validity of the environmental chloride method for recharge evaluation of coastal aquifers india the work presented in the paper was carried out with the objective of ascertaining the validity of environmental chloride method for evaluation of groundwater recharge to the coastal aquifers situated in semi arid tropical area under the influence of monsoonic type of hydrologic regime towards this end a comparative study using environmental chloride in conjunction with injected tritium method the more commonly used method was undertaken in the coastal aquifers of pondicherry situated about 160 km south of madras along the coast of bay of bengal five each of environmental chloride repeated twice and injected tritium profiles were studied in the alluvium and cuddalore aquifers of pondicherry recharge from the chloride study was estimated using 1 concentration approach which involves estimating the relative enrichment of soil chloride concentration in relation to the input chloride and 2 flux approach determining the turnover time of soil moisture by estimating the total chloride in the profile and yearly input recharge from the injected tritium profiles was estimated by studying the displacement of soil moisture during the time interval between sampling and injection of the tracer repeated chloride profiles show fairly good reproducibility within 15 30 of recharge rates determined by the two approaches for two different sampling times at the same site also the results compare well among the two approaches used for the chloride method mean recharge rates obtained by the injected tritium method for the cuddalores is about 26 cm yr 1 and by the chloride method about 22 cm yr 1 and for the alluvium the respective rates are 10 and 14 cm yr 1 this shows fairly good agreement between the two methods the study thus demonstrates conformity of recharge rates determined by the environmental chloride method and injected tritium technique and proves the validity of the chloride method for recharge measurements for tropical coastal aquifers situated in semi arid regions

water salinization in arid regions observations from the negev desert israel abstract the processes affecting salinization of precipitation surface water vadose water and groundwater were studied in the negev desert israel observations spanning 18 years included the collection of rainfall at three rain sampling stations flood water at six flood stations vadose water from four coreholes penetrating chalk formations and groundwater from 16 monitoring wells tapping the chalk aquitard dissolved carbonate dust and evaporation of the falling raindrops result in ca hco 3 2 facies and increased ion concentration of the rainwater with respect to inland more humid regions the exposure of flood water to evaporation during flood events is minimal the observed ca hco 3 2 facies and salt enrichment by a factor of three to five in the flood water with respect to precipitation results primarily from interactions of the flood water with the chalk and limestone bedrock including ion exchange on na and k bearing minerals and the dissolution of calcite gypsum and halite the presence of these salts at and near land surface results from the complete evaporation of rainwater in land surface depression storage areas following most rain events except for a small portion moving through the low permeability chalk matrix most of the vadose water moves through preferential pathways and is typically not exposed to evaporation this dual movement of water accounts for the nacl facies of vadose water and the variable rates of isotopic depletion and salt dilution observed in the underlying heterogeneous groundwater in the saturated zone although the variable mixing with low salinity isotopically depleted water percolating from the fractures accounts for the depleted isotopic composition of the groundwater its relatively low solute content cannot modify the groundwater nacl facies consequently only groundwater salinity in the chalk is reduced by the preferentially flowing water but the ca hco 3 2 facies prevailing in the rainwater and flood water disappears and the nacl imprint from the vadose zone prevails

a thermoconvective interpretation of heat flow data in the area of ocean drilling program leg 116 in a distal part of the bengal fan we present the results of a numerical simulation study of the thermo convective circulation in a sedimentary pile in the distal part of the bengal fan the occurrence of faults and the variability of surface heat flow data led previous workers to suggest hydrothermal circulation in this area according to the purpose of ocean drilling program survey leg 116 data were collected which are adequate to constrain a model for the comprehension and the quantification of the relationship between ocean basin heat flow and pore fluid circulation in this paper the sedimentary pile is modeled as an anisotropic and inclined porous layer interrupted by faults with a periodic distribution an important observation the model tries to reproduce is the shift of approximately 2 3 km between the surface expression of the heat flow maximum and the fault zone near site 718 the influence of permeability anisotropy and of permeability within those fault zones is analyzed when the maximum vertical permeability in the fault zones is 5 times greater than the vertical permeability of the porous block the circulation consists of longitudinal rolls i e rolls with their axis oriented downslope with more vigorous convection in fault zones when the maximum permeability of the fault zone is 10 or more times greater than the vertical permeability of the porous layer convection is primarily restricted to the fault plane in all cases maximum heat flow values are located directly above faults this paper shows that the best agreement between those data suggests a 1 m yr 1 forced convection and a permeability of the sediments of 0 5 darcy 5 10 13 m2 and 5 mdarcy respectively in the horizontal and vertical derictions

re os isotope systematics and weathering of precambrian crustal rocks implications for the marine osmium isotope record the effects of weathering of freshly exposed precambrian rocks on the mobility of osmium were studied on soils developed on a chronosequence of glacial moraines from the western wind river range in wyoming the os budget of the precambrian granitoid source rocks is dominated by os rich trace phases such as magnetite amongst the major silicates biotite or a trace phase in biotite carries most of the os and re and is also the most radiogenic mineral with 187os 186os of 113 and 187re 186os of 2 000 re os isotope systematics of source rocks and soils indicate that rapid oxidation of magnetite mobilizes os with an isotopic composition similar to the isotopic composition of the bulk soils a very radiogenic fraction of os is mobilized through preferential weathering of biotite radiogenic runoff from precambrian shields inferred from osmium isotope analyses of freshwater fe mn nodules suggests that high latitude precambrian shields are important source areas of radiogenic os in seawater we propose that glacial scouring and weathering of glacial tills exposed after deglaciation of precambrian shields surrounding the north atlantic provides a mechanism for the slightly more radiogenic nature of north atlantic seawater compared to other seawater masses glacial interglacial variations in the osmium isotopic composition of seawater seem plausible and may be triggered by changes in weathering regimes on glacial interglacial time scales in high latitude shield areas surrounding the north atlantic

an isotopic study 2h and 18o of water movements in clayey soils under a semiarid climate we applied the natural variations of stable isotopes in water to the study of infiltration in clayey soils and to the study of groundwater recharge in the small drainage basin of barogo in west africa the comparison between the variations in isotopic contents of soil water and rainwater in 1988 and 1989 led us to characterize two infiltration processes 1 an infiltration through the soil matrix of rainwater that mixed with mobile water which was held in the superficial part of the soil and was enriched in heavy isotopes by evaporation and 2 a fast and deeper infiltration by preferential flow along macropores that bypassed the superficial part of the soil the study of the variations in groundwater isotopic content led us again to separate the recharge process into two components 1 a slow infiltration through the soil matrix and the weathered basement distributed recharge and 2 a fast and direct recharge through conducting fissured zones localized recharge a schematic and local representation of groundwater recharge in the barogo basin allowed us to estimate that direct recharge represented around 70 of the total recharge in 1989

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

annual replenishable ground water potential of india an estimate based on injected tritium studies abstract natural recharge is a vital parameter to be known for ground water budgeting management and modelling percolation of a portion of the rainfall through the vadose zone is the principal source of natural recharge to the aquifer systems in india the tritium injection method based on piston flow model is particularly suitable for quantifying the downward flux of moisture in the vadose zone and for measuring natural recharge in indian climatic condition where about 80 of the annual rainfall is received as pulses and occurs during the four monsoon months from june to september natural recharge measurements using the tritium injection method have been carried out in india during the last 25 years in several basins and watersheds located in varying climatic and hydrogeological situations the mean natural recharge values for 35 study areas well distributed over 17 major river basins are presented the recharge rates range from 24 to 198 mm yr 1 or 4 1 to 19 7 of the local average seasonal rainfall the natural recharge data are grouped into four main hydrogeological provinces namely granitic basaltic sedimentary and alluvial and the regression equations between rainfall and natural recharge are derived for each province these equations enable one to determine the approximate value of natural recharge in any watershed basin from the rainfall data for any year the regression equations are used to compute the total annual replenishment of ground water reserves of the country for an average rainfall year the calculated annual input is about 476 10 9 m 3 yr 1 this can be considered as a minimal quantity as it represents the natural recharge due to precipitation alone and does not account for seepage from ponds lakes stream bed canals and return flow from surface water irrigation

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

characterising deep vadose zone water movement and solute transport under typical irrigated cropland in the north china plain understanding the dynamics and mechanisms of soil water movement and solute transport is essential for accurately estimating recharge rates and evaluating the impacts of agricultural activities on groundwater resources in a thick vadose zone 0 15 m under irrigated cropland in the piedmont region of the north china plain soil water content matric potential and solute concentrations were measured based on these data the dynamics of soil water and solutes were analysed to investigate the mechanisms of soil water and solute transport the study showed that the 0 15 m vadose zone can be divided into three layers an infiltration and evaporation layer 0 2 m an unsteady infiltration layer 2 6 m and a quasi steady infiltration layer 6 15 m the chloride nitrate and sulphate concentrations all showed greater variations in the upper soil layer 0 1 m compared to values in the deep vadose zone below 2 m the average concentrations of these three anions in the deep vadose zone varied insignificantly with depth and approached values of 125 242 and 116 mg l the accumulated chloride sulphate and nitrate was 2179 113 1760 383 and 4074 421 kg ha respectively the soil water potential and solute concentrations indicated that uniform flow and preferential flow both occurred in the deep vadose zone and uniform flow was the dominant mechanism of soil water movement in this study the piston like flow velocity of solute transport was 1 14 m yr and the average value of calculated leached nitrate nitrogen was 107 kg ha yr below the root zone the results can be used to better understand recharge processes and improve groundwater resources management this article is protected by copyright all rights reserved

assessment and estimation of groundwater recharge for a catchment located in highland tropical climate in central ethiopia using catchment soil water balance swb and chloride mass balance cmb techniques two commonly applied groundwater recharge estimation techniques namely soil water balance swb and the chloride mass balance cmb methods were applied and compared to quantify and analyse groundwater recharge in the akaki catchment located in central ethiopia the semi distributed swb method estimated natural groundwater recharge at 105 mm a 10 of the mean annual areal precipitation maap the chloride mass balance method applied to the same catchment estimated mean annual groundwater recharge at 273 mm a 25 of the maap the swb recharge value is much less than the recharge estimated by cmb method highlighting the importance of preferential flow path recharge mechanism which is not captured by the swb method in situ permeability measurements undertaken as part of this research and an earlier investigation based on environmental isotopes have demonstrated that the catchment gets recharged both from direct and preferential flow recharge mechanisms which explains the discrepancy between recharge estimated through the two methods therefore swb model result which only takes into consideration the piston type flow recharge mechanism should be taken as the minimum possible groundwater recharge for the catchment characterized by fractured aquifers the mean recharge estimate from the two methods represents the maximum possible recharge estimate for the catchment investigated although calibration of the recharge estimates was not possible the swb recharge estimate is found to be highly sensitive to changes in precipitation input the findings of this research underline the fact that multiple recharge estimation methods are important to understand and capture possible recharge mechanisms and to reach to an acceptable recharge estimate

reply to comment on field study of spatial variability in unsaturated flow beneath and adjacent to playas by bridget r scanlon and richard s goldsmith

local recharge processes in glacial and alluvial deposits of a temperate catchment summary this study demonstrates that the composition and structure of quaternary deposits and topography significantly influence rates of recharge and distribution of diffuse agricultural pollution at the hillslope scale analyses were made of vertical profiles of naturally occurring chloride and nitrate and artificially introduced bromide in unsaturated and saturated sections of borehole cores of glacial till and alluvium under different land uses in the upper eden valley uk estimates of local potential recharge were made based on chloride mass balance and nitrate peak methods persistent chloride bulges below the root zone were observed and are interpreted to result from filtration processes at lithological boundaries changes in the shape of chloride profiles downslope corroborated by nitrate profiles indicate the roles of surface or near surface runoff and runon and the existence of lateral subsurface flows at depth these findings have implications for estimation of recharge rates through unsaturated zones in quaternary deposits and the interpretation of potential hot spots of diffuse agrochemicals particularly nitrates moving through quaternary deposits into groundwater

the os isotopic composition of himalayan river bedloads and bedrocks importance of black shales re os data are presented for bedrocks and bedloads of selected rivers from the himalayan range in central nepal and bangladesh these data demonstrate that the os isotopic composition of most of the bedrocks is similar to that of the average continental crust notable exceptions to this are the black shales from the lesser himalaya lh which contain large quantities of radiogenic osmium in the black shales the os is not concentrated in the sulfides and may instead be associated with organic matter bedloads collected from rivers which include lh black shales in their catchment basins have notably high os ratios 187os 188os 3 this radiogenic signature persists into the ganga river in contrast the brahmaputra river is less radiogenic suggesting an ophiolite input in the headwater region simple physical mixtures of lh black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high os ratios observed at the outflow of the range assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture respectively this observation suggests that erosion may not be occurring at steady state in addition mass balance calculations indicate that about 20 of the os and 60 of the re are carried in dissolved form implying that chemical erosion plays an important role in the osmium budget finally the contrast in os isotope ratio between ganga bedloads and bulk sediments in the bengal fan suggests that radiogenic os carried by particulate matter and later remobilized may significantly influence the os composition of seawater

post depositional mobility of platinum iridium and rhenium in marine sediments the discovery of high concentrations of iridium in cretaceous tertiary boundary sediments engendered the hypothesis1 that a meteorite collided with the earth 65 million years ago coincident with the mass extinction that occurred at that time iridium spikes of various magnitudes have subsequently been reported at more than 10 other extinction horizons2 11 it has been suggested on the other hand that geochemical processes might create or modify many of these spikes5 11 4 but a critical evaluation of these suggestions has been hindered by incomplete understanding of low temperature iridium geochemistry other platinum group elements ru rh pd re os pt au are often found to be associated with ir spikes and inter element ratios have been used to assess the cosmic or terrestrial nature of the enrichments5 7 9 28 29 but the geochemical influences on these relative abundances are also poorly constrained here we describe analyses of recent abyssal marine sediments which allow us to characterize the behaviour of pt re and ir during early diagenesis these elements are redistributed by changes in sedimentary redox conditions such changes can probably account for many of the small platinum group element spikes found in the geological record and may render ambiguous attempts to interpret inter element ratios

thermochronology constraints for the propagation sequence of the south pyrenean basement thrust system france spain 1 in this work we combined apatite fission track and biotite k feldspar 40ar 39ar ages with tectonic data in the west central part of the axial zone of the pyrenees we discuss the exhumation ages and rates of the neouvielle bordere louron and bielsa variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the pyrenean orogenic prism the 40ar 39ar ages on k feldspars from the neouvielle massif sample nv7 seem to indicate tectonic movements on the eaux chaudes thrust during the early middle eocene fission track results suggest that the exhumation of the neouvielle massif occurred around 35 ma and exhumation of the bordere louron massif around 32 ma in relation to thrusting on the gavarnie thrust the bielsa massif was exhumed from around 19 ma by out of sequence movements on the bielsa thrust we thus show that whereas most of the pyrenean basement thrust faults here the eaux chaudes gavarnie and guarga thrusts were active in sequence toward the southern foreland from the early eocene to the earliest miocene some of them here the bielsa thrust were activated out of sequence in the hinterland later than the generally accepted aquitanian age for the end of the pyrenean compression finally the apatite fission track modeling indicate a last cooling episode starting around 5 ma which is most certainly related to the pliocene reexcavation of the southern and northern flanks of the pyrenees

variations of the187os 186os ratio of seawater over the past 28 million years as inferred from metalliferous carbonates abstract the os concentration and isotopic composition of metalliferous carbonates deposited on the east pacific rise over the past 28 ma are reported with complimentary sr isotope data variations in the os isotopic composition of these samples are interpreted as a record of past changes in the os isotopic composition of seawater these results are consistent with isotopic analyses of leachable os in pelagic clays which have also been interpreted as a record of the187os 186os ratio of seawater through time 1 the metalliferous carbonate record clearly shows that seawater os and sr isotope systems are partially decoupled from one another over the past 28 ma accelerated weathering of ancient organic rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the187os 186os ratio of seawater over the past 15 ma this rapid increase suggests that the seawater os record can potentially be used as a stratigraphic tool in some neogene marine deposits

geochemical estimates of paleorecharge in the pasco basin evaluation of the chloride mass balance technique the pasco basin in southeastern washington state provides a unique hydrogeologic setting for evaluating the chloride mass balance technique for estimating recharge this basin was affected by late pleistocene catastrophic floods when glacial dams in western montana and northern idaho were breached it is estimated that multiple missoula floods occurred between 13 000 and 15 000 years b p and reached a high water elevation of 350 m these floods removed accumulated chloride from the sediment profile effectively resetting the chloride mass balance clock at the beginning of the holocene the rate of chloride accumulation qcl in the sediments was determined by two methods and compared the first method measured qcl by dividing the calculated natural fallout of 36cl by a measured ratio of 36cl cl in the pore water while the second method used the total mass of chloride in the profile divided by the length of time that atmospheric chloride had accumulated since the last flood although the two methods are based on different approaches they showed close agreement in laboratory studies the sediment to water ratio for chloride extraction was sensitive to the grain size of the sediments low extraction ratios in silt loam sediments led to significant underestimation of pore water chloride concentration br cl ratios were useful for distinguishing nonatmospheric e g rock sources of chloride field studies showed little spatial variability in estimated recharge at a given site within the basin but showed significant topographic control on recharge rates in this semiarid environment an extension of the conventional chloride mass balance model was used to evaluate chloride profiles under transient time varying annual precipitation conditions this model was inverted to determine the paleorecharge history for a given soil chloride profile and the parameters of the root extraction model required to estimate paleoprecipitation

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

estimation of natural groundwater recharge in the karoo aquifers of south africa abstract a 3 year project to study the natural groundwater recharge of aquifers in the semi arid karoo formations of south africa was undertaken two typical karoo aquifers at dewetsdorp and de aar were selected for study purposes data were collected from both the saturated and unsaturated zone neutron probe measurements showed that there was no increase in the water content beneath a depth of 1m below the surface even with the exceptionally high rainfall in february 1988 neutron measurements indicated that very little soil matrix flow occurred which implied that most of the recharge occurred along preferred pathways a triangular finite element network was used to determine the relative saturated volume fluctuations svf of the aquifers from the observed water level changes over a period of time which allowed determination of the storativity s and the recharge the main advantage of the method lies in determining recharge and storativity which are both unknowns in the water balance equation and which both contribute to the water level response the svf method showed that the recharge in the karoo formations of south africa varies between 2 and 5 of the annual rainfall in areas which are overlain by a thick soil cover the recharge is less than 3 while recharge in hilly areas with a thin soil cover may be of the order of 5

new magnetostratigraphic dating of the palaeogene syntectonic sediments of the west central pyrenees tectonostratigraphic implications financial support to develop this investigation was provided by projects cgl2009 08969 cgl2010 21968 c02 02 cgl2009 14214 cgl2010 17479 and cgl2014 55900 p of the former spanish ministry of science and innovation micinn

sources and sinks of unradiogenic osmium runoff from papua new guinea the fly and sepik are two of the largest rivers draining the island of new guinea and among the world s large rivers in discharge and sediment yield sediment from the upper fly river and its delta have low 187os 188os of 0 511 0 560 and sediments from the upper and lower sepik river have even lower ratios of 0 294 0 418 filtered waters 1 2 burial of os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the gulf of papua there is a negative correlation between the os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on c isotopes the systematic relationship between c and os isotopic compositions in these samples indicates that organic matter is the major host of os in tropical estuarine sediments the os corg of gulf of papua surface sediments is intermediate between that of other modern and ancient sediments approximately 1011 mol yr of corg and 20 57 mol yr of os are buried in the inner shelf 50 m depth of the gulf of papua over an area of only 21 000 km2 corresponding to 1 3 of the global marine os burial flux in 0 006 of the total sea surface area these results suggest that a large proportion of the global burial flux of os may take place in conjunction with the deposition of low corg sediments lowering of the os isotopic composition of ambient seawater due to a large flux of unradiogenic riverine os may be indicated by the os isotopic composition of water from the coral sea 187os 188os 0 844 and marine sediments within the gulf of papua the island of new guinea is estimated to provide 4 5 of the global riverine os flux given the very large particulate and dissolved flux to the oceans from rivers in the wet tropics the effect of the weathering of young arc related crust in the sw pacific is an important source of unradiogenic os to modern seawater

basin geomorphological controls on the mechanism of recharge and discharge and its effect on salt storage and mobilization comparative study using geophysical surveys abstract downhole electromagnetic em profiles have been used to study the salt distribution in four catchments in the wheatbelt of western australia the good correlation r 2 0 7 0 9 obtained by relating the apparent conductivity profiles measured by the downhole em with salt profiles from soil cores enabled estimation of the salt storage in the uncored wells the salt distribution was compared with ground conductivity surveys using em31 and em34 instruments in three catchments and with an input aerial electromagnetic survey aem in a fourth catchment the study revealed the presence of five types of apparent electrical conductivity profiles eca which are correlated with the basin geomorphological units the conductivity profiles are 1 low eca recharge profile 2 subsurface peak discharge profile 3 two bulge profiles a single bulge accumulation weathering profile and a split aquifer development profile 4 reduced bulge leaching profile 5 high eca irregular palaeochannel profile the salt distribution showed a systematic increase in salinity from the watersheds to the valleys with salinity increasing upstream of geological structures the salt distribution was found to be controlled by the geomorphologic properties of the basins which control the hydrological and hydrogeological processes and by the recharge discharge mechanisms which influence salt mobilization and accumulation

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

the sis palaeovalley a record of proximal fluvial sedimentation and drainage basin development in response to pyrenean mountain building the sis conglomerate body represents the middle eocene to oligocene transfer zone trunk palaeovalley fill of the sis fluvial system a drainage system established within the pyrenees during late palaeocene times the spatial stability of the fluvial transfer zone active for at least 38 my and hence the longevity of its aggradational palaeovalley component 19 5 my was controlled by its location between long lived pre existing structures coarse grained fluvial facies dominate the palaeovalley fill with alluvial fan facies shed from its defining marginal structures the detailed sedimentology of very proximal fluvial facies deposited within the dominantly erosional realm of an active mountain belt has rarely been documented before because of their poor preservation potential the sis conglomerate body contains a robust internal stratigraphy with stratigraphic units defined by distinct bounding surfaces across which there are pronounced changes in facies and provenance these mark the reorganization of the headward portions of the sis fluvial system during the evolution of the pyrenean axial zone antiformal stack major changes in discharge resulted demonstrating the highly variable nature of even mountain belt scale fluvial systems when viewed on timescales of several to tens of millions of years provenance details indicate that initial unroofing of hercynian granitoids situated within the pyrenean axial zone occurred around 54 5 ma early ypresian immediately before the first significant exhumation event within the drainage basin of the sis fluvial system this is earlier than previously constrained by apatite fission track studies rock uplift accelerated in the lutetian and bartonian with the initial aggradation of the palaeovalley fill the cajigar and cornudella formations and sis one and two members this became marked in the priabonian sis three and four members with significant activity on local structures including the morreres backthrust an increase in basement derived clasts and a headwater decapitation event also indicate pronounced axial zone antiformal stack development at this time axial zone development intensified further in the oligocene with the deposition of the collegats formation and the switch in the main depositional loci of the system from the tremp graus thrust sheet top basin to the ebro basin to the south

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

water recharge and solute transport through the vadose zone of fractured chalk under desert conditions this study focuses on water flow and solute migration through unsaturated fractured chalk in an arid area the chalk underlies a major industrial complex in the northern negev desert where groundwater contamination has been observed four dry drilling holes were bored through the vadose zone core and auger samples collected at 30 to 50 cm intervals were used for chemical and isotopic analyses enabling the construction of the following profiles 1 a tritium profile to estimate the rate of water flow through the unsaturated zone 2 oxygen 18 and deuterium profiles to assess the evaporation of water at land surface before percolation and in the upper part of the vadose zone after infiltration and 3 chloride and bromide profiles as tracers for inert solutes and pollutants the tritium and bromide profiles showed the rate of infiltration through the unsaturated matrix to be very slow 1 6 11 cm yr the chemical and isotopic data from the core holes suggested that the pore water changes characteristics with depth close to land surface the pore water is strongly evaporated 18o 5 94 and highly concentrated 29 meq cl 100 g rock but changes gradually with depth to amore dilute concentration 4 meq cl 100 g rock and isotopically depleted composition 18o 4 4 closer to the isotopic composition of precipitation and groundwater nearby monitoring wells have shown anthropogenic contribution of heavy metals organic compounds and tritium nativ and nissim 1992 a conceptual model is proposed in which a small portion of the rainwater percolates downward through the matrix while a larger percentage of the percolating water moves through preferential pathways in fractures the water flowing through the fractures penetrates the matrix across the fracture walls where it increases the tritium concentrations depletes the stable isotopic composition and dilutes the salt concentrations the observed rapid downward migration of tritium and heavy metals through the profuse fractures makes the chalk inefficient as a hydrologic barrier

the isotopic composition of leachable osmium from river sediments the 187os186os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of os delivered to sea water from the continents the 187os186os values for river sediment leaches from the eastern and central u s the ganges river and the rio maipo range from 10 1 to 21 5 these results suggest that the 187os186os of the soluble river load delivered from the major continental areas to the oceans is on average more radiogenic than average currently eroding continental crust 10 5 sediment leaches from three rivers from the western u s that drain ophiolitic peridotites have distinctly lower 187os186os values 1 4 7 1 such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187os186os of 8 6

high chloride concentrations in the soil and groundwater under an oak hedge in the west of france an indicator of evapotranspiration and water movement chloride is a major anion in soil water and its concentration rises essentially as a function of evapotranspiration compared to herbaceous vegetation high transpiration rates are measured for isolated trees shelterbelts or hedgerows this article deals with the influence of a tree hedge on the soil and groundwater cl concentrations and the possibility of using cl as an indicator of transpiration and water movements near the tree rows cl concentrations were measured over 1 year at different depths in the unsaturated zone and in the groundwater along a transect intersecting a bottomland oak hedge we observed a strong spatial heterogeneity of cl concentrations with very high values up to 2 g l 1 in the unsaturated zone and 1 2 g l 1 in the upper part of the groundwater this contrasts with the low and homogeneous concentrations 60 70 mg l 1 in the deeper part of the groundwater cl accumulation in the unsaturated zone at the end of the vegetation season allows us to identify the active root zone extension of trees in winter upslope of the tree row downwards leaching partly renews the soil solution in the root zone while the slow water movement under the trees or farther downslope results in cl accumulation and leads to a salinization of the soil and groundwater this salinization is of the same order as experimental conditions produce negative effects on oak seedlings the measurement of cl concentrations in the unsaturated zone under tree rows at the end of the vegetation season would indicate whether certain topographic pedological or climatic conditions are likely to favour a strong salinization of the soil as observed in the present study copyright 2009 john wiley sons ltd

groundwater recharge estimation using chloride stable isotopes and tritium profiles in the sands of northwestern senegal a study of environmental chloride deuterium oxygen 18 and tritium in deep sand profiles 35 m has been carried out in order to estimate their relative value for measuring average groundwater recharge the investigation was located at a 0 1 km2 site in quaternary sands near the northwestern coast of senegal in a zone of rainfed agriculture by using a steady state model for duplicate unsaturated zone chloride profiles the long term average recharge at the site was estimated to be 30 mm yr 1 or around 10 of the average precipitation 290 mm the chloride concentration of adjacent shallow groundwater was relatively uniform and comparable to the unsaturated zone average while the spatial variability in the depth distribution of cl in the unsaturated zone was considerable stable isotope deuterium and oxygen 18 data show that there is some isotopic enrichment due to direct evaporation through the soil surface the degree of heavy isotope enrichment is proportional to the extent of evaporative loss and there is good correspondance with the chloride enrichment nevertheless stable isotopes cannot be used quantitatively to estimate the recharge the excellent preservation of the peak in thermonuclear tritium in precipitation in the unsaturated zone at depths between 12 and 20 m enables an estimated annual recharge of 24 mm yr 1 in this area to be calculated using the piston flow model agreement therefore between cl and3h as tools for recharge measurement is reasonable over the site

groundwater recharge estimation using chloride deuterium and oxygen 18 profiles in the deep coastal sands of western australia the depth distributions of environmental chloride deuterium and oxygen 18 in the deep sands 20 m were monitored with a view to estimate average recharge to groundwater the investigated area is located on the southwestern coast of western australia and supports a perennial native woodland vegetation by using a steady state model based on the conservation of chloride the average areal recharge was estimated to be approximately 15 of the average precipitation 775 mm yr 1 whilst the cl concentration of groundwater was relatively uniform there was a considerable spatial variability in the depth distribution of cl in the unsaturated zone an approximate method of data analysis is developed application of this to cl data shows that possibly some 50 of the total annual recharge occurs via movement of water through preferred pathways thus bypassing the soil matrix stable isotope deuterium and oxygen 18 data show that there has been some isotopic enrichment due to evaporation of the rainfall but the extent of enrichment appears to be too small to estimate recharge rates reliably it is argued that relatively small isotopic enrichment occurs in the system studied since the direct evaporation from soil is a rather small component of the total evapotranspiration the observations on the depth distribution of isotopes qualitatively support the presence of a bimodal system for water movement through the profile as was suggested by the analysis of chloride data

comparison of water table fluctuation and chloride mass balance methods for recharge estimation in a tropical rainforest climate a case study from kelantan river catchment malaysia estimated groundwater recharge for selected locations in northeast peninsular malaysia north kelantan river catchment was determined using the water table fluctuation wtf and chloride mass balance cmb methods the wtf method recharge estimates were compared to the cmb method estimates to see if results are similar and the methods can be applied in a humid tropical region such as malaysia effective specific yields of 0 18 and 0 16 were obtained for sites which are much lower than values in the literature for use with the wtf method the wtf gives mean recharge values of 447 and 319 mm year at pc61 and wakaf bharu wb respectively the difference between sites may be attributed to the difference in lithology whereby less water table fluctuation is observed for finer grained lower permeability soil or sediment and higher water table fluctuation observed for more granular larger grain soil or sediment for the site with lower permeability the time lag between the storm events and water level rise in a well is longer and water does not reach the water table for small storms recharge from chloride profile study was estimated through measurement of enrichment of chloride concentration in soil rain fed groundwater direct recharge ranged from 263 3 to 627 7 mm year in wb and averaged 691 8 mm year for pengkalan chepa recharge estimates from unsaturated zone chloride strongly correlate with soil texture generally and is greater in the coastal area due to a higher percentage of sand content parts of the study area located toward the interior of the peninsula showed lower recharge due to the presence of fine grained sediment comparison of methods from different sites indicates that lithologic setting has a significant role in controlling natural recharge rate the inconsistency observed between recharge value estimated by the wtf and cmb method may in part be due to adsorption desorption process and ion exchange in the unsaturated soil which affects the initial assumption that chloride is a conservative tracer

evaporation and concentration gradients created by episodic river recharge in a semi arid zone aquifer insights from cl δ 18 o δ 2 h and 3 h summary this study has significantly advanced our understanding of the origin of groundwater recharge in a semi arid zone region of the darling river catchment australia the generally accepted hypothesis in arid zone environments in australia that river water forms the primary groundwater recharge source has proven difficult to monitor this is due to the time lags between large floods the remoteness and expense of studying these hydrologically complex systems in detail in addition the highly episodic nature of dryland rivers complicates the interpretation of the groundwater signal a range of hydrochemical tracers chloride oxygen 18 deuterium and tritium measured in rain river water soil water and groundwater were used in this multi year study to trace the pathways of groundwater recharge under wet and dry climatic conditions the evaporation and cl concentrations observed in the unsaturated zone confirmed that small volumetric inputs from periodic rainfall were not the major recharge mechanism sampling which included an overbank flooding event in march 2012 provided firm evidence for groundwater originating from high flow episodic river recharge the use of long term environmental data to understand how economically important water resources respond to climate change with increasing temperatures is considered essential for future sustainability

the groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks an application of natural environmental tracers isotope data of precipitation and groundwater in parts of the voltaian basin in northern ghana were used to explain the groundwater recharge regime in the area groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area it is therefore important to establish the processes and sources of groundwater recharge 18o and 2h data for local precipitation suggest enrichment relative to the global meteoric water line gmwl and indicate that precipitation takes place at a relative humidity less than 100 the groundwater data plot on an evaporation line with a slope of 5 suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone this finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates groundwater recharge estimates from the chloride mass balance cmb method suggest recharge in the range of 1 8 32 of the annual average precipitation in the form of rainfall the highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area in the northern parts of the study area groundwater recharge is lower than 12 the recharge so computed through the application of the cmb methodology takes on a spatial distribution akin to the converse of the spatial pattern of both 18o and 2h in the area as such the locations of the highest recharge are associated with the most depleted values of the two isotopes this observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water the percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates at the same time the amount of water that finally reaches the water table is considerably reduced copyright 2013 john wiley sons ltd

re os isotope systematics in black shales from the lesser himalaya their chronology and role in the 187os 188os evolution of seawater abstract re and os abundances and os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines maldeota and durmala in the lesser himalaya the re and os concentrations in these samples exhibit wide range 0 2 to 264 ng g and 0 02 to 13 5 ng g respectively with a mean re os of 25 the 187 os 188 os of these samples also show a broad range 1 02 to 11 6 with many of them far more radiogenic than the currently eroding continental crust the black shales from the maldeota and durmala mines collected a few meters above the krol tal pc c boundary and occurring in the same stratigraphic horizon yield 187 re 187 os isochron ages of 554 16 and 552 22 ma respectively consistent with fossil evidences and those assigned for the pc c boundary at various other locations these results indicate closed system behaviour of re and os in these mine samples and reaffirm the validity of 187 re 187 os pair to date organic rich sediments the age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary re os age of 839 138 ma for black shales from theog collected from the inner belt these initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt however more analyses of black shales are needed to confirm this the role of weathering black shales from the himalaya in contributing to the os isotope evolution of seawater over the past 25 ma was assessed using a simple budget model for seawater os and assuming values for os fluxes and 187 os 188 os based on the available limited data on os concentration and its 187 os 188 os in rivers and oceans these calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187 os 188 os over the past 16 ma is difficult to satisfy by varying only the os flux from htp rivers 187 os 188 os kept constant at 1 324 or their 187 os 188 os 188 os flux constant at today s value 131 moles yr the requirements to balance os isotope budget in ocean through weathering of black shales however is easier to accommodate if both the os flux from htp himalayan tibetan plateau rivers and their 187 os 188 os are allowed to vary measurements of os abundance in htp rivers and its isotopic composition are needed to test the validity of the model results

groundwater chemistry and palaeorecharge in the amadeus basin central australia abstract carbon isotope chemistry indicates episodic palaeorecharge of groundwater in the arid amadeus basin central australia in this hydrogeologically complex region groundwater has been recharged by three important mechanisms direct infiltration of rainwater through sand dune cover or fissures in calcrete through river bed sands following floods and through joints in bedrock outcrops modern and holocene groundwaters 0 5000 years b p are found in the unconfined calcrete and sand dune aquifers which have evolved hydrochemically to cl so4 na waters with ca and mg as a result of evaporative concentration holocene groundwaters 3 10 000 years b p have been dated in river bed recharge situations these groundwaters are mainly of the hco3 cl na type with ca and mg and preserve the hydrochemical signature of the flood recharge waters most groundwater sampled in the folded and jointed rocks of the basin has a low modern 14c content and was recharged in the holocene and late pleistocene 12 32 000 years b p these waters are intermediate in their ionic composition covering a spectrum between the hco3 cl na and cl so4 na types solution is the dominant process int heir hydrochemical evolution stable isotope signatures and derived parameters indicate that the intensity of rainfall is an important factor in the evolution of arid zone groundwaters modern reharged is limited implying that projected large scale groundwater development in this region will use an effectively nonrenewable resource and should be managed accordingly

significance of stemflow in groundwater recharge 1 evaluation of the stemflow contribution to recharge using a mass balance approach stemflow was evaluated in a water balance and its contribution to groundwater recharge determined gross precipitation throughfall and stemflow were measured for one year in a pine forest tsukuba japan to determine each component of the water balance in the forest groundwater recharge rates by stemflow and throughfall were calculated from a mass balance method using chloride in subsurface waters the stemflow in the water balance was relatively small when estimated as a value per canopy projected area of the tree in the forest however the results for the mass balance of chloride in subsurface waters indicated that it was impossible to disregard the stemflow in determining groundwater recharge although the ratio of stemflow to the net precipitation was small in the water balance the effect of stemflow on groundwater recharge was relatively large

sediment volume and mass beneath the bay of bengal rates of sediment accumulation and the amount of sedimentary fill in depocenters lying downstream of erosion in the himalayas and tibet can provide some insight into tectonics and geological history the objective of this paper is to put on record the best estimates which are possible with existing data of the volume and mass of sediments sedimentary rock and metasedimentary rock beneath the sea floor of the bay of bengal the sedimentary section in the bay of bengal is divided into two parts 1 eocene through holocene sediments and sedimentary rocks which post date the initial india asia collision volume 12 5 106 km3 mass 2 88 1016 t this is most of the bengal fan including its eastern lobe the nicobar fan plus some of the outer bengal delta 2 early cretaceous through paleocene pre collision sedimentary and metasedimentary rocks volume 4 36 106 km3 mass 1 13 to 1 18 1016 t these are interpreted as continental rise and pelagic deposits

understanding hydrological processes in a highly stressed granitic aquifer in southern india the results of a study evaluating the recharge discharge conditions of an unconfined stressed granitic aquifer situated in a semi arid region of andhra pradesh southern india are presented over the last three decades excessive withdrawal of groundwater has drastically lowered the water table to the bedrock the watershed studied was divided into four zones based on geomorphology and hydrogeological conditions using environmental chloride data pertaining to groundwater soil depth profiles and some hydrogeologic and hydrochemical observations a recharge model for the watershed was developed the model revealed that the bulk of the vertical recharge in the western elevated land occurs through preferred pathways and that a small fraction occurs through the soil matrix in addition the watershed has a poor hydrogeologic fabric as indicated by the small range of matrix flow recharge 1 to 1 5 of rainfall among the four zones the dominating preferential flow was high 16 of the annual average rainfall in the valley fills but decreased to 5 5 5 in the plains furthermore although the bulk of the recharge occurs vertically considerable lateral movement of groundwater down the slope indicates that sequential hydrochemical changes occur distinct geomorphological features that exist in the watershed support the proposed model situations similar to those described above may exist in numerous watersheds in the granitic hard rock region therefore information obtained from investigations conducted in this watershed can aid in the development of plans enabling the sustainable exploitation of watersheds that have not yet been developed as well as implementation of appropriate rainwater conservation measures in over exploited watersheds copyright 2009 john wiley sons ltd

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

a new middle to late eocene continental chronostratigraphy from ne spain abstract the calibration of the european paleogene mammal biochronology with the international reference geochronological scale is unconstrained due to the lack of direct marine continental correlations and insufficient robust magnetostratigraphic data for mammal fossil bearing sequences the currently accepted european continental biochronology argues for a correlation of the paleogene mp14 to mp16 mammal reference levels with the bartonian stage and of the mp17 to mp20 levels with the priabonian however new magnetostratigraphic data of the continental sediments of the south central pyrenees substantially challenge this chronology our new results from the la pobla de segur basin and sierra de sis have been integrated into the framework of previous marine continental stratigraphic correlations and magnetostratigraphic data of the south central pyrenees in this new chronology mp14 and mp15 reference levels correspond to the lutetian whereas mp16 and early mp17 correlate with the early bartonian this calibration represents a significant revision of currently accepted marine continental correlations in europe but is not in conflict with the available biostratigraphic data of the south pyrenean ebro foreland basin and other western european reference basins

himalayan uplift and osmium isotopes in oceans and rivers previous studies have shown that 187 os 188 os in seawater has become increasingly radiogenic over the last 40 ma in a manner analogous to strontium this rapid rise in the marine 187 os 188 os over the last 17 ma has been attributed to an increase in the bulk silicate weathering rates resulting from the rise of the himalayas and or selective weathering and erosion of highly radiogenic organic rich ancient sediments the key test of this hypothesis is the 187 os 188 os and the total osmium concentration of the himalayan rivers we report the concentration and isotopic composition of osmium in the ganges the brahmaputra and the indus rivers the 187 os 188 os of the ganges close to its source at kaudiyal 30 05 n 78 50 e is 2 65 and os 45 fm kg a second sample of the lower reaches of the ganges at patna 25 30 n 85 10 e gives 187 os 188 os 1 59 and os 171 fm kg the 187 os 188 os of the brahmaputra at guwahati 26 10 n 91 58 e is 1 07 and os 52 fm kg a sample of the indus besham 34 55 n 72 51 e has a 187 os 188 os of 1 2 and os 59 fm kg we infer that the himalayas do not provide either a high flow of osmium or a highly radiogenic osmium component to the oceans the overall trend for osmium and strontium could be explained by a regularly increasing input of global continental weathering sources but the himalayas themselves appear not to be the dominant source

a new chloride leaching approach to the estimation of diffuse recharge following a change in land use abstract a new approach has been developed to estimate the increase in groundwater recharge following land use modification the approach uses the degree of leaching of chloride to quantify soilwater drainage below the root zone which ultimately leads to groundwater recharge it is more general than similar previously reported techniques for analysing transient chloride profiles to infer recharge rates and hence has wider application we have applied the technique to a field situation in southern australia where clearing of native vegetation for agricultural production leads to large increases in groundwater recharge the examples serve to demonstrate the technique and some of the practical difficulties in the application of solutes techniques to recharge estimation

partitioning sources of recharge in environments with groundwater recirculation using carbon 14 and cfc 12 summary groundwater recirculation occurs when groundwater is pumped from an aquifer onto the land surface and a portion of that water subsequently infiltrates back to the aquifer in environments where groundwater is recirculated differentiation between various sources of recharge e g natural rainfall recharge vs recirculated water can be difficult groundwater age indicators in particular transient trace gases are likely to be more sensitive tracers of recharge than stable isotopes or chloride in this setting this is because unlike stable isotopes or chloride they undergo a process of equilibration with the atmosphere and historical atmospheric concentrations are known in this paper groundwater age indicators 14 c and cfc 12 were used as tracers of recharge by surplus mine water that is discharged to streams ternary mixing ratios were calculated based on 14 c and cfc 12 concentrations measured along three transects of piezometers and monitoring wells perpendicular to the creeks and from dewatering wells uncertainty in calculated mixing ratios was estimated using a monte carlo approach ternary mixing ratios in dewatering wells suggest that recharge by mine water accounted for between 10 and 87 of water currently abstracted by dewatering wells the calculated mixing ratios suggest that recharge by mine water extends to a distance of more than 550 m from the creeks these results are supported by seepage flux estimates based on the water and chloride balance along the creeks which suggest that 85 90 of mine water discharged to the creeks recharges the aquifer and recharge by mine water extends between 110 and 730 m from the creeks mixing calculations based on gaseous groundwater age indicators could also be used to partition recharge associated with agricultural irrigation or artificial wetland supplementation

os sr nd results from sediments in the bay of bengal implications for sediment transport and the marine os record sr nd and os isotopic data are presented for sediments from diverse locations in the bay of bengal these data allow the samples to be divided into three groups related to their sedimentary contexts the first group mainly composed of sediments from the shelf off bangladesh and the currently active fan has sr and nd characteristics consistent with a dominantly himalayan source their 187os 188os ratios 1 2 1 5 show that the average detrital material delivered by the ganga brahmaputra g b river system is not unusually radiogenic a large difference in 187os 188os ratio exists between these bengal fan sediments and ganga bedloads 187os 188os 2 5 pierson wickmann et al 2000 this difference mainly reflects addition of a less radiogenic brahmaputra component though mineralogical sorting and loss of radiogenic os during transport may also play some role the second sample group contains sediments from elsewhere in the bay particularly those located on the continental slope they display os isotopic compositions 0 99 1 11 similar to that of present seawater and higher os and re concentrations these characteristics suggest the presence of a large hydrogenous contribution consistent with the lower sedimentation rate of these samples sr and nd ratios indicate that a significant fraction of these sediments is derived from erosion of non himalayan sources such as the indo burman range these observations could be explained by the deflection of sediments from the g b river system by westward currents in the head of the bay the third group contains only one sample but shows that in addition to a himalayan source sediment discharge from sri lanka may influence the detrital component in the distal part of the fan the similarity between the isotopic compositions of the group i r v sonne samples and those of ocean drilling program leg 116 france lanord et al 1993 reisberg et al 1997 suggests that the material eroding in the himalayas has been roughly constant since the miocene the high os isotopic ratios of leachates of both sonne group i and miocene leg 116 sediments imply that much of the leachable highly radiogenic os component was conserved during transport through the estuary or interaction with seawater in constrast samples with lower but still relatively high sedimentation rates sonne groups ii and iii and pliocene leg 116 seem to have significantly adsorbed or exchanged os and re with seawater this suggests that in some cases the os isotopic ratios of leachates of detrital sediments can be used to constrain the ancient marine os record or conversely to date unfossiliferous sediments

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

sr nd os evidence for a stable erosion regime in the himalaya during the past 12 myr modern erosion of the himalaya the world s largest mountain range transfers huge dissolved and particulate loads to the ocean it plays an important role in the long term global carbon cycle mostly through enhanced organic carbon burial in the bengal fan to understand the role of past himalayan erosion the influence of changing climate and tectonic on erosion must be determined here we use a 12 myr sedimentary record from the distal bengal fan deep sea drilling project site 218 to reconstruct the mio pliocene history of himalayan erosion we use carbon stable isotopes 13c of bulk organic matter as paleo environmental proxy and stratigraphic tool multi isotopic sr nd and os data are used as proxies for the source of the sediments deposited in the bengal fan over time 13c values of bulk organic matter shift dramatically towards less depleted values revealing the widespread late miocene ca 7 4 ma expansion of c4 plants in the basin sr nd and os isotopic compositions indicate a rather stable erosion pattern in the himalaya range during the past 12 myr this supports the existence of a strong connection between the southern tibetan plateau and the bengal fan the tectonic evolution of the himalaya range and southern tibet seems to have been unable to produce large re organisation of the drainage system moreover our data do not suggest a rapid change of the altitude of the southern tibetan plateau during the past 12 myr variations in sr and nd isotopic compositions around the late miocene expansion of c4 plants are suggestive of a relative increase in the erosion of high himalaya crystalline rock i e a simultaneous reduction of both transhimalayan batholiths and lesser himalaya relative contributions this could be related to an increase in aridity as suggested by the ecological and sedimentological changes at that time a reversed trend in sr and nd isotopic compositions is observed at the plio pleistocene transition that is likely related to higher precipitation and the development of glaciers in the himalaya these almost synchronous moderate changes in erosion pattern and climate changes during the late miocene and at the plio pleistocene transition support the notion of a dominant control of climate on himalayan erosion during this time period however stable erosion regime during the pleistocene is suggestive of a limited influence of the glacier development on himalayan erosion

water movement in desert soil traced by hydrogen and oxygen isotopes chloride and chlorine 36 southern arizona abstract understanding soil water movement is important for water resource management and for analyzing pollutant transport in the vadose zone seasonal variations in shallow soil profiles may have profound effects on deep soil water and solutes we have investigated seasonal soil water movement in the top meter of undisturbed desert soil in the southern arizona using 2 h 18 o cl and bomb 36 c1 six soil profiles were sampled from a young terrace holocene during 1991 to 1992 on a seasonal basis one soil profile was sampled from an older terrace latest pleistocene in october 1992 and one from a yet older fan surface late pleistocene in march 1992 the results indicate that repeated seasonal cyclic movement of soil water in the top 60 80 cm active zone tends to produce a consistent stable isotope composition for the soil water below the active zone in different seasons the deep 18 o on the oldest surface is about 6 heavier than on the younger surfaces probably resulting from greater evaporative loss due to the larger proportion of fines in the older soil this deep isotopic composition is closely related to the composition of the local average annual precipitation an annual average evaporation rate of 35 mm year 1 was estimated using a steady state diffusion model whereas the actual regional evapotranspiration rate is 175 250 mm year 1 this suggests that about 80 of the soil water is lost through transpiration and first stage evaporation before quasi steady state is reached the long term average infiltration rate below the active zone is about 4 mm year 1 for the younger terrace based on both chloride mass balance and bomb 36 cl and 0 02 mm year 1 for the older terrace and the fan surface based on chloride mass balance the correlation between the deep 18 o the reduction of downward flux and the surface age suggests that increasing soil development has resulted in a significant decrease of soil water infiltration and hence an increase in evaporation and surface runoff

environmental and injected tracers methodology to estimate direct precipitation recharge to a confined aquifer abstract direct precipitation recharge to a confined aquifer is a vital parameter for groundwater budgeting management and modelling we describe the conjunctive use of environmental isotopes and geochemical tracer technique and injected tracer method to estimate direct precipitation recharge to an important coastal aquifer undergoing large withdrawal stress the methodology evolved delineates the intake area of the confined aquifer based on environmental isotope and geochemical data and then utilises the recharge rates of the intake area only as determined using injected tracer and geochemical data to estimate the amount of recharge by direct precipitation to the confined aquifer

fluoride dynamics in the granitic aquifer of the wailapally watershed nalgonda district india high concentrations of fluoride up to 7 6 mg l are a recognized feature of the wailapally granitic aquifer of nalgonda district andhra pradesh india the basement rocks provide abundant sources of f in the form of amphibole biotite fluorite and apatite the whole rock concentrations of f in the aquifer are in the range 240 990 mg kg calcretes from the shallow weathered horizons also contain comparably high concentrations of f 635 950 mg kg the concentrations of water soluble f in the granitic rocks and the calcretes are usually low 1 of the total or less but broadly correlate with the concentrations observed in groundwaters in the local vicinity the water soluble fraction of fluoride is relatively high in weathered calcretes compared to fresh calcretes groundwater major ion composition shows a well defined trend with flow downgradient in the wailapally aquifer from na ca hco3 dominated waters in the recharge area at the upper part of the catchment through to na mg hco3 and ultimately to na hco3 and na hco3 cl types in the discharge area in the lowest part the evolution occurs over a reach spanning some 17 km groundwater chemistry evolves by silicate weathering reactions although groundwaters rapidly reach equilibrium with carbonate minerals favouring precipitation of calcite and ultimately dolomite in the lower parts of the watershed this precipitation is also aided by evapotranspiration decreasing ca activity downgradient leads to a dominance of fluorite undersaturated conditions and consequently to mobilisation of f despite the clear downgradient evolution of major ion chemistry concentrations of f remain relatively uniform in the fluorite undersaturated groundwaters most being in the range 3 0 7 6 mg l the rather narrow range is attributed to a mechanism of co precipitation with and or adsorption to calcrete in the lower sections of the aquifer the model may find application in other high f groundwaters from granitic aquifers of semi arid regions

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

os isotopic compositions of leachates and bulk sediments from the bengal fan os isotopic compositions and os and re concentrations were measured in h2o2 h2so4 leachates and bulk sediment samples from holes 717c and 718c of odp leg 116 in the bengal fan os isotopic results indicate that at the sediment surface the leachable os fraction is derived from seawater in contrast leachable os from ganges river sediments has 187os 188os ratios 1 much higher than the marine value this difference suggests that the leachable radiogenic os carried by the river sediments is completely released to the oceans prior to sediment deposition in the fan a simple calculation assuming these sediments to be typical of those delivered by the ganges brahmaputra river system suggests that this process can account for a substantial part of the rise in the seawater os isotopic ratio observed over the past 16 m y bengal fan leachate 187os 188os ratios increase with increasing depositional age in contrast to the seawater os isotopic ratio which decreases with increasing age several lines of evidence suggest that at the time of sediment burial the leachate os compositions most likely reflected the seawater values thus the current divergence is probably the result of post depositional processes one such process in situ radiogenic ingrowth of187os can be excluded because the measured re concentrations of these sediments are too low similarly since most of the bulk rock os isotopic ratios were lower than those of the associated leachates the high leachate 187os 188os values cannot be explained by in situ sediment alteration instead it is proposed that the increase with age results from radiogenic os brought in by thermoconvective circulation from further upslope in the fan the ultimate source of this187os would then be alteration of radiogenic sediments or post depositional radioactive decay of re in sediments rich in organic carbon finally the divergence between the results obtained on bengal fan sediments and those obtained in the open ocean 2 by the same leaching technique suggest that os sediment leachate data must be interpreted with caution

a hydrogeological and hydrochemical explanation of the groundwater composition under irrigated land in a mediterranean environment algarve portugal in the campina de faro in the south of portugal agricultural practices have a large impact on groundwater composition these practices involve pumping of water for irrigation from combinations of large diameter shallow wells noras and small diameter deep boreholes furos excess irrigation water returns to the aquifer and mixes with water from the regional groundwater flow system this irrigation return flow is concentrated by strong evapotranspiration and by flushing of fertilisers the concentration increase induces cation exchange whereby ca on the soil exchanger is replaced by na the mixing in the aquifer allows application of a mixing cell model which may then be used to calculate transmissivities from the cl mass balance the calculations are complicated by the time variant behaviour of cl and the method is adjusted to calculate the change of chloride in time results from the calculations appear to be in good agreement with hydrochemical observations

study of evaporation and recharge in desert soil using environmental tracers new mexico usa the purpose of this study is to investigate the rates and mechanisms of recharge and evaporation in soils of a desert environment using two environmental tracers chloride and oxygen 18 the profiles of chloride concentration and oxygen 18 enrichment in soil water together with the depth distribution of water content in soil reveal information about long term recharge and instantaneous evaporation processes without needing to know the physical properties of the soil three holes were hand augured in different desert settings in southeastern new mexico the chloride concentration profiles were used with the chloride mass balance method to estimate long term recharge rates in these three holes as 0 5 0 8 and 2 4 mm yr 1 analysis using a bimodal flow and transport model shows that possibly 85 of the recharge occurs via movement of water through preferred pathways in the root zone preferential flow was evident in all three sampling sites clay layers have a noticeable effect on the development of water content distribution and thus on oxygen 18 enrichment and chloride concentration profiles the spatial variation in clay layering partly explains the variation in recharge rate estimates

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

isotope study of moisture sources recharge areas and groundwater flow paths within the eastern batinah coastal plain sultanate of oman oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern batinah coastal plain of northern oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area a northern mediterranean source and a southern indian ocean source as a result two new local meteoric water lines were defined for the study area isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the batinah coastal alluvial aquifer is high altitude rainfall from the adjacent jabal akhdar mountains originating from a combination of northern and southern moisture sources the groundwater recharged at high altitude forms two plumes of water which is depleted in the heavy isotopes 18o and 2h and stretches from the mountains across the coastal plain to the sea thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m in contrast in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified near the coast saline intrusion results in abrupt changes in chloride concentrations and isotope values

mechanisms of recharge in a fractured porous rock aquifer in a semi arid region abstract eleven porewater profiles in rock core from an upland exposed sandstone vadose zone in southern california with thickness varying between 10 and 62 m were analyzed for chloride cl concentration to examine recharge mechanisms estimate travel times in the vadose zone assess spatial and temporal variability of recharge and determine effects of land use changes on recharge as a function of their location and the local terrain the profiles were classified into four groups reflecting the range of site characteristics century to millennium average recharge varied from 4 to 23 mm y 1 corresponding to 1 moreover the temporal variability of recharge was estimated and along each profile past recharge rates calculated based on the sequence of cl concentrations in the vadose zone recharge rates increased at specific times coincident with historical changes in land use the consistency between the timing of land use modifications and changes in cl concentration and the match between observed and simulated cl concentration values in the vadose zone provide confidence in porewater age estimates travel times recharge estimates and reconstruction of recharge histories this study represents an advancement of the application of the chloride mass balance method to simultaneously determine recharge mechanisms and reconstruct location specific recharge histories in fractured porous rock aquifers the proposed approach can be applied worldwide at sites with similar climatic and geologic characteristics

a stable isotope study of recharge processes in the english chalk the 2h and 18o values of water contained in unsaturated chalk have been measured in drillcore profiles taken over a period of 28 months on arable land in cambridgeshire eastern england the isotopic composition of rainfall and lysimeter drainage on the same site has also been monitored over a period of four years the distribution of isotope values in the upper few metres of soil and unsaturated chalk shows that the mechanism of infiltration is not simple piston like downward displacement since the scale of vertical fluctuations is incompatible with estimated annual infiltration and the apparent rates of movement of matrix water derived from thermonuclear tritium studies lysimeter drainage is not isotopically identical to matrix water at the same depth suggesting that different routes to water table are associated with consistently different isotopic content although there is an apparent difference between matrix water beneath arable and permanent grassland these differences appear to cancel out in the composition of bulk recharge beneath these land types the regional aquifer has a uniform isotopic composition similar in value to weighted average rainfall and lysimeter drainage suggesting that the recharge abstraction system has been in isotopic equilibrium for many years despite changes in pumping rates and land use two other chalk sites in southern england have been investigated in less detail but indicate clear difference in infiltration behaviour from that seen in cambridgeshire this seems to be related to a higher matrix conductivity and annual rainfall amount

a possible link between the seawater osmium isotope record and weathering of ancient sedimentary organic matter the os isotopic composition of leachable os from a north pacific pelagic clay sequence pegram et al 1992 and bulk sediment samples of metalliferous carbonates deposited near the east pacific rise ravizza 1993 display similar patterns of temporal variation fig 1 this similarity indicates that the composite record of t87os 186os ratio variations reflects changes in the os isotopic composition of seawater temporal changes in the sr isotopic composition of seawater record changes in the relative rates of continental weathering and oceanic crustal alteration the os isotopic composition of seawater should be influenced by similar processes in both the rb sr and re os systems the continental crust is characterized by large time integrated parent daughter ratios compared to the deep earth imparting relatively radiogenic sr and os signatures to continental material however the seawater sr and os records are decoupled from one another over the past 27 ma from 27 to 15 ma 87sr 86sr increased rapidly while the 18vos 186os ratio of seawater remained nearly constant at 15 ma the 87os ts6os ratio of seawater began to increase rapidly but the rate