multiple sources of quaternary tephra layers in the mariana trough abstract tephra layers in quaternary sediments stolper and newman 1994 model of binary mixing of source components with one endmember being the nmorb source of stolper and newman 1994 and the other one being a compositionally variable slab derived h2o rich component similar to the h2o component of stolper and newman 1994 this interpretation implies that the variation in k2o content in the arc derived glasses about a factor of 3 at 60 wt sio2 reflects a magmatic diversity that is inherent to the central mariana arc and is not necessarily reflective of temporal changes of the composition of arc magma sources

fluid flow in partially saturated welded nonwelded tuff units abstract a discrete fracture porous matrix model and a composite medium model were used to study hydrological responses to cycles of pulse infiltration at yucca mountain a potential site for a nuclear waste repository the pulses were applied to fractures at the top of a vertical column composed of alternating layers of welded and nonwelded volcanic tuff for average infiltration rates of 0 1 mm yr pulses expressed as short durations separated by periods up to 5000 yr most effects of the transient infiltration pulses were damped by the paintbrush nonwelded unit the effects of eastern tilting of the units at yucca mountain on the steady state fluid flow distribution were studied using a two dimensional model ghost dance fault was modeled as a seepage face under the expected flux conditions saturation increased just to the west of the fault but the water did not enter the fault with the seepage boundary condition

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 model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

the influence of coatings and fills on flow in fractured unsaturated tuff porous media systems a numerical study of a single fracture embedded in a porous matrix was performed to investigate the role of fracture coatings and fills on water movement in permeable fractured porous media the variables considered were conductivity and continuity of fracture coatings location length and conductivity of fracture fills combinations of fills and coatings initial matrix saturation and inflow boundary conditions results from the simulations indicate that in low saturation high capillarity tuff systems the conditions under which fractures act as rapid flow paths are limited these conditions include a continuous coating with conductivity several orders of magnitude lower than that of the neighboring matrix and large inflow rates however as initial matrix saturation increases the amount of fracture flow also increases discontinuities in coatings substantially reduce their effectiveness in preventing matrix imbibition the presence of any coating however does produce increased infiltration depths fills appear to be effective barriers to fracture flow

mixing of event and pre event water in a shallow entisol in sloping farmland based on isotopic and hydrometric measurements sw china

a 700 year history of groundwater recharge in the drylands of nw china a 700 year semi quantitative history of diffuse groundwater recharge in the badain jaran desert inner mongolia is proposed on the basis of solute data from multiple unsaturated zone groundwater profiles using mass balance of chloride to establish recharge rates and profile chronologies four relatively humid 1330 1430 1500 1620 1700 1780 and 1950 1990 and three relatively arid phases 1430 1500 1620 1700 and 1900 1950 are discernable across the profiles the recharge history broadly reflects multidecadal to centurial timescale precipitation changes in the northern tibetan plateau and suggests that variations in east asian summer monsoon intensity affect desert recharge rates uncertainties in the records owing to assumptions about the cl inputs are examined by comparing deterministic and stochastic cl input scenarios such records are valuable for assessing spatial aspects of climate changes in the region as well as for informing sustainable water resource management strategies for northwestern china s drylands

along arc variations in the pre eruptive h2o contents of mariana arc magmas inferred from fractionation paths new experimental results are presented on the effects of dissolved h2o during low pressure 52 kbar crystal fractionation in mariana arc magmas the resulting fractionation paths are used to infer the pre eruptive h2o concentrations of mariana lavas from seamounts and islands estimated pre eruptive h2o concentrations for mariana seamounts 2 3 wt are relatively constant and similar to three out of eight of the subaerial volcanoes alamagan pagan and asuncion these h2o concentrations are also similar to measured h2o concentrations in mariana back arc lavas lavas from the remaining islands guguan agrigan uracas anatahan and possibly sarigan have significantly higher h2o 5 6 than the other seamounts and islands these high h2o islands are distributed throughout the arc and do not show any relation to variations in subduction parameters such as subduction angle or obliquity analysis of the h2o concentrations of olivine hosted melt inclusions from seven islands guguan pagan agrigan anatahan alamagan asuncion and sarigan and one seamount fukujin match the estimates inferred from the liquid lines of descent one interpretation of our results is that the flux of volatiles from the mariana sub arc mantle is fundamentally heterogeneous alternatively the variations in pre eruptive h2o concentrations could reflect variations in the depth and extent of fractionation of mariana magmas

nd and sr isotopic compositions of lavas from the northern mariana and southern volcano arcs implications for the origin of island arc melts nd and sr isotopic data are reported for lavas from 23 submarine and 3 subaerial volcanoes in the northern mariana and southern volcano arcs values of end range from 2 4 to 9 5 whereas 87sr 86sr ranges from 0 70319 to 0 70392 these vary systematically between and sometimes within arc segments the nd and sr isotopic compositions fall in the field of ocean island basalt oib and extend along the mantle array lavas from the volcano arc mariana central island province and the southern part of the northern seamount province have end to 10 and 87sr 86sr 0 7032 to 0 7039 these are often slightly displaced toward higher 87sr 86sr at similar end in contrast those lavas from the northern part of the mariana northern seamount province as far north as iwo jima show oib isotopic characteristics with end and 87sr 86sr 0 7035 to 0 7039 plots of 87sr 86sr and end versus ba la and la yb n support a model in which melts from the mariana and volcano arcs are derived by mixing of oib type mantle or melts therefrom and a metasomatized morb type mantle or melts therefrom an alternate interpretation is that anomalous trends on the plots of nd and sr isotopic composition versus incompatible element ratios found in some s nsp lavas suggest that the addition of a sedimentary component may be locally superimposed on the two component mixing of mantle end members

distribution of environmental chloride in relation to subsurface hydrology abstract chloride distributions in 32 deeply weathered profiles up to 39 m deep were used to investigate the subsurface hydrology typical of the saline landscapes of the south west of western australia studies took place in two forested areas of differing rainfall and landform to compare the processes of water movement a steady state model of water and chloride movement which included the effects of diffusion was used to estimate vertical soil water flux density q w from observed concentrations of chloride these patterns of water flow were compared to the physical properties of the profiles a great deal of variability was found between profiles and there was a marked difference in the magnitude of q w between the areas of different rainfall however consistent patterns of subsurface water movement can be identified thin coarse textured surface soils are well leached by rainfall but in the clayey unsaturated zone below vertical soil water flux densities are very small due to the uptake of water by the eucalyptus forest where rainfall was 800 mm yr 1 q w was typically of the order 0 4 mm yr 1 and in the area of 1150 mm yr 1 rainfall q w was 2 5 mm yr 1 rates of recharge to groundwater estimated from chloride concentration in the saturated zone were as much as two orders of magnitude greater than q w above the water table it is concluded that preferred water flow in structural and textural heterogeneities within the regolith is the dominant mechanism of recharge the preferred flow paths are distributed throughout the landscape but only constitute a small proportion of it

recharge in karst and dune elements of a semi arid landscape as indicated by natural isotopes and chloride abstract the rates and mechanisms of local recharge in a semi arid environment have been investigated beneath two major landscape settings in the murray basin in south australia these were calcrete flats with sinkholes and sand dunes in adjacent landscape settings five minor settings were investigated and identified as undisturbed calcrete primary older sinkholes secondary younger sinkholes sand dunes with native vegetation and sand dunes with introduced pasture data from a limited series of boreholes were interpreted to suggest that recharge varied from in excess of 100 mm yr 1 for secondary sinkholes to less than 0 1 mm yr 1 beneath sand dunes with native vegetation the data suggest that recharge under sand dunes has increased by more than two orders of magnitude following clearing of the native vegetation 50 yr ago as 90 of an area of 10 000 km2 has been cleared this clearing has ensured that inflow of saline groundwater to the adjacent river murray will increase and in view of the amount of salt stored in both the unsaturated and saturated zones will continue for a very long time at sites where the inferred recharge is lowest profiles of the chloride concentration of soil water are consistent with the hypothesis that there is in excess of 50 000 yr recharge stored in the thick unsaturated zone some evidence for changes in recharge rate over this time scale is seen

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

conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone a conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone was developed based on the results of lithological studies and a series of ponded infiltration tests conducted at the box canyon site near the idaho national engineering and environmental laboratory the infiltration tests included one 2 week test in 1996 three 2 day tests in 1997 and one 4 day test in 1997 for the various tests initial infiltration rates ranged from 4 1 cm d 4 75 10 7 m s to 17 7 cm d 2 05 10 7 m s and then decreased with time presumably because of mechanical or microbiological clogging of fractures and esicular basalt in the near surface zone as well as the effect of entrapped air the subsurface moisture redistribution was monitored with tensiometers neutron logging time domain reflectrometry and ground penetrating radar a conservative tracer potassium bromide was added to the pond water at a concentration of 3 g l to monitor water flow with electrical resistivity probes and water sampling analysis of the data shows evidence of preferential flow rather than the propagation of a uniform wetting front we propose a conceptual model describing the saturation desaturation behavior of the basalt in which rapid preferential flow occurs through the largest vertical fractures followed by a gradual wetting of other fractures and the basalt matrix fractures that are saturated early in the tests may become desaturated thereafter which we attribute to the redistribution of water between fractures and matrix lateral movement of water takes place within horizontal fracture and rubble zones enabling development of perched water bodies

the relationship between the nitrate concentration and hydrology of a small chalk spring israel discharge from a spring draining a small perched cretaceous chalk aquifer in the upper galilee israel was monitored over a period of two years the water has elevated nitrate concentrations with 15n 14n and chemical data suggesting that it is a mixture of low nitrate and high nitrate end members the latter derived from the sewage of a centuries old village served by septic tanks hydrograph data allowed distinction between fissure flow during the period of winter rainfall and matrix drainage during the dry summer months these different flow types however did not have markedly different nitrate concentrations a 50 fold increase in spring discharge due to fissure flow compared with matrix drainage was reflected in only a 35 decrease in nitrate concentrations the relatively high nitrate concentrations in the fissure waters suggests that they have had close contact with and are possibly displaced from the matrix this should help to accelerate the decline in the spring s nitrate concentrations following the recent completion of the village s central sewage drainage system

field study of spatial variability in unsaturated flow beneath and adjacent to playas we quantified unsaturated flow beneath playa and adjacent interplaya settings at a site in the southern high plains united states to resolve issues related to where and how water moves through the unsaturated zone this is the first study in which the data density 39 boreholes and the variety of techniques used physical chemical and isotopic were sufficient to quantify spatial variability in unsaturated flow water contents water potentials and tritium eoneentrations were much higher and chloride eoneentrations were much lower beneath playas than in interplaya settings which indicated that playas focus recharge these results refute previous hypotheses that playas act as evaporation pans or that recharge is restricted to the annular region around playas water fluxes estimated from environmental tracers ranged from 60 to 120 mm yr 1 beneath playas and were 0 1 mm yr 1 during the past 2000 5000 years beneath natural interplaya areas not subjected to ponding to evaluate the apparent inconsistency between high recharge rates and thick clay layers beneath playas we applied bromide and fd c blue dye to evaluate flow processes these applied tracer experiments showed preferential flow along roots and desiccation cracks through structured clays in the shallow subsurface in playas

a mechanistic model for water seepage through thick unsaturated zones in fractured rocks of low matrix permeability the theme developed in this paper is that water seepage in thick unsaturated zones in fractured rocks of low matrix permeability cannot be understood by considering spatial and temporal averages we suggest that most such seepage proceeds in an unsteady episodic manner in localized preferential pathways mechanisms are proposed and explored which permit water to flow relatively freely in networks of interconnected fractures in the presence of strong suction pressures from an unsaturated rock matrix imbibition into the rock matrix is reduced by limited wetted area the episodic nature of flow and possibly also by the presence of mineral coatings of low permeability on the fracture walls these effects and conditions combine to limit total imbibition rates to values less than saturated matrix hydraulic conductivity leaving the rock matrix in partially saturated conditions even as water is flowing freely in portions of the fracture network the proposed conceptual model is elaborated and substantiated with analytical estimates and numerical simulation studies mechanisms are demonstrated that can funnel distributed seepage into spatially localized preferential paths subsequent horizontal broadening from dispersive mechanisms is found to be a slow process for fractures of high intrinsic permeability the presence of an unsaturated rock matrix provides constraints on fracture matrix interface areas for imbibition and on the frequency of episodic deep seepage events further studies are needed to test the proposed model

dolomitization and sulfate reduction in the mixing zone between brine and meteoric water in the newly exposed shores of the dead sea pleistocene dolomites are associated either with evaporative processes such as in sabkhas and playas or with a mixing zone where mixing between two different solutions e g seawater and groundwater takes place we report here on the very recent formation of dolomite at shallow depths 6 12 cm in newly exposed gypsum rich sediments on the western shores of the dead sea sem and eds analysis as well as x ray diffraction analysis indicate that this dolomite is euhedral and close to ideal dolomite in composition these dolomite crystals differ from anhedral detrital ca rich dolomites from the cretaceous section of the watershed found in the whole section taking into account the sedimentation rate at the shore vicinity the maximal age of the euhedral dolomite was estimated as less than 60 years in the three profiles analysed euhedral dolomite was most abundant at a single layer where the gypsum content was locally lowered due to bacterial reduction of sulfate the sediments solution at the dead sea shore localities represent a mixing zone between dead sea residual solution and subsurface freshwater springs under such conditions formation of dolomite occurs at highly saline environment where very high mg ca ratios are attained

the effect of melt composition and oxygen fugacity on manganese partitioning between apatite and silicate melt abstract oxygen fugacity and melt composition are both known to have a strong influence on the partitioning of trace elements between coexisting minerals and melt previous work has suggested that mn partitioning between apatite and silicate melt may be strongly affected by oxygen fugacity and could therefore act as an oxybarometer here we present a new study on the partitioning of mn between apatite and melt at high temperature 1400 1250 c and 1 gpa pressure for various melt compositions and oxygen fugacities nno 4 7 to nno 10 we find that there is no demonstrable variation in the partition coefficient for mn between apatite and silicate melt dmnap m across the range of fo2 conditions studied here instead we find that dmnap m varies significantly with melt composition and that in particular the proportion of non bridging oxygens strongly influences partitioning of mn between apatite and melt we propose that variations in the mn content of natural apatite previously thought to reflect variations in fo2 are instead related to the degree of melt polymerisation these findings are consistent with the results of mn k edge xanes spectroscopy which demonstrate that mn in coexisting apatite and silicate glass is present predominantly as mn2 regardless of fo2 furthermore xanes spectra from a series of silicate glasses synthesised at various oxygen fugacities demonstrate that mn2 is the predominant species and that the average mn oxidation state does not vary over a wide range of fo2 t conditions

processes affecting interstitial water in the unsaturated zone at the newly exposed shore of the dead sea israel abstract a main process affecting interstitial water and solutes at shallow depths on the newly formed shores of the dead sea ds is evaporation the evaporation rate from the unsaturated zone as calculated based on stable isotope profiles ranges from 0 5 to 36 mm yr 1 the high tritium concentrations 20 40 tu as compared with the main implication of the present study is that the evaporitic sediments can undergo rapid chemical and isotopic changes which later can be found preserved in the sequence thus the isotopic and chemical record of some of the phases found in saline ancient evaporitic sequences may have a freshwater signature

impact of ambient temperature on evaporation from surface exposed fractures 1 surface exposed fractures sefs form a unique link between the atmosphere and the deep vadose zone quantifying evaporation and salt accumulation rates within these sefs is essential for understanding processes leading to groundwater salinization and contamination via these fractures in this study evaporation from sefs esefs was quantified mainly as a function of ambient atmospheric temperature by using large scale laboratory experiments and measuring evaporation under controlled conditions in addition esef was theoretically quantified based on the physical processes that govern it the theoretical model was used to analyze esef rates as a function of ambient temperature temperature gradient fracture aperture and matrix pore size esef was experimentally found to increase as the ambient temperature decreased measured evaporation rates were between about 110 and 260 g d 1 per square meter of fracture surface for temperature differences between rock bottom and the atmosphere of 0 and 13 c respectively comparing these values with model results suggests that convection is the driving process for enhanced evaporation at low ambient temperatures finally we show that esef rates decrease as a result of salt precipitation during a 9 month period with an imposed temperature difference of 13 c esef decreased from 260 to 95 g d 1 m 2 due to salt accumulation near and on the fracture surfaces evaporation rates began decreasing after about 100 g m 2 of salt had precipitated and decreased to less than 50 of the initial rate after 160 g m 2 of salt had precipitated we thus show that not only temperature but also salt precipitation largely affect esef rates

upscaling of constitutive relations in unsaturated heterogeneous tuff matrix when numerical models are used for modeling large scale flow and transport processes in the subsurface upscaling is generally needed to determine large scale hydraulic properties from small scale measurements this study is focused on the upscaling of constitutive relations among relative permeability capillary pressure and saturation for unsaturated tuff matrix or a porous medium with a large air entry value unsaturated flow in tuff matrix is of interest at a number of existing and proposed waste disposal sites as well as in connection with environmental contamination in arid and semiarid regions based on the notion that a large air entry value corresponds to a spatially uniform capillary pressure distribution even at a relatively large scale for steady state unsaturated flow we present an upscaling approach for constitutive relations of tuff matrix numerical experiments were used to verify and demonstrate the usefulness of the approach

effect of isolated fractures on accelerated flow in unsaturated porous rock 1 fractures that begin and end in the unsaturated zone or isolated fractures have been ignored in previous studies because they were generally assumed to behave as capillary barriers and remain nonconductive we conducted a series of experiments using berea sandstone samples to examine the physical mechanisms controlling flow in a rock containing a single isolated fracture the input fluxes and fracture orientation were varied in these experiments visualization experiments using dyed water in a thin vertical slab of rock were conducted to identify flow mechanisms occurring due to the presence of the isolated fracture two mechanisms occurred 1 localized flow through the rock matrix in the vicinity of the isolated fracture and 2 pooling of water at the bottom of the fracture indicating the occurrence of film flow along the isolated fracture wall these mechanisms were observed at fracture angles of 20 and 60 degrees from the horizontal but not at 90 degrees pooling along the bottom of the fracture was observed over a wider range of input fluxes for low angled isolated fractures compared to high angled ones measurements of matrix water pressures in the samples with the 20 and 60 degree fractures also demonstrated that preferential flow occurred through the matrix in the fracture vicinity where higher pressures occurred in the regions where faster flow was observed in the visualization experiments the pooling length at the terminus of a 20 degree isolated fracture was measured as a function of input flux calculations of the film flow rate along the fracture were made using these measurements and indicated that up to 22 of the flow occurred as film flow these experiments apparently the first to consider isolated fractures demonstrate that such features can accelerate flow through the unsaturated zone and should be considered when developing conceptual models

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

stochastic simulations of steady state unsaturated flow in a three layer heterogeneous dual continuum model of fractured rock abstract unsaturated flow through fractured rocks is a concern in the siting and performance of waste disposal facilities such as the proposed geological repository at yucca mountain nevada we simulated a small two dimensional cross section of welded volcanic tuff representative of yucca mountain stratigraphy using spatially correlated randomly heterogeneous fracture permeability fields and homogeneous matrix permeability continua representing various degrees of welding ten realizations each of fracture permeability fields for four different variances 2 0 5 1 0 1 5 and 2 0 were generated by the direct fourier transform method robin m j l gutjahr a l sudicky e a wilson j l 1993 cross correlated random field generation with the direct fourier transform method water resour res 29 7 2385 2398 independently for the welded tiva canyon tuff tcw the non welded paintbrush tuff ptn and the welded topopah spring tuff tsw the latter being the proposed primary repository horizon numerical simulations were run for steady state flow at three different uniform water flux boundary conditions boundary conditions along the sides were impermeable and the base was open to gas and liquid flow numerical simulations were performed using the dual continuum two phase flow simulator metra which represents matrix and fractures as dual overlapping continua where liquid flux between continua can be restricted by a uniform factor fracture matrix interaction was modeled as being less restricted in the ptn as compared to the tcw tsw heterogeneous fracture permeability fields generated strong preferential flow in the tcw tsw fracture continuum and significant preferential flow in the uniformly permeable ptn matrix continuum flow focusing led to a local increase in saturation which in turn increased relative permeability to water along the preferential pathways causing water to flow faster the development of the preferential pathways reduced the wetted surface area for fracture matrix interaction leaving a large volume of the rock isolated from the preferential flow pathways statistical analysis of water flux values in the three units showed that the magnitude of the ensemble variance indicating preferential flow pathways increased with both the variance of fracture permeability and the water flux boundary condition reaching a plateau in the tcw tsw fracture continuum units after flowing approximately 10 correlation scales of the vertical fracture permeability ensemble covariance of water flux normal to the layering revealed long range correlations in all units which is longer than the correlation length of the fracture permeability fields this suggests that the water flux boundary condition influences preferential flow in unsaturated dual continua media these results suggest that careful analysis of information on fracture permeability variability obtained from pneumatic and hydraulic tests is an important component in understanding deep percolation processes

estimating groundwater recharge in hebei plain china under varying land use practices using tritium and bromide tracers summary tritium and bromide were used as applied tracers to determine groundwater recharge in hebei plain north china to evaluate the impacts of different soil types land use irrigation and crop cultivation practice on recharge additional objectives were to evaluate temporal variability of recharge and the effect on results of the particular tracer used thirty nine profiles at representative locations were chosen for investigation average recharge rates and recharge coefficient determined by tritium and bromide tracing for different sites were 0 00 1 05 mm d and 0 0 42 5 respectively the results showed relative recharge rates for the following paired influences items within each pair are listed with the influence producing greater recharge first flood irrigated cropland and non irrigated non cultivation land flood irrigation 0 42 0 58 mm d and sprinkling irrigation 0 17 0 23 mm d no stalk mulch 0 56 0 80 mm d and stalk mulch 0 44 0 60 mm d vegetable e g chinese cabbage and garlic 0 70 mm d and wheat maize 0 38 mm d peanut 0 51 mm d and peach 0 43 mm d the results also showed greater recharge for the first year of tracer travel than for the second because total precipitation and irrigation were greater in the first year than in the second this may reflect temporal variability of recharge the method may not be applicable where the water table is shallow less than 3 m a comparison of the near ideal tritium tracer with the more common but less ideal bromide showed that bromide moved approximately 23 faster than tritiated water perhaps because of anion exclusion

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 interaction of two major old water bodies and its implication for the exploitation of groundwater in the multiple aquifer system of the central and northern negev israel abstract in the beer sheva region of the negev desert the only significant fresh groundwater is contained within the judea group carbonate aquifer it is found that this aquifer holds two distinctly different old water bodies one such groundwater body has evolved in equilibrium with the carbonate aquifer rocks after being recharged during the holocene in the hebron mountains north of the study area at present modern recharge as denoted by the tritium and radiocarbon contents is very minor a subtle piston effect generated by contemporary replenishment is discussed in representative hydrographs in beer sheva wells another groundwater body identified in the judea group aquifer derives from the underlying kurnub group aquifer the regional artesian kurnub group aquifer nubian sandstone contains an older and brackish groundwater body which has been recharged in sinai during pleistocene pluvials faulting in the beer sheva region facilitated hydrologic contact between the two aquifers exploitation of the judea group has released confining pressures and resulted in the intrusion of kurnub group water into the overlying judea group carbonate aquifer this process is most significant in those wells drilled close to major faults where salinity increases with pumping the intruding water originating from the kurnub group sandstone aquifer has not yet equilibrated chemically with the carbonate host the low ph and high temperatures that have been encountered indicate continuing and very recent intrusion in the beer sheva area in the absence of direct significant modern recharge as determined from tritium and 14 c values all waters should be considered as paleowaters that are being mined a complete revision of the hydrologic concept by which the multiple aquifer system can be exploited is required to take into account the fact that the fresh judea group groundwater is actually an old holocene water body intruded by brackish and older pleistocene water along fault zones

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

influence of fracture intersections under unsaturated low flow conditions recent experimental evidence suggests that the capillary heterogeneity associated with fracture intersections can act to impose temporal and spatial structure on network scale flows a simple intersection between orthogonal fractures one horizontal and the other vertical has been shown to integrate unsaturated flows at low flows the intersection forms a capillary barrier that accumulates water in a growing pool eventually the retaining meniscus snaps discharging a pulse of water here we develop a mechanistic explanation for this observed behavior and experimentally consider three perturbations to the geometry of the simple orthogonal intersection two of the perturbations also act as capillary barriers while the third formed a capillary bridge across the intersection at low flow all of our experimental intersections imposed a temporal signal with the nature of that signal dependent on intersection geometry and participation by the horizontal fractures in dynamic storage at high flow a continuous fluid tendril spanned the system from inlet to outlet with water pooled above the intersection caused by a narrow fluid connection that restricted flow across the intersection results from all experiments suggest that pulsation is critically sensitive to small variations in the geometry of fracture intersections and storage in the horizontal fractures when combinedmore with dependency on supply rate this sensitivity can generate pulsation of flow across a wide range of time periods and discharge volumes less

groundwater recharge in semi arid carbonate aquifers under intensive use the estepa range aquifers seville southern spain quantifying groundwater recharge in carbonate aquifers located in semi arid regions and subjected to intensive groundwater use is no easy task one reason is that there are very few available methods suitable for application under such climatic conditions and moreover some of the methods that might be applied were originally designed with reference to non carbonate aquifers in addition it is necessary to take into account the fact that in any given aquifer groundwater recharge is modified by the groundwater exploitation here we focus on four methods selected to assess their suitability for estimating groundwater recharge in carbonate aquifers affected by intensive exploitation the methods were applied to the estepa range aquifers of seville southern spain which are subjected to different degrees of exploitation two conventional methods were used chloride mass balance and daily soil water balance these results were compared with the results obtained by means of two non conventional methods designed for application to the carbonate aquifers of southern spain the aplis and eras methods the results of the different methods are analogous comparable to those obtained in nearby non exploited carbonate aquifers confirming their suitability for use with carbonate aquifers in either natural or exploited regimes in a semi arid climate

unsaturated flow and transport through a fault embedded in fractured welded tuff 1 to evaluate the importance of matrix diffusion as a mechanism for retarding radionuclide transport in the vicinity of a fault located in unsaturated fractured rock we carried out an in situ field experiment in the exploratory studies facility at yucca mountain nevada this experiment involved the release of 82 000 l of water over a period of 17 months directly into a near vertical fault under both constant positive head at 0 04 m and decreasing fluxes a mix of conservative tracers pentafluorobenzoic acid pfba and bromide applied in the form of lithium bromide was released along the fault over a period of 9 days 7 months after the start of water release along the fault as water was released into the fault seepage rates were monitored in a large cavity excavated below the test bed after the release of tracers seepage water was continuously collected from three locations and analyzed for the injected tracers observations of bromide concentrations in seepage water during the early stages of the experiment and bromide and pfba concentrations in the seepage water indicate the significant effects of matrix diffusion on transport through a fault embedded in fractured welded rock

anion exclusion during transport through the unsaturated zone a 20 year chronological record of the flow of water and anions along 27 m in the unsaturated zone of a phreatic aquifer was reconstructed water was traced according to its tritium content using the difference between the environmental tritium content of rain and irrigation water anions were traced using data about their sequential input to the overlying cultivated field and their concentration in the profile evidences of anion exlcusion were found along a 10 m thick clay loam layer the vertical velocities of water molecules and anions so2 4 and cl were calculated to be 0 7 0 05 and 1 35 0 05m yr respectively the average thickness of the water films and the equivalent distance of exclusion at a 15 gravimetric water content were 25 and 12a respectively these field data fit and support the theoretical relationship between the water film thickness and the relative exclusion concentration proposed by bresler 1973

solute transport in the vadose zone and groundwater during flash floods events were investigated in the lower reach of the kuiseb river namibia and in controlled column experiments simultaneous measurements of water level and electrical conductivity of the ood water in the stream channel and in the groundwater together with variations in the vadose zone water content temperature and pressure proles allowed a detailed analysis of the various mechanisms governing solute transport in the subsurface during ash oods the results indicated that on the land surface ash oods emit at their wetting fronts instantaneous compression waves that propagate downward through the unsaturated zone to the water table these compression waves generate abrupt solute displacement events in the groundwater immediately after the arrival of the ood on the land surface long before deep percolation and groundwater recharge begin each ood event launches into the vadose zone a wetting front that propagates down through the vadose zone and recharges the groundwater upon arrival at the water table therst wetting front of each ood season leaches out soluble salts that have accumulated in the vadose zone during the dry season however water percolation through the unsaturated zone does not leach out the entire soluble salt capacity of the sediment even if percolation takes place under high water head ooding conditions for long periods the incomplete leaching of the unsaturated zone by the percolating water releases soluble salts into the groundwater during every recharge event as a result of the rise of the water table into the vadose zone this process results in a temporal increase of the groundwater electrical conductivity ec

chemical weathering of fractured eocene chalks in the negev israel abstract ba ca fe k mg mn sr and insoluble residue i r contents of eocene chalks and of vein filled derivative matter from the northern negev israel were analyzed the eocene chalk country rock weathered physically and chemically and the eroded material has filled the fault planes and some of the joints two types of filling material were found calcite crystals and soft fine carbonate material the latter as the chalk are sometimes associated with fe and mn oxides i r ca mg ca sr ca and k ca values decrease from the country rock chalk to the fine carbonates and are lower in the calcite minerals the ba ca values are low in the soft fine carbonates and high in the calcite minerals barite was found in places in the chalk fe ca and mn ca values are higher in the soft fine carbonate based on k d values the expected ba ca mg ca and sr ca values in the vein carbonates are lower and the expected fe ca and mn ca are higher than the actual values the analysis of the soft fine carbonates from the various joints and faults shows that chemical precipitation was unaffected by these structures this possibly suggests that the soft fine carbonates are younger and not contemporaneous with the structures

dripping into unsaturated rock underground excavations literature review and geologic and hydrogeologic setting description a literature review of dripping in underground constructions in deep unsaturated geologic media was performed as part of a phased study the objective is to develop and test a formulation that can be used for studying unsaturated flow through rough multi segmented fractures with emphasis on predicting dripping initiation time geologic and hydrogeologic setting for the yucca mountain ym and its exploratory studies facility which is the site where the model will be tested are described

soil water movement under natural site and waste site conditions a multiple year field study in the mojave desert nevada soil water movement under natural site and simulated waste site conditions were compared by monitoring four experimental sites in the mojave desert nevada during a 5 year period one vegetated soil profile one soil profile where vegetation was removed and two nonvegetated test trenches precipitation ranged from 14 to 162 mm yr temporal changes in water content measured by neutron probe were limited to the upper 0 5 1 m values ranged from 0 01 to 0 19 m3 m3 water potential and temperature were measured by thermocouple psychrometers 77 remained operable for 4 5 years for vegetated soil precipitation that accumulated in the upper 0 75 m of soil was removed by evapotranspiration water potentials decreased seasonally by 4 to 8 mpa during 2 years with below average precipitation water potentials below the app arent root zone decreased by 2 3 1 2 m depth to 0 4 mpa 5 m depth and the gradients became predominantly upward water potentials then rebounded during 2 years with near and above average precipitation and seasonally variant water potential gradients were reestablished above the 4 2 m depth under nonvegetated waste site conditions data indicated the long term accumulation and shallow but continued penetration of precipitation water potentials showed moisture penetration to depths of 0 75 1 85 m the method of simulated waste drum placement stacked versus random and the associated differences in subsidence showed no measurable influence on the water balance of the trenches subsidence totaled 13 mm during the study water potentials below the trenches and below the 2 m depth for the nonvegetated soil remained low 5 5 to 7 5 mpa and indicated the persistence of typically upward driving forces for isothermal water flow water fluxes estimated from water potential and temperature data suggested that isothermal liquid isothermal vapor and nonisothermal vapor flow need to be considered in the conceptualization of unsaturated flow at the field sites below the depth of temporal water content change the estimated liquid fluxes ranged from 10 10 to 10 15 cm s isothermal vapor fluxes ranged from 10 10 to 10 13 cm s and the nonisothermal vapor fluxes ranged from 10 8 to 10 10cm s

field observation of flow in a fracture intersecting unsaturated chalk flow through a natural fracture crossing unsaturated chalk in an arid region was investigated in a field experiment using a specially designed experimental setup the setup allowed complete control of the flow domain inlet and outlet water flux into and out of the fracture was measured in small segments of the fracture openings and flow trajectories were identified using seven fluorobenzoic acid tracers a 5 day percolation experiment on a 5 3 m long fracture showed significant spatial and temporal variability of the flow regime flow through fracture openings did not reach a steady state either in individual segments or across the entire flow domain although the boundary conditions were kept relatively steady for the entire duration of the experiment flow trajectories within the fracture plane varied over time however most of the flow was confined to small sections of the fracture over 70 of the flux was transmitted through 20 of the studied fracture openings observations from the tracer tests suggest that flow paths can coexist near each other without water mixing probably because the fracture fill generates unconnected flow paths across the main fracture void

impact of coating and weathering on the properties of chalk fracture surfaces the surface topography of a natural fracture intersecting a chalk formation was mapped using a high resolution laser scanning device and its roughness was evaluated using five different criteria two coated and two uncoated slices of the natural fracture surface were encased in flow cells and exposed to short 24 and 8 hours interactions with percolating synthetic rainwater and industrial wastewater followed by long drying periods weeks these flow experiments simulated the intermittent infiltration of surface runoff and industrial effluents typical of the study area and resulted in erosion of the fracture surfaces and modification of their roughness the temporal variations in surface roughness were evaluated using three commonly used criteria standard deviation from mean heights differences between maximum and minimum heights and the root mean square roughness and two newly developed measures namely the slopes on the surfaces and a calculated roughness related ratio rrr the mean slope maps and rrr calculations were found to be good criteria for evaluating surface topography and its uniformity across the fracture surface the coated surfaces were significantly rougher had greater relief more heterogeneous topography and a larger surface area than the uncoated surfaces the results suggest that coating and fast weathering caused by intermittent flow events significantly change roughness surface area relief and the heterogeneity of a fracture surface these in turn may affect the spatial distribution of flow paths across that fracture surface consequently when exploring the properties of fracture surfaces and fracture flow the impact of surface skin and variations of the surface properties over short timescales should be taken into account

petrology and geochemistry of the island of sarigan in the mariana arc calc alkaline volcanism in an oceanic setting isotopic studies of rocks from oceanic island arcs such as the marianas indicate that little if any recycling of continental material e g oceanic sediments occurs in these arcs because oceanic arcs are on the average more mafic than the dominantly andesitic continental arcs an important question is whether the andesites of continental arcs are produced by a fundamentally different more complex mechanism than the lavas of oceanic arcs an excellent opportunity for study of this question is provided by the island of sarigan in the mariana active arc on which calc alkaline andesites including hornblende bearing types are exposed along with more mafic lavas

surface zone flow along unsaturated rock fractures although fractures in rock are well recognized as pathways for fast percolation of water processes which permit fast flow along unsaturated fracture pathways remain to be identified and understood earlier aperture based models of flow in partially saturated fractures permit fast flow only through a continuous network of locally saturated segments film flow was recently identified as a mechanism capable of sustaining fast flow along truly unsaturated fractures when the matric potential is very close to zero another mechanism for fast flow along unsaturated fractures is introduced in this study surface zone flow which can be important when the permeability of the rock along fractures fracture skin is significantly greater than that of the bulk rock matrix in such systems the fracture surface zone provides low resistance pathways through which fast flow relative to the bulk matrix rock can occur even when the fractures are at very low water saturation initial experimental tests of surface zone fast flow were performed surface zone fast imbibition of water was measured on a welded tuff and a rhyolite however because 1 imbibition rates are also strongly influenced by rock wettability 2 these initially air dry rocks exhibited finite contact angles upon exposure to water and 3 we lack methods to reliably measure permeabilities of thin regions on rock surfaces quantification of permeability contrasts was not possible in these initial tests

field monitoring and dual permeability modelling of water flow through unsaturated calcareous rocks summary environmental monitoring was carried out in order to investigate the role of topsoil rock matrix and fractures in controlling the water flow in unsaturated zone of calcareous rocks and in determining the timing and the magnitude of groundwater recharge a comprehensive dataset of climate data soil moisture and rock pressure heads was used to evaluate a physically based 1d dual permeability model in order to simulate the water flow in the vertical profile to the groundwater table the parameters of water retention and unsaturated hydraulic conductivity curves in soil and rock matrix were estimated using two evaporation experiments in the laboratory and the tension infiltrometer in the field the other sensitive parameters of the model were calibrated using an optimization procedure based on combinations of randomly sampled parameters once the model had been calibrated it was used to obtain insights into the hydrological processes through the unsaturated profile down to the water table the soil acts as a attenuation layer determining the timing and the magnitude of drainage fluxes towards the unsaturated rock zone the low permeability petrocalcic horizon below the soil which frequently occurs in semi arid regions plays a key role in controlling the water exchanges between the soil and the rock most water flow in the top of the rock profile occurs through the fractures this fracture flow becomes less along the profile as a part of it gradually infiltrates into the unsaturated rock matrix fracture water infiltrates entirely into the matrix only when the unsaturated rock zone is very thick so that in sites with a shallow water table fracture flow may be the dominant groundwater recharge mechanism the flow through the matrix is continuous over time and at the water table it becomes constant and independent of large seasonal and annual variations in rainfall the flow through the unsaturated matrix is the dominant groundwater recharge mechanism in dry summers and in drought years the continuous matrix water flow sustains the recharge thus maintaining high groundwater levels when more water is extracted this is important in regions where groundwater from unconfined calcareous aquifers are important water resources the recharge through the fractures is sensitive to the annual rainfall pattern and also contributes to the groundwater in years when the rainfall is greater

hydrologic issues in arid unsaturated systems and implications for contaminant transport analysis of unsaturated flow and transport in arid regions is important not only in water resource evaluation but in contaminant transport as well partic ularly in siting waste disposal facilities and in remediat ing contaminated sites the water fluxes under consid eration have a magnitude close to the errors inherent in measuring or in calculating these water fluxes which makes it difficult to resolve basic issues such as direction and rate of water movement and controls on unsaturated flow the purpose of this paper is to review these issues on the basis of unsaturated zone studies in arid settings because individual techniques for estimating water fluxes in the unsaturated zone have limitations a variety of physical measurements and environmental tracers should be used to provide multiple independent lines of evidence to quantify flow and transport in arid regions the direction and rate of water flow are affected not only by hydraulic head gradients but also by temperature and air pressure gradients the similarity of water fluxes in a variety of settings in the southwestern united states indicates that vegetative cover may be one of the pri mary controls on the magnitude of water flow in the unsaturated zone however our understanding of the role of plants is limited most unsaturated flow in arid systems is focused beneath topographic depressions and diffuse flow is limited thick unsaturated sections and low water fluxes typical of many arid regions result in preservation of paleoclimatic variations in water flux and suggest that deep vadose zones may be out of equilib rium with current climate whereas water movement along preferred pathways is common in humid sites field studies that demonstrate preferential flow are restricted mostly to fractured rocks and root zones in arid regions results of field studies of preferential flow in humid sites generally restricted to the upper 1 2 m because of shallow water tables cannot be applied readily to thick vadose zones in arid regions

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

sources of salinity and boron in the gaza strip natural contaminant flow in the southern mediterranean coastal aquifer isotopic 87 sr 86 sr d 11 b d 18 o d 2 h and d 34 sso4 compositions of groundwater from the southern mediterranean coastal aquifer israel and the gaza strip in order to elucidate the origin of salinity and boron contamination the original salinity in the eastern part of the aquifer is derived from discharge of saline groundwater from the adjacent avedat aquitard na cl 1 high b cl so4 cl and hco3 87 sr 86 sr 0 7083 d 11 b 48 although the d 18 o d 2 h slope is identical to that of the avedat aquitard the geochemical data suggest that dissolution of pedogenic carbonate and gypsum minerals in the overlying loessial sequence generated the ca rich solution that triggered base exchange reactions and produced na and b rich groundwater the geochemical data show that most of the salinization process in the gaza strip is derived from the lateral flow of the na rich saline groundwater superimposed with seawater intrusion and anthropogenic nitrate pollution the methodology of identification of multiple salinity sources can be used to establish a long term management plan for the gaza strip and can also be implemented to understand complex salinization processes in other similarly stressed coastal aquifers

review on soil water isotope based groundwater recharge estimations groundwater recharge estimations are necessary for sustainable management of groundwater resources among various hydraulic hydrogeological and hydrological approaches tracer methods are proposed to improve groundwater recharge estimations soil water isotope based estimates of groundwater recharge rates were developed in the 1960s and have been applied in more than 40 studies reviewed within this manuscript this comprehensive review research distinguishes three fundamental research approaches 1 labelling method with tritium or deuterium which can be used to trace unsaturated zone water movement 2 tracing soil water movement using a seasonal signal of stable isotopes in precipitation mainly applied in humid zones and 3 interpretation of an evaporation signal that impacts soil water stable isotope composition mainly applicable in arid and semiarid regions more recently advances in soil water extraction and analytical methods allow a higher sampling resolution and in situ measurements of soil water stable isotopes analytical advances may strengthen and improve the applicability of stable isotope methods for quantitative recharge we present compare and discuss studies of unsaturated zone isotope profiles with an emphasis on necessary prerequisites such as a substantial thick porous sedimentary layer or negative influences through high clay and silt contents or dry soil conditions copyright 2015 john wiley sons ltd