chlorine stable isotope evidence for salinization processes of confined groundwater in southwestern nobi plain aquifer system central japan summary a confined aquifer system isolated from modern seawater is developed in argillaceous marine and freshwater sediments of pliocene holocene age in southwestern nobi plain swnp central japan a tongue of brackish confined groundwater cl 1000 mg l which extends from the shoreline of ise bay inland mostly has negative 37 cl values with 0 90 to 0 21 the cl isotopic compositions are negatively correlated with paleo seawater cl concentrations discriminated by a rayleigh distillation model with 34 s values while they are not correlated with either total cl concentrations or 34 s values furthermore cl concentrations from modern seawater are positively correlated with 37 cl values in addition to these observations diffusion model calculations suggest that paleo seawater cl has diffused out from argillaceous marine sediments whereas modern seawater cl has not been affected by preferential diffusion of cl isotopes because it has migrated by advection via both an unconfined aquifer and non pumping wells moreover the brackish groundwater is characterized by an excess of na cl ratio and deficits of mg cl and ca cl ratios compared to those predicted from simple mixing of freshwater with seawater this would be caused by cation exchange reactions in the confined aquifer system in which groundwater is freshening after salinization by both paleo seawater and or modern seawater

sulfate reduction and sulfide oxidation in anoxic confined aquifers in the northeastern osaka basin japan summary we used 34s values and chemical compositions of groundwater to investigate the influence of sulfate reduction and sulfide oxidation processes in a confined aquifer system in the northeastern osaka basin neob central japan shallow confined groundwater hco 3 throughout the basin however concentrations of redox sensitive species such as dissolved oxygen no 3 fe2 and mn2 show that groundwater conditions become increasingly anoxic along the flowpaths moreover so4 so4 2hco3 molar ratios decrease with increasing 34s along the flowpaths which demonstrates that sulfate is reduced in the neob aquifer system groundwater with both high total dissolved solids and high so4 content was observed mainly in areas down flow from faults because of the high so4 content the anion composition of this groundwater cannot be adequately explained by a simple sulfate reduction process a rayleigh distillation model with e 20 which allows for sulfide oxidation within marine sediments in proximity to faults explains the chemistry of all groundwater samples including those with high so4 content the model demonstrates that 76 of initial sulfate is reduced at maximum and that reduced so 4 2 content is up to 48 5 mg l after sulfide oxidation in the neob aquifer system

salinization processes in paleowaters in coastal sediments of suriname evidence from δ37cl analysis and diffusion modelling in the coastal plain of suriname a stagnant body of fresh 250 mg l cl and moderately brackish 250 1000 mg l cl groundwater of meteoric origin is found in permeable tertiary formations this groundwater body formed during the last wisconsin regression extends offshore into deposits on the continental shelf the authors found that this paleowater is slowly being salinized by downward solute transport from overlying holocene marine clays and upward transport from saline cretaceous sediments the downward transport has been studied at two sites by relating analyses of chloride contents and 37cl 35cl isotope ratios in pore water with computer simulations of diffusive transport optimization of process parameters yielded an effective diffusion coefficient of and a fractionation factor of 1 0027 which agrees well with earlier studies with the computer model the following periods of marine influence were found 6000 4 100 yr bp and 10 000 500 yr bp at the sites located 20 and 3 km from the coastline respectively according to the diffusion model the downward flux of salts has not penetrated deeper than 100 m salts below this depth are thought to originate from the cretaceous sediments however groundwater chloride concentration and chlorine isotope data are scarce below this depth while uncertainty regarding the various regressions and transgressions precludes solute transport modelling clay layers at the base of the tertiary appear to inhibit the upward transport by lateral dispersive mixing at the tertiary cretaceous boundary oil reservoirs are also related to these clay seals the presence of the seal and perhaps the oil below can therefore be predicted by the chloride profile in the upper 250 m

an integrated modelling approach to reconstruct complex solute transport mechanisms cl and δ37cl in pore water of sediments from a former brackish lagoon in the netherlands abstract a one dimensional transport model was developed to reconstruct historical conservative transport of chloride and 37 cl in pore water of sediments from a former brackish lagoon in the netherlands an area now covered by the freshwater lakes ijssel and marken knowledge of the mechanism of historical solute transport in the sediments and environmental conditions during transport is critical in understanding observed pore water chemistry and will form a basis for simulating effects of changing environmental climate change conditions the model synthesizes present knowledge of geology and historical information on storm surges in the area and takes into account processes such as erosion of sediments mixing of pore water sedimentation and diffusion emsd the chemistry of pore water from one particular boring in the area was found to be mainly controlled by alternating seawater and freshwater diffusion models with a constant averaged porosity 0 55 and tortuosity factor 0 3 showed similar results as models incorporating the measured bulk porosity variations 0 4 0 8 and variable tortuosity factors calculated with archie s law the relatively small tortuosity factor either results from anion exclusion or from the heterogeneous build up of the profile in which a peaty layer in the middle part may obstruct diffusion diffusion of 35 cl was found to be 1 0017 times faster than of 37 cl seawater diffusion into the sediments started at least 400 years ago and refreshening took place since the lagoon was isolated from the sea by a dam in 1932

sulfur isotope constraint on the provenance of salinity in a confined aquifer system of the southwestern nobi plain central japan abstract a combination of 34 s values and chemical compositions of brackish groundwater were used to examine the provenance of salinity in a confined aquifer system in the southwestern nobi plain central japan a tongue of brackish confined groundwater cl 1000 mg l which extends from the shoreline of ise bay inland has somewhat lower so 4 cl ratios and higher 34 s values 79 than those of the present seawater although the cation compositions of the brackish groundwater are consistent with values calculated for a mixture of fresh recharge water and seawater the anion compositions cannot be adequately interpreted as derived from such a mixing process alone using a rayleigh distillation model we found that the groundwater chemistry could be explained by sulfate reduction in combination with the mixing of two types of seawaters the present seawater and so 4 free seawater with the fresh recharge water the so 4 free seawater may consist mainly of fossil seawater that was trapped in an aquiclude for thousands of years model calculations based on cl and so 4 2 contents and 34 s values showed that the present and fossil seawaters compose at most 10 7 and 9 4 respectively of the brackish groundwater volume and the reduced so 4 2 content is up to 353 mg l in the confined aquifer the model s discrimination of the two seawaters is also in agreement with the spatial distribution patterns of groundwater composition from the west to the east in succession the main influence on the groundwater chemistry is fresh recharge water the present seawater and the fossil seawater moreover the area of intrusion of present seawater predicted by the model agrees well with the area of seawater intrusion determined from water quality data obtained a decade ago indicating that the model calculations can be reasonably used to discriminate quantitatively between present and fossil seawaters

isotopic and geochemical characterization of salinization in the shallow aquifers of a reclaimed subsiding zone the southern venice lagoon coastland summary the coastal plain bordering the southern venice lagoon is a reclaimed lowland characterized by high subsidence rate and ground level and water table depth below sea level in this agricultural region where the surface hydrologic network is entirely artificially controlled by irrigation drainage canals salinization problems have long been encountered in soils and groundwaters here we use isotopic and geochemical tracers to improve our understanding of the origin of salinization and mineralization of the semi confined aquifer 0 40 m and the freshwater inputs to this hydrological system water samples have been collected at different seasons in the coastal adriatic sea lagoon rivers and irrigation canals as well as in the semi confined aquifer at depths between 12 and 35 m 14 boreholes and in the first confined aquifer three boreholes drilled between 40 and 80 m depth stable isotopes 18 o and d and conductivity profiles show that direct saline intrusion from the sea or the lagoon is observed only in a restricted coastal strip while brackish groundwaters are found over the entire topographic and piezometric depression in the centre of the study area fresh groundwaters are found only in the most western zone the sharp isotopic contrast between the western and central regions suggests disconnected hydrological circulations between these two parts of the shallow aquifer the border between these two regions also corresponds to the limits of the most strongly subsiding zone our results can be interpreted in terms of a four end member mixing scheme involving 1 marine water from the lagoon or the open sea 2 alpine and pre alpine regional recharge waters carried either by the main rivers adige bacchiglione and brenta irrigation waters or by the regional groundwater circulation 3 local precipitation and 4 evaporated waters infiltrated from the surface infiltration from the surface is also revealed by the stratification of the electrical conductivity profiles showing that the brackish groundwaters are overlain by a shallow layer of less saline water all over the central depression in the first confined aquifer the groundwaters have isotopic compositions similar to the deep groundwaters of the venetian confined aquifers 40 400 m depth the isotopic data and the br cl ratio show that the origin of the salinization of the phreatic aquifer can be ascribed to seawater intrusion alone with no indication of the involvement of deep brines identified at 450 m depth in the process the chemical composition of the saline and brackish groundwaters is characterized by an excess of sodium and a deficit of calcium compared to conservative mixing between fresh groundwaters and seawater this suggests that the phreatic aquifer is progressively freshening as a consequence of the beneficial influence of the extensive irrigation drainage network including raised canals acting as a hydraulic barrier along the coast this freshening tendency may have been lasting since the reclamation in the mid twentieth century and has probably been accelerated by the ban on groundwater abstraction since the 1970s

using 87sr 86sr δ18o and δ2h isotopes along with major chemical composition to assess groundwater salinization in lower shire valley malawi abstract groundwater resources in some parts of the lower section of shire river valley malawi are not useable for rural domestic water supply due to high salinity in this study a combined assessment of isotopic 87 sr 86 sr 18 o and 2 h and major ion composition was conducted in order to identify the hydro geochemical evolution of the groundwater and thereby the causes of salinity three major end members representing fresh and saline groundwater and evaporated recharge were identified based on major ion and isotopic composition the saline groundwater is inferred to result from dissolution of evaporitic salts halite and the fresh groundwater shows influence of silicate weathering conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end members hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater on the other hand the groundwater with low tds found at some distance from areas of high salinity is influenced by mixing of evaporated recharge and fresh groundwater only close to the shire marshes where there is shallow groundwater composition of stable isotopes of water indicates that evaporation may also be an important factor

contributions of c3 c4 organic materials and carbonate rock to dissolved inorganic carbon in a karst groundwater system on miyakojima island southwestern japan summary groundwater 13 c values and chemical compositions were employed to quantitatively evaluate the controlling processes and sources of dissolved inorganic carbon in a karst aquifer system on miyakojima island mi southwestern japan most mi groundwater is ca hco 3 type water but some na cl ca cl or na hco 3 type groundwaters occur formed mainly by seawater intrusion and partly by cation exchange reactions calculations using the wateq4f and phreeqc programs revealed that all mi groundwater not just the ca hco 3 type was strongly influenced by calcite dissolution in a karst aquifer system open with respect to soil co 2 initially derived from organic materials with mainly around 10 50 matm as pco 2 and that most groundwater was saturated with respect to calcite moreover oxidation of ammonium sulfate applied as fertilizer added h to the mi groundwater resulting in surplus calcite dissolution these processes sufficiently explained contents of alkalinity dic and ca 2 in the groundwater and were evaluated by model calculation using the phreeqc program with measured groundwater 13 c and ph values the results showed that the average mass fractions of dissolved inorganic carbon dic initially from calcite dissolution and c3 and c4 organic materials in the groundwater were 46 4 18 5 and 35 1 respectively the model results regarding the origins of dic in the groundwater agreed fairly well with land use distributions on mi in particular with the spatial distribution of forest and sugarcane fields and gave us some constrains of groundwater recharge areas and flowpaths

a survey of groundwater levels and hydrogeochemistry in irrigated fields in the karamay agricultural development area northwest china implications for soil and groundwater salinity resulting from surface water transfer for irrigation analysis of the water budget along with hydrochemistry and stable isotopes in shallow groundwater were carried out in the karamay agricultural development area kada in order to assess the impact of transfer of irrigation water from the irtysh river in particular in relation to the mechanisms of salinization and the nature of the water table regime in terms of aquifer dynamics the addition of the irrigation water without any groundwater abstraction has caused a sharp rise in the water table is and the development of serious soil salinity together with an almost complete attenuation of inter seasonal water table oscillations the mean rise in the groundwater table from september 1997 to october 2009 was 6 9 m representing an accumulated total water storage change of close to 150 million cubic meters the analysis of aquifer water budget shows that infiltration of irrigation water occupied over 90 of the total recharge of the groundwater in the kada sources of groundwater recharge and mechanisms of salinization in the kada were also investigated using geochemical and isotopic techniques the groundwater is characterized by cl so 4 na type generally becoming more na and cl dominated with increasing salinity the total dissolved solids tds content of the groundwater ranges from 0 5 g l to over 65 g l with greater tds values in areas of low topographic relief and shallow water tables where the sediments are more permeable e g due to the presence of palaeochannels tds values are generally lower and the seasonal water table fluctuations greater the ratios of k cl ca cl na cl and mg cl decrease with increasing cl concentrations especially in the shallow groundwater from 10 to 15 m depth indicating hydrogeochemical evolution via minor water rock interaction feldspar weathering and significant evaporation the stable isotopic compositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetrically important source of recharge to the shallow aquifer preferential recharge of river water after irrigation events and or precipitation from rare heavy rain events is likely responsible for the depleted 2 h and 18 o values in some of the groundwater samples the negative relationship between deuterium excess and 18 o values indicates that even in groundwater with relatively depleted 2 h and 18 o values evaporation has occurred to a significant degree careful management of water quantity and quality and implementation of salinity management strategies are considered necessary in order to reduce the risk of further salt accumulation and damage to farming and local ecosystems

the last glaciation of bear peninsula central amundsen sea embayment of antarctica constraints on timing and duration revealed by in situ cosmogenic 14c and 10be dating abstract ice streams in the pine island thwaites region of west antarctica currently dominate contributions to sea level rise from the antarctic ice sheet predictions of future ice mass loss from this area rely on physical models that are validated with geological constraints on past extent thickness and timing of ice cover however terrestrial records of ice sheet history from the region remain sparse resulting in significant model uncertainties we report glacial geological evidence for the duration and timing of the last glaciation of hunt bluff in the central amundsen sea embayment a multi nuclide approach was used measuring cosmogenic 10be and in situ 14c in bedrock surfaces and a perched erratic cobble bedrock 10be ages 118 144 ka reflect multiple periods of exposure and ice cover not continuous exposure since the last interglacial as had previously been hypothesized in situ 14c dating suggests that the last glaciation of hunt bluff did not start until 21 1 5 8 ka probably during the last glacial maximum and finished by 9 6 0 9 ka at the same time as ice sheet retreat from the continental shelf was complete thickening of ice at hunt bluff most likely post dated the maximum extent of grounded ice on the outer continental shelf flow re organisation provides a possible explanation for this with the date for onset of ice cover at hunt bluff providing a minimum age for the timing of convergence of the dotson and getz tributaries to form a single palaeo ice stream this is the first time that timing of onset of ice cover has been constrained in the amundsen sea embayment

deep electromagnetic sounding in turkmenia summary this paper presents the results of interpretation of magnetotelluric and magnetovariational observations in a vast region including the southern part of the turanian plate and the south caspian megadepression both l d and 2 d interpretations fail to explain the main peculiarities of the natural magnetotelluric and magnetovariational fields observed in the region the 3 d interpretation used in the paper is based on thin sheet modelling and inversion algorithms developed by the authors the final model consists of an inhomogeneous surface layer and a conductive layer embedded in the otherwise laterally uniform medium in the crust under the kopet dagh mountains the surface layer conductance varies between 100 s and 13 ooo s and the crustal anomaly has a conductance of about 2500 s the layered regional structure includes a conductive layer at a depth of 80 100 km whose conductance is about 1800 s the model explains all of the main features of the observed magnetotelluric and magnetovariational fields in the region

controls on bacterial sulphate reduction in a dual porosity aquifer system the lincolnshire limestone aquifer england abstract chemical and sulphur isotopic analyses are presented of fissure waters and pore waters in the deep confined zone of a dual porosity carbonate aquifer some of the fissure waters show good evidence for bacterial sulphate reduction with low concentrations of sulphide present which is strongly to moderately depleted in 34 s relative to sulphate the sulphur geochemistry is best interpreted as mixing between i a reduced water with sulphide 60 depleted in 34 s relative to sulphate and ii a sulphate rich water from up dip in the aquifer in addition sulphide oxidation occurs where sufficiently oxidizing water is drawn in by abstractions the large isotope fractionation factor associated with the sulphidic waters is probably the result of redox cycling of sulphur with little net reduction rather than a true kinetic fractionation factor by contrast pore waters in the sulphate reducing zone show little or no evidence for the effects of sulphate reduction despite the fact that the pore waters represent a significant reservoir of sulphate for reduction some pore waters have been modified recognizably by diffusional exchange with the fissure waters but the aquifer matrix has not been colonized by sulphate reducing bacteria probably because porethroats in the limestone are too small for bacteria to pass physical exclusion of bacteria from the aquifer matrix and limited diffusional exchange are likely to exert fundamental controls on bacterial redox processes in dual porosity aquifer systems and other systems with low permeability due to small pore interconnections

mechanical limits to microbial activity in deep sediments the observed decline in microbial abundance with increasing depth has been associated to various environmental factors meanwhile the role of geometrical constraints and soil bacteria mechanical interactions remains poorly analyzed pore and pore throat sizes may restrict habitable pore space and traversable interconnected porosity and sediment cell interaction may cause puncture or tensile failure of the cell membrane in this study we compile published evidence on the presence of bacteria in deep sediments as well as pore and pore throat size data in sediments at different depths to establish possible geometrical conditions for the sediment cell complex compiled data are complemented with experimental results gathered through controlled axial compression experiments that reproduce the mechanical consolidation of deep sediment sequences then we analyze the mechanical interaction between bacteria and sediments that may cause cell death finally we combine data and model predictions to define the main regions in a particle size versus depth space that characterize the fate of bacteria active and motile trapped inside pores and dead or dormant these regions constrain hypotheses related to the role of biological activity in deep sediments research protocols and sampling methods the viability of bioremediation strategies for contaminated sites and the potential development of bioengineered sediments

chlorine stable isotope studies of old groundwater southwestern great artesian basin australia abstract stable cl isotope ratios 37 cl 35 cl were measured in groundwater samples from the southwestern flow system of the great artesian basin australia to gain a better understanding of the cl sources and transport mechanisms 37 cl values range from 0 to 2 5 smoc and are inversely correlated with cl concentration along the inferred flow direction the cl isotopic compositions in conjunction with other geochemical parameters suggest that cl in groundwaters is not derived from salt dissolution mixing of the recharge water with saline groundwater cannot explain the relationship between 37 cl and cl concentration measured marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the cl concentrations observed in wells that are close to the recharge area and in groundwaters sampled along the southern transect 37 cl values measured in the leachate of the bulldog shale suggest that the aquitard is the subsurface source of cl for the majority of groundwater samples studied diffusion is likely the mechanism through which cl is transported from the pore water of the bulldog shale to the aquifer however a more detailed study of the aquitard rocks is required to verify this hypothesis

sulfide oxidation and sulfate reduction in a shallow groundwater system oderbruch aquifer germany abstract detailed groundwater monitoring was carried out over a period of two years in an anoxic river recharged aquifer of the oderbruch polder north eastern germany isotope data from wells located in a 5 km transect along the flow direction was used to determine sources and sinks of so 4 2 in the aquifer the so 4 2 originates from river water infiltration and from oxidative dissolution of fes 2 within the alluvial loam covering the aquifer sands a change of confined hydraulic conditions near the river to unconfined conditions in the central polder effects the hydrochemistry of the aquifer the confined areas are dominated by sulfate reduction increasing 34 s so 4 values suggest continuous but slow t 1 2 50 years sulfate reduction from the beginning of inflow onwards with 34 s so 4 values ranging from 1 8 to 44 7 versus cdt and an enrichment factor of 33 a zone with a strong sulfate depletion 34 s so 4 of up to 85 7 exists in a shallow microenvironment rich in solid phase organic carbon between river and levee in the unconfined areas of the central polder a so 4 2 plume with concentrations exceeding the original river water content indicates fes 2 oxidation by o 2 and or no 3 within the alluvial loam the lowered 34 s so 4 value reflects the input of the isotopically lighter so 4 2 from the sulfide

sulphur and oxygen isotopes of dissolved sulphur species in formation waters from the dogger geothermal aquifer paris basin france isotopic analyses of the s in sulphides and sulphates from formation waters were made at 35 geothermal wells exploiting the dogger geothermal aquifer of the paris basin isotopic analyses of the o of the dissolved sulphates were also made on 12 of these the results show a distribution of the 34s of the sulphates according to geographic zones that also correspond to variations in the geochemistry of the fluids in particular the sulphide content samples taken in the seine st denis area and in the areas north and west of paris show high 34s values ranging from 26 3 to 48 9 values of 34s for sulphides range from 8 5 to 5 and are interpreted as reflecting the effect of bacterial reduction in a confined part of the basin modelling this reduction by a rayleigh distillation mechanism made it possible to calculate a value of 1 038 0 003 for the coefficient of fractionation between the sulphates and sulphides we show that an important part of the sulphides formed by bacterial reduction has been subtracted from the fluid by deposition south of paris and in the val de marne the 34s values for the sulphates are more uniform ranging between 22 4 and 26 6 despite the existence of bacterial activity this is most probably due to a higher rate of flow of the waters entailing renewal of the sulphate stock the isotopic composition of the o of the sulphates for the seine st denis area and the areas west and north of paris is very uniform between 16 1 and 17 1 despite the wide range in 34s 26 3 to 48 9 for the same samples the calculated isotopic temperatures are close to those measured in situ these results suggest either that sulphate water isotopic equilibrium was established after the reduction or that the coefficient of o fractionation is very low 1 003 during bacterial reduction

lithological controls on biological activity and groundwater chemistry in quaternary sediments depth profiles of solute chemistry and sulfate isotopic compositions are presented for groundwater and pore water in a sequence of quaternary glacial outwash sediments sand units show evidence for hydraulic connection to the surface and thus modern sources of solutes finer grained sediments show a general pattern of increasing solute concentrations with depth with sulfate derived from ancient rainwater and pyrite oxidation in the soil drift in these sediments sulfate has undergone bacterial sulfate reduction bsr to produce biogenic sulfide in clay sediments with d10 1 6 m high concentrations of sulfate and acetate now co exist implying that bsr is inhibited the correlation with smaller sediment grain size indicates that this is due to pore size exclusion of the sulfate reducing bacteria mechanical restriction of microbial function thus provides a fundamental limitation on microbial respiration in buried clay rich sediments which acts as a control on the chemical evolution of their pore waters copyright 2009 john wiley sons ltd

processes affecting groundwater chemistry in a zone of saline intrusion into an urban sandstone aquifer abstract samples have been collected from inflows into railway tunnels in the triassic sandstone aquifer beneath liverpool and the mersey estuary england u k these provide a profile through a saline freshwater mixing zone analyses were made of major anions and cations 34s and 18o in so4 13c in dissolved inorganic c and 87sr 86sr the data demonstrate that the presence of a low permeability fault exerts a strong control on the local groundwater chemistry on the estuary side of the fault groundwater chemistry is dominated by mixing of intruding estuary water which is modified by so4 reduction and calcite dissolution with fresh groundwater the environment of so4 reduction in the tidal estuary is one of repeated reduction and re oxidation of s in an open system and has resulted in virtually no change in s isotopic composition but an enrichment in residual so4 18o of 1 5 groundwater chemistry on the landward side of the fault is primarily the result of recharge in an urban environment there is also evidence that saline water has been present in this region of the aquifer in the past and that this has now been flushed by fresh groundwaters this saline water was either transported along the landward side of the fault from nearer the estuary or more probably transmitted across the fault both mechanisms would have been driven by large landward head gradients caused by heavy industrial abstraction earlier this century this has produced a zone of groundwaters depleted in ca and radiogenic sr and enriched in na as a result of ion exchange between the fresh groundwaters and the aquifer previously occupied by more saline water sulphur isotopic composition however shows no variation since so4 does not undergo significant ion exchange a tracer test from a borehole to the tunnels showed multiple breakthroughs to some locations indicating a number of different flow paths through the aquifer the maximum flow velocity recorded in this test was 140 m d suggesting flow along fractures

preferential diffusion of 35cl relative to 37cl in sediments of kau bay halmahera indonesia kau bay a 470 m deep basin is separated from the pacific ocean by a shallow 40 m deep sill during the last glaciation this sill was above sea level and the bay turned into a freshwater lake after glaciation the sea level rose and the bay turned saline again since then chloride from the newly formed saline sediments diffused into the freshwater sediments as the sedimentation rate was constant throughout the holocene it is relatively easy to model the chloride concentration in the sediment pore water the diffusion coefficient of 35cl is slightly higher than the diffusion coefficient of 37cl thus variations in 37cl were expected in the pore water because the pore water history of kau bay is well known it was possible to use 37cl variations to determine the diffusion coefficient ratio d35d37 for the two stable isotopes of chlorine it was found that this ratio is 1 0023 in the pore water from sediments in this bay

controls on δ 34 s and δ 18 o of dissolved sulfate in aquifers of the murray basin australia and their use as indicators of flow processes the usefulness of stable isotopes of dissolved so4 34s and 18o to study recharge processes and to identify areas of significant inter aquifer mixing was evaluated in a large semi arid groundwater basin in south eastern australia the murray basin the distinct isotopic signatures in the oxidizing unconfined murray group aquifer and the deeper reducing renmark group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections 34s values in the unconfined murray group aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20 8 to 0 3 the concomitant increasing so4 cl ratios as well as relatively low 18oso4 values suggest that vertical input of biogenically derived so4 via diffuse recharge is the predominant source of dissolved so4 to the aquifer further along the hydraulic gradient towards the discharge area near the river murray 34s values in the unconfined murray group aquifer increase and so4 cl ratios decrease due to upward leakage of waters from the confined renmark group aquifer which has a distinctly low so4 cl and high 34s 14 9 56 4 relatively positive 34s and 18oso4 values and low so4 cl in the renmark group aquifer is typical of so4 removal by bacterial reduction the s isotope fractionation between so4 and hs of 24 estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation 70 even though the confined groundwater residence time is 300 ka years mapping the spatial distribution of 34s and so4 cl of the unconfined murray group aquifer provides an indicative tool for identifying the approximate extent of mixing however the poorly defined end member isotopic signatures precludes quantitative estimates of mixing fractions

fractionation of sulphur isotopes during biogenic sulphate reduction below a sandy forested recharge area in south central canada abstract detailed groundwater monitoring below a sandy forested recharge area in south central canada shows that atmospherically derived so2 4 occurring at concentrations of 6 27 mg l 1 in the shallow aquifer is completely consumed within a zone of less than 6 m thickness encountered at about 15 m depth the so2 4 depletion zone is anoxic which suggests that biogenic sulphate reduction is the principal so2 4 depleting process the field evidence suggests that in this environment the reduction reaction is similar to a first order decay process with a relatively short half life of about 3 years isotopic fractionation of so2 4 s is observed during the reaction and can be described by a rayleigh type distillation process governed by an enrichment factor averaging 15 5

chloride and chlorine isotopes 36cl and δ37cl as tracers of solute migration in a thick clay rich aquitard system detailed vertical profiles of dissolved cl and its isotopes 36cl and 37cl provided new information on the origin and systematics of this conservative tracer in pore waters of a thick aquitard system the aquitard system consists of surficial quaternary clay rich till 80 m thick deposited 30 20 kyr b p overlying cretaceous marine clay 76 m thick deposited 71 ma the distribution of cl 37cl and br showed the presence of five distinct end members for cl the top of the unoxidized till a regional aquifer underlying the cretaceous clay two localized geological heterogeneities sand streaks in the till and glacial meltwater emplaced with the till and still present at depths of between 36 and 60 m numerical simulations of the transport of cl from the sand streaks indicated that this geochemical profile has been developing throughout most of the holocene the 36cl measurements showed that the age of the dissolved cl in the upper cretaceous clay is likely between 0 75 and 1 9 myr the 36cl measurements further suggested that the dissolved cl in the till was not directly derived from the underlying cretaceous clay finally it was not possible to quantify the effects of isotopic fractionation of 37cl relative to 35cl because of diffusion in this aquitard system

controls on the regional scale salinization of the ogallala aquifer southern high plains texas usa an extensive saline plume 250 km 2 within the regionally important unconfined aquifer in the neogene ogallala formation overlies the panhandle oil and gas field in the southern high plains texas usa relative to upgradient ogallala water the plume waters have d 18 o 6 7 to 8 8 and d d 42 to 88 values that tend to be depleted and have higher cl 150 mg l and so4 75 mg l concentrations various end member mixing models suggest that the plume composition reflects the presence of paleowaters recharged during middle to late wisconsinan time rather than salinization associated with petroleum production paleowaters probably mixed with salt dissolution zone waters from the underlying upper permian formations before discharging upward into the ogallala formation cross formational discharge is controlled primarily by the geometry of the underlying units as influenced by the amarillo uplift pinch out of the laterally adjoining confined aquifer in the triassic dockum group variations in the saturated thickness of the ogallala aquifer and the presence of potential pathways related to salt dissolution 2000 elsevier science ltd all rights reserved

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

hydrogeochemical evolution of confined groundwater in northeastern osaka basin japan estimation of confined groundwater flux based on a cation exchange mass balance method abstract a confined aquifer system has developed in argillaceous marine and freshwater sediments of pliocene holocene age in the northeastern osaka basin neob in central japan the shallow groundwater 3 type water which changes as it flows toward the sw to mg hco 3 type and then to na hco 3 type water comparison of the chemical and sr isotopic compositions of the groundwater with those of the bulk and exchangeable components of the underground sediments indicates that elements leached from the sediments contribute negligibly to the neob aquifer system moreover model calculations show that contributions of paleo seawater in the deep horizon and of river water at the surface are not major factors of chemical change of the groundwater instead the zonal pattern of the hco 3 dominant groundwater is caused by the loss of ca 2 from the water as it is exchanged for mg 2 in clays followed by loss of mg ca as they are exchanged for na k in clays between the ca hco 3 type recharge water and the exchangeable cations in the clay layers which were initially enriched in na part of this process was reproduced in a chromatographic experiment in which na type water with high 87 sr 86 sr was obtained from mg type water with low 87 sr 86 sr by passing it through marine clay packed in a column the flux of recharge water into the confined aquifer system according to this chromatographic model is estimated to be 0 99 mm day which is compatible with the average recharge flux to unconfined groundwater in japan 1 mm day

use of isotope fractionation of sulfate sulfur and sulfate oxygen to assess bacterial desulfurication in a sandy aquifer abstract the unconfined aquifer of the fuhrberger feld consists of 20 30m sands and gravelly sands with unevenly distributed reduced sulfur compounds and small lignitic pebbles in vertical direction two hydrochemically different zones with specific solute transformations are present an upper portion with bacterial denitrification with reduced sulfur compounds as electron donors and a deeper portion with hydrochemical indications of reduction of the aqueous sulfate in the study area ten multilevel groundwater sampling wells were installed sampling and interpretation was based on a two dimensional vertical plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells the concentration and isotopic composition of the sulfate at the entrance into the zone of sulfate reduction is controlled by sulfate of groundwater recharge as well as sulfate formed during denitrification the recharge sulfate shows clear landuse specific differences in concentration and isotopic composition under arable land an average concentration of 60 mg so 4 l 1 with values of 34 s close to 3 cdt diablo meteorite standard canon and of 18 o about 8 standard mean ocean water smow was measured whereas under coniferous forest an average of 100 mg so 4 l 1 with 34 s 2 and 18 o 4 5 was found in the denitrification zone no significant sulfur isotope fractionation occurs during oxidation of reduced sulfur the oxygenisotopic composition of the newly formed sulfate denitrification sulfate depends on the 18 o content of nitrate acting as oxygen donor and on the 18 o content of groundwater in which the oxidation occurs under certain assumptions a 18 o 0 54 was calculated for the oxygen of the newly formed sulfate consequently with increasing sulfate concentrations i e with the admixture of denitrification sulfate a decrease of the 18 o values from about 8 to 2 was observed in the zone of sulfate reduction both the 34 s and 18 o values of the residual sulfate increase with decreasing sulfate concentrations thus proving the existence of bacterial reduction of the aqueous sulfate this sulfate reduction follows a rayleigh process with calculated enrichment factors of 34 9 7 for 34 s and 18 6 for 18 o respectively a plot of 34 s vs 18 o gives a good linear correlation with a slope close to 1 1 4 data on concentration and isotopic composition of sulfate and on the hydraulically derived groundwater age are used for kinetic considerations the results of a multilevel well for depths between 10 and 17m are given as an example the bacterial reduction can be considered as first order reaction with a half life between 75 and 100 years

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

the influence of groundwater currents on diffusion processes in a lake bottom an old report reviewed an internal report by the senior author brought out in 1942 is presented and reviewed with the intention to show the historical developments made around 1940 the diffusion process from a clayey and saline lake bottom towards fresh supernatant water proved to be influenced by slow upward or downward groundwater currents the deviations from the expected diffusion profiles as observed during the period 1936 1938 could be used to find the velocities of such currents even if they are as low as 10 mm year 1 there were areas where water from the underlying pleistocene aquifier discharged into the lake and elsewhere lake water infiltrated to recharge the aquifier the conclusions of the study were in accordance with the geohydrology of the area as existed at that time the theoretical formulation was originally not in closed form but it is shown to be equivalent to a recent analytical solution

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes