major element chemistry of the huai river basin china the chemistry of major ions ca mg na k hco3 so4 cl and si in the water of the huai river basin was studied based on samples from 52 sites from nine different water bodies in july 2008 ions and total dissolved solids tds displayed clear spatial patterns with lower concentrations in the south and higher in the north of the basin the same conditions were also found in the east line of south north water transfer project snwtp in this region the huai river main channel and hongze lake have moderate ion concentrations relative to the whole basin tds concentrations versus the weight ratios of na na ca and ternary ions demonstrate that the southern rivers shi r and pi r are mainly controlled by the weathering of carbonates whereas the northern water systems guo r shaying r nansi lake and its tributaries are dominated by the weathering of evaporites the huai river main channel hongze lake and the east line of snwtp are synergistically influenced by weathering of evaporites and carbonates yet hongze lake and the east line of snwtp are mainly controlled by evaporation and crystallization processes this study also confirmed that the huai river is the geographic division between southern and northern china most rivers of this basin have very high ionic composition relative to the global median and other world rivers the spatial patterns and ionic composition also suggest that intensive anthropogenic activities in northern areas of this basin are well characterized a comparison with who and chinese standards for drinking water indicates that the northern water systems of this basin are not suitable for use as drinking water sources and pollution control should be improved and enhanced in northern areas of the basin crown copyright c 2010 published by elsevier ltd all rights reserved

detection of snowmelt regions on the greenland ice sheet using diurnal backscatter change snowmelt regions on greenland ice are mapped daily with the seawinds wideswath ku band 13 4 ghz scatterometer on the quikscat satellite the approach exploits the high temporal resolution of seawinds quikscat data for the melt mapping using diurnal backscatter change independent of the absolute calibration the results reveal several pronounced melting and refreezing events and effects of topography are evident in the melt patterns the spatial resolution is sufficient to identify melt features on the sukker toppen iskappe west of the main ice sheet an anomalous warming event caused by downward mixing of warm air is detected in late september 1999 over the west flank of the southern greenland ice sheet time series images of melt regions are presented over the period from summer to the fall freeze up the satellite observations are verified with in situ measurements from the greenland climate network stations

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

subsidence of normal seafloor observations do indicate flattening 1 seafloor topography is a key observational constraint upon the evolution of the oceanic lithosphere specifically plots of oceanic depth z versus crustal age t for normal seafloor are well explained by depth age predictions of thermal contraction models such as the half space and cooling plate model old seafloor t 70 ma shallower than that predicted by half space cooling i e z t or flattening is a key but debated discriminator between the two models korenaga and korenaga 2008 in a recent paper find normal seafloor depths of all ages to be consistent with a z t model thus supporting a cooling half space model for all ages of seafloor upon reevaluation however the mean depths of their normal seafloor flatten at ages 70 ma e g by 723 2 0 5 m 1 standard error for t 110 ma this observed inconsistency with the z t model is statistically significant 99 9 and remains robust 94 even if the number of effective independent depth observations is argued to be low e g n 10 so if any statistically significant conclusion can be drawn from the observed depths of rare old normal seafloor it is that old seafloor flattens which is incompatible with the cooling half space model applying to all ages of seafloor but does not preclude a cooling plate style approximation to lithospheric evolution

hydrogeochemistry of three watersheds the erlqis zhungarer and yili in northern xinjiang nw china abstract in the arid region of northern xinjiang one of the least studied areas in china three watersheds namely those of the yili zhungarer and erlqis have become the focus of attention due to rapidly increasing human population and water demands the hydrogeochemistry of natural water from the three watersheds was investigated the ionic chemistry of natural waters from these watersheds changes considerably on a regional scale the waters are neutral to alkaline in nature and most of them are soft fresh waters the total dissolved solid tds varies over two orders of magnitude with a mean value of 580 mg l about 1 2 times and 4 6 times those of the huanghe yellow river and the world spatial median respectively but only 40 and 0 8 of those of the tarim and the western alashan watersheds respectively much of the solutes and physicochemical parameters in these waters are under the highest desirable limits of the world health organization who for drinking purpose and a plot of sodium adsorption ratio versus ec shows that most waters are of good water quality for irrigation water rock interaction and saturation index si for selected minerals are evaluated the si of these natural waters is out of equilibrium undersaturated with respect to major carbonates calcite and dolomite and evaporites gypsum and halite the high concentrations of alkali earth metals alkalinity and the high ca mg na k and na cl ratios indicate that the release of major solutes in these waters is controlled largely by dissolution processes of carbonate and partly by silicate weathering while cation exchange reactions soil salt leaching and evaporation processes also play an important role the effects of local pollution are minimal in the montane and piedmont areas of these watersheds but are significant in the oases and central areas of the drainage basins

the holocene salinity history of bosten lake xinjiang china inferred from ostracod species assemblages and shell chemistry possible palaeoclimatic implications abstract a sediment core from bosten lake the largest freshwater lake in the tianshan mountains and in the northwesternmost province of china provided a high resolution record of environmental change covering the last 8500 cal a bp higher salinity levels of bosten lake were reconstructed from assemblages the stable isotope composition and sr ca and mg ca ratios of ostracod shells between 7800 and 5600 cal a bp a period of low and moderate salinities between 5600 and 4900 cal a bp was followed by the re establishment of higher salinities between 4900 and 4300 cal a bp since then bosten lake has recorded fluctuating conditions with a number of multi centennial phases of low and moderate salinities although the salinity lake level relationship of bosten lake is not fully understood a higher salinity at the core site seems to correspond to periods of higher lake levels this contradictory interpretation is explained tentatively by the changing distance of the core site to the freshwater providing river mouth with changing lake levels and potentially resulting lateral shifts of the salinity distribution pattern within the lake assuming this explanation is correct the record from bosten lake reflects higher moisture availability and a strong climatic influence of the indian monsoon in the early mid holocene until about 4000 cal a bp and more unstable drier conditions susceptible to minor changes in the regional circulation patterns and temperature variations afterwards

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

spatial and temporal analysis of water chemistry records 1958 2000 in the huanghe yellow river basin 1 the chemistry of major dissolved ions ca2 mg2 na k hco3 so42 cl and dissolved silica sio2 in the river water of the huanghe yellow river china was studied from historical records at 100 stations in the drainage basin for the period 1958 2000 not all the parameters were continuously monitored during the entire period this river system 750 000 km2 presents an exceptional temporal and spatial water chemistry variability compared to other major rivers the total dissolved solid tds concentration of the huanghe varied over 2 to 3 orders of magnitude throughout the basin with a median tds concentration of 452 mg l which is about 4 times the world spatial median value wsm in particular the concentrations of na k so42 and cl were 10 20 times higher than in other major world rivers similar to the changjiang yangtze river and many other himalayan rivers the tds at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2 0 despite a water dilution of fourfold to fivefold in the summer flood season in addition to chemical weathering of sedimentary rocks evaporation and fractional crystallization were found to be the major natural process controlling the major element chemistry of the huanghe owing to the abundance of loess and clastic rocks under arid and semiarid climates a persistent increasing trend from year to year has been observed in the concentrations of tds and all the salts except for hco3 at all main channel stations except for the uppermost lanzhou the rate of increase in the tds concentration was the highest in the middle reaches 10 52 mg l yr 1 at toudaoguai and remained to be unusually high in the lower reaches 5 5 mg l yr 1 at stations luokou and lijin the increasing trend coincided with a significant decrease in water discharge at most of the main channel stations in the past 40 years and is attributed to increasing regulations of reservoirs and intensive water withdrawal for irrigation and diversions as well as many other anthropogenic processes despite the increasing trend in tds concentrations the seaward tds flux to the sea by the huanghe has decreased dramatically from more than 20 109 kg yr in the 1960s to less than 10 109 kg yr at present due to the sharp decrease in water discharge sometimes completely dried up in the lower reaches of the river the significant decreases in sea ward fluxes of water and dissolved salts are expected to have profound physical ecological and socio economic impacts on the lower reaches of the river the coastal areas and the bohai sea

dry late glacial and early holocene climate in arid central asia indicated by lithological and palynological evidence from bosten lake china abstract stratigraphical and chronological investigations of four sediment cores from bosten lake the largest inland freshwater lake in china provide a reliable regional environmental evolution record since the late glacial the stratigraphy of the four cores has been well correlated according to their lithology and chronology osl and 14c dates pollen and grain size data from bosten lake show evidence for a dry regional climate during late glacial and early holocene 16 8 cal ka bp indicated by a thick layer of aeolian sand deposit 100 cm although the climate became humid after 8 cal ka bp analysis of pollen assemblages pollen a c ratio and ephedra percentage also indicates that the climate was relatively dry in the bosten lake area between 8 and 6 cal ka bp while afterwards more humid conditions ca 6 1 5 cal ka bp are assumed comparison with other lake records from arid central asia influenced by the westerly winds generally supports the assumption of late glacial to early holocene dry climates in westerly dominated regions hence they contrast the holocene climate development in monsoon asia relatively wet conditions during the late holocene 6 1 5 cal ka bp might be induced by stronger westerly circulation

geochemistry and solute sources of surface waters of the tarim river basin in the extreme arid region nw tibetan plateau abstract major ion concentrations of river lake and snow waters were measured to better understand the water quality hydrochemical processes and solute sources of surface waters within the tarim river basin in the extreme arid region surface waters are slightly alkaline and are characterized by high total dissolved solids tds tds values varies over two orders of magnitude from fresh 76 to brackish 24 with a mean value of 1000 mg l higher than the global river average and river waters draining the himalayas and the southeastern tibetan plateau most of the samples were ca2 mg2 hco 3 type and suited for drinking and irrigation water quality of aksu river ak hotan river ht and northern rivers nr is better than the others rock weathering ion exchange and precipitation are the major hydrogeochemical processes responsible for the solutes in rivers waters anthropogenic input to the water chemistry is minor and human activities accelerate increase of river tds the quantitative solute sources are first calculated using a forward model in this area the results show that evaporite dissolution carbonate weathering atmospheric input and silicate weathering contributed 58 3 25 7 8 7 and 8 2 of the total dissolved cations for the whole basin evaporite dissolution dominated in lake waters lw ht yarkant river yk tarim river tr and southern rivers sr contributing 73 5 53 4 56 7 77 and 74 2 of the total dissolved cations respectively carbonate weathering dominated in ak and nr contributing 48 and 44 4 of the total dissolved cations respectively the tds flux of ht tr ak yk was 66 0 118 6 134 9 and 170 4 t km2 yr respectively higher than most of the rivers in the world knowledge of our research can promote effective management of water resources in this desert environment and add new data to global river database

water geochemistry of the xijiang basin rivers south china chemical weathering and co2 consumption abstract the xijiang river the mainstream of the zhujiang pearl river which is the second largest river in china in terms of discharge flows through a large carbonate rock region in south china the chemical and sr isotopic compositions of the xijiang waters were determined during the high flow season in order to understand the chemical weathering processes associated co2 consumption and anthropogenic influences within the carbonate dominated basin the major ion compositions of the river waters are characterized by the dominance of ca2 mg2 hco 3 and are significantly rich in so 4 2 the so 4 2 is mainly derived from the oxidation of sulfide minerals and acid precipitation caused by coal combustion chemical and sr isotopic compositions of the river waters indicate that four reservoirs carbonates silicates evaporites and anthropogenic inputs contribute to the total dissolved loads the chemical weathering rates of carbonates and silicates for the xijiang basin are estimated to be approximately 78 5 and 7 45 ton km 2 a 1 respectively the total chemical weathering rate of rocks for the xijiang basin is approximately 86 1 ton km 2 a 1 or 42 mm ka 1 which is much higher than global mean values the budgets of co2 consumption by carbonate and silicate weathering are estimated to be 284 109 and 54 3 109 mol a 1 respectively it would appear that h2so4 is involved as a proton donor in weathering reactions in the xijiang basin calculated results show that the contribution of cations from rock weathering induced by h2so4 accounts for approximately 11 2 results from this study show that the flux of co2 released into the atmosphere is approximately 0 1 106 mol c km 2 a 1 or 0 41 1012 g c a 1 produced by h2so4 induced carbonate weathering in the basin when extrapolated to the entire surface area of carbonate in sw china the flux of co2 released to the atmosphere by h2so4 induced carbonate weathering is about 1 41 1012 g c a 1

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

major element chemistry of the changjiang yangtze river the chemistry of major elements ca mg na k hco3 so4 cl and si in the river water of the changjiang yangtze river was studied based on continuously monitored data at 191 stations in the drainage basin for the period 1958 1990 the results show that the total dissolved solid tds concentration of the changjiang varies over an order of magnitude throughout the basin 49 7 518 1 mg l with a medium tds concentration of 205 9 mg l about three times the global average in contrast the tds at a given main channel station varies only slightly in different seasons with a variation factor less than 2 0 despite a substantial water dilution in the summer flood season the major element chemistry of the changjiang is mainly controlled by rock weathering with the anion hco3 and the cation ca dominating the major ion composition due to the abundance of carbonate rocks in the basin a persistently increasing trend has been observed in the concentrations of so4 and to a lesser extent cl in the changjiang a signature of considerable anthropogenic impacts e g acid deposition flux calculations at datong the most downstream main channel station without tidal influence indicate that the changjiang transports ca 154 106 tons year of tds to the sea second only to the amazon in the world

the fluvial geochemistry of the rivers of eastern siberia ii tributaries of the lena omoloy yana indigirka kolyma and anadyr draining the collisional accretionary zone of the verkhoyansk and cherskiy ranges fundamental to the global carbon cycle over geologic time scales is the control of atmospheric co2 by aluminosilicate weathering much of the information on the rates of this process comes from rivers in the tropics and subtropics to understand the possible climatic influences systematic studies are needed for the arctic subarctic regions this is the second in a series of papers addressing this problem by systematic studies of the pristine rivers of the russian far east the region to the east of the siberian platform huh et al 1998 is a geologically complex terrain formed by the mesozoic collision and accretion of the siberian and kolyma plates because of the arid continental climate it has not been glaciated in the recent past thus it is possible to study weathering processes in an arctic environment dominated solely by cryogenic interactions without contamination by heterogeneous components derived from scouring glaciers all the major rivers and their tributaries in this area have been sampled on expeditions to individual basins 100 samples on a reconnaissance basis at falling stage usually in july and august the total dissolved cation levels tz are moderate up to 3 100 eq and the major ion chemistry is indicative of ca aluminosilicate and carbonate weathering with significant contributions from black shales in some tributaries the si tz si na k and 87sr 86sr ratios indicate that the weathering is superficial i e only to cation rich secondary minerals the areal total dissolved solid fluxes range from 0 04 to 0 39 106 mol km2 yr up to an order of magnitude lower than for the amazon orinoco draining the andes in the tropics 0 6 4 1 106 mol km2 yr the co2 consumption by aluminosilicate weathering 18 230 103 mol km2 yr is also at the lower end of the range observed in the amazon orinoco headwaters 143 1 000 103 mol km2 yr however as the north american counterparts in similar latitudes and with comparable relief the mackenzie yukon and fraser draining the rockies also have high dissolved solids 0 2 2 9 106 mol km2 yr and co2 19 1 750 103 mol km2 yr fluxes these low values seem to be more a function of lithology than simply climate ice action in cold environments appears to overcome the inhibiting effects of the decreased temperatures and lack of precipitation in producing a high chemical yield but results in superficial weathering in the case of aluminosilicates

seasonally chemical weathering and co2 consumption flux of lake qinghai river system in the northeastern tibetan plateau the major cation and anion compositions of waters from the lake qinghai river system lqrs in the northeastern tibetan plateau were measured the waters were collected seasonally from five main rivers during pre monsoon late may monsoon late july and post monsoon middle october the lqrs waters are all very alkaline and have high concentrations of tds total dissolved solids compared to rivers draining the himalayas and the southeastern tibetan plateau seasonal variations in the water chemistry show that except the daotang river the tds concentration is high in october and low in july in the lqrs waters the forward models were used to quantify the input of three main rivers buha river shaliu river and hargai river from rain halite carbonates and silicates the results suggest that 1 atmospheric input is the first important source for the waters of the buha river and the shaliu river contributing 36 57 of the total dissolved cations 2 carbonate weathering input and atmospheric input have equal contribution to the hargai river water 3 carbonate weathering has higher contribution to these rivers than silicate weathering and 4 halite is also important source for the buha river the daotang river water is dominated by halite input owing to its underlying old lacustrine sediments the water compositions of the heima river are controlled by carbonate weathering and rainfall input in monsoon season and groundwater input may be important in pre monsoon and post monsoon seasons after being corrected the atmospheric input average co2 drawdown via silicate weathering in the lqrs is 35 103 mol km2 per year with highest in monsoon season lower than himalayas and periphery of tibetan plateau rivers but higher than some rivers draining shields

a holocene sedimentary record from bosten lake china abstract a 9 24 m long sediment record from the kaidu river delta margin of bosten lake northwestern china provides evidence for changes in water balance of the lake during the past 8600 calendar years quantitative and qualitative analyses of detrital components authigenic calcite toc and sr ca molar ratios as well as comparisons with selected ostracod assemblages show that lake level fluctuations at minimum 5 6 m display changes in effective moisture supply mainly driven by the west wind system distinct periods of negative water balances and thus dry conditions are dated to 8 5 8 1 7 3 7 1 around 6 0 at 5 4 5 0 4 6 4 3 3 9 3 6 3 4 3 2 2 6 2 5 1 9 1 1 0 5 0 3 and 0 18 0 05 cal ky bp and match the regional and global pattern of climate shifts during the holocene temporal shifts of moisture availability during mid holocene time were recognised as well and may be attributed to regionally different airflow conditions the last 150 years of rising lake levels are accompanied by strong eutrophication as a result of increased human impact

fluvial geochemistry of the eastern slope of the northeastern andes and its foredeep in the drainage of the orinoco in colombia and venezuela abstract the fluvial geochemistry of the tributaries of the orinoco draining the eastern branch of the northern andes in colombia and venezuela is determined by lithology and ranges from rivers dominated by aluminosilicate weathering mainly of shales and mafic rocks to those bearing the signatures of dissolution of marine limestones and evaporites and of continental playa deposits these left bank tributaries of the orinoco provide the overwhelming proportion of the suspended and dissolved loads transported by the main stem although feeding only half the discharge however due to the extreme severity of weathering on the guayana shield the right bank tributaries supply about half the silica and 40 of the k carried by the orinoco there is a similar partitioning between the andes and the lowlands in the amazon drainage in contrast the mackenzie which drains the northern extremity of the continental arc of the western americas is completely dominated by the weathering of limestones and evaporites and transports very little silica this again appears to be a reflection of lithology since the yukon in similar latitudes and terrain has silica concentrations comparable to the tropical systems in addition a conservative deconvolution of the data gives estimates of the net consumption of atmospheric co 2 by aluminosilicate weathering that follows the same pattern thus the available evidence from the western americas indicates that exposure and lithology rather than the climatic variables temperature and runoff dominate the weathering yields in active orogenic belts these observations contradict the conventional view of weathering processes and their controls and are at complete variance with the assumptions parameterised in most models of the geochemical cycle

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

geochemistry of the dissolved load of the changjiang basin rivers anthropogenic impacts and chemical weathering abstract this study focuses on the chemical and sr isotopic compositions of the dissolved load of the rivers of the changjiang basin one of the largest riverine systems in the world water samples were collected in august 2006 from the main tributaries and the main changjiang channel the chemical and isotopic analyses indicated that four major reservoirs carbonates silicates evaporites and agriculture urban effluents contribute to the total dissolved solutes the overall chemical weathering carbonate and silicate rate for the changjiang is approximately 40 ton km2 year or 19 mm kyr similar to that of the ganges brahmaputra system and the basin is characterized by carbonate and silicate weathering rates ranging from 17 to 56 ton km2 year and from 0 7 to 7 1 ton km2 year respectively in the lower reach of the changjiang main channel the weathering rates are estimated to be 36 and 2 2 ton km2 year for carbonates and silicates respectively it appears that sulphuric acid may dominate chemical weathering reactions for some sub basins the budgets of co2 consumption are estimated to be 646 109 and 191 109 mol year by carbonate and silicate weathering respectively the contribution of the anthropogenic inputs to the cationic tds of the changjiang is estimated to be 15 20 for the most downstream stations our study suggested that the changjiang is strongly impacted by human activities and is very sensitive to the change of land use

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

geochemistry and quality of groundwater of gummanampadu sub basin guntur district andhra pradesh india groundwater survey has been carried out in the area of gummanampadu sub basin located in guntur district andhra pradesh india for assessing the factors that are responsible for changing of groundwater chemistry and consequent deterioration of groundwater quality where the groundwater is a prime source for drinking and irrigation due to non availability of surface water in time the area is underlain by the archaean gneissic complex over which the proterozoic cumbhum rocks occur the results of the plotting of ca2 mg2 versus hco3 co32 ca2 mg2 versus total cations na k versus total cations cl so42 versus na k na versus cl na versus hco3 co32 na versus ca2 and na cl versus ec indicate that the rock water interaction under alkaline condition is the main mechanism in activating mineral dissociation and dissolution causing the release of ca2 mg2 na k hco3 co32 so42 and f ions into the groundwater the ionic relations also suggest that the higher concentrations of na and cl ions are the results of ion exchange and evaporation the influences of anthropogenic sources are the other cause for increasing of mg2 na cl so42 and no3 ions further the excess alkaline condition in water accelerates more effective dissolution of f bearing minerals moreover the chemical data plotted in the piper s gibbs s and langelier ludwig s diagrams computed for the chloro alkaline and saturation indices and analyzed in the principal component analysis support the above hypothesis the groundwater quality is thus characterized by na ca2 mg2 k hco3 co32 cl so42 no3 f facies on the other hand majority of groundwater samples are not suitable for drinking with reference to the concentrations of tds th mg2 and f while those are not good for irrigation with respect to ussl s and wilcox s diagrams residual sodium carbonate and magnesium hazard but they are safe for irrigation with respect to permeability index thus the study recommends suitable management measures to improve health conditions as well as to increase agricultural output

chemical weathering in the upper huang he yellow river draining the eastern qinghai tibet plateau we examined the fluvial geochemistry of the huang he yellow river in its headwaters to determine natural chemical weathering rates on the northeastern qinghai tibet plateau where anthropogenic impact is considered small qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution most samples are supersaturated with respect to calcite dolomite and atmospheric co2 with moderate 0 710 0 715 87 sr 86 sr ratios while six out of 21 total samples have especially high concentrations of na ca mg cl and so4 from weathering of evaporites we used inversion model calculations to apportion the total dissolved cations to rain evaporite carbonate and silicate origin the samples are either carbonate or evaporite dominated but the relative contributions of the four sources vary widely among samples net co2 consumption rates by silicate weathering 6 120 10 3 mol km 2 yr are low and have a relative uncertainty of 40 we extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide the ganges brahmaputra draining the himalayan front has higher co2 consumption rates 110 570 10 3 mol km 2 yr and more radiogenic 87 sr 86 sr 0 715 1 24 than the upper huang he but the rivers at higher latitudes are similar to or lower than the upper huang he in co2 uptake by silicate weathering in these orogenic zones silicate weathering rates are only weakly coupled with temperature and become independent of runoff above 800 mm yr copyright 2005 elsevier ltd

major ion chemistry weathering process and water quality of natural waters in the bosten lake catchment in an extreme arid region nw china the concentrations of major ions in the surface water and the groundwater of the bosten lake catchment before and during rainy seasons were analyzed to determine the major ion chemistry geochemical process and to assess the water quality for drinking and irrigation purposes natural waters were hard fresh water with an alkaline nature and a ca2 hco3 water type although much of physicochemical parameters were under the highest desirable limits set by the chinese government for drinking purpose some samples were not suitable for drinking with reference to the concentrations of no3 and so4 2 the sodium adsorption ratio and sodium percentage na values indicated that most waters were suitable for irrigation seasonal variations of ion concentrations and water quality were minor saturation index in waters showed that most of the waters were oversaturated with respect to aragonite calcite dolomite and magnesite whereas under saturated to gypsum and halite carbonate weathering and evaporite dissolution were the primary and secondary sources of the dissolved ions whereas anthropogenic input played a minor role for the sustainable development of bosten lake a reduction of discharge water from salt washing and an increase in the fresh water inflow to the lake are needed

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

melt season duration on canadian arctic ice caps 2000 2004 1 the extent and duration of summer melt on ice caps in the queen elizabeth islands qei nunavut canada in 2000 2004 were mapped using enhanced resolution quikscat qscat scatterometer images the mean melt duration depends mainly on surface elevation and distance from baffin bay over most ice caps inter annual variations in melt duration and the variation in melt duration with elevation are closely related to variations in the july 500 hpa height over the qei pressure related variability in the vertical gradient of near surface air temperature appears to be a major control on the inter annual variations in average melt duration