petrochemical features of miocene volcanism around the cubukludag graben and karaburun peninsula western turkey implications for crustal melting related silicic volcanism abstract widespread neogene volcanism mainly intermediate and rarely mafic and felsic in composition was controlled by the extensional tectonic regime in western turkey the karaburun and cumaovasi volcanics are the cases for understanding the magma source s and petrological processes producing the extension related mafic and felsic volcanism the karaburun volcanics kv are mainly oriented north to south in the karaburun peninsula and span a wide spectrum from basalt 20 ma to rhyolite 16 ma and younger trachyte and trachydacites 13 ma the products of the subaerial silicic volcanism the cumaovasi volcanics cv 17 ma which are represented by cluster of rhyolite domes related pyroclastics occur within the ne sw trending cubukludag graben and intermediate and mafic volcanic rocks are lack in this area the lavas of the cumaovasi volcanics are high silica rhyolites and rare dacites which are calc alkaline peralumious and enriched significantly in lile extremely low sr ba values extremely eu depletions and very low la n yb n ratios are typical for the rhyolites of cv similar to the topaz rhyolites the karaburun volcanics with the exception of the minor alkaline basaltic and trachytic lavas are mainly calc alkaline and metaluminous intermediate lavas 87 sr 86 sr ratios of the kv and dacitic samples of cv are close to each other and range from 0 708 to 0 709 while sr isotopic ratios of the rhyolites are significantly high and variable 0 724 0 786 143 nd 144 nd ratios of the cv and kv except for the alkaline samples are similar for both sequences vary from 0 51230 to 0 51242 geological geochemical isotopic and radiochronologic data reveal that the kv and cv were formed in extensional tectonic setting but evolved by different petrological processes in different magma chambers during the neogene underplated mafic magma was injected into the crust and hybridized by mantle and crustal derived materials geochemical features and trace element modeling for the mafic members of the kv indicate that they were derived from enriched lithospheric mantle and modified by fractional crystallization from basalt to rhyolite helvaci et al 2009 unexpectedly the felsic lavas from cumaovasi region have a unique chemical composition and similar to the extension related rhyolites formed from small magma bodies our data reveal that extension related mafic inputs caused crustal anatectic melting and formed felsic melts that rapidly ascended into the upper crust the cumaovasi felsic rocks were differentiated into the highly evolved silica rich melts within the magma chambers trapped near the surface

evolution of neogene calc alkaline to alkaline volcanism in the aliaga foca region western anatolia turkey abstract in the foca region a complete miocene volcano sedimentary succession outcrops this succession includes a well developed central volcano gradually interdigitating with flank erruptions and a lacustrine sedimentary succession the dumanlidag volcano consists of three laterally and vertically interdigitating rock associations the yuntdag volcanics the foca volcanics and the aliaga limestones the lowermost unit is the yuntdag volcanics comprising dominantly andesitic and trachyandesitic lava flows domes and dykes and interbedded blocky pyroclastic flow deposits these different facies together form a central volcano with a caldera structure surrounding its summit the andesitic volcanic succession grades laterally into and is overlain by the rhyolitic foca volcanics that erupted along the flank of the dumanlidag volcano and comprise a thick rhyolitic pyroclastic sequence with small rhyolite domes and dykes in the uppermost parts the foca volcanics include sporadic occurrences of alkaline dykes and lavas this volcanic sequence interfingers laterally with lacustrine sedimentary rocks the volcanism was calc alkaline during the formation of the yuntdag volcanics and controlled by ne sw trending regional scale weakness zones along these fault or fracture zones three linearly aligned volcanic vents developed the volcanism was dominated by flank eruptions in the later stages and both subaerial and lacustrine volcano sedimentary deposits of the foca volcanics were formed during the latest phase volcanism was bimodal and alkaline trachyandesitic to phonolitic lavas and dykes coevally formed with the calc alkaline rhyolitic volcanics along ne sw trending fracture zones the flank of the dumanlidag volcano and extensive areas in western anatolia were covered by shallow lakes and widespread lacustrine limestones were deposited field studies and geochemical characteristics of the volcanic rocks indicate that the volcanism tectonic activity and the sedimentary deposition were progressive without any pronounced interruption and were controlled by nw se trending extension throughout the formation of the miocene succession

retardation of arsenic transport through a pleistocene aquifer holocene aquifers are the source of much arsenic poisoning in south and southeast asia whereas pleistocene aquifers are mostly safe here the delayed arsenic contamination of a pleistocene aquifer is described and modelled millions of people across southeast asia are exposed to arsenic contaminated drinking water drawn from holocene aquifers layers of sand deposited less than 5 000 years ago by contrast pleistocene aquifers deposited about 12 000 years ago have lower levels of contamination and are increasingly being exploited as safe sources of drinking water this study reports the gradual penetration of arsenic into a low arsenic pleistocene aquifer south of hanoi vietnam changes in groundwater flow and the redox state of the aquifer sands induced by pumping are introducing contamination from the high arsenic holocene aquifer contamination so far is limited owing to the absorption of arsenic onto aquifer sands which delays arsenic movement by decades groundwater drawn daily from shallow alluvial sands by millions of wells over large areas of south and southeast asia exposes an estimated population of over a hundred million people to toxic levels of arsenic1 holocene aquifers are the source of widespread arsenic poisoning across the region2 3 in contrast pleistocene sands deposited in this region more than 12 000 years ago mostly do not host groundwater with high levels of arsenic pleistocene aquifers are increasingly used as a safe source of drinking water4 and it is therefore important to understand under what conditions low levels of arsenic can be maintained here we reconstruct the initial phase of contamination of a pleistocene aquifer near hanoi vietnam we demonstrate that changes in groundwater flow conditions and the redox state of the aquifer sands induced by groundwater pumping caused the lateral intrusion of arsenic contamination more than 120 metres from a holocene aquifer into a previously uncontaminated pleistocene aquifer we also find that arsenic adsorbs onto the aquifer sands and that there is a 16 20 fold retardation in the extent of the contamination relative to the reconstructed lateral movement of groundwater over the same period our findings suggest that arsenic contamination of pleistocene aquifers in south and southeast asia as a consequence of increasing levels of groundwater pumping may have been delayed by the retardation of arsenic transport

progressive development of the buyuk menderes graben based on new data western turkey oblique and normal fault systems exposed in the buyuk menderes graben bmg region record two successive and independent complex tectonic events the first group tectonic event is defined by an e w extension related to n s contraction and transpression this group is responsible for the development of nw and ne trending conjugate pairs of oblique faults which controlled early middle miocene basin formation between the early middle miocene and plio quaternary strata exists an unconformity indicating a period of folding uplift and severe erosion associated with n s shortening the second group of events was the change in tectonic regime from e w extension to n s extension which controlled the formation of the buyuk menderes graben by three progressive pulses of deformation the first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the menderes massif mm with the development of the e trending buyuk menderes detachment fault bmdf the minimum age of this pulse is constrained by the older plio quaternary fluviatile deposits of the buyuk menderes graben that range in age from the plio pleistocene boundary interval to late pleistocene the second pulse which is marked by the rapid deposition of alluvial deposits initiated the formation of approximately e w trending high angle normal faults synthetic and antithetic to the buyuk menderes detachment fault on the northern margin during holocene times these faults are interpreted as secondary steeper listric faults that merge with the main buyuk menderes detachment fault at depth the third pulse was the migration of the buyuk menderes graben depocentre to the present day position by diachronous activity of secondary steeper listric faults these steeper faults are the most seismically active tectonic elements in western turkey according to the stratigraphic and structural data the n s extension in the buyuk menderes graben region produced a progressive deformation phase with different pulses during its plio quaternary evolution with migration of deformation from the master fault to the hangingwall the formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the buyuk menderes detachment fault hence the southward migration of the deformation and of the buyuk menderes graben depocentre should be related to the evolution of detachment in the region the presence of the seismically active splays of secondary faults implies an active detachment system in the region this young plio quaternary n s extension in the buyuk menderes graben may be attributed to the combined effects of the two continuing processes in aegean region the first process is back arc spreading or probably the roll back of african slab below the south aegean arc which seems to be responsible for the change in the stress tensor from e w extension to n s extension the second and later event is the southwestward escape of the anatolian block along its boundary fault that is the north anatolian fault naf

reversible adsorption and flushing of arsenic in a shallow holocene aquifer of bangladesh the spatial heterogeneity of dissolved arsenic as concentrations in shallow groundwater of the bengal basin has been attributed to transport of as and reactive carbon from external sources or to the release of as from within grey sand formations we explore the latter scenario in this detailed hydrological and geochemical study along a 300 m transect of a shallow aquifer extending from a groundwater recharge area within a sandy channel bar to its discharge into a nearby stream within the 10 20 m depth range groundwater ages along the transect determined by the 3h 3he method increase from 10 yr in the recharge area to a maximum of 40 yr towards the stream concentrations of groundwater as within the same grey sands increase from 10 to 100 to 500 g l along this transect evidence of reversible adsorption of as between the groundwater and sediment was obtained from a series of push pull experiments traditional batch adsorption experiments and the accidental flooding of a shallow monitoring well assuming reversible adsorption and a distribution coefficient kd of 0 15 1 5 l kg inferred from these observations a simple flushing model shows that the increase in as concentrations with depth and groundwater age at this site and at other sites in the bengal and red river basins can be attributed to the evolution of the aquifer over 100 1000 years as aquifer sands are gradually flushed of their initial as content a wide range of as concentrations can thus be maintained in groundwater with increases with depth governed by the history of flushing and local recharge rates without external inputs of reactive carbon or as from other sources

relative roles of source composition fractional crystallization and crustal contamination in the petrogenesis of andean volcanic rocks there are well established differences in the chemical and isotopic characteristics of the calc alkaline basalt andesite dacite rhyolite association of the northern n v z central c v z and southern volcanic zones s v z of the south american andes volcanic rocks of the alkaline basalt trachyte association occur within and to the east of these active volcanic zones the chemical and isotopic characteristics of the n v z basaltic andesites and andesites and the s v z basalts basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere conversely the alkaline lavas are derived from basaltic parent magmas formed from mantle of within plate character recent basaltic andesites from the cerro galan volcanic centre to the se of the c v z are derived from mantle containing both subduction zone and within plate components and have experienced assimilation and fractional crystallization a f c during uprise through the continental crust the c v z basaltic andesites are derived from mantle containing subduction zone components probably accompanied by a f c within the continental crust some c v z lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing the petrogenesis of the c v z lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation fractional crystallization and magma mixing during uprise through the continental crust

comparison of young volcanic associations of western and eastern anatolia formed under a compressional regime a review abstract turkey is characterised by widespread post oligocene volcanism in western anatolia volcanic activity began during the late oligocene early miocene in a compressional regime a widespread suite of andesitic and dacitic calc alkaline rocks was erupted in this period they were accompanied by locally developed high level granitic intrusions the abrupt change from n s compression to n s stretching in the middle miocene was accompanied by a gradual transition to alkali basaltic volcanism in eastern anatolia the collision related compressional tectonics and associated volcanic activity began in the late miocene to pliocene and continued almost without interruption into historical times one minor and two major volcanic phases may be distinguished an initial minor eruptive phase of basic and intermediate alkaline rocks was followed by widespread eruptions of andesitic and dacitic calc alkaline rocks during the pliocene partly penecontemporaneous with this a second more important major phase of volcanism involving alkaline and transitional lavas began and continued during the quaternary the calc alkaline lavas of both regions were erupted at a time when the compressional regime led to crustal thickening these lavas display many geochemical and isotopic signatures that may be interpreted in terms of contamination of magma involving continental crustal materials the alkaline lavas in both regions began during the final stage of the compressional regime and form two groups one group is geochemically and isotopically similar to the calc alkaline rocks and the other is more typically alkaline the volcanic evolution of these two regions of turkey followed a somewhat similar pattern producing highly contaminated calc alkaline lavas at the beginning and evolving towards uncontaminated alkaline lavas at the end

growth destruction and volcanic facies architecture of three volcanic centres in the miocene usak gure basin western turkey subaqueous subaerial volcanism in a lacustrine setting abstract early to mid miocene extension in western anatolia related to plate tectonic motions resulted in the development of a number of normal fault bounded sedimentary basins as well as different styles and compositions of volcanic activity the usak and gure basins accumulated a thick fluvio lacustrine fill in which three distinct volcanic edifices elmadag itecektepe and beydagi and their deposits can overlap with each other and with the sediments produced by the background sedimentation in addition complete facies architectures of small volume monogenetic volcanoes have been recognised in association with the three large complex polygenetic volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place all three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits with abundant evidences of magma water interaction such as peperites for non explosive magma water interaction with the lacustrine water saturated sediment and standing water body in a large alkaline lake during the constructive phase proximal successions of pyroclastic flows pyroclastic falls and rarely surge deposits are associated with distally emplaced debris flow deposits sometimes of mixed volcanogenic and terrestrial origins and are interbedded with lacustrine sediments of the inay group all three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15 ma ago most likely related to a combination of tectonic movements on ne sw trending basement faults which triggered multiple flank collapses and volcanic debris avalanches elmadag and voluminous ignimbrite eruptions that triggered caldera formation itecektepe and beydagi volcanic centres lacustrine conditions persisted during the destruction and post destruction stages of the volcano s evolution as evidenced by indications of magma water interactions within the central collapse structures which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores

tracing organic matter composition and distribution and its role on arsenic release in shallow cambodian groundwaters biogeochemical processes that utilize dissolved organic carbon are widely thought to be responsible for the liberation of arsenic from sediments to shallow groundwater in south and southeast asia the accumulation of this known carcinogen to hazardously high concentrations has occurred in the primary source of drinking water in large parts of densely populated countries in this region both surface and sedimentary sources of organic matter have been suggested to contribute dissolved organic carbon in these aquifers however identification of the source of organic carbon responsible for driving arsenic release remains enigmatic and even controversial here we provide the most extensive interrogation to date of the isotopic signature of ground and surface waters at a known arsenic hotspot in cambodia we present tritium and radiocarbon data that demonstrates that recharge through ponds and or clay windows can transport young surface derived organic matter into groundwater to depths of 44 m under natural flow conditions young organic matter dominates the dissolved organic carbon pool in groundwater that is in close proximity to these surface water sources and we suggest this is likely a regional relationship in locations distal to surface water contact dissolved organic carbon represents a mixture of both young surface and older sedimentary derived organic matter ground surface water interaction therefore strongly influences the average dissolved organic carbon age and how this is distributed spatially across the field site arsenic mobilization rates appear to be controlled by the age of dissolved organic matter present in these groundwaters arsenic concentrations in shallow groundwaters 20 m groundwaters we suggest that while the rate of arsenic release is greatest in shallow aquifer sediments arsenic release also occurs in deeper aquifer sediments and as such remains an important process in controlling the spatial distribution of arsenic in the groundwaters of se asia our findings suggest that any anthropogenic activities that alter the source of groundwater recharge or the timescales over which recharge takes place may also drive changes in the natural composition of dissolved organic carbon in these groundwaters such changes have the potential to influence both the spatial and temporal evolution of the current groundwater arsenic hazard in this region

arsenic toxicity of groundwater in parts of the bengal basin in india and bangladesh the role of quaternary stratigraphy and holocene sea level fluctuation arsenic toxicity in groundwater in the ganges delta and some low lying areas in the bengal basin is confined to middle holocene sediments dissected terraces and highlands of pleistocene and early holocene deposits are free of such problems arsenic rich pyrite or other arsenic minerals are rare or absent in the affected sediments arsenic appears to occur adsorbed on iron hydroxide coated sand grains and clay minerals and is transported in soluble form and co precipitated with or is scavenged by fe iii and mn iv in the sediments it became preferentially entrapped in fine grained and organic rich sediments during mid holocene sea level rises in deltaic and some low lying areas of the bengal basin it was liberated subsequently under reducing conditions and mediated further by microbial action intensive extraction of groundwater for irrigation and application of phosphate fertilizer possibly triggered the recent release of arsenic to groundwater this practice has induced groundwater flow mobilizing phosphate derived from fertilizer as well as from decayed organic matter which has promoted the growth of sediment biota and aided the further release of arsenic however the environment is not sufficiently reducing to mobilize iron and arsenic in groundwater in the ganges floodplains upstream of rajmahal thus arsenic toxicity in the groundwater of the bengal basin is caused by its natural setting but also appears to be triggered by recent anthropogenic activities

a model for the evolution in water chemistry of an arsenic contaminated aquifer over the last 6000 years red river floodplain vietnam aquifers on the red river flood plain with burial ages ranging from 500 to 6000 years show with increasing age the following changes in solute concentrations a decrease in arsenic increase in fe ii and decreases in both ph ca and bicarbonate these changes were interpreted in terms of a reaction network comprising the kinetics of organic carbon degradation the reduction kinetics of as containing fe oxides the sorption of arsenic the kinetics of siderite precipitation and dissolution as well as of the dissolution of caco3 the arsenic released from the fe oxide is preferentially partitioned into the water phase and partially sorbed while the released fe ii is precipitated as siderite the reaction network involved in arsenic mobilization was analyzed by 1 d reactive transport modeling the results reveal complex interactions between the kinetics of organic matter degradation and the kinetics and thermodynamic energy released by fe oxide reduction the energy released by fe oxide reduction is strongly ph dependent and both methanogenesis and carbonate precipitation and dissolution have important influences on the ph overall it is the rate of organic carbon degradation that determines the total electron flow however the kinetics of fe oxide reduction determines the distribution of this flow of electrons between methanogenesis which is by far the main pathway and fe oxide reduction modeling the groundwater arsenic content over a 6000 year period in a 20 m thick aquifer shows an increase in as during the first 1200 years where it reaches a maximum of about 600 g l during this initial period the release of arsenic from fe oxides actually decreases but the adsorption of arsenic onto the sediment delays the build up in the groundwater arsenic concentration after 1200 years the groundwater arsenic content slowly decreases controlled both by desorption and continued further but diminishing release from fe oxide being reduced after 6000 years the arsenic content has decreased to 33 g l the modeling enables a quantitative description of how the aquifer properties the reactivity of organic carbon and fe oxides the number of sorption sites and the buffering mechanisms change over a 6000 year period and how the combined effect of these interacting processes controls the groundwater arsenic content

petrochemistry of the south marmara granitoids northwest anatolia turkey post collision magmatic rocks are common in the southern portion of the marmara region kapidag karabiga gonen yenice can areas and also on the small islands marmara avsa pasalimani in the sea of marmara they are represented mainly by granitic plutons stocks and sills within triassic basement rocks the granitoids have ages between late cretaceous and miocene but mainly belong to two groups eocene in the north and miocene in the south the miocene granitoids have associated volcanic rocks the eocene granitoids do not display such associations they are both granodioritic and granitic in composition and are metaluminous calc alkaline medium to high k rocks their trace elements patterns are similar to both volcanic arc and calc alkaline post collision intrusions and the granitoids plot into the volcanic arc granite vag and collision related granite areas colg of discrimination diagrams the have high 87sr 86sr 0 704 0 707 and low 143nd 144nd 0 5124 0 5128 during their evolution the magma was affected by crustal assimilation and fractional crystallization afc nd and sr isotopic compositions support an origin of derivation by combined continental crustal afc from a basaltic parent magma a slab breakoff model is consistent with the evolution of south marmara sea granitoids

arsenic in groundwater of the red river floodplain vietnam controlling geochemical processes and reactive transport modeling abstract the mobilization of arsenic as to the groundwater was studied in a shallow holocene aquifer on the red river flood plain near hanoi vietnam the groundwater chemistry was investigated in a transect of 100 piezometers results show an anoxic aquifer featuring organic carbon decomposition with redox zonation dominated by the reduction of fe oxides and methanogenesis enhanced pco2 pressure causes carbonate dissolution to take place but mainly in the soil and unsaturated zone the concentration of as increases over depth to a concentration of up to 550 g l most as is present as as iii but some as v is always found arsenic correlates well with nh4 relating its release to organic matter decomposition and the source of as appears to be the fe oxides being reduced part of the produced fe ii is apparently reprecipitated as siderite containing less as results from sediment extraction indicate most as to be related to the fe oxide fractions the measured amount of sorbed as is low in agreement speciation calculations for a fe oxide surface suggest as iii to constitute only 3 of the surface sites while the remainder is occupied by carbonate and silica species the evolution in water chemistry over depth is homogeneous and a reactive transport model was constructed to quantify the geochemical processes along the vertical groundwater flow component a redox zonation model was constructed using the partial equilibrium approach with organic carbon degradation in the sediment as the only rate controlling parameter apart from the upper meter a constant degradation rate of 0 15 c mmol l yr could explain the redox zonation throughout the aquifer modeling also indicates that the fe oxide being reduced is of a stable type like goethite or hematite arsenic is contained in the fe oxides and is first released during their dissolution our model further suggests that part of the released as is adsorbed on the surface of the remaining fe oxides and in this way may be retarded

the impact of aquifer flushing on groundwater arsenic across a 35 km transect perpendicular to the upper brahmaputra river in assam india well testing in the floodplain of the brahmaputra river in golaghat and jorhat districts of assam india shows that groundwater arsenic as concentrations increase with distance from the river to establish the origin of this pattern an additional 900 wells 60 m deep were tested for as and 9 sites were drilled along a 35 km transect perpendicular to the river the field data show no relation between groundwater as concentrations ranging from 1 to 660 g l along the transect and a as concentrations of 1 5 mg kg in cuttings of aquifer sand recovered while drilling or b the degree of reduction of iron oxides in these cuttings the drilling indicates however a marked increase in the thickness of a clay layer capping the aquifer starting from 1 5 m near the river to over 60 m at the most distant site towards the base of the naga foothills organic radiocarbon ages of 18 46 kyr obtained from all but one of 13 clay samples indicate pre holocene deposition of the underlying sands across the entire transect radiocarbon ages of dissolved inorganic carbon of 0 2 4 7 and 17 8 kyr were measured in groundwater from 3 monitoring wells installed to 30 60 m depth at distances of 10 20 and 40 km from the river respectively a conceptual groundwater flow model consistent with monitored heads and groundwater ages suggests that thick clay layers capping the aquifer further from the river inhibited flushing of the aquifer and as a result preserved higher as levels in groundwater

river bank geomorphology controls groundwater arsenic concentrations in aquifers adjacent to the red river hanoi vietnam many aquifers that are highly contaminated by arsenic in south and southeast asia are in the floodplains of large river networks under natural conditions these aquifers would discharge into nearby rivers however large scale groundwater pumping has reversed the flow in some areas so that rivers now recharge aquifers at a field site near hanoi vietnam we find river water recharging the aquifer becomes high in arsenic reaching concentrations above 1000 g l within the upper meter of recently 50 g l aqueous arsenic concentrations are found in aquifer regions adjacent to zones where the river has recently deposited sediment and low arsenic concentrations are found in aquifer regions adjacent to erosional zones high arsenic concentrations are even found adjacent to a depositional river reach in a pleistocene aquifer a type of aquifer sediment which generally hosts low arsenic water using geochemical and isotopic data we estimate the in situ rate of arsenic release from riverbed sediments to be up to 1000 times the rates calculated on inland aquifer sediments in vietnam geochemical data for riverbed porewater conditions indicate that the reduction of reactive poorly crystalline iron oxides controls arsenic release we suggest that aquifers in these regions may be susceptible to further arsenic contamination where riverine recharge drawn into aquifers by extensive groundwater pumping flows through recently deposited river sediments before entering the aquifer

methane in aquifers used for public supply in the united states abstract in 2013 to 2015 833 public supply wells in 15 principal aquifers in the u s were sampled to identify which aquifers contained high methane concentrations 1 mg l and determine the geologic hydrologic and geochemical conditions associated with high concentrations this study represents the first national assessment of methane in aquifers used for public supply in the u s and as such advances the understanding of the occurrence and distribution of methane in groundwater nationally methane concentrations 1 and 10 mg l occurred in 6 7 and 1 1 of the samples respectively most high concentrations occurred in aquifers in the atlantic and gulf coastal plain regions and upper midwest high methane concentrations were most commonly associated with tertiary and younger aquifer sediments old groundwater 60 years and concentrations of oxygen nitrate n and sulfate

release of arsenic to deep groundwater in the mekong delta vietnam linked to pumping induced land subsidence deep aquifers in south and southeast asia are increasingly exploited as presumed sources of pathogen and arsenic free water although little is known of the processes that may compromise their long term viability we analyze a large area 1 000 km2 of the mekong delta vietnam in which arsenic is found pervasively in deep pliocene miocene age aquifers where nearly 900 wells at depths of 200 500 m are contaminated there intensive groundwater extraction is causing land subsidence of up to 3 cm y as measured using satellite based radar images from 2007 to 2010 and consistent with transient 3d aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988 we propose a previously unrecognized mechanism in which deep groundwater extraction is causing interbedded clays to compact and expel water containing dissolved arsenic or arsenic mobilizing solutes e g dissolved organic carbon and competing ions to deep aquifers over decades the implication for the broader mekong delta region and potentially others like it across asia is that deep untreated groundwater will not necessarily remain a safe source of drinking water

hydrological and sedimentary controls leading to arsenic contamination of groundwater in the hanoi area vietnam the impact of iron arsenic ratios peat river bank deposits and excessive groundwater abstraction groundwater contamination by arsenic in vietnam poses a serious health threat to millions of people in the larger hanoi area elevated arsenic levels are present in both the holocene and pleistocene aquifers family based tubewells predominantly tap the holocene aquifer while the hanoi water works extract more than 600 000 m3 day of groundwater from the pleistocene aquifer detailed groundwater and sediment investigations were conducted at three locations exhibiting distinct geochemical conditions i e i high levels of dissolved arsenic av 121 g l at the river bank ii low levels of dissolved arsenic av 21 g l at the river bank and iii medium levels of dissolved arsenic 60 g l in an area of buried peat and excessive groundwater abstraction seasonal fluctuations in water chemistry were studied over a time span of 14 months sediment bound arsenic 1 3 22 g g is in a natural range arsenic correlates with iron r2 0 8 with variation related to grain size sediment leaching experiments showed that arsenic can readily be mobilized at each of the three locations low levels of arsenic in groundwater 10 g l generally exhibit manganese reducing conditions whereas elevated levels are caused by reductive dissolution under iron and sulphate reducing conditions average arsenic concentrations in groundwater are twofold higher at the river bank than in the peat area the lower levels of arsenic contamination in the peat area are likely controlled by the high abundance of iron present in both the aqueous and sediment phases with median molar fe as ratios of 350 in water and 8700 in the sediments of the peat area reduced iron possibly forms new mineral phases that resorb or sequester previously released arsenic to the sediment despite similar redox conditions resorption is much less significant at the river bank fe as aq 68 fe as s 4700 and hence arsenic concentrations in groundwater reach considerably higher levels drawdown of holocene water to the pleistocene aquifer in the peat area caused by the pumping for the hanoi water works clearly promotes reducing conditions in pleistocene groundwater this demonstrates that excessive abstraction of water from deep wells i e wells tapping water below the arsenic burdened depth can cause a downward shift of iron reducing conditions and concurrently mobilize arsenic along the way vertical migration of reduced groundwater may also impact aquifers under natural hydrological conditions seepage of doc enriched groundwater derived from degradation of organic matter in the clayey sediments at the river bank was observed to enhance and maintain iron reducing conditions in the aquifer where organic matter is scarce once the aquifer becomes reduced arsenic is released from the aquifer solid hosts but additionally derives from the arsenic enriched groundwater seeping from the clay into the aquifer this behaviour is an important mechanism for arsenic contamination in aquifers that might not necessarily contain enough organic matter in their sediments to induce reducing conditions independently

coeval plutonism and metamorphism in a latest oligocene metamorphic core complex in northwest turkey a metamorphic core complex of latest oligocene age crops out in the kazdag mountain range in northwest turkey the footwall of the core complex consists of gneiss amphibolite and marble metamorphosed at 5 1 kbar and 640 50 c the average muscovite and biotite rb sr ages from the gneisses are 19 ma and 22 ma respectively and imply high temperature metamorphism during latest oligocene times the hangingwall is made up of an unmetamorphosed lower tertiary oceanic accretionary melange with upper cretaceous eclogite lenses the hangingwall and footwall are separated by an extensional ductile shear zone two kilometres thick mylonites and underlying high grade metamorphic rocks show a n trending mineral lineation with the structural fabrics indicat ing down dip top to the north shear sense the shear zone the accretionary melange and the high grade metamorphic rocks are cut by an undeformed granitoid with a 21 ma rb sr biotite age analytically indistinguishable from the rb sr biotite ages in the surrounding footwall gneisses the estimated pressure of the metamorphism and that of the granitoid emplacement indicate that the high grade metamorphic rocks were rapidly exhumed at 24 ma from a depth of 14 km to 7 km by activity along the shear zone the subsequent exhumation of the metamorphic rocks to the surface occurred during pliocene quaternary times in a transpressive ridge between two overstepping fault segments of the north anatolian fault zone the high grade metamorphic rocks of the kazdag range are surrounded by voluminous calc alkaline volcanic and plutonic rocks of late oligocene early miocene age which formed above the northward dipping hellenic subduction zone the magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest turkey prior to the onset of extension suggest that the latest oligocene regional extension was primarily related to the roll back of the subduction zone rather than to the gravitational collapse

redox controls on arsenic enrichment and release from aquifer sediments in central yangtze river basin abstract more than 100 million people in asia are presently exposed to groundwater with arsenic as concentrations exceeding the world health organization standard of 10 g l 1 arsenic contaminated groundwater within basins of the central portion of the yangtze river has recently been reported but the processes controlling arsenic concentrations have yet to be resolved we examined the hydrologic and geochemical factors controlling arsenic within the jianghan plain an inland sedimentary basin of the yangtze river where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing schaefer et al 2016 hydrologic fluctuations alter redox conditions in the aquifer leading to oscillations between arsenic iron reduction and oxidation here we investigate the depth distribution of solid and aqueous phase iron and arsenic species and through a series of laboratory manipulations constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations in sediment incubations from 20 m below the surface where solid phase arsenic concentrations exceed 100 mg kg 1 both unamended and glucose amended sediment samples result in arsenic release to the aqueous phase in situ carbon was capable of promoting as release in the sediment in contrast sediment batch incubations from other depths resulted in limited as release solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods in sediments below the as enriched zone glucose amendment resulted in arsenic reduction but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the jianghan plain aquifer leads to rapid release of as to groundwater arsenic release from sediments at 20 m depth is sufficient to explain arsenic concentrations throughout the aquifer and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater

controlling geological and hydrogeological processes in an arsenic contaminated aquifer on the red river flood plain vietnam abstract geological and hydrogeological processes controlling recharge and the mobilization of as were investigated in a shallow holocene aquifer on the red river flood plain near hanoi vietnam the geology was investigated using surface resistivity methods geophysical borehole logging drilling of boreholes and installation of more than 200 piezometers recharge processes and surface groundwater interaction were studied using i time series of hydraulic head distribution in surface water and aquifers ii the stable isotope composition of waters and iii numerical groundwater modeling the red river and two of its distributaries run through the field site and control the groundwater flow pattern for most of the year there is a regional groundwater flow towards the red river during the monsoon the red river water stage rises up to 6 m and stalls the regional groundwater flow the two distributaries recharge the aquifer from perched water tables in the dry season whilst in the flooding period surface water enters the aquifer through highly permeable bank sediments the result is a dynamic groundwater flow pattern with rapid fluctuations in the groundwater table a transient numerical model of the groundwater flow yields an average recharge rate of 60 100 mm a through the confining clay and a total recharge of approximately 200 mm a was estimated from 3h 3he dating of the shallow groundwater thus in the model area recharge of surface water from the river distributaries and recharge through a confining clay is of the same magnitude being on average around 100 mm a the thickness of the confining clay varies between 2 and 10 m and affects the recharge rate and the transport of electron acceptors o2 no 3 and so 4 2 into the aquifer where the clay layer is thin an up to 2 m thick oxic zone develops in the shallow aquifer in the oxic zone the as concentration is less than 1 g l but increases in the reduced zone below to 550 g l in the holocene aquifer as is mobilized at a rate of around 14 g l a an as mass balance for the field site shows that around 1100 kg of as is annually leached from the holocene sand and discharged into the red river corresponding to 0 01 of the total pool of as now present in the holocene sand

reconstructing the evolution of an eroded miocene caldera volcano yamanlar volcano izmir turkey abstract the miocene yamanlar composite volcano is located in the central part of a shear zone in western turkey the volcano s deeply eroded interior provides excellent three dimensional exposure of a faulted caldera floor and caldera fill rocks as well as surrounding extracaldera ignimbrites we present a much revised stratigraphy and geological map of yamanlar in order to quantify the evolutionary stages of the volcano the yamanlar volcanic cone was composed of 800 m of basaltic andesite to andesite lavas and lava domes the volcano underwent at least one phase of caldera formation associated with an explosive eruption that deposited an ignimbrite sheet within and outside the caldera lithofacies architecture analysis is applied to the proximal and medial exposures of the early middle yamanlar formation which occurs outside of the caldera field evidence of the succession indicates a caldera forming eruption our results indicate that the formation of the yamanlar caldera resulted from one major catastrophic eruption that generated several sustained pyroclastic density currents pdcs subdivided by fall deposits with sharp contacts the ignimbrite sheet is composed of four flow units the presence of numerous coarse grained lithic rich horizons within the ignimbrite sheet is consistent with caldera subsidence post caldera volcanism is indicated by intrusions and lava domes erupted along the inferred caldera bounding faults some of which record 90 m of displacement widespread coarse grained breccias that overlie the ignimbrite sheet are interpreted as debris avalanche deposits resulting from gravitational failure of the flanks of the volcano or the caldera wall during or after caldera subsidence

geology of the ignimbrites and the associated volcano plutonic complex of the ezine area northwestern anatolia abstract the ezine region is located in the northwestern part of anatolia where young granitic and volcanic rocks are widespread and show close spatial and temporal association in this region magmatism began with the kestanbol granite which intruded into metamorphic basement rocks and formed contact metamorphic aureole to the east and southeast the pluton is surrounded by hypabyssal rocks which in turn are surrounded by volcanic associations the volcanic rocks may be divided into two main groups on the basis of their lithological properties lavas and lahar deposits dominate the northern sector while ignimbrites dominate the southern sector the ignimbrite eruptions were formed partly coevally with the plutonic and the associated volcanic rocks during the early miocene they appear to have been associated in a caldera collapse environment geochemical properties of the plutonic and the associated volcanic assemblages indicate that the magmas are hybrid and co genetic and were formed from a similar mantle source under a compressional regime prior to the opening of the present e w trending graben of the aegean western anatolian region

new evidence and model on the evolution of the southeast anatolian orogen this paper describes the orogenic evolution of the southeast anatolian orogenic belt based mostly on new geologic data collected from its constituent tectonic units in the course of new mapping programs of the past decade the southeast anatolian orogenic segment of the alpides may be divided into three approximately east west trending zones from south to north they are the arabian platform followed by a zone of imbrication and then a zone of nappes the arabian platform includes a mostly marine sedimentary succession deposited from early cambrian to middle miocene time the zone of imbrication is a narrow belt sandwiched between the arabian platform and the zone of nappes it consists of imbricated thrust slices emplaced onto a late cretaceous to early miocene sequence the zone of nappes is the highest tectonic unit consisting of two stacks of nappes simply designated the lower and upper nappes the lower nappe is represented by the slices of a polyphase metamorpbic ophiolitic assemblage and the maden group the upper nappe rests on the lower nappe and is represented by the bitlis and poturge metamorphic massifs southeastern anatolia underwent two major episodes of alpide deformation the first occurred during the late cretaceous period when ophiolite was emplaced on the arabian platform this event was not the consequence of a continental collision the ophiolite obduction onto the arabian platform was followed by a regionwide extension and a new marine transgression over the platform immediately after the ophiolite obduction the second episode of deformation occurred during middle eocene miocene time in two distinct stages as a result of the progressive elimination and complete closure of the ocean s which led to the collision between the zone of nappes located to the north being a part of eurasia and the arabian plate the maden marginal basin formed north of the subduction zone that eliminated the ocean between eurasia and arabia along the southern margin of the taurus belt and abutted the arabian plate much later during the final collision the second episode of deformation formed the present orogenic segment leading to the amalgamation of different tectonic units these amalgamated nappes collided with the arabian plate and welded onto it at the latest stage of the orogenic evolution during the miocene epoch

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

post collision magmatism and tectonics in northwest anatolia a suite of biotite hornblende granodiorite intrusions has been emplaced into blueschist facies metasediments in northwest anatolia following collision between two continental margins now represented by the tavsanli and sakarya zones the 40ar 39ar ages of phengites and glaucophanes from the blueschists metamorphosed under unusually high p low t conditions p 20 2 kbar t 430 30 c suggest that metamorphism apparently occurred over a period spanning at least 20 ma from 108 to 88 ma post tectonic granodiorites were emplaced during the eocene 53 to 48 ma resulting in a cordierite and andalusite bearing thermal aureole indicative of pressures of 3 kbar trace element systematics of the granodiorites are consistent with a derivation either from mantle derived magmas by fractional crystallisation in shallow magma chambers or from anatexis of crustal lithologies of internediate composition at pressures 10 kbar the preservation of high p low t assemblages in the blueschists together with the range of ages determined for blueschist facies metamorphism are indicative of rapid exhumation of delaminated fragments from a subducted continental margin however decompression melting of the crust is unlikely to have been a significant cause of magmatism both because exhumation of the blueschists from deep crustal levels predated magmatism by at least 25 ma and because of the small melt fraction 0 1 that may be generated in crustal lithologies by this process melting in the mantle wedge is required either to generate a primary melt for the derivation of magmas of intermediate composition or to provide an advective heat source for crustal melting the cause of melt formation in the upper mantle may be related to the termination of subduction following collision during the mid eocene

arsenic release and attenuation in a multilayer aquifer in the po plain northern italy reactive transport modeling abstract groundwater as concentrations who limit 10 g l are frequently found in the po plain n italy although several hypotheses on as mobilization exist i e reductive dissolution driven by peat degradation the mechanisms of as release and subsequent attenuation acting in the multilayer aquifer in the po plain were poorly understood the present work aims at implementing a reactive transport modeling of the aquifer system in cremona affected by as the model based on a partial equilibrium approach revealed that the observed as fe and mn chemistry could be mostly explained by the simultaneous equilibrium between fe oxide and sulfate reduction and fes precipitation and by the equilibrium of rhodochrosite precipitation dissolution model results together with litholog analysis supported the assumption of peat as the likely source of organic matter driving as release the model fitted to measured data showed that the peak in the organic carbon degradation rate at 20 40 m below surface average of 0 67 mm y corresponding to the shallow peaty aquitard and the upper portion of the underlying semiconfined aquifer is associated with the peak of net release of as average of 0 32 m y that is followed just downstream by a net precipitation in iron sulfides at 40 60 m below surface average of 0 30 m y these results support the assumptions of peaty aquifers as drivers of as release and iron sulfides as as traps the model also outlined the following aspects that could have a broad applicability in other alluvial as affected aquifers worldwide a shallow peaty aquitards may have a greater role in driving the as release since they likely have young and more reactive organic matter b the occurrence of fe oxide reduction and fes precipitation that represent the as source and sink together with sulfate reduction occurring simultaneously close to equilibrium may restrict the as mobility limiting the extent of contamination just downstream the source of organic matter that drives its release

late cenozoic volcanic evolution of the northeastern aegean region abstract late cenozoic volcanism occurred in an extensional tectonic regime in the northeastern aegean activity commenced in northeastern greece during the early oligocene and in northwestern turkey during the late oligocene early miocene the beginning of activity was characterized by calc alkaline intermediate acid volcanism however alkaline intermediate basic volcanism became dominant from the late miocene until the pleistocene this change in nature of volcanism is not related to a change of regional tectonic regime as previously thought instead we propose that the volcanic evolution reflects an increasing asthenospheric contribution facilitated by a thinned extended lithosphere arising from the regional extensional tectonics

hydrogeochemical zonation and its implication for arsenic mobilization in deep groundwaters near alluvial fans in the hetao basin inner mongolia summary high as groundwater has been found in shallow aquifers of the flat plain of the hetao basin but little is known about as concentration in deep groundwaters around piedmont areas which are the major drinking water resources one hundred and three groundwater samples from wells with depths 50 m and seven samples from one multi level monitoring well 89 m in depth were analyzed for chemical compositions and 18o and d isotopes to examine the geochemical processes controlling as mobilization according to hydrogeological setting chemical and isotopic characteristics of deep groundwater three distinguished hydrogeochemical zones are delineated including recharge oxic zone zone i groundwater flow moderate reducing zone zone ii and groundwater flow reducing zone zone iii zone i is located in proximal fans in the recharge area with oxic conditions where low as groundwater generally occurs in zone ii located in the intermediate between the fans and the flat plain with fe reduction predominated groundwater as is moderate zone iii lies in the flat plain with the occurrence of so 4 2 reduction where high as groundwater is mostly found this indicates that release of as to groundwater is primarily determined by reduction sequences arsenic is immobilized in o 2 no 3 reduction stage in zone i and released in fe reducing conditions of zone ii and displays a significant elevated concentration in so4 reducing stage in zone iii dissolution of carbonate minerals occurs in zone i while ca2 and mg2 are expected to precipitate in zone ii and zone iii in the multi level monitoring well both chemical and isotopic compositions are dependent of sampling depths with the similar trend to the hydrogeochemical zonation along the flow path the apparent increases in d and 18o values in zone iii reveal the possibility of high as shallow groundwater recharge to deep groundwater it indicates that deep groundwaters in proximal fans have low as concentrations and are considered as safe drinking water resources in the hetao basin however high as concentration is frequently observed in deep groundwater in the flat plain which should be routinely monitored in order to avoid chronic as poisoning

geochemical evolution of groundwater flowing through arsenic source sediments in an aquifer system of west bengal india the source of geogenic arsenic as contaminating a shallow aquifer in west bengal was traced to fine grained sediments deposited in an abandoned river channel along with as bearing phases these sediments contain 0 46 co deposited organic carbon the release of as and the geochemistry of groundwater within the channel fill deposits is investigated using a detailed mass balance model supported by aqueous solid phase and mineralogical data the model describes the evolution of groundwater chemistry along a flow path extending from its recharge in an abandoned channel pond through the channel fill to the underlying aquifer variations in groundwater composition are explained in terms of mineral weathering of host sediments driven by organic carbon decay arsenic is released through the reductive dissolution of goethite and the weathering of chlorite concomitantly some as is sequestered in precipitating vivianite these competing processes reach equilibrium deeper in the channel fill sequence as groundwater as concentrations stabilize the model yields estimates of mineral reaction or precipitation rates including rates of organic carbon oxidation 1 15 mmol c l 1 a 1 and net as release 4 57 10 4 mmol l 1 a 1 fine grained slightly permeable deposits such as channel fill containing reactive organic carbon and as bearing goethite and phyllosilicates are centers of intense chemical weathering conducive to as mobilization

integration of aquifer geology groundwater flow and arsenic distribution in deltaic aquifers a unifying concept groundwater arsenic as presents a public health risk of great magnitude in densely populated asian delta regions most acutely in the bengal basin west bengal india and bangladesh research has focused on the sources mobilisation and heterogeneity of groundwater as but a consistent explanation of as distribution from local to basin scale remains elusive we show for the bengal aquifer system that the numerous discontinuous silt clay layers together with surface topography impose a hierarchical pattern of groundwater flow which constrains as penetration into the aquifer and controls its redistribution towards discharge zones where it is re sequestered to solid phases this is particularly so for the discrete periods of as release to groundwater in the shallow subsurface associated with sea level high stand conditions of quaternary inter glacial periods we propose a hypothesis concerning groundwater flow silt clay layers impose hierarchical groundwater flow patterns constraining arsenic progression siha which links consensus views on the as source and history of sedimentation in the basin to the variety of spatial and depth distributions of groundwater as reported in the literature siha reconciles apparent inconsistencies between independent in some cases contrasting field observations we infer that lithological and topographic controls on groundwater flow inherent to siha apply more generally to deltaic aquifers elsewhere the analysis suggests that groundwater as may persist in the aquifers of asian deltas over thousands of years but in certain regions particularly at deeper levels as will not exceed low background concentrations unless groundwater flow systems are short circuited by excessive pumping

groundwater arsenic concentrations in vietnam controlled by sediment age arsenic contamination of groundwater threatens the health of millions of people in southeast asia measurements in an arsenic contaminated aquifer in vietnam point to sediment age as a key determinant of groundwater arsenic concentrations

evolution of the bayramic magmatic complex northwestern anatolia abstract during the oligocene middle miocene period widespread magmatic activity developed in western anatolia following the continental collision between the sakarya continent and the tauride anatolide platform this produced both intrusive and extrusive rocks which appear to be associated in space and time as exemplified from the bayramic area in the bayramic area the magmatic activity started with the intrusion of the evciler granite and the coeval lower volcanic association this was followed by the development of the upper volcanic association these rock groups form collectively the bayramic magmatic complex which was generated under an on going north south compressional regime the bayramic magmatic complex has a subalkaline composition displaying a calcalkaline trend trace elements and ree contents resemble to island arc and collision related magmas according to the isotope values the bayramic magmatic complex was derived from the magmas of lithospheric mantle origin which were later contaminated while passing through the thick continental crust in a post collisional tectonic setting during the oligocene early miocene period the latest product of the magmatism is the late miocene pliocene basalt lavas their geochemical properties are clearly different from the oligocene early miocene magmatic rocks the basalts were generated when the north south compression gave way to the north south extensional regime

sedimentogenesis and hydrobiogeochemistry of high arsenic late pleistocene holocene aquifer systems geogenic enrichment of arsenic as in groundwater has been a topic of worldwide concern over the past several decades due to the severe health threat to an estimated over one hundred million people despite the genetic diversity and the spatial variability of as concentrations the most common geogenic as enriched groundwater occurs in flat low lying river floodplains and fluvial lacustrine plains within river systems draining the himalaya tectonic movement sedimentological processes and palaeoclimatic optima after the last glacial maximum have created favorable conditions for the formation of high as aquifer systems mainly within the late pleistocene holocene deposits the co deposition of as bearing fe oxides and reactive organic matter within sediments of deltas floodplains or fluvial lacustrine plains forms the premise for as release under reducing geochemical environments however depending on the reactivity of organic matter and as bearing fe oxides as well as the availability of aqueous sulfate geochemical mechanisms controlling as enrichment in the groundwater differ between the coastal floodplains of south and southeast asia and the fluvial lacustrine plains of north and central china the indigenous geomicrobes thriving to adapt to specific aquifer environments may mediate fe s as biogeochemical cycling responsible for as speciation transformation dissolution desorption and hence mobilization hydrologic processes regulated by the local and regional groundwater flow regimes control as transport as well as its spatial distribution special attention must be paid to anthropogenic perturbation from intensive groundwater pumping and land use changes that affect the aquifer hydrological conditions and the biogeochemical processes thus altering groundwater as levels to decipher the patterns of as variation within the aquifers an integrated approach characterizing the major sedimentological hydrobiogeochemical and anthropogenic processes influencing as release and transport needs to be applied to ensure sustainable water supply for domestic and agricultural needs

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

adsorption and desorption of arsenic to aquifer sediment on the red river floodplain at nam du vietnam abstract the adsorption of arsenic onto aquifer sediment from the red river floodplain vietnam was determined in a series of batch experiments due to water supply pumping river water infiltrates into the aquifer at the field site and has leached the uppermost aquifer sediments the leached sediments remain anoxic but contain little reactive arsenic and iron and are used in our experiments the adsorption and desorption experiments were carried out by addition or removal of arsenic from the aqueous phase in sediment suspensions under strictly anoxic conditions also the effects of hco3 fe ii po4 and si on arsenic adsorption were explored the results show much stronger adsorption of as v as compared to as iii full reversibility for as iii adsorption and less so for as v the presence or absence of hco3 did not influence arsenic adsorption fe ii enhanced as v sorption but did not influence the adsorption of as iii in any way during simultaneous adsorption of as iii and fe ii as iii was found to be fully desorbable while fe ii was completely irreversibly adsorbed and clearly the two sorption processes are uncoupled phosphate was the only solute that significantly could displace as iii from the sediment surface compiling literature data on arsenic adsorption to aquifer sediment in vietnam and bangladesh revealed as iii isotherms to be almost identical regardless of the nature of the sediment or the site of sampling in contrast there was a large variation in as v adsorption isotherms between studies a tentative conclusion is that as iii and as v are not adsorbing onto the same sediment surface sites the adsorption behavior of arsenic onto aquifer sediments and synthetic fe oxides is compared particularly the much stronger adsorption of as v than of as iii onto red river as well as on most bangladesh aquifer sediments indicates that the perception that arsenic phosphate and other species compete for the same surface sites of iron oxides in sediments with properties similar to those of for example a synthetic goethite probably is not correct a simple two component langmuir adsorption model was constructed to quantitatively describe the reactive transport of as iii and po4 in the aquifer

mobility of arsenic in a bangladesh aquifer inferences from geochemical profiles leaching data and mineralogical characterization aquifer geochemistry was characterized at a field site in the munshiganj district of bangladesh where the groundwater is severely contaminated by as vertical profiles of aqueous and solid phase parameters were measured in a sandy deep aquifer depth 150 m below a thick confining clay 119 to 150 m a sandy upper aquifer 3 5 to 119 m above this confining layer and a surficial clay layer 3 5 m in the deep aquifer and near the top of the upper aquifer aqueous as levels are low 10 g l but aqueous as approaches a maximum of 640 g l at a depth of 30 to 40 m and falls to 58 g l near the base 107 m of the upper aquifer in contrast solid phase as concentrations are uniformly low rarely exceeding 2 g g in the two sandy aquifers and never exceeding 10 g g in the clay layers solid phase as is also similarly distributed among a variety of reservoirs in the deep and upper aquifer including adsorbed as as coprecipitated in solids leachable by mild acids and reductants and as incorporated in silicates and other more recalcitrant phases one notable difference among depths is that sorbed as loads considered with respect to solid phase fe extractable with 1 n hcl 0 2 m oxalic acid and a 0 5 m ti iii citrate edta solution appear to be at capacity at depths where aqueous as is highest this suggests that sorption limitations may in part explain the aqueous as depth profile at this site competition for sorption sites by silicate phosphate and carbonate oxyanions appear to sustain elevated aqueous as levels in the upper aquifer furthermore geochemical profiles are consistent with the hypothesis that past or ongoing reductive dissolution of fe iii oxyhydroxides acts synergistically with competitive sorption to maintain elevated dissolved as levels in the upper aquifer microprobe data indicate substantial spatial comapping between as and fe in both the upper and deep aquifer sediments and microscopic observations reveal ubiquitous fe coatings on most solid phases including quartz feldspars and aluminosilicates extraction results and xrd analysis of density magnetic separates suggest that these coatings may comprise predominantly fe ii and mixed valence fe solids although the presence of fe iii oxyhydroxides can not be ruled out these data suggest as release may continue to be linked to dissolution processes targeting fe or fe rich phases in these aquifers copyright 2004 elsevier ltd

mobilization of arsenic and iron from red river floodplain sediments vietnam abstract sediments from the red river and from an adjacent floodplain aquifer were investigated with respect to the speciation of fe and as in the solid phase to trace the diagenetic changes in the river sediment upon burial into young aquifers and the related mechanisms of arsenic release to the groundwater goethite with subordinate amounts of hematite were using mossbauer spectroscopy identified as the iron oxide minerals present in both types of sediment the release kinetics of fe as mn and po 4 from the sediment were investigated in leaching experiments with hcl and 10 mm ascorbic acid both at ph 3 from the river sediments most of the fe and as was mobilized by reductive dissolution with ascorbic acid while hcl released very little fe and as this suggests as to be associated with an fe oxide phase for oxidized aquifer sediment most fe was mobilized by ascorbic acid but here not much as was released however the reduced aquifer sediments contained a large pool of fe ii and as that is readily leached by hcl probably derived from an unidentified authigenic fe ii containing mineral which incorporates as as well extraction with ascorbic acid indicates that the river sediments contain both as v and as iii while the reduced aquifer sediment almost exclusively releases as iii the difference in the amount of fe ii leached from river and oxidized aquifer sediments by ascorbic acid and hcl was attributed to reductive dissolution of fe iii the reactivity of this pool of fe iii was quantified by a rate law and compared to that of synthetic iron oxides in the river mud fe iii had a reactivity close to that of ferrihydrite while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic fe oxides as a reference sediments were incubated both unamended and with acetate added and monitored for up to 2 months the river mud showed the fastest release of both fe and as while the effect of acetate addition was minor this suggests that the presence of reactive organic carbon is not rate limiting in the case of the river and aquifer sediments the release of fe and as was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor the reduced aquifer sediment apparently can sustain slower but prolonged microbially driven release of as the highly reactive pools of fe iii and as in the river mud could be due to reoxidation of as and fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of as onto the floodplain and into the underlying aquifers

hydrological control of as concentrations in bangladesh groundwater 1 the elevated arsenic as content of groundwater from wells across bangladesh and several other south asian countries is estimated to slowly poison at least 100 million people the heterogeneous distribution of dissolved arsenic in the subsurface complicates understanding of its release from the sediment matrix into the groundwater as well as the design of mitigation strategies using the tritium helium 3h 3he groundwater dating technique we show that there is a linear correlation between groundwater age at depths 20 m and dissolved as concentration with an average slope of 19 g l 1 yr 1 monitoring wells only we propose that either the kinetics of as mobilization or the removal of as by groundwater flushing is the mechanism underlying this relationship in either case the spatial variability of as concentrations in the top 20 m of the shallow aquifers can to a large extent be attributed to groundwater age controlled by the hydrogeological heterogeneity in the local groundwater flow system

role of sulfur redox cycling on arsenic mobilization in aquifers of datong basin northern china sulfur redox cycling potentially exerts important influences on arsenic as fate in shallow groundwater systems hydrochemical and sediment geochemical analysis combined with thermodynamic modeling study were conducted at datong basin to elaborate the effects of sulfur redox cycling on as speciation and mobilization under a strongly reducing environment dissolved as and sulfide concentration in 32 groundwater samples with depths of 19 40 m below the land surface varied from 8 to 2700 g l and from 5 to 490 g l respectively while dissolved fe ii was relatively low ranging from 20 to 280 g l the apparent co increase in dissolved sulfide and as concentration especially for samples with as content larger than 500 g l indicates that sulfidogenesis may significantly contribute to the mobilization of as via sulfide induced reduction of both as bearing fe iii oxide minerals and as v thermodynamic calculations indicate that groundwater as might be also thiolated in the presence of high level sulfide particularly to a large extent for as v speciation instead of sequestration by as sulfide precipitates results of sequential extraction and scanning electron microscopy array on sediments indicate the presence of fe ii sulfide mineral phases and an appreciable amount of co existent as in the sediments suggesting the precipitation of fe ii sulfides can restrict the build up of dissolved fe ii and sequester as from groundwater but not strongly enough thereby lowering down as to a moderate level of about 500 g l thus redox processes involving as s and fe species under sulfidic conditions as observed in datong basin not only facilitate the enrichment of as iii species and as v potentially existing as thiolated species but also the depletion of fe ii concentration in groundwater due to fe ii sulfide formation

use of sf6 to label drilling air in unsaturated fractured rock studies risk of over purging abstract sulfur hexafluoride was injected as a tracer gas into the air stream during air drilling of a borehole in the unsaturated zone of a partially welded fractured tuff at apache leap arizona one meter intervals were later isolated at multiple depths and pumped to purge drilling air from each interval the volume of air purged at 1 atm 20 c ranged from a low of 0 3 m 3 in an unfractured interval to a high of 252 m 3 in a highly fractured interval the concentration of sf 6 remained high throughout the purge in all intervals and often increased over time measurements of 13 c 14 c and co 2 concentration indicated that atmospheric air was eventually drawn into several of the intervals in spite of the fact that sf 6 concentrations remained high possible explanations include mixing of atmospheric air drawn through fractures with partially purged matrix air and delayed removal of sf 6 relative to atmospheric gases due to adsorption of sf 6 within the tuff matrix dissolution into pore water or diffusion from dead end pores with restricted openings in this system following a long delay between drilling and purging it was found that the risk of contamination from surface air by over purging was substantially greater than the risk of contamination from residual drilling air by under purging

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

geology and petrology of the simav magmatic complex nw anatolia and its comparison with the oligo miocene granitoids in nw anatolia implications on tertiary tectonic evolution of the region the oligo miocene granitic plutons and their related volcanic subvolcanic successions form a nw se trending magmatic belt along the northern border of the menderes massif this belt evolved within a nappe package consisting of the menderes metamorphics sakarya continent afyon zone and tavsanli zone and also intruded this nappe package the ezine evciler eybek kozak alacam koyunoba egrigoz and the baklan plutons emplaced along this belt and show similarities in their internal structures emplacement mechanisms and petrological characteristics these different granitic plutons cut and stitch various combinations of the nappe package of the above mentioned tectonic belts and evolved during and following the alpine collision they all show characteristic map patterns of shallow seated plutons and range from granite to monzogranite the granitic plutons display calc alkaline i type and post collisional geochemical characteristics the egrigoz koyunoba plutons and their subvolcanic volcanic phases simav magmatic complex were studied in detail the geochemical characteristics and field occurences of the simav magmatic complex were compared to the other magmatic associations in western anatolia and it was determined that it is of collisional origin and not related to an extensional tectonic regime as suggested in some recent studies