the erlqis yili wulungu jingou and numerous lesser streams which has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts the scale of the terrain sampled in terms of area is comparable to that of the huanghe and includes a diverse range of geologic and climatic environments in this paper the chemical fluxes from the stable sedimentary basin of the northern xinjiang platform will be presented and compared to published results from analogous terrains in the monsoon basins of china and world overall the fluvial geochemistry of northern xinjiang in westerly climate is similar to that of the chinese rivers huanghe and yangtze in the east asian monsoon climate both in property property relationships and concentration magnitudes the range in the chemical signatures of the various tributaries is large this reflects that lithology exerts the dominant influence in determining the weathering yield from the sedimentary terrains rather than the weathering environment the effect of different rock weathering ranges from rivers dominated by aluminosilicate weathering mainly of granites sandstones and shales to those bearing the signatures of dissolution of carbonates and evaporites and of continental playa deposits carbonates are the general predominant lithology undergoing dissolution particularly within the lesser arid areas the pco2 in the study rivers is out of equilibrium with respect to atmospheric pco2 about up to 20 times supersaturated relative to the atmosphere but not to such an extent as the amazon in the floodplain a roughly positive relationship is observed between solute concentrations and the drought index di for natural waters in the region indicating a coupled mountain basin climate has a direct effect the relative contributions of end member solute sources to the total dissolved cations from each watershed have been quantitatively estimated using dissolved load balance models showing the results as evaporite dissolution carbonate weathering silicate weathering atmospheric input for the whole catchment the areal total dissolved fluxes range from 0 05 to 2 53106mol km2 yr 0 02 2 09106mol km2 yr and 0 01 1 04106mol km2 yr in the yili zhungarer and erlqis respectively comparable to those of chinese and siberia rivers draining sedimentary platforms even though they are in drastically different climatic regimes in general the fluxes from rivers in sedimentary basins are comparable to those from orogenic zones but are much higher than in the shield regions the co2 consumption by aluminosilicate weathering 0 2 284103mol km2 yr is much smaller than in active orogenic belts 19 1750103mol km2 yr in similar latitudes and 143 1000103mol km2 yr in the tropical basins but comparable to those of the chinese 7 106103mol km2 yr and siberia 16 112103mol km2 yr rivers 2013 elsevier b v

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

geochemical evolution of groundwater in the quaternary aquifer of calcutta and howrah india abstract groundwater in the quaternary aquifer of the twin city calcutta and howrah occur in a confined condition coarse clastic deposits consisting of fine to coarse sand at places mixed with gravels form the aquifer above and below lie clay sequences the average thickness of the top confining clay bed is 40 m and the aquifer continues down to a depth of at least 296 m below which the bottom clay bed of pliocene age occurs during the last five decades there is a distinct lowering of piezometric head in calcutta and howrah the groundwater flow pattern changed from an open system which was from north to south in the mid 1950s to a closed one in the mid 1980s with the formation of a groundwater trough this closed flow system persisted in the 1990s with the increase in the area of the trough detailed geochemical investigation of groundwater samples n 57 along with statistical analyses viz correlation principal component and mixing analyses on these chemical data reveal i that the groundwater samples can be categorised into eight hydrochemical facies which may be assigned to the three broad types fresh blended and brackish water ii a pronounced and well defined trend of variation of chemistry of the groundwater iii modified connate water and or interaction with the aquifer matrix was possibly responsible for the evolution of the brackish water iv mixing of fresh water and brackish water in ca 48 52 proportion is presently taking place due to heavy groundwater withdrawal and v such mixing will cause deterioration in quality from fresh water to the blended variety mean tds 724 mg l

evaluation of oxygen isotopes in carbonate as an indicator of lake evolution in arid areas the modern qinghai lake qinghai tibet plateau abstract the oxygen isotopic composition of carbonate in lakes has been used as a useful indicator in palaeolimnological research and has made some important contributions to our understanding of lacustrine systems for modern lakes in arid or cold areas however there are few data available to test the effect of lake salinity and temperature on the oxygen isotopic composition of various carbonate sources such as ostracod bulk carbonate and fine grained carbonate for arid high altitude lake qinghai our results suggest that variations in the 18o values of carbonate in lake qinghai are mainly controlled by the oxygen isotope ratio of the lake water changing with water salinity as a secondary effect increasing water depth leads to cooler bottom and surface water which may result in more positive 18o values of ostracod and bulk carbonate

strontium isotope geochemistry of groundwater in the central part of the dakota great plains aquifer usa abstract 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

chemical and physical weathering in the min jiang a headwater tributary of the yangtze river abstract the min jiang is a major headwater tributary of the yangtze chang jiang its source is in the undeveloped eastern tibetan plateau but it flows through the heavily populated sichuan four rivers basin on its way to join the yangtze main channel the dissolved major element composition was determined in the tibetan headwaters at the rising stage and at four hydrologic stations in a monthly time series the min jiang is alkaline and has high dissolved load compared to other world rivers carbonate weathering dominates especially in the source region of the min jiang main channel and silicate weathering and evaporite dissolution gain some importance in the dadu he tributary the si na k ratios of the dissolved load and the clay mineralogy of the bed material suggest that silicate weathering in the watershed is superficial i e soluble cations are being preferentially leached many major elements show lower concentrations at high summer discharge but there is also additional input such that the concentration discharge relationship is not purely a result of dilution the discharge weighted total dissolved solid tds flux based on data from the three upstream monitoring stations is 10 10 6 tons year 6 of the yangtze at mouth and the chemical denudation rate as measured by tds yield is 115 tons km 2 year for the min jiang higher than the average yangtze basin 85 tons km 2 year the common extrapolation using annual average discharge and spot sampling of dissolved and suspended material during rising or falling stage can reasonably estimate chemical fluxes to 20 but seriously underestimate the physical flux sampling the peak flash flow is critical for the suspended particulate material concentrations of so 4 cl and ca are significantly elevated as the river debouches onto the populated sichuan basin

kinetic and mineralogic controls on the evolution of groundwater chemistry and 87sr 86sr in a sandy silicate aquifer northern wisconsin usa abstract substantial flowpath related variability of 87sr 86sr is observed in groundwaters collected from the trout lake watershed of northern wisconsin in the extensive shallow aquifer composed of sandy glacial outwash groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter lake uplands 87sr 86sr of groundwater derived mainly as seepage from a precipitation dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase in contrast 87sr 86sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed due to suppression of plagioclase dissolution together with preferential leaching of sr from radiogenic phases such as k feldspar and biotite the results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic sr whereas stagnant waters obtain relatively radiogenic sr nearly the entire range of strontium isotope composition observed in groundwaters from the watershed was measured in the experimental product waters the constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions in contrast episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution perhaps due to accumulation of clay mineral nuclei on its reactive surfaces differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior this study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations

chemical weathering in the upper reaches of xijiang river draining the yunnan guizhou plateau southwest china abstract chemical and strontium isotopic compositions of nanpanjiang river and beipanjiang river in the upper reaches of xijiang river draining the yunnan guizhou plateau southwest china were measured with a main purpose to understand the rock weathering and associated co 2 consumption rates in the karstic landform dominated area the chemical ion composition of the river water is characterized by dominance of ca 2 mg 2 and hco 3 and so 4 2 which account for more than 90 of total ion concentration 87 sr 86 sr ratios of nanpanjiang river water range between 0 7080 and 0 7140 while those of most beipanjiang river water vary within a limited range from 0 7075 to 0 7085 weathering of carbonate rocks dominate chemistry of major ions especially in the water of beipanjiang river whereas weathering of silicate minerals in the upper reaches of nanpanjiang river basin is obvious in addition to carbonate weathering mainly according to the sr isotopic composition of the river water analyses of the stoichiometry of the river water show that the water chemistry is controlled by carbonate dissolution not only by carbonic but also by sulfuric acid and indicate that sulfuric acid plays an important role in carbonate weathering the sulfate in river water is mainly from atmospheric input by coal combustion industries and from oxidation of sulfide minerals during weathering of coal containing strata and coal mining in the catchment the chemical weathering rates of silicate and carbonate and associated co 2 consumption rates by both carbonic and sulfuric acid and by only carbonic acid are respectively estimated the results show that chemical weathering rates of carbonate and silicate weathering in beipanjiang river basin are higher than those of nanpanjiang river basin showing linkages of geology and geography in the catchment to crustal weathering the involvement of sulfuric acid in carbonate weathering greatly enhances the carbonate weathering but lowers the co 2 consumption rates indicating that sulfide acid is an important agent to rock weathering and the role of sulfide acid should further be clarified in view of the regional and global budget of co 2

geochemical and isotopic characteristics of shallow groundwater within the lake qinghai catchment ne tibetan plateau abstract major ions isotopic ratios of strontium 87 sr 86 sr hydrogen d and oxygen 18 o of groundwater samples were analyzed to decipher spatial variation controlling factors solute sources and the recharge source of shallow groundwaters within the lake qinghai catchment shallow groundwaters in this area are slightly alkaline with 97 being fresh water of good quality though there are high concentrations of nitrate and sulfide in buha and lakeside groundwaters most of the shallow groundwaters are of the ca 2 hco 3 type whereas part of groundwaters surrounding the lake ls belongs to the na cl type as lake water qhl groundwater geochemistry is controlled by regional lithological association ion exchange and mineral precipitation the dissolved sr concentrations and 87 sr 86 sr ratios vary from 1 0 to 15 6 mol l and from 0 709859 to 0 715779 respectively the first quantitative calculation in groundwater using a forward model shows that 40 of dissolved sr is from carbonate weathering 33 from evaporite dissolution 17 from silicate weathering and the remainder from atmospheric input for the whole catchment carbonate weathering dominates groundwater geochemistry in shaliu sl hargai hg and buha bh samples while evaporite dissolution dominates ls and daotang dt samples d and 18 o data show that rain water is the major recharge source of both river water and shallow groundwater within the lake qinghai catchment qinghai lake water is characterized by buha type water but its sr geochemistry is different from the shallow groundwater due to carbonate precipitation although shallow groundwater contributes 5 of the dissolved sr to the qhl groundwater must be taken into account when the chemistry and budget of lake water are characterized