retardation of 238u and 232th decay chain radionuclides in long island and connecticut aquifers abstract knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the 238u and 232th decay chains groundwaters of varying chemical composition were analyzed from wells in long island new york and connecticut aquifer lithologies are arkose quartz sandstone granite and glacial drift adsorption k1 and desorption k2 coefficients for ra and pb were calculated using 222rn activity as a measure of the supply of other recoil nuclides laboratory tests of the validity of this assumption were made by measuring the flux of 224ra and 222rn from aquifer solids the ratio k 1 k 2 is the distribution coefficient k which is effectively equal to r the retardation factor the average value of k for ra is 6 102 in long island aquifers and 5 104 in connecticut the distribution coefficient for pb is 104 in long island and 105 in connecticut results from this and other studies reveal a strong dependence of retardation on ph o 2 and ionic strength that tends to overwhelm any dependence of retardation on lithology

seasonal variability of element fluxes in two central siberian rivers draining high latitude permafrost dominated areas in order to constrain the origin and fluxes of elements carried by rivers of high latitude permafrost dominated areas major and trace element concentrations as well as sr and u isotopic ratios were analyzed in the dissolved load of two siberian rivers kochechum and nizhnyaya tunguska regularly sampled over two hydrological cycles 2005 2007 large water volumes of both rivers were also collected in spring 2008 in order to perform size separation through dialysis experiments this study was completed by spatial sampling of the kochechum watershed carried out during summer and by a detailed analysis of the main hydrological compartments of a small watershed from element concentration variations along the hydrological cycle different periods can be marked out matching hydrological periods during winter baseflow period october to may there is a concentration increase for major soluble cations and anions by an order of magnitude the spring flood period end of may beginning of june is marked by a sharp concentration decrease for soluble elements whereas dissolved organic carbon and insoluble element concentrations strongly increase when the spring flood discharge occurs the significant increase of aluminum and iron concentrations is related to the presence of organo mineral colloids that mobilize insoluble elements the study of colloidal ree reveals the occurrence of two colloid sources successively involved over time spring colloids mainly originate from the uppermost organic rich part of soils whereas summer colloids rather come from the deep mineral horizons furthermore u and sr isotopic ratios together with soluble cation budgets in the kochechum river impose for soluble elements the existence of three distinct fluxes over the year a at the spring flood a surface flux coming from the leaching of shallow organic soil levels and containing a significant colloidal component b a subsurface flux predominant during summer and fall mainly controlled by water rock interactions within mineral soils and c a deep groundwater flux predominant during winter which enters large rivers through unfrozen permafrost paths detailed study of the kochechum watershed suggests that the contribution of this deep flux strongly depends on the depth and continuous nature of the permafrost

u sr isotopic speedometer fluid flow and chemical weathering rates in aquifers abstract both chemical weathering rates and fluid flow are difficult to measure in natural systems however these parameters are critical for understanding the hydrochemical evolution of aquifers predicting the fate and transport of contaminants and for water resources water quality considerations 87 sr 86 sr and 234 u 238 u activity ratios are sensitive indicators of water rock interaction and thus provide a means of quantifying both flow and reactivity the 87 sr 86 sr values in ground waters are controlled by the ratio of the dissolution rate to the flow rate similarly the 234 u 238 u ratio of natural ground waters is a balance between the flow rate and the dissolution of solids and recoil loss of 234 u from the solids by coupling these two isotope systems it is possible to constrain both the long term ca 100 s to 1000 s of years flow rate and bulk dissolution rate along the flow path previous estimates of the ratio of the dissolution rate to the infiltration flux from sr isotopes 87 sr 86 sr are combined with a model for 234 u 238 u to constrain the infiltration flux and dissolution rate for a 70 m deep vadose zone core from hanford washington the coupled model for both 234 u 238 u ratios and the 87 sr 86 sr data suggests an infiltration flux of 5 2 mm yr and bulk silicate dissolution rates between 10 15 7 and 10 16 5 mol m 2 s the process of recoil enrichment while primarily responsible for the observed variation in 234 u 238 u of natural systems is difficult to quantify however the rate of this process in natural systems affects the interpretation of most u series data models for quantifying the recoil loss fraction based on geometric predictions surface area constraints and chemical methods are also presented the agreement between the chemical and theoretical methods such as direct measurement of 234 u 238 u of the small grain size fraction and geometric calculations for that size fraction is quite good

time scale and conditions of weathering under tropical climate study of the amazon basin with u series the rio solimoes amazonas amazon river and its major tributaries have been analyzed for u series nuclides 238 u 234 u 230 th 226 ra disequilibria have been measured in the dissolved 0 2 lm as well as bed sands u series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering moreover while the dissolved load records present day weathering suspended particles integrate the erosion his tory over much longer time scales 100 ka lowland rivers are characterized by long time scales of chemical erosion p100 ka result ing in a high weathering intensity moreover exchange between suspended particles and the dissolved load may explain the u series signature for these rivers by combining u series and pb isotopes in suspended particles we show that erosion in the rio madeira basin occurred as a multi step process whereby the pristine continental crust was eroded several hundreds of ma ago to produce sediments that have then been integrated in the cordillera by crustal shortening and are currently eroded in contrast recent erosion of a pristine crust is more likely for the rio solimoes amazonas 10 ka the suspended particles of the rivers draining the andes solimoes ama zonas madeira suggest time scales of weathering ranging between 4 and 20 ka this indicates that suspended particles transported by those rivers are not stored for long periods in the andean foreland basin and the tropical plain the sediments delivered to the ocean have resided only a few ka in the amazon basin 6 3 1 ka for the rio amazonas at obidos nevertheless a large fraction of the sediments coming out from the andes are trapped in the foreland basin and may never reach the ocean erosion in the andes is not operating in steady state u series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady state erosion and that is a consequence of soil destruction greater than production by relating this observation to the short time scales of weathering inferred for the andes a few ka it appears that the erosion regime has been recently perturbed resulting in high denudation rates a possible explanation would be the increase in precipitation less than 5 ka proposed by recent paleoclimatic studies our results indicate that erosion responds rapidly to high frequency climatic fluctuations

modeling non steady state radioisotope transport in the vadose zone a case study using uranium isotopes at pena blanca mexico current models using u and th series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady state situation these models have limited applicability to the vadose zone uz where the concentration and migratory behavior of radioisotopes in fluid are often transitory we present here as a first attempt of its kind a model simulating the non steady state intermittent fluid transport in vadose layers it provides quantitative constraints on in situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock water interaction or water transit time for uranium the simulation predicts that intermittent flushing in the uz leads to a linear relationship between reciprocal u concentration and 234u 238u ratio in percolating waters with the intercept and slope bearing information on the rates of dissolution and recoil of u isotopes respectively the general validity of the model appears to be borne out by the measurement of uranium isotopes in uz waters collected at various times over a period during 1995 2006 from a site in the pena blanca mining district mexico where the nopal i uranium deposit is located enhanced 234u 238u ratios in vadose zone waters resulting from lengthened non flushing time as prescribed by the model provide an interpretative basis for using 234u 238u in cave calcites to reconstruct the regional changes in hydrology and climate we also provide a theoretical account of the model s potential applications using radium isotopes

occurrence and geochemistry of radium in water from principal drinking water aquifer systems of the united states abstract a total of 1270 raw water samples before treatment were collected from 15 principal and other major aquifer systems pas used for drinking water in 45 states in all major physiographic provinces of the usa and analyzed for concentrations of the ra isotopes 224 ra 226 ra and 228 ra establishing the framework for evaluating ra occurrence the us environmental protection agency maximum contaminant level mcl of 0 185 bq l 5 pci l for combined ra 226 ra plus 228 ra for drinking water was exceeded in 4 02 39 of 971 of samples for which both 226 ra and 228 ra were determined or in 3 15 40 of 1266 of the samples in which at least one isotope concentration 226 ra or 228 ra was determined the maximum concentration of combined ra was 0 755 bq l 20 4 pci l in water from the north atlantic coastal plain quartzose sand aquifer system all the exceedences of the mcl for combined ra occurred in water samples from the following 7 pas in order of decreasing relative frequency of occurrence the midcontinent and ozark plateau cambro ordovician dolomites and sandstones the north atlantic coastal plain the floridan the crystalline rocks granitic metamorphic of new england the mesozoic basins of the appalachian piedmont the gulf coastal plain and the glacial sands and gravels highest concentrations in new england the concentration of ra was consistently controlled by geochemical properties of the aquifer systems with the highest concentrations most likely to be present where as a consequence of the geochemical environment adsorption of the ra was slightly decreased the result is a slight relative increase in ra mobility especially notable in aquifers with poor sorptive capacity fe oxide poor quartzose sands and carbonates even if ra is not abundant in the aquifer solids the most common occurrence of elevated ra throughout the usa occurred in anoxic water low dissolved o 2 with high concentrations of fe or mn and in places high concentrations of the competing ions ca mg ba and sr and occasionally of dissolved solids k so 4 and hco 3 the other water type to frequently contain elevated concentrations of the ra radioisotopes was acidic low ph and had in places high concentrations of no 3 and other acid anions and on occasion of the competing divalent cations mn and al one or the other of these broad water types was commonly present in each of the pas in which elevated concentrations of combined ra occurred concentrations of 226 ra or 228 ra or combined ra correlated significantly with those of the above listed water quality constituents on the basis of the non parametric spearman correlation technique and loaded on principal components describing the above water types from the entire data set and for samples from the pas with the highest combined ra concentrations concentrations of 224 ra and 226 ra were significantly correlated to those of 228 ra spearman s rank correlation coefficient 0 236 and 0 326 respectively activity ratios of 224 ra 228 ra in the water samples were mostly near 1 when concentrations of both isotopes were greater than or equal to 0 037 bq l 1 pci l the level above which analytical results were most reliable co occurrence among these highest concentrations of the ra radionuclides was most likely in those pas where chemical conditions are most conducive to ra mobility e g acidic north atlantic coastal plain the concentrations of 224 ra were occasionally greater than 0 037 bq l and the ratios of 224 ra 228 ra were generally highest in the pas composed of alluvial sands and cretaceous tertiary sandstones from the western usa likely because concentrations of 224 ra are enhanced in solution relative to those of 228 ra by alpha recoil from the aquifer matrix rapid adsorption of the two ra isotopes controlled by the alkaline and oxic aquifer geochemistry combined with preferential faster recoil of 224 ra generates a 224 ra 228 ra ratio much greater than 1 the 228 ra 226 ra activity ratio was locally variable and was generally lower than 1 226 ra rich in samples from pas with carbonate bedrock but was typically greater than 1 228 ra rich in pas composed of unconsolidated sand

radium mobility and the age of groundwater in public drinking water supplies from the cambrian ordovician aquifer system north central usa abstract high radium ra concentrations in potable portions of the cambrian ordovician c o aquifer system were investigated using water quality data and environmental tracers 3h 3hetrit sf6 14c and 4herad of groundwater age from 80 public supply wells psws groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern 1 myr in the most downgradient confined portions of the potable system more than 80 and 40 percent of mean groundwater ages were older than 1000 and 50 000 yr respectively anoxic fe reducing conditions and increased mineralization develop with time in the aquifer system and mobilize ra into solution resulting in the frequent occurrence of combined ra rac 226ra 228ra at concentrations exceeding the usepa mcl of 185 mbq l 5 pci l the distribution of the three ra isotopes comprising total ra rat 224ra 226ra 228ra differed across the aquifer system the concentrations of 224ra and 228ra were strongly correlated and comprised a larger proportion of the rat concentration in samples from the regionally unconfined area where arkosic sandstones provide an enhanced source for progeny from the 232th decay series 226ra comprised a larger proportion of the rat concentration in samples from downgradient confined regions concentrations of rat were significantly greater in samples from the regionally confined area of the aquifer system because of the increase in 226ra concentrations there as compared to the regionally unconfined area 226ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength of groundwater mineralization indicating that ra is mobilized to solution from solid phases of the aquifer as adsorption capacity is diminished the amount of 226ra released from solid phases by alpha recoil mechanisms and retained in solution increases relative to the amount of ra sequestered by adsorption processes or co precipitation with barite as adsorption capacity and the concentration of ba decreases although 226ra occurred at concentrations greater than 224ra or 228ra the ingestion exposure risk was greater for 228ra owing to its greater toxicity in addition 224ra added substantial alpha particle radioactivity to potable samples from the c o aquifer system thus monitoring for ra isotopes and gross alpha activity gaa is important in upgradient regionally unconfined areas as downgradient and gaa measurements made within 72 h of sample collection would best capture alpha particle radiation from the short lived 224ra

transport of radionuclides in an unconfined chalk aquifer inferred from u series disequilibria abstract u series disequilibria measured in waters and rocks from a chalk aquifer in france have been used as an analog for long term radionuclide migration drill core samples from a range of depths in the vadose zone and in the saturated zone as well as groundwater samples were analyzed for 238 u 234 u 232 th and 230 th to determine transport mechanisms at the water rock interface and to quantify parameters controlling the migration of radionuclides isotope measurements in rocks were done by tims whereas 234 u 238 u and 230 th 232 th activity ratios in water samples were measured by multi collector icp ms both depletion and enrichment in 234 u relative to 238 u were observed in carbonate rock samples resulting from chemical weathering in the unsaturated zone and calcite precipitation in the zone of water table oscillation respectively the correlation between 230 th 232 th activity ratios and 87 sr 86 sr ratios found in the chalk samples indicates that thorium is mainly contained in a minor silicate phase whose abundance is variable in chalk samples water samples are all characterized by 234 u 238 u 1 resulting from recoil effect of 234 th groundwaters are characterized by a more radiogenic signature in 87 sr 86 sr than the rocks moreover 230 th 232 th activity ratios in the waters are lower than in the rocks and increase with distance from the water divide which suggests that th transport is controlled by colloids formed during water infiltration in the soil a 1 d transport model has been developed in order to constrain the u series nuclide transport considering a transient behavior of radionuclides in the aquifer and a time dependent composition for the solid phase this model permits a prediction of the time scale of equilibration of the system and an estimation of parameters such as weathering rate distribution coefficients and recoil fractions retardation factors of 10 35 and from 1 10 4 to 2 10 5 were predicted for u and th respectively and can be used to predict the migration of radionuclides released as contaminants in the environment at the scale of our watershed 32 km 2 a characteristic migration time from recharge to riverine discharge of 200 600 yr for u and 0 2 3 7 myr for th was obtained

hafnium and neodymium isotopes in seawater and in ferromanganese crusts the element perspective abstract hafnium and nd isotopes are increasingly used as paleoceanographic proxies comparing the mantle crust array and the seawater array in plots of e hf vs e nd it has been observed that for a given e nd value the corresponding e hf value is higher for seawater than it is for terrestrial rocks while this difference had initially been explained by significant hydrothermal input of mantle hf into seawater the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine hf input we here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese fe mn crusts we distinguish between a truly dissolved and a dissolved hf and nd pool the latter being comprised of truly dissolved and colloid bound colloidal hf and nd while there exists a hydrothermal pathway for colloid bound dissolved mantle hf into the oceans there is in marked contrast to nd no important riverine pathway for colloidal or truly dissolved continental hf owing to their respective chemical speciation in seawater there exists truly dissolved nd in the ocean while the amount of truly dissolved hf is insignificant neodymium is in exchange equilibrium between local seawater and both the hydrous fe and mn oxides hydrogenetic fe mn crusts are composed of due to continuous ad and desorption there is continuous isotopic re equilibration and the isotopic composition of nd in a fe mn crust reflects that of truly dissolved nd in local ambient seawater in contrast hf is only associated with the hydrous fe oxides on which it forms surface precipitates that do not exchange with seawater due to this lack of isotopic re equilibration the isotopic composition of hf in a fe mn crust is the average of that of all the hf scavenged during the lifetime of the hydrous fe oxide particles since the hf bearing hydrous fe oxides in a fe mn crust do not form from local ambient seawater at the crust s growth site but are advected as colloids or fine particles their hf isotopic composition depends on the origin and migration pathway of these colloids hence while nd isotopes in fe mn crusts provide reliable information on truly dissolved nd in local ambient seawater hf isotopes rather indicate the origin and pathway of hydrous fe oxide colloids and might differ from truly dissolved hf in local ambient seawater this may explain the occasional decoupling of nd and hf isotopes in fe mn crusts and supports the notion of a significant hydrothermal mantle signal of hf in seawater

the importance of colloids and mires for the transport of uranium isotopes through the kalix river watershed and baltic sea the importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire rich kalix river drainage basin in northern sweden and the baltic sea ultrafiltration techniques were used to separate uranium and other elements associated with colloids 10 kd and 3 kd from solute uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples uranium concentrations in 0 45 m filtered kalix river water samples increased by a factor of 3 from near the headwaters in the caledonides to the river mouth while major cation concentrations were relatively constant 234 u 238 u ratios were high 234 u 770 1500 throughout the basin without showing any simple pattern and required a supply of 234 u rich water throughout the kalix river a large fraction 30 90 of the uranium is carried by 10 kd colloids which is compatible with uranium complexation with humic acids no isotopic differences were found between colloid associated and solute uranium within the baltic sea about half of the uranium is removed at low salinities the proportion that is lost is equivalent to that of river derived colloid bound uranium suggesting that while solute uranium behaves conservatively during estuarine mixing colloid bound uranium is lost due to rapid flocculation of colloidal material the association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior mire peats in the kalix river highly concentrate uranium and are potentially a significant source of recoil 234 u to the mirewaters and river waters however mirewater data clearly demonstrate that only small 234 u 238 u shifts are generated relative to inflowing groundwater a simple box model of uranium accumulation in peat and transport through the mire that is compatible with the mire data demonstrates that with efficient removal of uranium from solution only small shifts in 234 u 238 u ratios can be generated in mirewater uranium the measurements and model calculations show that mirewaters are not the primary source of the uranium in the river bedrock groundwaters with high 234 u 238 u ratios and uranium concentrations must be the dominant source of riverine uranium

using natural distributions of short lived radium isotopes to quantify groundwater discharge and recharge radium activity in pore water of wetland sediments often differs from the amount expected from local production decay and exchange with solid phases this disequilibrium results from vertical transport of radium with groundwater that flows between the underlying aquifer and surface water in situations where groundwater recharge or discharge is significant the rate of vertical water flow through wetland sediment can be determined from the radium disequilibrium by a combined model of transport production decay and exchange with solid phases we have developed and tested this technique at three sites in the freshwater portion of the everglades by quantifying vertical advective velocities in areas with persistent groundwater recharge or discharge and estimating a coefficient of dispersion at a site that is subject to reversals between recharge and discharge groundwater velocities v were determined to be between 0 and 20 5 cm d 21 for a recharge site and 1 5 6 0 4 cm d 21 for a discharge site near levee 39 in the everglades strong gradients in 223 ra and 224 ra usually occurred at the base of the peat layer which avoided the problems of other tracers e g chloride for which greatest sensitivity occurs near the peat surface a zone readily disturbed by processes unrelated to groundwater flow this technique should be easily applicable to any wetland system with different production rates of these isotopes in distinct sedimentary layers or surface water the approach is most straightforward in systems where constant pore water ionic strength can be assumed simplifying the modeling of radium exchange

modeling radium distribution in coastal aquifers during sea level changes the dead sea case abstract we present a new approach to studying the behavior of radium isotopes in a coastal aquifer in order to simulate radium isotope distributions in the dynamic flow field of the dead sea aquifer a multi species density dependent flow model sutra ms was used field data show that the activity of 226 ra decreases from 140 to 60 dpm l upon entering the aquifer from the dead sea and then further decreases linearly due to mixing with ra poor fresh water on the other hand an increase is observed in the activity of the shorter lived isotopes up to 52 dpm l 224 ra and 31 dpm l 223 ra which are relatively low in dead sea water up to 2 5 dpm l 224 ra and 0 5 dpm l 223 ra the activities of the short lived radium isotopes also decrease with decreasing salinity which is due to the effect of salinity on the adsorption of radium the relationship between 224 ra and salinity suggests that the adsorption partition coefficient k is linearly related to salinity simulations of the steady state conditions show that the distance where equilibrium activity is attained for each radium isotope is affected by the isotope half life k and the groundwater velocity resulting in a longer distance for the long lived radium isotopes k affects the radium distribution in transient conditions especially that of the long lived radium isotopes the transient conditions in the dead sea system with a 1 m yr lake level drop together with the radium field data constrains k to be relatively low 226 ra cannot be explained by adsorption and it is better explained by removal via coprecipitation probably with barite or celestine

sea level during the penultimate interglacial period based on a submerged stalagmite from argentarola cave italy accurate constraints are presented for the absolute age duration and sea level for the highstand corresponding to marine isotope stage mis 7 1 our work is based on a stalagmite collected in a currently submerged cave from italy argentarola cave flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms precise uranium thorium u th ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during mis 7 2 and mis 6 the penultimate glacial period in addition the period of marine transgression is bracketed between 202 and 190 kyr bp defining a mis 7 1 duration of 11 2 kyr comparison with previous studies provides a new constraint on the sea level during mis 7 1 that has approximately remained between 318 and 39 m relative to present sea level the timing of the mis 7 1 highstand is in full agreement with the specmap chronology which contrasts with the growing body of evidence showing a significant phase difference for mis 5 5 a tempting conclusion is that second order sea level highstands such as mis 7 1 may be purely driven by astronomical changes in contrast with major terminations such as termination ii atmospheric co2 levels may partly explain this contrast since the two sea level transitions mis 7 2 7 1 and mis 6 5 5 are characterized by very different co2 rises 20 vs 100 ppm fl 2002 elsevier science b v all rights reserved

using short lived nuclides of the u and th series to probe the kinetics of colloid migration in forested soils abstract the recent chemical dynamics of a podzolic forest soil section from the strengbach watershed france was investigated using u and th series nuclides analyses of 238 u 230 th 226 ra 232 th 228 ra and 228 th activities in the soil particles the seepage waters and the mature leaves of the beech trees growing on this soil were performed by tims or gamma spectrometry the simultaneous analysis of the different soil sl compartments allows to demonstrate that a preferential th leaching over ra must be assumed to explain the 226 ra 230 th 228 ra 232 th and 228 th 228 ra disequilibria recorded in the soil particles the overall ra and th transfer schemes are entirely consistent with the prevailing acido complexolysis weathering mechanism in podzols using a continuous open system leaching model the 226 ra 230 th and 228 ra 232 th disequilibria measured in the different soil layers enable dating of the contemporary processes occurring in this soil in this way we have determined that a preferential th leaching from the shallow ah horizon due to a strong complexation with organic colloids began fairly recently 18 years ago at most the continual increase in ph recorded in precipitations over the last 20 years is assumed to be the cause of this enhanced organic complexation a lower soil horizon 50 60 cm is also affected by preferential th leaching though lasting over several centuries at least with a much smaller leaching rate the migration of th isotopes through this soil section might hence be used as a tracer for the organic colloids migration and the induced radioactive disequilibria demonstrate to be useful for assessing the colloidal migration kinetics in a forested soil ra and th isotopic ratios also appear to be valuable tracers of some mineral water plant interactions occurring in soil the 228 ra 226 ra ratio enables discrimination of the ra flux originating from leaf degradation from that originating from mineral weathering in shallow 10 cm seepage soil waters it appears that at least in some cases the ra isotopic ratio measured in forest soil seepage waters may not be representative of the ra isotopic ratio released from mineral weathering indicating that the different origins of the dissolved 226 ra and 228 ra must be taken into account

paleoclimatic inferences from an isotopic investigation of groundwater in the central san juan basin new mexico groundwater from the ojo alamo and nacimiento aquifers in the central san juan basin new mexico has yielded 14c ages ranging from modern to 35 000 yr b p the pleistocene age samples are characterized by a stable isotope content about 25 lighter in d and 3 lighter in 18o than modern precipitation and groundwater we attribute this difference to a colder mean annual temperature and perhaps increased winter precipitation consideration of various factors controlling the stable isotope composition of the groundwater allows estimation of a 5 to 7 c temperature decrease during the late wisconsin accompanied by increased effective precipitation a similar estimate of the temperature change is obtained from noble gas paleothermometry these data support a model of moderately cooler late pleistocene climate in the american southwest characterized by summers with less precipitation than today but wetter winters

uranium series dating applications in natural environmental science uranium series u series analyses are an essential component of many research projects in earth and environmental science oceanography hydrology and science based archaeology topics range from magma chamber evolution and volcanic hazard prediction global climatic change through dating of authigenic carbonate deposits human evolution through dating of bone to the study of groundwater evolution the u series decay chains contain many elements that can be fractionated in environmental and geological processes half lives of radioactive isotopes of such elements range from seconds to many millennia and application depends on the natural timeframe of the process or the elapsed time this review will be limited to some aspects of the 238u 234u 230th 226ra system with half lives of 245 kyr 76 kyr and 1 6 kyr respectively in environmental systems fractionation of uranium and thorium is a very efficient process because thorium is extremely insoluble while hexavalent uranium in oxidising conditions is relatively soluble many authigenic precipitates of calcite contain virtually no thorium and inorganic precipitates have u ca ratios very similar to the ratio of dissolved uranium and calcium almost no radiogenic 230th in the precipitate means that the radiogenic clock starts effectively at zero however pure authigenic precipitates are rare and many contain some allogenic material mostly silicate with 238u in secular equilibrium with significant 230th some of the characteristics of different types of samples and various methods to accommodate or correct for inherited 230th will be discussed authigenic material should remain a closed system with respect to the relevant isotopes but that requirement is sometimes difficult to maintain because radioactive decay results in damage to the crystal lattice of the host mineral consequences of this recoil effect and correction schemes will be discussed dating archaeological bone based on the systematics of diffusion and adsorption to effectively model open system behaviour is also included

recoil emanation theory applied to radon release from mineral grains abstract in this paper the recoil emanation theory is presented as a major mechanism for rn release from solid materials the basic theory is developed for rn emanation from geometrical shapes spheres and cylinders having variable thickness of precursor ra containing material subsequently a sphere pore model of emanation from mineral grains like those in rocks soils etc is developed in this model a surface of the grain is constructed as a superposition of in and out directed spherical caps and cylindrical pores the model incorporates processes like rn embedding pore overlap water effect and emanation from the edges using such a geometrical model it is shown how the rn emanating power measurements can give a clue to the ra distribution and surface properties of the samples in particular it is shown that for grains reasonably larger than the recoil range and for surface ra distribution the emanating power is independent of the grain size but the total ra concentration varies with the reciprocal of the grain size the opposite is true for ra distributed uniformly throughout the volume of the grain it is shown how the rn emanating power is related to the surface porosity of the grain also implications are made with respect to u transport in nature and with respect to low emanating power from lunar soil finally a failure of the emanation theory is discussed to reproduce emanation curves for the samples having high specific surface areas and ra distributed throughout the volume

wetter and cooler late holocene climate in the southwestern united states from mites preserved in stalagmites the presence of at least 12 species of well preserved mites in two late holocene stalagmites from hidden cave guadalupe mountains new mexico depicts changing climate over the past 3200 yr growth of both stalagmites determined by uranium series dating occurred from at least 3171 48 yr ago and ceased by 819 82 yr ago some of the 12 subfossil genera and species in the stalagmites are like those currently found in wetter and cooler climates northern like and distinctly different from those known in the cave n 16 and on the surface immediately around the cave n 32 the mismatch of genera and species in the stalagmites cave and surface near the cave argues for a wetter and cooler late holocene climate in the southwestern united states from ca 3200 to 800 yr ago

geochemistry of speleothem records from southern illinois development of 234u 238u as a proxy for paleoprecipitation natural waters universally show fractionation of uranium series u series parent daughter pairs with the disequilibrium between 234 u and 238 u 234 u 238 u commonly used as a tracer of groundwater flow because speleothems provide a temporal record of geochemical variations in groundwater precipitating calcite 234 u 238 u variations in speleothems provide a unique method of investigating water rock interaction processes over millennium time scales we present high precision thermal ionization mass spectrometric tims u series analyses of speleothems and drip waters from fogelpole cave in southern illinois data from all speleothems from the cave show an inverse correlation between 234 u 238 u and u concentration following the pattern observed in groundwaters globally within a 65 cm long stalagmite concordant 234 u 238 u 230 th and 235 u 231 pa ages for 5 samples indicate accurate chronology from 78 5 ka to 30 ka notably 234 u 238 u o which differs from most speleothems by having 234 u 238 u ob1 positively correlates with speleothem growth rate we generalize this to the observation that speleothems globally show 234 u 238 u o deviating farther from secular equilibrium at lower growth rates and approaching secular equilibrium at higher grow rates based on the fogelpole observations we suggest that groundwater 234 u 238 u is controlled by the u oxidation state the u concentration of the water and the fluid velocity a transport model whereby u series nuclides react and exchange with mineral surfaces can reproduce the observed trend between growth rate and 234 u 238 u o based on this result we suggest that 234 u 238 u o in speleothems may record changes in hydrologic flux with time and thus could provide a useful proxy for long term records of

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

natural radioelement solution by circulating groundwaters in the stripa granite natural radioelement concentrations in groundwaters from the fracture flow regime in the stripa granite were monitored during the period 1977 1986 uranium concentrations from depths of 80 m or less and in minewaters from above the hydraulic sink produced by the deepest mining level 410 m range from 10 to 90 ppb 234u238u activity ratios are characteristic of chemical leaching processes at the shallower depths whilst at about 350 m groundwaters occur which have an additional component of 234u by alpha recoil processes at greater depths u concentrations are indicative of the changed redox conditions and are subject to activity ratio enhancement by the alpha recoil process groundwater residence times may be estimated from the rate of such recoil solution of 234u in zones where chemical leaching of u is not active the 222rn contents of the minewaters are extremely high and can be related to the 222rn flux from fracture surfaces and the fracture width the fracture apertures range from 10 mm for the shallow groundwater zone 222rn contents m for water from the deepest borehole section 222rn content 100 kbq kg 1 the activity ratios 234th238u 210pb222rn and 210po222rn have been used to estimate residence times for th pb and po isotopes solution of ra is controlled by chemical rather than alpha recoil processes the 226ra content of the groundwater increases with salinity and is well correlated with groundwater ca content the 228ra226ra activity ratios in the groundwaters suggest that water rock interaction occurs predominantly with the average granitic matrix rather than with highly uraniferous fracture mineralisation the behaviour of ra th and po isotopes may be used to assess that of homologous fission product and actinide constituents of nuclear wastes in groundwaters

groundwater ages and reaction rates during seawater circulation in the dead sea aquifer the dead sea system provides a unique opportunity to study flow velocities and reaction rates during seawater circulation in the aquifer we present here a novel application of calculating groundwater age and velocity along the flow path of the hypersaline water from the dead sea into the aquifer using the buildup rate of 228 ra in this water the calculated circulation velocities are 1 10 m y which is in agreement with estimates based on the na cl ratios in this water 1 5 4 m y the latter is unique to the dead sea aquifer system where the na cl ratio has been decreasing during the past 50 years due to the precipitation of halite in the lake the velocity estimates facilitated the calculation of the rates of water rock interactions in the dead sea aquifer

mobility of u series nuclides during basalt weathering an example from the deccan traps india abstract u series disequilibria have been measured by tims and mc icp ms in dissolved phases and suspended sediments of the main basaltic rivers from the deccan trap region india for dissolved phases 234u 238u 230th 238u and 226ra 238u range between 1 11 and 1 28 between 0 03 10 2 and 1 35 10 2 and between 0 02 and 0 16 respectively for suspended particles 234u 238u 230th 238u and 226ra 238u range from 0 95 to 1 1 from 1 23 to 1 59 and from 0 1 to 0 47 respectively 230th 238u and 234u 238u systems show direct links with indices of weathering the data also indicate possible redistributions between the solid and aqueous phases and indicate that erosion processes do not presently operate at steady state because present day physical erosion rates are higher than expected 100 400 mm ka versus 40 mm ka for a steady state process for the narmada and the tapti basins models assuming either discrete or continuous particle leaching yield timescales for chemical erosion of 40 90 ka in contrast with basins located in northern latitudes erosion in the deccan basins does not appear to have been significantly disturbed during the last glaciation 234u 238u disequilibria in the dissolved phase of large rivers world wide are also explored and two key factors are highlighted in this study the dissolution of carbonates releasing dissolved u at secular equilibrium and the silicate weathering rate estimated at the scale of the watershed in particular a positive correlation is found between dissolved 234u 238u and basaltic weathering rates for the deccan that could reflect a key role of physical erosion since for silicate monolithological basins chemical erosion rates are primarily controlled by physical erosion rates for basins with mixed lithology dissolved organic matter also plays a key role in the preferential release of 234u from silicate minerals 234u 238u ratios in rivers therefore reflect a mixture between u released by carbonate dissolution and 234u preferentially released from silicate minerals located in high physical erosion and peat areas

rapid desorption of radium isotopes from black shale during hydraulic fracturing 2 a model reconciling radium extraction with marcellus wastewater production abstract radium in hydraulic fracturing wastewaters derives from two isotopically distinct end members in the shale labile 228ra hosted by mineral surfaces 226ra 228ra atom ratio 250 and exchangeable 226ra hosted by organic surfaces 226ra 228ra 10 000 here we use mass balance and isotope mixing models to reconcile extraction of ra from these phases with mechanisms of marcellus wastewater production radium isotopic mass balance requires that the characteristic water rock ratio between wastewater and shale is exceedingly low on the order of 0 04 and that this ratio decreases with time during wastewater production an evolving water rock interaction drives increasing ra concentrations ra and 226ra 228ra ratios during wastewater production all mediated by increasing ca2 that favors desorption of 226ra from organics our observations and models of ra isotope geochemistry are best reconciled with observations of water and salinity mass balance 18o na br cl and 87sr 86sr if wastewater is produced by mixing of injected fluids with a limited volume of pore brine on the order of 13 by volume accompanied by contemporaneous extraction of excess alkaline earth elements by water rock exchange validated using ra isotope data this model attributes the extreme salinity and ra in wastewaters to the progressive hydrologic enrichment of injected fluids during hydraulic fracturing

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

application of radon and radium isotopes to groundwater flow dynamics an example from the dead sea abstract this study presents the behavior of radon and radium isotopes and their application to groundwater age and flow dynamics the research was conducted in the complex dead sea groundwater system which includes a large variety of sediments groundwater salinities flow mechanisms and groundwater ages groundwater around the dead sea contains high activities of radon up to tens of thousands dpm l and radium up to hundreds dpm l adsorption of radium which is partially salinity controlled is an important source of unsupported 222 rn which is used for estimating the adsorption partition coefficient of radium in addition to salinity the concentration of mn and fe oxides and aquifer heterogeneity are important factors controlling the adsorption partition coefficient the different nature of the rocks on both sides of the dead sea transform with lower th u ratios in the carbonate rocks on the western catchment of the dead sea compared to higher ratios in the sandstone aquifer east of the dead sea is reflected in a higher 228 ra 226 ra activity ratio in the eastern compared with the western groundwaters averages of 0 76 and 0 15 respectively the different groundwater groups around the dead sea contain secular or non secular equilibrium ratios which depend on the age of the groundwater the time since the groundwater entered the aquifer or whether the groundwater system is in a steady state the age of the groundwater system young groundwater such as the dead sea water that circulates in the aquifer or freshwater springs is depleted in the long lived radium isotopes compared to the short lived isotopes whereas old groundwater contains relatively high activity of 226 ra 500 dpm l and the radium activity ratios are close to secular equilibrium the common secular equilibrium ratios between all four radium isotopes in the dead sea groundwaters suggest that many of the groundwater flow paths did not change significantly during the past 8000 years

study of an aplite dyke from the beira uraniferous province in fornos de algodres area central portugal trace elements distribution and evaluation of natural radionuclides abstract a uranium rich aplite dyke with spheroidal alteration sited in the beira uraniferous province in fornos de algodres area northern central portugal was studied focusing on trace element distributions especially u in the aplite a vertical profile different size fractions and various concentrically weathered layers of rock were examined the main goal of the work is to better understand the geochemical behavior and distribution of natural radionuclides in fine grained granitic rocks and changes that occur during weathering the rock samples obtained from this site were examined using chemical and mineralogical methods instrumental neutron activation analysis inaa and the x ray diffraction xrd field gamma spectrometry fgs and high resolution gamma spectrometry hrgs in the laboratory were also performed in order to determine concentrations of the natural radionuclides k th and u responsible for terrestrial gamma radiation and for comparison of results with inaa measurements enabling some information concerning radon losses the u concentration in the studied samples vary between 4 5 and 83 ppm always higher than upper continental crust value with the higher values detected in the clay and sand fractions of weathered aplite residual clay and in the rounded boulders of aplite with spheroidal weathering especially in the core strong variations in natural radionuclide contents especially observed between residual clay and soil relate to differences in source material the large difference between pre rn and post rn values obtained by hrgs suggests high loss of radon 40 minimum which is in accordance with field measurements due to generally high concentration of u the aplite is a potentially strong source of emission of radon to the atmosphere with consequent radiological hazards

an isotopic investigation of groundwater in the central san juan basin new mexico carbon 14 dating as a basis for numerical flow modeling carbon 14 dating of groundwater can be used to help determine the transmissivity distributions of aquifers this method may offer significant advantages in certain respects over traditional aquifer pumping test techniques we have applied 14c dating to a hydraulic analysis of a multilayer aquifer system in the central san juan basin of new mexico after corrections for geochemical evolution of the solutes the influence of dispersive processes on the 14c distribution was investigated a model incorporating stochastic dispersion theory indicated that macroscopic dispersion exerted only a small influence on the measured 14c activities the 14c derived transmis sivity distribution was used to construct a numerical flow model which was applied to an analysis of interaquifer leakage the model showed that even though vertical flow between aquifers was significant in this case it did not cause the 14c distribution to differ significantly from that predicted by a simple piston flow model carbon 14 can be used as a basis for detailed hydraulic evaluations of groundwater flow in areas where traditional well hydraulics methods are not practical

geochemical behaviour of radium isotopes and radon in a coastal thermal system balaruc les bains south of france abstract the behaviour of the four ra isotopes measured by gamma spectrometry and 222 rn measured with an alphaguard ionisation chamber has been investigated in nacl rich thermal waters of balaruc les bains on the mediterranean coast south of france this study allows identification of the deep thermal water signature and reveals the influence of seawater or karst water inflows on ra isotopes and 222 rn the deep thermal water has 226 ra and 222 rn activities of 840 and 1900 mbq l respectively a 228 ra 226 ra activity ratio of 0 59 and low 224 ra 228 ra and 223 ra 226 ra ratios of 0 67 and 0 025 respectively several arguments suggest a dominant role of radioactive decay for short lived ra isotopes and rn during the relatively rapid ascent of thermal water through wide open fractures and drains the low 223 ra 226 ra ratio constrains the maximum ascent velocity of thermal water to 8 10 m h seawater inflow into the hydrothermal system results in an enrichment in short lived ra isotopes and 222 rn the high 223 ra 226 ra ratio 0 23 suggests that 223 ra 224 ra and 222 rn produced by alpha recoil in the upper jurassic limestone are entrained by seawater percolation through the coastal basement due to active pumping in one of the near shore production well this process would be enhanced by a low water rock ratio i e in a low porosity micro fractured limestone mixing of this enriched seawater with thermal water induces barite precipitation with co precipitation of a large fraction of ra short lived ra isotopes may thus be useful tracers of seawater flux towards the continent conversely the inflow and mixing of karst groundwater result in a general dilution of all dissolved elements only a small enrichment in 224 ra and 223 ra but a large enrichment in 222 rn up to 26 bq l the combination of ra isotopes and 222 rn data provides a good way to trace the dynamics of different water masses along coastal areas

occurrence and mobilization of radium in fresh to saline coastal groundwater inferred from geochemical and isotopic tracers sr s o h ra rn abstract salinization in groundwater systems can induce water rock interaction including the release of naturally occurring trace elements of health significance such as radium ra with possible implications for the usability of water resources in addition to the increase of dissolved solids tds concentrations in general radium mobility is limited by chemical removal mechanisms including adsorption onto clays and or mn and fe oxides exchange processes and coprecipitation with secondary barite in order to examine the effect of aquifer salinity gradients on the distribution of naturally occurring ra in fresh to saline groundwater and the relationship to water rock interaction and ra removal mechanisms two contrasting systems were investigated the shallow unconfined coastal aquifer in agadir southwestern morocco and the confined cretaceous cape fear and pliocene yorktown aquifers of the atlantic coastal plain north carolina usa geochemical and isotopic indicators of salinity sources e g cation ratios 18o 2h br cl 34 s so 4 2 18 o so 4 2 were used to identify the relative contributions of seawater and other saline waters and subsequent geochemical modification by water rock interaction radium activities 224ra 226ra 228ra radon 222 alkaline earth metal mg ca sr ba concentrations and ratios and 87sr 86sr ratios were analyzed to identify water rock interaction processes affecting alkaline earth metals including ra the morocco coastal aquifer is generally oxic exhibits a range of salinity and water types cl 163 2120 mg l median 932 mg l and exhibits ca na ratios above the seawater value typical of monovalent divalent cation exchange base exchange reactions in coastal aquifers in contrast the atlantic coastal plain aquifers are anoxic sulfate reducing cover a wider salinity range cl 5 9890 mg l median 800 mg l representing a transition between na hco 3 and na cl waters and exhibit ca na ratios below that of modern seawater typical of reverse base exchange reactions possible salinity sources in the morocco coastal aquifer include seawater intrusion mesozoic evaporites other natural saline waters and or wastewater whereas the atlantic coastal plain is primarily affected by old seawater present in the aquifer system radium activities are generally low and vary significantly within each aquifer for example 226ra ranges from 1 8 27 7 mbq l in the morocco coastal aquifer median 8 1 mbq l and 1 9 214 mbq l in the atlantic coastal plain median 18 9 mbq l the highest ra activities were observed in the most saline wells sampled in the atlantic coastal plain at total dissolved solids tds concentrations above an apparent threshold of 5000 mg l radium activities increase in a generally linear fashion with salinity in the atlantic coastal plain broadly comparable to previous studies indicating a threshold range of 3000 10 000 mg l at lower tds concentrations water rock interaction processes that vary with local aquifer conditions appear to control ra distribution rather than merely salinity in the morocco coastal aquifer adsorption of ra and coprecipitation with secondary barite are apparently favorable to control ra levels in groundwater radium removal in the anoxic atlantic coastal plain aquifers appears to be associated with adsorption and or exchange processes with the additional possibility of barite precipitation in the cape fear aquifer indicated by barite saturation overall the locally variable factors that can control ra sources and mobility in fresh to brackish groundwater at near neutral ph include variation in solid phase radioactivity redox state affecting adsorption sites availability of competing divalent cations and barite saturation

u isotope ratios as tracers of groundwater inputs into surface waters example of the upper rhine hydrosystem major elements trace elements and sr and u isotopes were analyzed in the dissolved load of water samples collected in the main reservoirs of the rhine graben i e the rhine river its main tributaries and the shallow and deep ground waters in several different aquifers our results confirm that the variations of major elements trace elements especially sr and rb and sr isotope ratios of the water samples are mainly correlated to the lithological variations of the watershed the atmospheric inputs can be considered as a minor cause for the chemical variability of the surface waters in the rhine hydrosystem except for a few chemical elements in the mountain streams human activity in particular the pollution by the exploitation of the alsace potash mines mainly affects the na and cl concentrations of the rhine and the south alluvial groundwaters but remains negligible for the other water samples the specific study of the lauter stream located in the lower triassic sandstones buntsandstein sequences demonstrates the importance of groundwater influences onto the chemical composition of river waters up to 50 of the total dissolved load tds of this stream is supplied by deep waters this contribution significantly modifies the chemical composition of the stream especially the 238u 234u radioactive disequilibrium which in turn can be used as a specific tracer of deep water inputs into surface waters and could be useful to distinguish in the dissolved load of rivers surface weathering fluxes from deeper ones

comparative study of 222rn 40ar 39ar and 37ar leakage from rocks and minerals implications for the role of nanopores in gas transport through natural silicates we have measured the leakage of radiogenic 222rn and 40ar and reactor produced 39ar and 37ar in samples of granites plagioclase orthoclase cleavelandite and hornblende to assess the role of nanopores in gas transport through them the 39ar and 37ar were produced by fast neutron irradiation of the samples in vacuum sealed ampoules the leakage of all three ar isotopes was barely measurable in contrast the leakage of 222rn ranged between 1 45 18 1 orders of magnitude higher than that of the ar isotopes the extremely low ar isotope leakage suggests that the samples studied are not permeated by extensive nanopore networks which intersect grain surfaces the relatively high 222rn loss from these samples therefore has to be attributed to preferential enrichment of 226ra 238u on grain surfaces or to the existence of u th accessory minerals in or around grain boundaries from which substantial quantities of 222rn escape

radium isotopes radon and 210pb in karstic waters example of the lez system south of france we present in this study the first data on ra isotopes 222rn and 210pb in waters from the lez karst system one of the main ground water resources in the south of france the low ra isotope activities of the lez system waters from 0 35 to 3 45 mbq l of 226ra were measured by gamma spectrometry using the method developed in our previous work our data reveal the coherent behavior of 226ra in lez spring waters well correlated to other major and trace elements like cl na k mg li rb and ba the 228ra 226ra ratios are distinct between the lez spring 0 60 to 0 72 and two neighboring springs 0 52 to 0 65 showing the spatial variability in karst systems in spite of their small variations in the lez spring it was possible to trace different water components and mixing processes from lower cretaceous upper jurassic and middle jurassic end members in agreement with previous studies based on major and trace elements data obtained on waters derived from the upper jurassic karst reveal that their 228ra 226ra ratios are not related to the th u ratio of the jurassic limestone but are rather influenced by the soil and alterite cover of the recharge area 222rn activities in the lez spring are relatively low 0 5 to 3 7 bq l compared to other karst regions the highest 222rn activities are found in diluted waters following heavy rainfall episodes suggesting a subsurface origin of rn soil and alterite samples that have much higher 226ra activities from 51 to 130 bq kg compared to those from the main aquifer rocks from 2 9 to 16 bq kg are probably the main source of rn rather than the rocks of the karst itself the study of several flood episodes reveals the correlation between rn peak values or total activity discharged at the spring with cumulative rainfall finally 222rn dissolved in water decays to 210pb and our data show that constraints on transfer times of underground waters can potentially be obtained from their coupled measurement

orbital control of long term moisture in the southwestern usa 1 regional lake sediment records including late pleistocene lake estancia new mexico show that the southwestern usa was wetter than present over the last glacial maximum and drier during the holocene chronology of speleothems that mark groundwater levels in cavenee caverns near lake estancia indicates water level lowering through the cave during the early to middle holocene 8500 yr bp consistent with the timing of desiccation of lake estancia and deflation of the basin floor the speleothem record also shows the same wetter to drier climatic shift during the penultimate glacial and interglacial transition at 134 kyr bp subaqueous crusts formed when cave submerged to 121 kyr bp cave rafts formed during water table drop our data support wet glacials and dry interglacials as being a general feature of pleistocene climate in the southwestern usa the timing suggests that the process is orbitally controlled

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

can 234u 230th dating be used to date large semi arid tufas challenges from a study in the naukluft mountains namibia the large extensive tufa deposits of the semi arid naukluft mountains namibia are potentially important palaeoenvironmental indicators in an area with few proxy records tufas are reliable indicators of increased moisture availability and have been shown to be amenable to 234u 230th dating although two challenges are detrital contamination and open system behaviour densely cemented tufa facies are good candidates for dating minimising these problems we report attempts to date five densely cemented units which are only found rarely within the naukluft deposits we applied a detailed methodology using multiple subsample analysis measurement of insoluble residues application of isochron mixing lines and attempted open systems modelling alongside observations of micromorphology and cathodoluminescence in order to assess the validity of any obtained dates surprisingly densely cemented tufas were found not always to be suitable for dating two units contained detrital contamination which could not be corrected for using a single leachate correction or isochron methods two units contained excess 230th this could result under a closed system if initial 234u 238u was sufficiently high alternatively this may be the result of open system behaviour and loss of uranium or incorporation of initial unsupported 230th which render samples unsuitable for 234u 230th dating micromorphological appearance and cathodoluminescence behaviour are used to explore these possibilities this study exemplifies the need for careful sample selection and highlights the importance of analysing multiple subsamples from any tufa sample the detailed methodology applied proves to be a powerful tool for identifying the range of problems that can be encountered when selecting suitable candidate samples for successful dating it also shows that semi arid tufa sequences may contain very little material suitable for dating a reliable age of c 80 ka was obtained for a banded unit within a large fluvial barrage with less reliable dates suggesting tufa deposition during times since 350 ka through to the late holocene copyright 2010 john wiley sons ltd

the extent of seawater circulation in the aquifer and its role in elemental mass balances a lesson from the dead sea abstract this paper shows for the first time a field based estimation of the volume of dispersive density driven long term seawater circulation in coastal aquifers which is crucial to the understanding of water rock interaction and to the assessment of its potential impact on elemental mass balances in the sea the dead sea is an ideal place for studying this type of circulation due to the absence of tides and the accessibility of the shallow fresh saline transition zone the unique antithetical behavior of 226 ra and 228 ra during seawater circulation in the dead sea aquifer where 228 ra is added and 226 ra is removed provides a robust new method for quantifying aquifer circulation here we estimate water circulation through the dead sea aquifer to be 400 million m 3 yr 2 5 million m 3 yr per 1 km of shoreline which is 20 of the fresh water inflow prior to the 1960s this large volume can affect trace element concentrations in the dead sea e g it is a sink for 226 ra ba and u and a source for 228 ra and fe these results suggest that dispersive density driven seawater circulation in aquifers may play an important role in mass balances in other lacustrine and oceanic settings

anhydrite and the sr isotope evolution of groundwater in a carbonate aquifer major element concentrations and 87 sr 86 sr ratios were measured in groundwaters and bedrock from the madison aquifer in western south dakota in this region the madison aquifer is primarily comprised of dolomite belonging to the madison limestone group the purpose of the study was to investigate controls on the downgradient evolution of dissolved sr 2 in a carbonate groundwater system that is recharged by waters with high 87 sr 86 sr ratios draining precambrian basement rocks and to establish the sources of sr 2 added to the waters by reaction with the aquifer lithology a mass balance model following previous workers was used to calculate amounts and effective rates of mineral dissolution and precipitation during groundwater transport along a 240 km flow path both the calculated reaction rates and data for the sr isotope geochemistry of the reacting phases were then used to develop a self consistent and quantitative description of the concentration and isotopic composition of dissolved sr 2 in the aquifer waters the major ion chemistry of madison aquifer groundwater is known to evolve according to dolomite dissolution anhydrite dissolution calcite precipitation and ion exchange with clay minerals dissolved 87 sr 86 sr ratios in the madison aquifer decrease downgradient input waters draining the igneous black hills have 87 sr 86 sr ratios of 0 723 while highly evolved waters in the aquifer have 87 sr 86 sr ratios of 0 708 dissolved sr 2 concentrations undergo a concurrent increase from 1200 to 66 000 nmol l model results indicate that dolomite dissolution exerts a critical control on the major ion chemistry but is not the primary source of nonradiogenic sr 2 as both the dissolution rate and sr concentration of dolomite are very low anhydrite is readily soluble in water has a low 87 sr 86 sr ratio 0 708 and a very high sr concentration 50 000 nmol g anhydrite is also greatly undersaturated in the groundwaters and the downgradient evolution of sr 2 accompanies an 80 fold increase in dissolved so 4 2 while anhydrite has a very low abundance in the aquifer rocks the flow model indicates that anhydrite dissolution provides 300 times more sr 2 per liter of water relative to dolomite dissolution these findings suggest that anhydrite dissolution governs the sr 2 geochemistry of madison aquifer groundwaters whereas dolomite dissolution and calcite precipitation control the bulk chemistry lastly it is shown that the calculation of net mineral masses transferred to solution requires very high relative proportions of anhydrite and clay to dolomite mineral masses obtained by this approach actually represent bulk contributions without consideration of the intrinsic reaction rates of the phases or their modal abundances in the aquifer rocks however consideration of these parameters in a transport equation for flow through porous media shows that the high apparent abundances are not a real requirement this latter approach is consistent with laboratory experiments and indicates that as little as 0 04 wt of very soluble anhydrite and 0 3 wt of exchangeable clay in the aquifer rock are sufficient to produce the observed groundwater chemistry in most of the flow path

a method for determining the extent of bulk 210po and 210pb adsorption and retardation in aquifers abstract the naturally occurring radionuclides 210 po and 210 pb are normally found in very low concentrations in the environment however under some conditions 210 po contributes significantly to the radioactivity in ground waters and can constitute a health risk naturally occurring 210 pb can be used in predicting the behavior of contaminant pb while studies have identified the processes controlling 210 po and 210 pb behavior the extent of adsorption and rates of removal in an aquifer cannot be determined without quantifying the rates of supply of these isotopes from decay of parent nuclides on and within aquifer solids this study demonstrates how the isotope systematics of the 238 u decay series which includes 210 po and 210 pb can be used to quantify the adsorption and retardation factors of 210 po and 210 pb in aquifers the rates of 210 po and 210 pb supply to ground waters are determined from the concentrations of other radionuclides in the series especially 222 rn and so the distribution coefficients between aquifer solids and groundwater can be calculated the effects of different supply rates due to different distributions of parent radionuclides in the aquifer can then be separated from differences in adsorption which is controlled by aquifer water chemistry a review of groundwaters where 210 po 210 pb and 222 rn data are available indicates that systematic variations can be found in bulk effective adsorption coefficients and retardation factors overall a method is provided for future studies of 210 po and 210 pb behavior and greater understanding of the occurrence and migration of these radionuclides

sediment transport time measured with u series isotopes results from odp north atlantic drift site 984 abstract high precision uranium isotope measurements of marine clastic sediments are used to measure the transport and storage time of sediment from source to site of deposition the approach is demonstrated on fine grained late pleistocene deep sea sediments from ocean drilling program site 984a on the bjorn drift in the north atlantic the sediments are siliciclastic with up to 30 carbonate and dated by 18o of benthic foraminifera nd and sr isotopes indicate that provenance has oscillated between a proximal source during the last three interglacial periods volcanic rocks from iceland and a distal continental source during glacial periods an unexpected finding is that the 234u 238u ratios of the silicate portion of the sediment isolated by leaching with hydrochloric acid are significantly less than the secular equilibrium value and show large and systematic variations that are correlated with glacial cycles and sediment provenance the 234u depletions are inferred to be due to recoil loss of 234th and are used to calculate comminution ages of the sediment the time elapsed between the generation of the small 50 m sediment grains in the source areas by comminution of bedrock and the time of deposition on the seafloor transport times the difference between comminution ages and depositional ages vary from less than 10 ky to about 300 to 400 ky for the site 984a sediments long transport times may reflect prior storage in soils on continental shelves or elsewhere on the seafloor transport time may also be a measure of bottom current strength during the most recent interglacial periods the detritus from distal continental sources is diluted with sediment from iceland that is rapidly transported to the site of deposition the comminution age approach could be used to date quaternary non marine sediments soils and atmospheric dust and may be enhanced by concomitant measurement of 226ra 230th 230th 234u and cosmogenic nuclides

seasonal changes in groundwater input to a well mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets 226ra half life 1 600 yr and 228ra half life 5 75 yr were used as tracers to determine seasonal changes in groundwater input to the pettaquamscutt estuary from june 1999 to june 2000 ra isotopes were observed to be in excess of activities due to input from streams rhode island sound water and particle desorption the source of excess 226ra and 228ra within the estuary is attributed to groundwater transport of ra derived from the weathering of bedrock within the pettaquamscutt watershed short lived 224ra half life 3 66 d was used to calculate an average residence time of the estuary of 8 4 d box models used to constrain seasonal changes in groundwater input to the estuary indicate highest groundwater input in the summer 6 4 20 l m 2 d 1 and lowest values in the winter 2 1 6 9 l m 2 d 1 these ra derived groundwater fluxes are similar to rates of aquifer recharge over the annual cycle using these ra derived groundwater fluxes the input of inorganic nitrogen and phosphorus from groundwater to the pettaquamscutt was estimated at 61 180 mmol m 2 yr 1 and 4 4 13 mmol m 2 yr 1 respectively

seasonal cycles in radium and barium within a subterranean estuary implications for groundwater derived chemical fluxes to surface waters abstract there is increasing evidence that submarine groundwater discharge sgd is an important source of water and dissolved materials to the ocean one of the primary tracers of this process is the quartet of radium isotopes 223 ra 224 ra 226 ra and 228 ra whereby excess activities in surface waters can often be attributed to an input supplied via sgd this approach requires the radium end member activity to be well constrained however natural variability in groundwater radium may span several orders of magnitude therefore this variability is usually the main driver of uncertainties in volumetric sgd estimates to investigate the physical and biogeochemical controls on groundwater radium activities we conducted a three year time series of radium and barium a chemical analogue for radium within the subterranean estuary of a coastal aquifer waquoit bay ma usa gonneea et al 2013 demonstrated that movement of the salinity interface within the subterranean estuary is driven by changes in the hydraulic gradient between groundwater level and sea level height for waquoit bay seasonal scale sea level change not groundwater level was the main driver in hydraulic gradient fluctuations seasonal changes in groundwater chemistry can be attributed to the resulting movement of the salinity transition zone between terrestrial and marine groundwater landward movement of the interface results in a large release of radium isotopes 226 ra 1400 dpm 100 l 1 and barium 3000 nmol kg 1 associated with an increase in groundwater salinity the magnitude of these releases cannot be explained by in situ production or weathering alone but is likely due to salinity driven desorption from surface bound sediment inventory the timing of these peak concentrations is not always in phase with model derived estimates of sgd as a result the groundwater concentration rather than the water flux is the main driver of ra and ba inputs to waquoit bay surface waters the behavior of the subterranean estuary as an ion exchange reservoir has important implications for the timing and flux of various nutrients and pollutants that transit this region prior to discharge in addition to modulating chemical fluxes via submarine groundwater discharge on seasonal time scales transgression of the subterranean estuary may alter the input of chemicals to the ocean on decadal and longer time scales during this study the observed excess flux of 226 ra and ba from the subterranean estuary can be accounted for with sorbed sediment pools and accelerating rates of sea level rise in this region

using radon 222 and radium 226 isotopes to deduce the functioning of a coastal aquifer adjacent to a hypersaline lake in nw iran abstract this study aims to assess the hydrogeochemistry of coastal groundwater the occurrence of 222rn and 226ra and their isotopic response to salinity and associated chemical compositions of groundwater in the coastal urmia aquifer ua at the western side of urmia lake ul the results of the pca show that 87 3 of groundwater chemistry changes are controlled by six principal components the interaction between groundwater and coastal igneous and metamorphic rocks in eastern areas next to the ul results in complex hydrogeochemical conditions than western areas based on correlation of u and salinity some coastal samples display conservative and the others non conservative behaviors differed from most previous studies 226ra and 222rn concentrations in coastal groundwater samples of ua do not show a good correlation with salinity given 10 of groundwater 222rn is originated from host rocks the radon concentrations recorded in the coastal groundwater samples are relatively in range that can effectively be supplied by the local rocks 5 49 bq l results of different chemical and isotopic parameters in this area indicate that there is no direct connection between fresh groundwater and ul saltwater this is because that the hard and thick salty layer in the lakebed acts as an impermeable barrier to prevent the underground hydraulic connection results show that removing the salty layer of ul as an option to progress in rehabilitation program of this lake may result in more hydraulic connection between the lake and groundwater resources in some areas

processes controlling 234u and 238u isotope fractionation and helium in the groundwater of the st lawrence lowlands quebec the potential role of natural rock fracturing abstract the goal of this study is to explain the origin of 234 u 238 u fractionation in groundwater from sedimentary aquifers of the st lawrence lowlands quebec canada and its relationship with 3 he 4 he ratios to gain insight regarding the evolution of groundwater in the region 234 u 238 u activity ratios or 234 u 238 u act were measured in 23 groundwater samples from shallow quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the becancour river watershed the lowest 234 u 238 u act 1 14 0 01 was measured in ca hco 3 type freshwater from the quaternary shallower aquifer where bulk dissolution of the carbonate allows u to migrate into water with little 234 u 238 u isotopic fractionation the 234 u 238 u act increases to 6 07 0 14 in na hco 3 cl type groundwater preferential migration of 234 u into water by recoil is the underlying process responsible for this isotopic fractionation an inverse relationship between 234 u 238 u act and 3 he 4 he ratios has been observed this relationship reflects the mixing of newly recharged water with 234 u 238 u act close to the secular equilibrium and containing atmospheric tritiogenic helium and mildly mineralized older water 14 c ages of 6 6 kyrs with 234 u 238 u act of 6 07 and large amounts of radiogenic 4 he in excess of the steady state amount produced in situ the simultaneous fractionation of 234 u 238 u act and the addition of excess 4 he could be locally controlled by stress induced rock fracturing this process increases the surface area of the aquifer matrix exposed to pore water from which produced 4 he and 234 u can be released by recoil and diffusion this process would also facilitate the release of radiogenic helium at rates greater than those supported by steady state u th production in the rock consequently sources internal to the aquifers could cause the radiogenic 4 he excesses measured in groundwater

uranium isotopes in soils as a proxy for past infiltration and precipitation across the western united states the intermittent presence of large pleistocene lakes in the southwestern interior of north america a region that is now a semi arid desert suggests repeated oscillations between profoundly different climatic conditions the origin of these shifts is still unresolved due to inconsistencies in existing climate proxy data for example pollen lake levels and oxygen isotopes in speleothems to resolve the inconsistencies in the water balance over the last 10 to 60 kyr we use uranium isotopic variations in secondary soil minerals to quantify net infiltration and precipitation along a north south transect in western north america we show that winter infiltration increased by 30 to 100 percent and precipitation by a lesser amount in the valleys of the great basin and mojave deserts between 60 and 26 ka this increase in infiltration and precipitation preceded the last glacial maximum lgm and the timing of most lake highstands in the region by 5 to 10 kyr respectively suggesting a possible last precipitation maximum lpm that coincided with a minimum in winter insolation subsequent decreases in infiltration and precipitation after the lgm can be reconciled with the timing of lake highstands if colder summer temperatures due to a minimum in summer insolation reduced lake evaporation the soil records combined with a range of proxy data suggest that seasonal insolation is the long term driver for large shifts in both precipitation and surface water variability in the region

dissolution rates and vadose zone drainage from strontium isotope measurements of groundwater in the pasco basin wa unconfined aquifer abstract strontium isotope ratios 87sr 86sr measured in groundwater samples from 273 wells in the pasco basin unconfined aquifer below the us department of energy hanford site show large and systematic variations that provide constraints on groundwater recharge weathering rates for saturated zone dissolution of the aquifer host rocks communication between unconfined and deeper confined aquifers and vadose zone groundwater interaction the impact of millions of cubic meters of wastewater discharged to the vadose zone 103 105 times higher than ambient drainage shows up strikingly on maps of groundwater 87sr 86sr extensive access through the many groundwater monitoring wells at the site allows for an unprecedented opportunity to evaluate the strontium geochemistry of a major aquifer hosted primarily in unconsolidated sediments and relate it to both long term properties and recent disturbances groundwater 87sr 86sr increases systematically from 0 707 to 0 712 from west to east across the hanford site in the general direction of groundwater flow as a result of addition of sr from the weathering of aquifer sediments and from diffuse drainage through the pasco basin vadose zone the lower 87sr 86sr groundwater reflects recharge waters that have acquired sr from columbia river basalts based on a steady state model of sr reactive transport and drainage there is an average natural drainage flux of 0 1 4 mm yr near the western margin of the hanford site and ambient drainage may be up to 30 mm yr in the center of the site assuming an average bulk rock weathering rate of 10 7 5 g g yr the weathering rates cannot be higher than those assumed by more than a factor of 2 3 in order to match sr isotope data

hydraulic properties of a model dike from coupled bayesian and multi criteria hydrogeophysical inversion coupled hydrogeophysical inversion aims to improve the use of geophysical data for hydrological model parameterization several numerical studies have illustrated the feasibility and advantages of a coupled approach however there is still a lack of studies that apply the coupled inversion approach to actual field data in this paper we test the feasibility of coupled hydrogeophysical inversion for determining the hydraulic properties of a model dike using measurements of electrical resistance tomography ert our analysis uses a two dimensional 2d finite element hydrological model hydrus 2d coupled to a 2 5d finite element electrical resistivity code crmod and includes explicit recognition of parameter uncertainty by using a bayesian and multiple criteria framework with the dream and amalgam population based search algorithms to benchmark our inversion results soil hydraulic properties determined from ert data are compared with those separately obtained from detailed in situ soil water content measurements using time domain reflectometry tdr our most important results are as follows 1 tdr and ert data theoretically contain sufficient information to resolve most of the soil hydraulic properties 2 the dream derived posterior distributions of the hydraulic parameters are quite similar when estimated separately using tdr and ert measurements for model calibration 3 among all parameters the saturated hydraulic conductivity of the dike material is best constrained 4 the saturation exponent of the petrophysical model is well defined and matches independently measured values 5 measured ert data sufficiently constrain model predictions of water table dynamics within the model dike this finding demonstrates an innate ability of ert data to provide accurate hydrogeophysical parameterizations for flooding events which is of particular relevance to dike management and 6 the amalgam derived pareto front demonstrates trade off in the fitting of ert and tdr measurements altogether we conclude that coupled hydrogeophysical inversion using a bayesian approach is especially powerful for hydrological model calibration the posterior probability density functions of the model parameters and model output predictions contain important information to determine if geophysical measurements provide constraints on hydrological predictions

234u 238u activity ratios of dissolved uranium in groundwaters from a jurassic limestone aquifer in england abstract uranium contents and234u 238u activity ratios have been determined for groundwaters from the lincolnshire limestone artesian aquifer in eastern england changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone the western part of the aquifer closest to recharge is dominated by oxidising groundwaters which then enter a reducing zone towards the east where there is an abrupt decrease in eh and the chlorinity of the groundwaters begins to increase uranium contents in the oxidising zone range from 0 7 to 3 4 g kg 1 and234u 238u activity ratio of this dissolved uranium is close to unity the equilibrium value the uranium content decreases abruptly when the grounwaaters enter the reducing zone averaging 0 04 g kg 1 east of the oxidation reduction barrier simultaneously with the decrease in uranium content there is an increase in234u 238u activity ratio and this ratio increases to a maximum within 7 km of the oxidation reduction barrier this increase in activity ratio is attributed to enhanced234u solution due to234th recoil from uraniferous fissure surfaces east of the oxidising zone the activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234th recoil from the oolith surfaces however the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium 234th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium bearing surfaces in the process of oolith cementation

the transport of u and th series nuclides in sandy confined aquifers a comprehensive evaluation of the transport of u th ra and rn nuclides of the 238 u and 232 th decay series in an unconfined sandy aquifer long island ny was conducted groundwater data are compared with results of a theoretical transport model of weathering of aquifer grains and interaction with surface coatings to establish relationships between the concentrations of the radionuclide activities in the water and flow line distance the data provide estimates for geochemical parameters including weathering rates and chemical reactivities in both the vadose zone and the aquifer a theoretical treatment of the transport is presented that considers the reaction between the water and a reactive surface layer it is found that a model with chemical exchange between the surface layer and the water for all species is not valid and that the effects of saturation and irreversible precipitation of th is required the water table shows a relatively wide range in u activities the only element in the u th series for which vadose zone input is significant in the aquifer high weathering of u and recoil inputs of 234 u to the water occur in the upper 3 m of the vadose zone while lower weathering and removal of u from the water occur below the deeper aquifer has variable 238 u activities that can be accounted for by input from the vadose zone and is not a result of non conservative behavior the isotopic composition of u is shown to be directly related to the recoil rate relative to the weathering rate the wide range of 238 u in the aquifer waters is a reflection of diverse vadose zone inputs showing that dispersive mixing is not a dominant effect the higher values of 234 u in the aquifer reflect the recoil weathering input ratios from within the aquifer where the weathering rate is lower than the vadose zone both high u activities and high 234 u values cannot be obtained in the vadose zone or within reasonable flow distances in the aquifer radium isotopes are found to be in exchange equilibrium with the surface layer 224 ra 228 ra and 226 ra have comparable activities throughout the aquifer in the vadose zone the dominant input of ra to groundwater is weathering and recoil as found elsewhere the 222 rn in the water is a large fraction 5 of the rn produced in the aquifer rock this cannot be due to ra precipitation onto surface coatings in the aquifer as supported by present weathering with th in exchange equilibrium with the surface layer it is found that th is saturated in the waters under oxidizing conditions so that the weathering input is irreversibly precipitating onto surfaces however it is shown that under somewhat reducing conditions th activities are much higher and the th u ratio in the solution is approximately that of the rock we propose that under oxidizing conditions the source of rn is a surface coating enriched in 232 th and 230 th this th was precipitated in an earlier phase during rapid dissolution of readily weathered phases that contain 10 of the u th inventory of the rock with the associated u carried away in solution therefore the previously precipitated 230 th and 232 th produce daughter nuclides in the surface coating which are the dominant contributors of ra and rn to the ground water in particular rn is provided by very efficient losses by diffusion or recoil from the surface coating this then does not require recent large recoil losses from the parent rock or the presence of nanopores in the rock the first data of both long lived 232 th and short lived 234 th and 228 th in ground water is reported the th isotope activities indicate that desorption kinetics are slow and provide the first estimate based on field data of the th desorption rate from an aquifer surface the mean residence time of th in the surface coating is 3000 y while in the water it is 1 h ra is in partition equilibrium with the aquifer surface layer however the strong fixation of th on surface coatings is very susceptible to changes in oxidation state as is shown by a comparison of two adjacent aquifers this makes it difficult to define with certainty the retentive characteristics in natural systems in general it is shown that the distributions of naturally occurring nuclides can be used to calculate values for transport parameters that are applicable to the transport of anthropogenic nuclides

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

rapid desorption of radium isotopes from black shale during hydraulic fracturing 1 source phases that control the release of ra from marcellus shale abstract hydraulic fracturing of the marcellus shale produces wastewaters that are hypersaline and highly enriched in isotopes of radium radium is understood to derive from the marcellus shale itself but its source phases and their contributions to wastewater production have not been described using sequential extractions and experimental leachates we characterize two distinct end members that could contribute ra to wastewaters 1 a mineral phase which hosts labile 228 ra and has 226 ra 228 ra atom ratios 250 and 2 an organic phase which hosts exchangeable 226 ra and has 226 ra 228 ra 10 000 in leaching experiments we observed rapid extraction of ra from these phases with high ionic strength solutions leaching up to 14 of ra from the shale in just hours radium concentrations and 226 ra 228 ra ratios increase with ca 2 of the leaching solution and solutions approaching 1 m ca 2 produce 226 ra 228 ra ratios compatible with marcellus wastewaters in contrast pure water removes 226 ra 228 ra ratios incompatible with wastewaters experimental results and wastewater data together provide a coherent picture that the distinctive ra isotopic signature of marcellus wastewaters results from contemporaneous water rock interactions that promote desorption of 226 ra from organics during hydraulic fracturing

modelling the relationship between magnetic fabric and strain in polymineralic rocks abstract we present a model that is applicable to the relatively frequent case of rocks in which the magnetic fabric is dominated by uniaxial paramagnetic minerals and in which the deformation pure shear corresponds to the march fernandez model borradaile et al s procedure for the isolation of the magnetic fabric of monocrystals of anisotropic components allows us to obtain the magnetic properties equivalent to those of all the component minerals if they should be artificially aligned in the case of real component minerals with similar shape parameters dependent on dimension ratio these properties will correspond to those of a theoretical equivalent mineral therefore finite strain and orientation tensors may be determined from magnetic fabric measurements of such polymineralic rocks

234u 238u 230th 232th systematics in saline groundwaters from central missouri saline groundwaters with 4 7 to 26 total dissolved solids were sampled from springs and artesian wells in mississippian and ordovician carbonates and sandstones in central missouri u th isotopic variations provide a means of evaluating processes of water rock interaction and fluid mixing and estimating the time scales of element transport recently developed mass spectrometric techniques are used to make isotopic measurements on small volume groundwater samples 0 1 4 l with high precision e g 5 for 234 u 238 u activity ratios the groundwaters have a wide range of 238 u concentrations 50 10 12 to 200 10 12 g g 234 u 234 u activity ratios 2 15 16 0 232 th concentrations 0 10 10 12 to 33 10 12 g g and 230 th concentrations 0 91 10 17 to 26 10 17 g g unfiltered and filtered 0 4 m 0 1 m aliquots of a saline sample have the same isotopic composition and concentration of u indicating that 234 u and 238 u occur almost entirely as dissolved species the concentration of 232 th is up to seven times lower in filtered vs unfiltered aliquots indicating that 232 th is predominantly associated with particulates in the groundwaters in contrast most of the 230 th is in solution previous geochemical studies indicate that 1 the saline waters originated as meteoric recharge and evolved through halite dissolution reactions with silicates and saline dilute mixing processes during a long distance flow history and 2 interaction with limestone and dolomite aquifer rocks in central missouri has been limited a consistent relationship between u ca and 234 u 238 u activity ratio is observed in the groundwaters and provides constraints on the u ca ratios and 234 u 238 u activity ratios of end member reservoirs and on the processes of isotopic exchange in this water rock system model calculations that simulate 1 saline dilute groundwater mixing and 2 limited extents of dissolution of carbonate aquifer minerals by the groundwaters can account for the variations in u ca 234 u 238 u and 18 o 16 o in the suite of water samples the model calculations demonstrate that dissolved u isotopic compositions can be a sensitive indicator of water rock interaction which in turn limits the usefulness of 234 u 238 u disequilibria for groundwater age determinations the concentration of dissolved 230 th in the groundwaters is 1 two to three orders of magnitude below 230 th 234 u equilibrium activity levels and 2 significantly in excess of concentrations estimated for the supply of th to solution via desorption and dissolution a model involving the derivation of the excess 230 th from the in situ decay of dissolved 234 u in the groundwaters indicates the operation of an adsorption mechanism on the time scale of 10 10 3 years the results reported here may have broader application to the assessment and management of hazardous chemical species in natural environments

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage