groundwater composition hydrochemical evolution and mass transfer in a regional detrital aquifer baza basin southern spain abstract the physical chemical characteristics of the groundwater in the baza caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region defining geochemical zones with distinct groundwater types the least mineralized water is found closest to the main recharge zones and the salinity of the water increases significantly with depth towards the center of the basin geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system namely quaternary aquifer unconfined sector and shallow and deep confined sectors of the mio pliocene aquifer geochemical mass balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation dolomite dissolution and calcite precipitation driven by gypsum dissolution this process is highly developed in the central part of the basin due to the abundance of evaporites apart from this process there are others which influence the geochemical zoning of the system in the quaternary aquifer which behaves as a system open to gases and which receives inputs of co 2 gas derived from the intensive farming in the area the interaction of the co 2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water in the shallow confined sector of the mio pliocene aquifer the process of dedolomitisation evolves in a system closed to co 2 gas ca 2 na cation exchange and halite dissolution processes are locally important which gives rise to a relatively saline water finally in the deep confined sector a strongly reducing environment exists in which the presence of h 2 s and nh 4 in the highly mineralized groundwater can be detected in this geochemical zone the groundwater system is considered to be closed to co 2 gas proceeding from external sources but open to co 2 from oxidation of organic matter the geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to so 4 dissolution dedolomitisation and so 4 reduction coupled with microbial degradation of lignite

groundwater recharge circulation and geochemical evolution in the source region of the blue nile river ethiopia geochemical and environmental isotope data were used to gain the first regional picture of groundwater recharge circulation and its hydrochemical evolution in the upper blue nile river basin of ethiopia q mode statistical cluster analysis hca was used to classify water into objective groups and to conduct inverse geochemical modeling among the groups two major structurally deformed regions with distinct groundwater circulation and evolution history were identified these are the lake tana graben ltg and the yerer tullu wellel volcanic lineament zone ytvl silicate hydrolysis accompanied by co2 influx from deeper sources plays a major role in groundwater chemical evolution of the high tds na hco3 type thermal groundwaters of these two regions in the basaltic plateau outside these two zones groundwater recharge takes place rapidly through fractured basalts groundwater flow paths are short and they are characterized by low tds and are ca mg hco3 type waters despite the high altitude mean altitude 2500 masl and the relatively low mean annual air temperature 18 c of the region compared to sahelian africa there is no commensurate depletion in d 18 o compositions of groundwaters of the ethiopian plateau generally the highland areas north and east of the basin are characterized by relatively depleted d 18 o groundwaters altitudinal depletion of d 18 o is 0 1 100 m the meteoric waters of the blue nile river basin have higher d excess compared to the meteoric waters of the ethiopian rift and that of its white nile sister basin which emerges from the equatorial lakes region the geochemically evolved groundwaters of the ytvl and ltg are relatively isotopically depleted when compared to the present day meteoric waters reflecting recharge under colder climate and their high altitude 2005 elsevier ltd all rights reserved 1 background surface water of the blue nile river basin of ethiopia is not widely used for water supply because of its marked seasonality and lack of proper technology to retain it in the basin groundwater is the most important source of water and is the dominant source for domestic

hydrochemical and isotopic evidence of recharge apparent age and flow direction of groundwater in mayo tsanaga river basin cameroon bearings on contamination unplanned exploitation of groundwater constitutes emerging water related threats to mayotsanaga river basin shallow groundwater from crystalline and detrital sediment aquifers together with rain dams springs and rivers were chemically and isotopically investigated to appraise its evolution recharge source and mechanisms flow direction and age which were used to evaluate the groundwater susceptibility to contamination and the basin s stage of salinization the groundwater which is ca na hco3 type is a chemically evolved equivalent of surface waters and rain water with ca mg cl so4 chemistry the monsoon rain recharged the groundwater preferentially at an average rate of 74 mm year while surface waters recharge upon evaporation altitude effect of rain and springs show a similar variation of 0 4 for 18o 100 m but the springs which were recharged at 452 679 and 773 m asl show enrichment of 18o through evaporation by 0 8 corresponding to 3 of water loss during recharge the groundwater which shows both local and regional flow regimes gets older towards the basins margin with coeval enrichment in f and depletion in no3 incidentally younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride the basins salinization is still at an early stage

use of statistical analysis to formulate conceptual models of geochemical behavior water chemical data from the botucatu aquifer in sao paulo state brazil water chemical data from the botucatu sandstone aquifer in the sao paulo state part of the parana basin brazil was evaluated using geochemical methods and two statistical analyses cluster analysis and factor analysis the results were used to develop a conceptual geochemical model in which three geochemical regions were identified and their chemical behavior was modeled the characteristic chemicals changing from the recharge area to the center of the basin are sio2 hco3 and ca2 na co32 and so42 the distribution of the chemicals is interpreted as controlled by different water rock interaction processes in the different regions in the recharge area dissolution of alkali feldspar minerals in the sandstone is the main reaction observed in the mid section of the basin calcite dissolution results in high calcium and bicarbonate concentration in the center of the basin leakage from underlying layers becomes the governing factor

major ion hydrochemistry and environmental isotope signatures as a tool in assessing groundwater occurrence and its dynamics in a fractured volcanic aquifer system located within a heavily urbanized catchment central ethiopia summary hydrochemical and environmental isotope 2 h 18 o and 3 h data were used to characterize the groundwater flow occurrence and major ion chemistry in a complex fractured volcanic aquifer system located at the edge of the ethiopian rift the study has been supported by conventional hydrogeological mapping the result clearly indicates the presence of two distinct groundwater systems 1 the shallow groundwater characterized by low ionic concentration and in places isotopically enriched younger waters and 2 the deep thermal waters with relatively older age showing negative 18 o shifts and higher ionic concentration the deep groundwaters are manifested as thermal springs and deep confined and artisan wells mainly aligned along major regional faults the first group of groundwater is further divided into four subgroups indicating clear geo hydrological patterns along the groundwater flow path representing different lithologies residence time and anthropogenic influences the classification shows different degrees of rock water interaction and aquifer composition there are indications of aquifer recharge from highly evaporated surface waters this integrated study enabled to conceptualize the groundwater flow system vertically in to three zones namely shallow fast circulating fresh water mixed and moderately mineralized groundwaters representing the majority of wells and the deep old and mineralized thermal waters this study has very important implications on possible location and depth of future boreholes well head protection and in understanding the spread of pollutants that may originate from urban areas

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

application of hydrochemical and isotopic techniques to understand groundwater recharge and flow systems in the dawa river basin southern ethiopia the study of groundwater recharge and of flow systems is crucial to understand availability and sustainability of groundwater resources this study uses hierarchical cluster analysis hca and various graphical plots of hydrochemical and isotopic data to examine groundwater recharge and the dynamics of flow system in the dawa river basin hca has classified the water samples into five distinctive clusters clusters i ii and iii represent the volcanic and most parts of the basement terrain these clusters are distinguished by low ec high percentages of hco3 and ca2 mg2 or na and dominantly ca mg na k hco3 type water cluster iv contains sulfate type water with high percentage of ca2 mg2 and represents sedimentary terrain cluster v characterized by high ec and abundant na and so42 cl is sited at few locations along dry riverbeds in the basement terrain the chemical composition of groundwater varies greatly over short distances in most parts of the basin groundwater contains elevated levels of tritium at amount comparable to local rainfall these chemical characteristics supported with tritium data indicate the dominance of groundwater of local flow systems short residence time and modern recharge in the basin stable isotope data indicate that in the semi arid region recharge occurs from high intensity rainfall difference in 18o and 2h between the northern and the southern and southeastern groundwater supports distinct recharge sources and the absence of regional groundwater flow between the two regions converging evidences reveal that the traditional regional groundwater flow model which is common in most large river basins of ethiopia does not hold true in the dawa river basin

significance of the connection between bedrock alluvium and streams a spatial and temporal hydrogeological and hydrogeochemical assessment from queensland australia abstract catchment scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant however in many cases such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components particularly in regions dominated by cycles of droughts and flooding from a modelling perspective such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems in this study we use 3d geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the lockyer valley queensland australia a catchment impacted by a severe drought millennium drought from 1998 to 2009 followed by extensive flooding in 2011 we also demonstrate how discharge from the sub alluvial regional scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams the investigation of aquifer geometry via development of a three dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets this confirmed that most sub catchments within the lockyer valley have distinct water chemistry patterns which result from mixing of different water sources including discharge from the sub alluvial bedrock importantly in addition to the observed spatial variability time series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers streams and sub alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding affecting both catchment water quality and water balances

effects of channel confinement on pioneer woody plant community structure composition and diversity along the river drome se france river embankments are one of the main causes of a loss in active channel movement the knock on effects of river channel stabilization include important shifts in the ecohydrological conditions in the protected zone behind embankments which has already been well exemplified however few authors have attempted to investigate changes to pioneer units of vegetation colonizing the active channel following the construction of dikes as a consequence we studied the structure composition and diversity of pioneer vegetation units dominated by willow and poplar along the river drome in two adjacent but contrasting river reaches an embanked reach and an unconstrained reach each subject to the same flow regime but offering very different hydrogeomorphological contexts for vegetation colonization our results clearly demonstrate that river embankments affect channel geometry a reduction in channel width from between 200 and 500 m to less than 100 m leads to steeper elevational gradients with an overall coarser grain size and consequently drier overall conditions on colonizable landforms in the channelized reach pioneer vegetation responded by colonizing landforms at higher elevations above the low water mark and by occurring in smaller units within the channelized study reach there was also a reduction in species diversity a homogenization in vegetation unit structure and a predominance of more drought tolerant ligneous species p nigra in pioneer vegetation units in the channelized study reach

isotope characteristics of meteoric water and groundwater in the sahelo sudanese zone the stable isotopic concentration 18o and 2h of water in phreatic aquifers in the sahelo sudanese zone of africa is representative of the original mean rainfall contributing to ground water recharge the isotopic decrease of 18o in the rainwater and groundwater 0 084 100 km 1 showed an east west gradient this suggests a supply of water vapor transported by the zonal flows east african jet tropical easterly jet and easterly waves thus increasing the contribution from the evaporating surfaces of the indian ocean in relation to that of the guinean monsoon the gradient also indicates the importance of atmospheric recycling of continental water through evapotranspiration a model of conservation of the isotopic masses is presented which takes into account the return of continental vapor toward the rain giving clouds the remaining fraction of water vapor during the east west transit between djibouti and dakar is thus determined by evapotranspiration

egyptian mummies record increasing aridity in the nile valley from 5500 to 1500 yr before present abstract oxygen isotope compositions were measured in teeth n 29 and bones n 41 from egyptian mummies of humans n 48 in order to track the 18o evolution of the nile from 5500 to 1500 b p the combination of 18o values of apatite carbonate and phosphate was used to filter the database for post mortem alteration of bioapatites while 87sr 86sr ratios were used to detect potential allochthonous people buried in the various archeological sites located along the nile this approach led to only five apatite samples out of seventy to be discarded from the database the remaining oxygen isotope compositions of both tooth and bone phosphates from ancient egyptians were converted into the composition of ingested water ultimately originating from the nile it was found that 18o of nile waters increases progressively from 1 6 to 1 5 vsmow from the predynastic 5500 b p through the late period 2550 b p this trend towards higher nile 18o values acquired in more recent times is coherent with a general drying trend in northeast africa which was not limited to a drying spell at the end of the nabtian pluvial ca 12 000 b p ca 6000 b p but extended far into the following millennia nearly to the beginning of the common era 1950 b p

palaeohydrology of the lower cretaceous pre salt lacustrine system from rift to post rift phase santos basin brazil abstract large oil accumulation discoveries in the last decade in the pre salt rock succession off the brazilian coast aroused renewed interest in carbonate reservoirs prompting several studies aiming at unravelling the conditions of formation of these rocks despite that there are still many gaps in the knowledge concerning environmental conditions of the deposition of the pre salt carbonates of santos basin located at the southeastern brazilian margin in this study we present and discuss a new suite of geochemical and biostratigraphic data of the lacustrine rift to post rift succession broadly correlated with itapema and barra velha formations of the santos basin whose deposition occurred in the aptian the integration of the petrographic biostratigraphic and geochemical data serves the ultimate purpose of the study which is to apply the new radiogenic strontium data as a proxy for the reconstruction of the evolution of the lake hydrology associated with the deposition of the carbonates of the itapema and barra velha formations these data are integrated into numerical models whose results bring new ideas on the general hydrologic conditions of the lake system and on its evolution through time the mass balance calculations indicate that two end members alone can account as potential sources of sr to the palaeolake a mafic and a felsic component respectively the latter likely contributed with significantly higher fluxes roughly one to two and up to four orders of magnitude higher than the former end member for most of the depositional history in order to generate the 87sr 86sr trends observed in the carbonate rocks finally the results obtained from the integration of the observations with the numerical models point to decreasing fluxes of water with time as contributed from both sources suggesting that the formation of the deposits became very likely constrained to progressively more evaporitic and alkaline lake waters these results also open up a new window into the environmental conditions of the interior gondwana continent immediately prior to the definitive opening of the south atlantic ocean

uranium isotopic study of artesian and pluvial contributions to the nubian aquifer western desert egypt the groundwater systems of the nubian aquifer beneath six major oases baris kharga dakhla farafra bahariya and siwa in the western desert of egypt have been studied to establish their sources and mixing volumes using uranium isotopes one hundred six groundwater samples from different depths of the nubian aquifer have been analyzed for uranium content and 234u 238u activity ratio ar the aquifer under the western desert is known to have more than one source of water at bahariya and farafra oases the nubian artesian water migrating from the south has been augmented by local recharge during pluvial times at siwa oasis in the northwestern desert a shallower aquifer component migrating from the north or west is also present at dakhla kharga and baris oases in the southwestern desert the main source is the nubian artesian water migrating from southeast uweinat upland and northwest sudan these water masses have distinctive uranium isotopic signatures the nubian aquifer water is characterized by very low u concentrations 1 5 the shallow northwest aquifer water also has a high ar but a much higher u concentration the locally recharged pluvial waters have high u concentrations 0 1 ppb but low ars near unity a diagnostic derivative parameter is excess 234u content the deep nubian aquifer water is characterized by a relatively low excess 234u 0 02 ppb equivalent while the shallow siwa water has a very high excess 234u ar 1 u conc the bahariya and farafara waters are also high in this component probably because of pluvial water percolation through phosphate rich strata at all oases u isotopic mixing diagrams show that the deep aquifer sources predominate however the pluvial contributions are significant ranging from about 5 at remote baris oasis to about 26 at the more northerly farafra oasis the observed lowering of potentiometric surfaces in the western desert is caused not only by pumping at a rate greater than inflow from the aquifer systems but also by the withdrawal of pluvial water which in modern times is not being replaced at all

hydrologic and geologic factors controlling surface and groundwater chemistry in indian wells owens valley area southeastern california usa the indian wells owens valley area is located in the semi arid basin and range province which is characterized by alternating mountains and alluvial basins surface water resources are limited in this arid region and water demand is mainly met by groundwater pumpage in a classic basin and range groundwater system water flows from recharge areas in the mountains to discharge areas in adjacent valleys discharge areas are generally occupied by playas where large amounts of salt deposition occur due to evaporating groundwater hydrochemical data from a total of 1368 spring surface and well water samples collected over an 80 year period were used to evaluate water quality and to determine processes that control water chemistry q mode hierarchical cluster analysis hca was employed for partitioning the water samples into hydrochemical facies also known as water groups or water types five major water groups resulted from the hca analysis the samples from the area were classified as recharge area waters ca na hco3 water and na ca hco3 water transition zone waters na hco3 cl water and discharge area waters na cl water and more concentrated na cl water spatial plots of the major statistical groups show that the samples that belong to the same group are located in close proximity to one another suggesting the same processes and or flowpaths inverse geochemical models of the statistical groups were developed using phreeqc to elucidate the chemical reactions controlling water chemistry the inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area in a broad sense the reactions responsible for the hydrochemical evolution in the area fall into four categories 1 silicate weathering reactions 2 dissolution of salts 3 precipitation of calcite amorphous silica and clay minerals and 4 ion exchange

the evolution of alkaline groundwaters in the continental intercalaire aquifer of the irhazer plain niger this paper discusses the hydrochemical evolution of groundwaters in the multilayer artesian aquifer of the continental intercalaire the mainly jurassic agadez dabla sandstones aquifer of northern niger isotopic and chemical changes in relation to the geological setting suggest that the increasing hco3 alkalinity of the groundwaters is caused by interaction of deep co2 with the aquifer matrix alteration of feldspars by co2 with a 13c value of 3 0 accounts for the observed alkalinity and isotopic and trends carbon 14 ages have been estimated for recent and holocene groundwaters which have a distinct stable isotopic 2h and 18o signature compared with 14c dead groundwaters from further west on the irhazer plain recharge temperatures estimated by analysis of noble gas contents show that the 14c dead waters were recharged under conditions cooler than present averages in the region possibly at the beginning of deglaciation 16 ka b p or during the period 23 30 ka b p trends in the hydrochemistry of u are related to the deep co2 alteration process radiogenic he contents increase along the flow direction and extremely high values occur in the proximity of u ores denitrification in the paleowaters of the irhazer was assessed by measurements of nitrogen argon ratios

sources of groundwater recharge at the confluence of the niles sudan due to the rapid expansion of the sudanese capital city far away from its three niles it has become a necessity to estimate the sustainability of the groundwater resources in this arid area the purpose of this study based on the stable isotopic composition of groundwater is to identify the sources of recharge and their relative contribution the results show that groundwater infiltrated from the niles under the present prevailing arid climate with greater contribution from the white nile compared to the blue nile occupies an extension of 12 km from the niles within the two main aquifers paleogroundwater of meteoric origin infiltrated in the cooler pluvial earlier holocene occupies the outer zones beyond the niles effect a rational utilization policy is recommended to preserve the finite groundwater resources

a depositional model for spherulitic carbonates associated with alkaline volcanic lakes the south atlantic aptian pre salt reservoirs are formed by a combination of spherulitic carbonates and mg rich clays accumulated in volcanic alkaline lake settings with exotic chemistries so far outcrop analogues characterised by metre thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact in particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained little studied and hotly debated to shed light on this conundrum a spherulitic carbonate rich alkaline volcanic lacustrine succession has been analysed at outcrop scale the carboniferous east kirkton limestone scotland despite clays being very scarce and limited to layers of amorphous mg si minerals a diverse array of spherulitic calcitic components were formed including coated grains crusts and build ups this setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the pre salt subsurface occurrences but divorced from clay influence the integration of logs borehole data outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the east kirkton lacustrine succession in this model calcite spherule nucleation took place at the sediment water interface in the littoral zone driven by the co occurrence of 1 high alkalinity 2 ca mg rich hydrochemistry and 3 microbial derived colloidal exopolymeric substances these environmental conditions permitted the coeval development of spherulitic cementstone build ups and spherulitic grainstone packstone within the wave agitated zone and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking this model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex microbe solution interactions before any reliable facies model is envisaged

long term 1960 2010 trends in groundwater contamination and salinization in the ogallala aquifer in texas summary although numerous studies have expounded on depletion of the ogallala aquifer very few researchers have studied groundwater quality therein which relates to the usability of available groundwater resources the objective of this study was to elucidate regional trends in groundwater quality and salinization in the ogallala aquifer underlying 49 counties and two groundwater management areas gma 1 and 2 in texas on a decadal scale between 1960 and 2010 contrasting groundwater quality distinguished gma 1 northern ogallala from gma 2 southern ogallala and shallow wells depth 50 m wells the gma 2 was characterized by pronounced groundwater nitrate no 3 contamination accompanied by elevated levels of sulfate so 4 2 chloride cl and salinity tds marked by an abundance of mixed cation so 4 cl and na cl facies in contrast ca mg hco 3 and ca hco 3 facies prevailed in gma 1 with substantially lower salinization so 4 2 cl and no 3 contamination in shallow wells more abundant in gma 2 about 80 and 32 of observations exceeded the united state environmental protection agency s secondary maximum contaminant level smcl 500 mg l 1 for total dissolved solids tds and mcl 44 mg l 1 for no 3 respectively in the 2000s 2000 2010 with progressive increases in both parameters since the 1960s 1960 1969 majority 60 of the shallow observations since the 1980s 1980 1989 have exceeded the natural background of 11 mg l 1 of no 3 indicating anthropogenic sources the no 3 contamination was more apparent in domestic wells indicating substantial human health risk groundwater salinization in this aquifer resulted from a combination of natural e g upwelling of highly mineralized groundwater from the underlying formations seepage from playas and saline plumes and evaporative enrichment and anthropogenic processes irrigated agriculture and hydrocarbon exploration activities natural processes were largely aggravated by anthropogenic practices such as lowering of hydraulic heads in the ogallala aquifer due to prolonged irrigational pumping inducing cross formational flow from underlying highly mineralized older formations edwards trinity high plains which led to groundwater mixing between the formations and rise in salinity levels in the ogallala aquifer over time

the role of geodiversity on the groundwater resource potential in the upper blue nile river basin ethiopia groundwater has been the main source of water supply for large cities and towns over the last few decades in the upper blue nile river basin ethiopia however provision is often unsuccessful because of poor well productivity difficult drilling conditions poor well positioning or sometimes due to poor water quality the growing pressure of urban population and industrial development is focusing unprecedented attention on the groundwater potential of the basin the purpose of this work is to spatially characterize the groundwater potential of the upper blue nile river basin with respect to variable recharge and geodiversity the study shows that from the annual recharge obtained using the base flow separation method the renewable groundwater potential in the basin was estimated to be in the range of 1 2 and 2 billion m3 year the aquifers in the area are divided into three categories low to moderate productivity 3 5 l s which includes crystalline basement rocks acidic lava flows and domes and very fine alluvial sediments moderate to high productivity 5 5 l s that includes mesozoic sedimentary rocks sandstone limestone gypsum dolomite and high to very high productivity 20 l s which includes basic lava flows of the trap series quaternary lava flows and alluvial sediments

numerical modeling of the groundwater flow system of the gumera sub basin in lake tana basin ethiopia the groundwater flow contribution into lake tana was simulated using gumera river sub basin as a case study draining into lake tana the gumera sub basin boundary was delineated from a 90 m shuttle radar terrain mapping srtm digital elevation model dem using archydro tools the sub basin boundary served as the divide line of the groundwater flow while stream networks were used as internal drainage lines input parameters such as transmissivity and hydraulic conductivity were obtained from past studies and experts knowledge based on the geological information of the sub basin unconfined subsurface flow condition was considered and simulated using modular 3d finite difference ground water flow model modflow analytical solutions were also used for comparison purposes the result indicates that head contours are aligned to the streams showing their relationship as a subdued form of the surface water flow which are dictated by the morphology of the basin this suggested the need to account groundwater contribution of the sub basins to lake tana as baseflow and to estimate groundwater inflow from the floodplain separately the contribution from the floodplain was estimated using a finite differences method which showed an inflow of 0 15 billion cubic meter bcm from rivers into the floodplain out of which 0 09 bcm is flowing out to the lake tana and 0 06 bcm stored in the aquifers of the floodplain the stored quantity could meet irrigation demands as well as contribute to the preservation of the ecological structure and function of the area the study suggests further research on validation of parameters through inverse modeling approaches and optimization of water allocations

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

two way cluster analysis of geochemical data to constrain spring source waters abstract the purpose of the study was to use geochemical characteristics and apparent ages of sampled groundwaters to determine which of the two regionally extensive bedrock aquifers the lower bedrock aquifer or the upper bedrock aquifer is a more likely source of water discharging to springs in the nine springs watershed the use of summary statistics and our knowledge of the regional hydrostratigraphy resulted in the identification of three groups of monitoring points that are representative of groundwaters with distinct geochemical characteristics two way cluster analysis of the geochemical data supports these groupings and further identifies subtle geochemical characteristics of the groups one spring which is representative of smaller springs and seeps found in the watershed belongs to a group that is characterized by variable nitrate and chloride concentrations water discharging from this spring has a groundwater residence time of approximately 8 years based on the tritium helium 3 dating method the water discharging to this small spring is thought to have traveled primarily through the unlithified aquifer as opposed to either of the major bedrock aquifers most of the springs in the watershed belong to a group that is characterized by elevated but consistent nitrate sodium and chloride concentrations in addition cluster analysis revealed that potassium and alkalinity concentrations are somewhat low apparent groundwater ages for this group range from 10 to 15 years the water discharging from the majority of the springs in the watershed is thought to have traveled primarily through the unlithified aquifer and the upper bedrock aquifer before discharging into the former glacial lakebed wetland complex due to the relatively short groundwater residence times spring water quality and flow in the nine springs watershed are likely to be vulnerable to the rapid urban expansion occurring within the watershed

chemical evolution of groundwater in the river danube deposits in the southern part of the pannonian basin hungary processes controlling the groundwater chemical composition were studied in the river danube deposits in the southeastern part of hungary phreeqm a combined geochemical and one dimensional transport model and phreeqe netpath and wateqf geochemical computer codes were used to simulate these processes the main processes controlling water chemistry are equilibrium with calcite undersaturation in dolomite and albite weathering in the recharge area ion exchange along the flow path and ion exchange and mixing with old water at the end of the flow path ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied isotopic data support the geochemical model the groundwater ages adjusted for the modeled c mass transfer range from 3300 to 20 200 a b p cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred this displacement is attributed to tectonic and paleoclimatic events at the end of the pleistocene

geostatistical and geochemical analysis of surface water leakage into groundwater on a regional scale a case study in the liulin karst system northwestern china abstract the liulin karst system is typical of hydrogeological systems in northern china with a group of springs as the dominant way of regional groundwater discharge surface water leakage into groundwater has been observed in six sections of the rivers in the study area to extract hydrogeological information from hydrochemical data 29 water samples were collected from the system on a trilinear diagram most of the groundwater samples are clustered around the surface waters indicating the effect of leakage on their chemistry r mode factor analysis was made on seven variables na ca mg so 4 cl hco 3 and no 3 of the samples and three principal factors were obtained the f 1 factor is composed of ca mg and so 4 the f 2 of hco 3 and no 3 and the f 3 of na and cl these factors are then used as regionalized variables in ordinary kriging for unbiased estimates of the spatial variations of their scores considering regional hydrogeological conditions the hydrogeological implications of the spatial distribution of the factor scores as related to the effects of the surface leakage are discussed to evaluate the geochemical processes the geochemical modeling code netpath was employed the modeling results show that mixing commonly occurs in the system and dolomite dissolution is more important than calcite dissolution dedolomitization calcite precipitation and dolomite dissolution driven by anhydrite dissolution is locally important in the western flank of the system where the surface water leakage has the least effect

hydrochemical characteristics of aquifers near sutherland in the western karoo south africa the western karoo depends entirely on groundwater for domestic and agricultural use an understanding of the chemical evolution of the groundwater provides insight into the interaction of water with the environment and contributes to better resource management descriptive statistics correlation matrices and factor analysis together with stable isotope data were used to gain an understanding of the hydrochemical processes of the groundwaters in the fractured rocks around sutherland in the western karoo the main processes influencing the groundwater chemistry are salinisation mineral precipitation and dissolution cation exchange and human activity the stable isotope data indicate that the infiltration of evaporated water is partly responsible for the occurrence of saline subsurface waters the ionic oxygen and hydrogen stable isotope composition of the groundwaters suggests that the effects of localised topography are one of the overriding factors controlling the groundwater chemistry in higher lying areas ca hco3 2 type waters are prevalent while in topographical flat areas nacl type waters dominate in areas where water collects close to or at the surface saline soils are formed from these areas salts are leached to the subsurface during significant recharge periods these findings are important in that they contribute to the identification of suitable locations for developing groundwater resources that could yield a relatively better quality water q 2001 elsevier science b v all rights reserved

environmental isotopes and hydrochemical study applied to surface water and groundwater interaction in the awash river basin an environmental isotope and hydrochemical study was carried out to conceptualize the surface water and groundwater interaction and to explore the groundwater flow pattern in relation to the geological setting more emphasis is given to the afar depression where groundwater is a vital source of water supply conventional field hydrogeological study and river discharge records support the isotope and hydrochemical analysis the region is tectonically active comprising rift volcanic terrain bordered by highlands the result revealed that recent meteoric water is the major source of recharge three distinct groundwater zones were identified associated with the highlands transitional escarpment and the rift towards the rift the ionic concentration and isotopic enrichment 2h and 18dego increases following the groundwater flow paths which is strongly controlled by axial rift faults the groundwater flow converges to the seismically active volcano tectonic depressions with internal drainage and to the awash river within the afar depression at least four groundwater regimen are identified 1 fresh and shallow groundwater associated with alluvial deposits ultimately recharged by isotopically depleted recent highland rainfall and the evaporated awash river 2 cold and relatively younger groundwater within localized fractured volcanics showing mixed origin in axial fault zones 3 old groundwater with very high ionic concentration and low isotopic signature localized in deep volcanic aquifers and 4 old and hot saline groundwaters connected to geothermal systems the study demonstrated that dependable groundwater can only be obtained from the first two aquifer types in aerially restricted zones in flat plains following river courses local wadis and volcano tectonic depressions the conventional hydrogeological survey and discharge records indicate substantial channel losses from the awash river which becomes a more dominant source of recharge in central and lower awash valleys copyright 2007 john wiley sons ltd

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed