tidal wave propagation along the mekong deltaic coast a two dimensional barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the south china sea with a particular interest for its characteristics along the mekong deltaic coast the study indicates that tidal waves propagate from the pacific ocean into the south china sea mainly through the luzon strait ls where the k 1 diurnal tide dominates due to a quarter wavelength resonance in this semi enclosed basin and that the incoming tidal waves from the celebes open boundary play a more important role than those from the andaman and flores open boundaries previous studies have not explained why both adjacent seas including the south china sea and the gulf of thailand are dominated by a diurnal tide while a semidiurnal tide dominates along the eastern mekong deltaic coast by means of green s law continental shelf tidal resonance theory and standing wave theory this study clarifies that the large amplified m 2 semidiurnal amplitude leading to a prevailing mixed semidiurnal tide is caused not only by the shoaling effect and the continental shelf oscillation resonance phenomenon but also by the position on the standing wave anti node line moreover the finding of radial tidal currents occurring along the southern mekong estuarine coast has not been revealed in earlier studies based on a number of numerical geometrically schematised experiments we suggest that the interaction between the large amplified amplitude near the shoreline associated with the adjacent low amplitude band system causing convex hydraulic gradients of tidal amplitude due to basin geometry as well as sloping topography is the mechanism for developing these radial tidal current systems the results reveal that wind monsoon climate could cause either damped or amplified tidal amplitudes around the mekong deltaic coast of which approximately 2 3 cm is due to the changing atmospheric pressure the tangential stress of wind over the water surface and wind enhanced bottom friction also this study suggests that the tidal generating forces should be considered to achieve accurate model results depending on the geographical region of interest findings achieved from this study contribute to a deeper insight of tidal wave propagation from a deep ocean to a shallow flat basin similar to the south china sea and its mekong deltaic coast

recent seawater intrusion into deep aquifer determined by the radioactive noble gas isotopes 81kr and 39ar abstract radioactive noble gas isotopes tracers 81kr and 39ar are used for the first time to measure the residence times of deep 1000 m saline coastal groundwater and to determine its connection mode with the sea the average rate of seawater intrusion into the deep aquifer in israel located near the mediterranean sea is estimated 81kr ages of the saline water samples found to be younger than 40 ka contradict previously estimated ages of up to several million years based on hydrogeological considerations the new results imply a stronger and more recent connection between the aquifer and the sea and indicate that the intrusion occurred during the sea level rise that began about 20 ka ago these coastal aquifers need to be managed with caution because lowering of the adjacent fresh water level due to over pumping could accelerate seawater intrusion in a relatively short time this study demonstrates the suitability of these two noble gas tracers for the examination of hydrogeological systems in general and for the study of seawater intrusion in particular

towards a parametrization of river discharges into ocean general circulation models a closure through energy conservation diagnostic methods are defined in order to compare two numerical simulations of ocean dynamics in a region of freshwater influence the first one is a river plume simulation based on a high resolution numerical configuration of the pom coastal ocean model in which mixing parametrizations have been previously defined the second one is a simulation based on the nemo global ocean model used for climate simulations in its half a degree configuration in which a river inflow is represented as precipitation on two coastal grid cells both simulations are forced with the same freshwater inflows and wind stresses the divergence of volumetric fluxes above and below the halocline are compared results show that when an upwelling wind blows the two models display similar behavior although the impact of lack of precision can be observed in the nemo configuration when a downwelling wind blows the nemo global ocean configuration can not reproduce the coastally trapped baroclinic dynamics because its grid resolution is too coarse to find a parametrization to help represent these dynamics in ocean general circulation models a method based on energy conservation is investigated this method shows that it is possible to link the energy fluxes provided by river inflows to the divergence of energy fluxes integrated over the grid cells of ocean general circulation models a parametrization of the dynamics created by freshwater inflows is deduced from this method this enabled creation of a box model that proved to have the same behavior as the fluxes previously computed from the high resolution configuration

water rock interactions and seawater freshwater mixing effects in the coastal dunes aquifer coos bay oregon abstract groundwater from the seawater freshwater interface in sandy sediments was sampled using a unique profile well designed in which separate pvc tube screens were installed at various depths all major ions except chloride showed non conservative behavior in the mixing zone so4 mg2 and k are depleted and hco3 is enriched relative to cl na is enriched in solutions containing less than 20 seawater and depleted in solutions containing higher percentages of seawater the behavior of ca2 is the mirror image ofthat of na the chemical data on the stratification of groundwater above and within the interface zone were obtained using a unique profile well design in which separate pvc tube screens were installed at various depths thus making it possible to extract water samples at close vertical intervals the chemical changes in the groundwater reflect the following processes 1 a ca2 na and ca2 mg2 base exchange reactions 2 b oxidation of organic matter in the sediment 3 c reduction of sulfate probably due to bacterial processes 4 d reaction of hco3 and s2 with fe2 to produce mineral coatings and cements of pyrite and siderite 5 e k feldspar formation producing lower of k concentrations the authigenic phases were identified using scanning electron microscopy thermodynamic calculations suggest that all solutions are saturated with respect to quartz and chalcedony and many are saturated with respect to calcite dolomite siderite and hematite kaolinite is the stable clay mineral in the top of the freshwater column whereas smectite is the stable clay mineral in the lower part of the freshwater column and in the seawater freshwater mixing zone

cation exchange and caco3 dissolution during artificial recharge of effluent to a calcareous sandstone aquifer summary this research describes a field study and laboratory simulations of the geochemical evolution of groundwater following a recharge of effluent into aquifers the study was conducted in the soil aquifer treatment sat system of the shafdan sewage reclamation plant israel the sat system recharges secondary effluent into the calcareous sandstone sediments of the israeli coastal aquifer as a tertiary treatment the reclaimed effluent is recovered ca 500 m off the recharge basin and is used for unlimited irrigation the laboratory simulations in which effluent was pumped through experimental columns packed with pristine shafdan sediment showed that the chemical composition of the outflowing water was controlled mainly by cation exchange and caco 3 dissolution na k and mg 2 were adsorbed and ca 2 was desorbed during the initial stage of recharge the equilibrium distribution of the adsorbed cations was ca 2 60 mg 2 20 and na and k 10 each the ca 2 in the shafdan production wells and in the experimental columns outflow 5 meq l 1 was always higher than the ca 2 in the recharged effluent 3 5 meq l 1 indicating continuous caco 3 dissolution this study demonstrates that besides mixing a suite of geochemical processes should be considered when assessing groundwater quality following artificial recharge of aquifers

a multi isotope b sr o h and c and age dating 3h 3he and 14c study of groundwater from salinas valley california hydrochemistry dynamics and contamination processes 1 the chemical and isotope 11b 10b 87sr 86sr 18o 16o 2h h 13c 12c 14c and 3he 3h compositions of groundwater from the upper aquifer system of the salinas valley in coastal central california were investigated in order to delineate the origin and processes of groundwater contamination in this complex system the salinas valley has a relatively deep confined 400 foot aquifer overlain by a 180 foot aquifer and a shallower perched aquifer all made up of alluvial sand gravel and clay deposits groundwater from the aquifers have different 14c ages fossil 14c 21 3 percent modern carbon pmc for the 400 foot aquifer and modern 14c 72 2 98 2 pmc for the 180 foot aquifer fresh groundwater in all aquifers is recharged naturally and artificially through the salinas river the two modes of recharge can be distinguished chemically we identified several different saline components with distinguishable chemical and isotopic fingerprints 1 saltwater intrusion in the northern basin has c1 concentrations up to 1700 mg l a na cl ratio less than seawater a marine br cl ratio a ca cl ratio greater than seawater 11b between 17 and 38 and 87sr 86sr between 0 7088 and 0 7096 excess dissolved ca relative to the expected concentration for simple dilution of seawater correlates with 87sr 86sr ratios suggesting base exchange reaction with clay materials 2 agriculture return flow is high in no3 and so4 with a 87sr 86sr 0 7082 11b 19 and 13c between 23 and 17 the 3h 3he ages 5 17 years and 14c data suggest vertical infiltration rates of irrigation water of 3 10 m yr 3 nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg l high so4 na cl ratio 1 11b between 24 and 30 and 87sr 86sr 0 70852 this groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the coast range marine deposits of mesozoic to early cenozoic age the combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the so4 enriched no3 depleted saline plume that is located west of the city of salinas we suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination

a numerical solution for the movement of an interface in a layered coastal aquifer abstract this paper deals with seawater intrusion in a coastal aquifer where close to the coast the aquifer is divided into a number of subaquifers by impervious relatively thin layers as a result of changing the total fresh water discharge to the sea seawater intrusion occurs as a separate advancing wedge in each of the subaquifers assuming everywhere flow normal to the coast line and essentially horizontal in both the fresh water and the salt water zones the complete mathematical model is first stated in terms of depth to the interface in each subaquifer a numerical finite difference scheme is then presented for solving the model for the case of a two layered aquifer principles of a method for extending the model to a larger number of subaquifers is described

demarcating saline water intrusion pathways using remote sensing gis and geophysical techniques in structurally controlled coastal aquifers in southern india application of remote sensing and geographical information system gis with the help of ground truth studies like vertical electrical soundings ves and water quality measurements gave a comprehensive picture on saline water intrusion pathways in the structural controlled aquifers of uppanar and cauvery river systems located in sirkazhi and mannanpandal coastal areas of southern india the detailed geomorphic units and lineaments were mapped using irs liss iii 1 50 000 scale and srtm elevation digital data under gis environment the area is mainly alluvial deposits of holocene age and classified into three major geomorphic units i e fluvial fluviomarine and marine geomorphic units the identified lineaments are mostly trending north northeast nne south southwest ssw northeast ne southwest sw northwest nw southeast se east west ew and east northeast ene west southwest wsw directions some of them are potential for fresh groundwater occurrence and movement the lineaments trending ne sw nne ssw and ene wsw act as pathways for saline water intrusion to the inland the lineament l1 nne ssw trending conformed as a sinisterly shifted fault played a significant role in saline water intrusion the area within the parallel lineaments l2 and l3 oriented ene wsw direction indicates low topography beach ridges paleo channel sinuosity large aerial extent of tidal flats and backwater inundation all the above geomorphic units gave indirect evidence of land subsidence which was confirmed with the help of sub surface geo electrical signals obtained through ves and in situ groundwater quality measurements integrating all the above results the saline water spread and fresh water pockets were identified

water rock interactions in a modern coastal mixing zone the chemical evolution of ground water and the diagenetic history of the rocks in a modern saline fresh water mixing zone were investigated to test the hypothesis that this zone is a chemically active environment in which carbonate mineral diagenesis occurs the field site was in the unconfined section of the upper floridan aquifer system in west central florida a regionally extensive hydrostratigraphic unit composed of eocene oligocene limestone and dolomite the mixing zone marked by a steep concentration gradient is 90 m thick at the study site in new port richey pasco county florida interpretation of aqueous geochemical data indicates that the coastal zone is most likely a location where three waters of distinct composition mix a fresh ca hco3 water that derives its composition from calcite dissolution and co2 influx in the up gradient recharge area a na cl water that results from salt water intrusion and a ca so4 rich water that upwells subsequent to contact with underlying gypsiferous beds of the avon park formation are likely all converging in this coastal setting poor core recovery and an enlarged core hole provide evidence of dissolution the ground water however is oversaturated with respect to calcite thus the large scale dissolution features observed are unrelated to modern day mixing the mixing of ca so4 rich ground water in the coastal region led to oversaturation with respect to calcite at the petrographic scale there is little evidence of diagenesis related to the modern mixing zone calcite crystals from the lower section of the cored interval have isotopic signatures that are different than those from the upper section suggesting that the latter has undergone more water rock interactions calcium rich dolomite which occurred relatively late in the paragenetic sequence has thin cathodoluminescent zonations but shows no evidence of subsequent alteration the paragenetic sequence includes marine micritization and cementation meteoric mineralogic stabilization dissolution enhancement of porosity phreatic equant calcite cements and echinoderm overgrowths all typical of the region and not unique to the mixing zone

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete

residence time mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone this study aims at establishing groundwater residence times identifying mineralization processes and determining groundwater origins within a carbonate coastal aquifer with thick unsaturated zone and lying on a granitic depression a multi tracer approach major ions sio2 br ba sr2 18o 2h 13c 3h ne ar combined with a groundwater residence time determination using cfcs and sf6 allows defining the global setting of the study site a typical mineralization conditioned by the sea sprays and the carbonate matrix helped to validate the groundwater weighted residence times from using a binary mixing model terrigenic sf6 excesses have been detected and quantified which permits to identify a groundwater flow from the surrounding fractured granites towards the lower aquifer principally the use of cfcs and sf6 as a first hydrogeological investigation tool is possible and very relevant despite the thick unsaturated zone and the hydraulic connexion with a granitic environment

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

isotopic and geochemical characterization of salinization in the shallow aquifers of a reclaimed subsiding zone the southern venice lagoon coastland summary the coastal plain bordering the southern venice lagoon is a reclaimed lowland characterized by high subsidence rate and ground level and water table depth below sea level in this agricultural region where the surface hydrologic network is entirely artificially controlled by irrigation drainage canals salinization problems have long been encountered in soils and groundwaters here we use isotopic and geochemical tracers to improve our understanding of the origin of salinization and mineralization of the semi confined aquifer 0 40 m and the freshwater inputs to this hydrological system water samples have been collected at different seasons in the coastal adriatic sea lagoon rivers and irrigation canals as well as in the semi confined aquifer at depths between 12 and 35 m 14 boreholes and in the first confined aquifer three boreholes drilled between 40 and 80 m depth stable isotopes 18 o and d and conductivity profiles show that direct saline intrusion from the sea or the lagoon is observed only in a restricted coastal strip while brackish groundwaters are found over the entire topographic and piezometric depression in the centre of the study area fresh groundwaters are found only in the most western zone the sharp isotopic contrast between the western and central regions suggests disconnected hydrological circulations between these two parts of the shallow aquifer the border between these two regions also corresponds to the limits of the most strongly subsiding zone our results can be interpreted in terms of a four end member mixing scheme involving 1 marine water from the lagoon or the open sea 2 alpine and pre alpine regional recharge waters carried either by the main rivers adige bacchiglione and brenta irrigation waters or by the regional groundwater circulation 3 local precipitation and 4 evaporated waters infiltrated from the surface infiltration from the surface is also revealed by the stratification of the electrical conductivity profiles showing that the brackish groundwaters are overlain by a shallow layer of less saline water all over the central depression in the first confined aquifer the groundwaters have isotopic compositions similar to the deep groundwaters of the venetian confined aquifers 40 400 m depth the isotopic data and the br cl ratio show that the origin of the salinization of the phreatic aquifer can be ascribed to seawater intrusion alone with no indication of the involvement of deep brines identified at 450 m depth in the process the chemical composition of the saline and brackish groundwaters is characterized by an excess of sodium and a deficit of calcium compared to conservative mixing between fresh groundwaters and seawater this suggests that the phreatic aquifer is progressively freshening as a consequence of the beneficial influence of the extensive irrigation drainage network including raised canals acting as a hydraulic barrier along the coast this freshening tendency may have been lasting since the reclamation in the mid twentieth century and has probably been accelerated by the ban on groundwater abstraction since the 1970s

forced tidal response in the gulf of mexico 1 this study investigates the characteristics of tides in the gulf of mexico gom and the response to forcing by local tidal potential and tides propagating as waves through straits connecting this semienclosed sea to the caribbean sea and atlantic ocean numerical simulations performed with the navy coastal ocean model run in a barotropic configuration with 1 60 horizontal resolution are used to analyze the tidal response to different forcing mechanisms the tidal energy budget and tidal energy fluxes in the gom are calculated from the simulations results show that diurnal tides in the gom are dominantly due to co oscillation with the western atlantic and that a substantial amount of semidiurnal tidal energy also enters the gulf through the straits model experiments suggest that adding the local tidal potential significantly modifies the propagation of the semidiurnal tidal signal within the gom and reduces the tidal power associated with the diurnal tides in the basin an interesting phenomenon of nonlinear interaction between the two forcing mechanisms local forcing and propagation through the straits is described and explained by using a mechanistic mass spring system model

the influence of fish ponds and salinization on groundwater quality in the multi layer coastal aquifer system in israel abstract this study focuses on the impact of surface reservoirs fish ponds on a multi aquifer coastal system and the relation between the aquifer and the sea the study was conducted in an israeli mediterranean coastal aquifer which includes a sandy phreatic unit and two confined calcareous sandstone units the geological description is based on 52 wells from which 33 samples were collected for stable isotope analysis and 25 samples for organic and inorganic parameters hydraulic head and chemical measurements suggest that there is an hydraulic connection between the fish ponds above the aquifer and the phreatic unit whereas the connection with the confined units is very limited the phreatic unit is characterized by a low concentration of oxygen and high concentrations of ammonium and phosphate while the confined units are characterized by higher oxygen and much lower ammonium and phosphate concentrations organic matter fluorescence was found to be a tool to distinguish the contribution of the pond waters whereby a pond water signature characterized by proteinaceous tryptophan like and typical humic matter fluorescence was found in the phreatic aquifer the phreatic unit is also isotopically enriched similar to pond waters with 18o of 1 and d of 4 6 indicating enhanced evaporation of the pond water before infiltration whereas there is a depleted isotopic composition in the confined units 18o 4 3 d 20 4 which are also om poor the phreeqc model was used for quantitative calculation of the effect of pond losses on the different units the dissolved inorganic nitrogen din in the upper unit increases downstream from the ponds toward the sea probably due to organic matter degradation suggesting contribution of din from shallow groundwater flow to the sea 87sr 86sr and mg ca in the brackish and saline groundwater of the lower confined units increase toward seawater value suggesting that the salinization process in the region is connected to seawater intrusion and not to old brine from the underlying cretaceous aquitard

aquifer vulnerability and seawater intrusion risk using galdit gqiswi and gis case of a coastal aquifer in tunisia due to increase in population and agricultural activities the sfax coastal aquifer is under tremendous stress and seawater intrusion becomes a serious concern this situation needs an assessment of aquifer vulnerability and seawater intrusion risk a new approach for vulnerability mapping using galdit groundwater quality index for seawater intrusion gqiswi geostatistics the ghyben herzberg model and gis was developed the model is used to determine the trend of groundwater contamination by seawater intrusion in the coastal aquifer in sfax basin tunisia vulnerability assessment method is recognized through assessing weight and ratings of the galdit relevant parameter a second vulnerability map was realized based upon the groundwater quality index for seawater intrusion integrating the water quality parameters for delineating seawater intrusion in the aquifer the validation of gqiswi and galdit vulnerability maps was undertaken through comparison of areas of high jones ratio chloride and tds concentration and their relative vulnerability index the ghyben herzberg model has been used to predict the actual seawater intrusion extend and evaluate the freshwater saltwater dynamics the results reveal that the coastal area is currently undergoing seawater intrusion and its northern part is the most affected one by this contamination

modeling the nonlinear effect of wind on rectilinear tidal flow 1 observations of near bed alongshore flow in 4 10 m depth at terschelling netherlands show that strong alongshore winds 15 20 m s in the flood direction reduce the tide current range and alter the tidal flow curve by bringing maximum flood flow forward in time and delaying maximum ebb flow these nonlinear effects which are more pronounced in shallower water are reproduced well by a single point model in the vertical driven by large scale o km sea surface gradients and wind stress using a quadratic bottom stress formulation and a time dependent eddy viscosity derived from a k e turbulence closure model subsequent idealized model simulations using a terschelling based m2 sea surface gradient and wind speeds between 0 and 20 m s show that the wind induced modifications of the tidal flow are consistent with the interaction of the wind induced flow with the tidal flow through the quadratic bed stress the wind driven flow enhances friction during the flood phase more than it reduces friction during the ebb flow thereby increasing friction over a tidal cycle and as a consequence reducing the tide current range the predicted increase in asymmetry of bed friction during flood and ebb flow with increasing wind speed also increases decreases the m4 m6 amplitude consistent with the observations the m4 m2 amplitude ratio is predicted to be largest when the flow has just become unidirectional that is when the wind driven flow equals the tidal current

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

regional hydrogeochemistry of a modern coastal mixing zone in west central florida groundwater samples were collected along flow paths in the unconfined upper floridan aquifer that cross the inland freshwater recharge area and the coastal discharge area a groundwater flow and solute transport model was used to evaluate groundwater flow and mixing of fresh and saline groundwater along a cross section of the unconfined upper floridan aquifer results show that between 8 and 15 of the fresh and 30 31 of the saline groundwater penetrates to the depth in the flow system where contact with and dissolution of gypsum is likely the deeply circulating fresh and saline groundwater returns to the near surface environment discharging caso4 rich water to the coastal area where it mixes with fresh cahco3 groundwater resulting in a prediction of calcite precipitation in the modern mixing zone

trace elements li b mn and ba as sensitive indicators for salinization and freshening events in coastal aquifers abstract the current global intrusion of seawater into coastal aquifers causes salinization of groundwater and thus significant degradation of its quality this study quantified the effect of seawater intrusion and freshening events in coastal aquifers on trace elements li b mn and ba across the fresh saline water interface fsi and their possible use as indicators for these events this was done by combining field data and column experiments simulating these events the experiments enabled quantification of the processes affecting the trace element composition and examination of whether salinization and freshening events are geochemically reversible which has been seldom investigated the dominant process affecting trace element composition during salinization and freshening is ion exchange the results of the experiments show that the concentrations of major cations and li were reversible during salinization and freshening whereas b mn 2 and ba 2 were not during salinization li and b were depleted due to sorption by 10 and 100 mol l 1 respectively to about half of their expected conservative concentrations the relative depletion of li increased with distance from the shore representing the propagation of salinization ba 2 and mn 2 were desorbed from the sediment during salinization and enriched by tenfold in the aqueous phase compared to their concentration in seawater 0 1 eq l 1 during freshening both were depleted by almost tenfold compared to their concentration in fresh groundwater 0 7 eq l 1 the depletion of mn 2 is a sensitive marker for freshening because mn 2 has a strong affinity to the solid phase moreover this study shows that both mn 2 and ba 2 can be used as sensitive hydrogeochemical tools to distinguish between salinization and freshening events in the fsi zone in coastal aquifers

tide induced fluctuations of salinity and groundwater level in unconfined aquifers field measurements and numerical model the responses of the fresh saline water interface fsi and the groundwater level gwl to the mediterranean sea tide were monitored in the coastal aquifer of israel modeled numerically and analyzed using cross correlation analysis different time lags between sea level fluctuations and hydraulic head and salinity fluctuations were detected for the fsi and the gwl at the fsi the time lag of hydraulic head behind the sea level is much shorter than the lag of the salinity at the same point surprisingly similar time lags behind the sea level were measured for both the hydraulic head at the gwl and the salinity at the fsi both at the same distance from the shoreline results from a numerical model simulating the flow and transport processes at the field scale agree with field measurements in both the gwl and the salinity in the fsi fluctuate almost simultaneously while the hydraulic head in the fsi reacts faster to sea level fluctuations the actual movement of the fresh water body which is controlled by the unsaturated flow in the capillary fringe capillary effect lags behind the pressure head fluctuations in the deeper parts of the aquifer which is controlled by saturated parameters of the aquifer the overall results agree with the conceptual mechanism suggested by levanon et al 2016 in which the effect of sea tide on the coastal groundwater system comprises two main processes 1 tidal fluctuations at the sea floor boundary which cause pressure wave propagation into the aquifer and 2 attenuation at the gwl due to the capillary effect which control also the change in the salinity and the actual movement of the fsi

island groundwater resources impacts of abstraction and a drying climate rottnest island western australia abstract coastal aquifers provide a source of water for more than one billion people with island freshwater lenses being some of the most vulnerable coastal groundwater systems due to their susceptibility to saltwater intrusion basic hydrogeological and hydrochemical knowledge regarding the recharge and salinisation processes of freshwater lenses is important to ensure sustainable utilisation especially considering possible climate change effects this paper makes an assessment of the fate of a freshwater lens in a drying climate through a comparison of current and historic hydrochemical data which to the author s knowledge is unique to this study fresh groundwater stable isotope signatures 18 o 2 h reflect local amount weighted rainfall signatures 18 o 3 8 2 h 15 1 and confirm rainfall as the origin of fresh groundwater 18 o 4 47 to 3 82 2 h 20 0 to 16 6 mixing with seawater was identified through enriched groundwater 18 o and 2 h signatures maximum values of 0 36 and 1 4 respectively compared to local rainfall and higher salinity maximum 29 267 mg l total dissolved solids tds in a number of monitoring wells around the freshwater lens enhanced seawater intrusion detected in the northern section of the lens area was identified through significantly increased tds values over the last 20 40 years with increases of up to 3000 observed between 1990 and 2014 a reduction in the extent of freshwater by approximately 1 km 2 was identified since 1977 which was found to be primarily caused by a reduction in recharge to the freshwater lens due to a 20 decline in winter rainfall in the south west western australian region since the mid 1960s groundwater abstraction was found to equate to between 5 and 9 of the estimated recharge for the island and is not a significant factor in the reduction of the lens extent compared to the observed decline in rainfall recharge interestingly seawater intrusion into the fresh water lens was found to occur by older seawater 0 03 0 09 tu in regions of the lens that were previously fresh or slightly brackish while one sample 0 67 tu suggests either modern seawater intrusion or mixing of older saline groundwaters 60 years with rainfall recharge the use of tritium dating in this island aquifer was essential in identifying older seawater that was previously unidentified until now the isotopic and hydrochemical tools used in this paper quantify the effects of groundwater abstraction and climate variability on the freshwater lens and have implications for the sustainable management of the groundwater resource on rottnest island and elsewhere

processes affecting groundwater chemistry in a zone of saline intrusion into an urban sandstone aquifer abstract samples have been collected from inflows into railway tunnels in the triassic sandstone aquifer beneath liverpool and the mersey estuary england u k these provide a profile through a saline freshwater mixing zone analyses were made of major anions and cations 34s and 18o in so4 13c in dissolved inorganic c and 87sr 86sr the data demonstrate that the presence of a low permeability fault exerts a strong control on the local groundwater chemistry on the estuary side of the fault groundwater chemistry is dominated by mixing of intruding estuary water which is modified by so4 reduction and calcite dissolution with fresh groundwater the environment of so4 reduction in the tidal estuary is one of repeated reduction and re oxidation of s in an open system and has resulted in virtually no change in s isotopic composition but an enrichment in residual so4 18o of 1 5 groundwater chemistry on the landward side of the fault is primarily the result of recharge in an urban environment there is also evidence that saline water has been present in this region of the aquifer in the past and that this has now been flushed by fresh groundwaters this saline water was either transported along the landward side of the fault from nearer the estuary or more probably transmitted across the fault both mechanisms would have been driven by large landward head gradients caused by heavy industrial abstraction earlier this century this has produced a zone of groundwaters depleted in ca and radiogenic sr and enriched in na as a result of ion exchange between the fresh groundwaters and the aquifer previously occupied by more saline water sulphur isotopic composition however shows no variation since so4 does not undergo significant ion exchange a tracer test from a borehole to the tunnels showed multiple breakthroughs to some locations indicating a number of different flow paths through the aquifer the maximum flow velocity recorded in this test was 140 m d suggesting flow along fractures

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

suspended sediment dynamics during the inter monsoon season in the subaqueous mekong delta and adjacent shelf southern vietnam land ocean interactions in the coastal zone are severely influenced by tidal processes in regions of high sediment discharge like the mekong river delta in southern vietnam these processes are even more significant three cruises in 2006 2007 and 2008 were carried out to investigate the sediment suspension and their spatial distribution additionally we investigated the influence of the tidal currents in relation to the suspended sediment therefore all cruises took place during the inter monsoon season between march and may where wave and wind influences are not dominant in contrast to the summer monsoon may to early october and winter monsoon season november to early march suspended sediment concentrations sscs in the particle size range between 2 5 and 500 iim were measured with an lisst instrument laser in situ scattering and transmissiometry current velocities and directions were recorded with an acoustic doppler current profiler adcp additionally data of different tidal gauge stations in the mekong river delta were correlated and compared to the mixed semidiurnal diurnal tidal cycle our results show significant areas of sscs greater than 25 mu l l in the mekong river branches and its subaqueous delta during the inter monsoon season 20 of all measured sscs in the subaqueous mekong delta exceed 100 mu l l highest concentrations occur close to the seabed sscs decrease at the transition to the open shelf the shelf region contains only low suspension loads especially on the south eastern shelf 99 of all samples 25 close to the seabed in water depths of 20 25 m two surveys lasting 25 h each were performed on mooring stations in 12 m mooring 1 and 26 m mooring 2 water depth and located 3 2 km apart on the subaqueous delta slope similar patterns of ssc over time show that concentrations of suspension load correlate with the tidal current velocities high tidal current velocities of up to 0 6 m s near the sea bottom generate increasing sscs of more than 25 gl in the water column additionally a significant trend of decreasing ssc from the near seabed to the upper part of the water column can be observed in terms of sediment transport the ebb phase dominates the tidal cycle by its higher tidal current velocities but the flood phase has the longer duration the switch of the tidal current direction from ebb to flood phase occurs rapidly against which the change from flood to ebb phase requires up to 3 h this leads to an asymmetry of the tidal ellipses and may cause a net sediment transport from the shelf into the subaqueous mekong delta in the subaqueous mekong delta and adjacent shelf seven transects show similar patterns of sscs dependent to the tidal phase a hypopycnal sediment plume from the subaqueous mekong delta into the shelf region was not observed our results imply that resuspension by tidal currents dominates the sediment transport in the subaqueous mekong delta and adjacent shelf regions during the inter monsoon season c 2012 elsevier ltd all rights reserved

hydrogeochemistry of grand cayman british west indies implications for carbonate diagenetic studies abstract groundwater in the dolostone aquifers of the bluff group oligocene miocene on grand cayman is divided into fresh lightly and highly brackish and saline type i and ii zones according to chemical characteristics that were determined during a 3 year 1985 1988 monitoring program brackish and type i saline waters display the greatest variation in chemical properties whereas the type ii saline water has the most stable chemical characteristics most groundwaters from these dolostone aquifers are thermodynamically capable of precipitating calcite and or dolomite the saturation indices for these minerals however vary through time and space even in the context of small water lens simple mixing of fresh and sea water cannot explain the chemistry of the water found in the joint and karst controlled dolostone aquifers of grand cayman deviation from a simple mixing model is due to variations caused by tidal fluctuation the rate of rain water recharge influx of ca rich groundwater from the surrounding limestone aquifers influx of co 2 rich surface water from sinkholes and swamps and water rock interactions dissolution and precipitation of calcite and dolomite sustained groundwater abstraction from a lens can significantly alter the hydrochemistry of the water lens this suggests that hydrochemical characterization of small fresh water lenses like those on grand cayman cannot be based on spot or short term sampling interpretation of such fluids in terms of calcite dolomite precipitation and or dissolution must be treated with caution if the data base has not been derived from long term monitoring

hydrogeochemical characteristics in coastal groundwater mixing zone abstract this study presents the hydrogeochemical analysis in coastal groundwater mixing zone of a sandy aquifer ting kok hong kong groundwater samples collected along a sampling transection that covers the salinity transition zone were analyzed for spatial and temporal distribution of major ions cl so 4 2 na k mg 2 and ca 2 and ancillary parameters such as salinity ph temperature and total alkalinity the seawater freshwater interface sfi based on different ions ionic delta of major ions phreeqc based saturation index si of minerals are used to systematically investigate geochemical processes such as cation exchange precipitation dissolution of minerals and sulfate reduction under the effect of seasonal hydrologic variation compared to cl based sfi the landward movements of cation based sfi and seaward movement of so 4 2 based sfi indicate that the coastal aquifer serves as the source of cations and sink of so 4 2 for groundwater the sfi is sensitive to seasonal hydrologic variation due to the variation of land sea hydraulic gradient the cation exchange and precipitation dissolution of minerals are dynamic and complex in coastal groundwater mixing zone the simultaneous enrichment of all cations is found in the aquifer due to external input of a specific cation the sulfate reduction is responsible for so 4 2 depletion and also the enrichment of total alkalinity in coastal groundwater mixing zone because gypsum precipitation does not occur according to mineral si analysis the cation exchange is very sensitive to the seasonal hydrologic variation while the sulfate reduction is not obviously influenced

carbon isotopes in pore water of the unsaturated zone and their relevance for initial 14c activity in groundwater in the coastal aquifer of israel abstract this paper presents a study of the isotopic composition of dissolved inorganic carbon dic stable and radioactive in pore water of the unsaturated zone usz above the coastal aquifer of israel the carbon content and its isotopic composition in the gas and solid phases of the usz are also presented in the soil gas large quantities of co 2 with quite modern 14 c activity were measured along the section 0 15 to 2 7 and 97 to 109 pmc respectively in the inorganic fraction of the sediments the 14 c activity between 2 5 and 13 m was 33 to 1 5 pmc in the organic fraction the 14 c activity between 7 and 9 m was 40 to 33 pmc in the pore water the high values of tritium and 14 c at depths of 15 18 m have been attributed to the thermonuclear contamination of the 1960s a significant decrease with depth in the dic of pore water from 23 to 4 mmol c l along with a decrease with depth in dissolved inorganic 14 c from 100 pmc near the surface to 72 pmc at depth of 20 m were observed the 13 c values in the dic are similar to the values in the inorganic sediment 10 a first order reaction was applied to estimate the yearly rates of dic loss by net precipitation 3 2 year and of 14 c activity dpm l loss from the dic by gross precipitation from the dic on the sediment 4 4 year from the gradient of dissolved inorganic 14 c the initial level at the bottom of the usz which is the groundwater table of the coastal aquifer of israel was estimated to be 0 54 of contemporaneous atmospheric value of 14 c when the rain fell on the ground this value can be used for improved dating of groundwater with 14 c in the coastal aquifer of israel

geochemical investigation of salt water intrusion into a coastal carbonate aquifer mallorca spain geochemical processes occurring within the mixing zone on mallorca spain were investigated in relation to the diagenesis of carbonate minerals and to the development of porosity and permeability within the pleistocene limestone aquifer rock core and ground water samples were obtained from the fresh water zone the mixing zone and the top of the sea water zone at two sites near the coast ground water withdrawals in the vicinity of one study site depressed the water table to below sea level resulting in sea water encroachment and a thin mixing zone laboratory tests conducted on the rock core indicated that porosity and hydraulic conductivity were not enhanced within the transitory location of the present day mixing zone vuggy zones in the core correspond to the approximate location of the water table because the ground water was supersaturated with respect to the carbonate minerals dissolution of the limestone aquifer is no predicted for the present day mixing zone results of mass balance and source rock calculations indicated an excess of calcium and strontium in the mixing zone waters in relation to what was expected from conservative mixing these elevated concentrations are hypothesized to result from limestone dissolution in the vadose zone

anticipating and managing engineering problems in the complex karst environment karst environments are characterized by distinctive landforms and a peculiar hydrologic behavior dominated by subsurface drainage karst systems can be extremely complex heterogeneous and unpredictable due to the wide range of geological and hydrological controlling factors the great variability results in serious problems for engineers and in difficulties to characterize the karstified rock masses and in designing the engineering works to be performed the design and development of engineering projects in karst environments require specific approaches aimed at minimizing the detrimental effects of hazardous processes and environmental problems further karst aquifers that provide approximately 20 25 of the world s drinking water are extremely vulnerable to pollution due to the direct connection between the surface and the subsurface drainage the rapidity of the water flow in conduit networks and the very low depuration capability sinkholes are the main source of engineering problems in karst environments and may cause severe damage in any human structure the strategies and solutions that may be applied to mitigate sinkhole problems are highly variable and largely depend on the kind of engineering structure the karst setting and the typology and size of the sinkholes a sound geological model properly considering the peculiarities of karst and its interactions with the human environment is essential for the design of cost effective and successful risk reduction programs due to the unique direct interaction between surface and subsurface environments and the frequent ground instability problems related to underground karstification management of karst environments is a very delicate matter disregarding such circumstances in land use planning and development inevitably results in severe problems with high economic impacts karst environments require specific investigation methods in order to properly manage and safeguard the sensitive geo ecosystems and natural resources associated with them

the effect of salinization and freshening events in coastal aquifers on nutrient characteristics as deduced from field data summary the effect of seawater intrusion and freshening events in coastal aquifers on nutrient dissolved inorganic nitrogen species phosphate and silica dynamics across the fresh saline groundwater interface fsi were quantified using field data seasonal vertical profiles revealed a clear transition between nutrient species across the fsi which is also an oxycline in view of the results of our experimental simulations it is clear that the major process controlling the nutrient dynamics at the fsi besides the mixing that takes place between the two different water bodies is the seasonal variation between seawater intrusion salinization in summer and flushing of the aquifer freshening in winter aquifer salinization during the summer shifts the fsi and the anaerobic depth location upwards and leads to the enrichment of nh4 po43 and dsi dissolved silica in the saline groundwater nh4 and po43 are enriched due to ion exchange and dsi is enriched either by ion exchange as po43 or as a result of dissolution of biogenic silica denitrification occurs at the base of the fsi as indicated by the slight no3 depletion and the enrichment in 15n of no3 aquifer freshening during the winter shifts the fsi downward and the water becomes suboxic with the influence of the oxic fresh groundwater this leads to nitrification of the nh4 enrichment of no2 and depletion of 15n in the residual no3 in the fsi these cyclic processes generate a certain depletion of n and enrichment of p in the saline groundwater circulation of the saline groundwater below the fsi back to the sea can serve as a partial counterbalance to the high anthropogenic load of n impacting the coastal groundwater system

geochemical and isotopic evidence for palaeo seawater intrusion into the south coast aquifer of laizhou bay china this research aims to improve the current knowledge of groundwater salinisation processes in coastal aquifers using combined hydrochemical and isotopic parameters and inverse hydrochemical modelling field investigations were conducted in laizhou bay which is the area most seriously affected by seawater intrusion in north china during three sampling campaigns along a vertical transect in the changyiliutuan area 95 ground and surface water samples were collected for major ion and isotope analysis

multivariate statistical analysis and hydrogeochemical modelling of seawater freshwater mixing along selected flow paths case of korba coastal aquifer tunisia abstract groundwater sampling and piezometric measurements were carried out along two flow paths corresponding to two transects in korba coastal plain northeast of tunisia the study aims to identify hydrochemical processes occurring when seawater and freshwater mix those processes can be used as indicators of seawater intrusion progression and freshwater flushing into seawater accompanying submarine groundwater discharge sgd seawater fractions in the groundwater were calculated using the chloride concentration hierarchical cluster analysis hca was applied to isolate wells potentially affected by seawater in addition phreeqc was used to simulate the theoretical mixing between two end members seawater and a fresh brackish groundwater sample geochemical conventional diagrams showed that the groundwater chemistry is explained by a mixing process between two end members results also revealed the presence of other geochemical processes correlated to the hydrodynamic flow paths direct cation exchange was linked to seawater intrusion and reverse cation exchange was associated to the freshwater flushing into seawater the presence of these processes indicated that seawater intrusion was in progress an excess of ca that could not be explained by only cation exchange processes was observed in both transects dedolomitization combined to gypsum leaching is the possible explanation of the groundwater ca enrichment finally redox processes were also found to contribute to the groundwater composition along flow paths

impact of water diversion on the hydrogeochemical characterization of surface water and groundwater in the yellow river delta the yellow river delta is undergoing severe ecosystem degradation through salinization caused mainly by seawater intrusion the yellow river diversion project in operation since 2008 aims to mitigate a projected ecosystem disaster we conducted field investigations across three ecosystems farmland wetland and coast in the delta to assess the effectiveness of the annual water pulse and determine the relationships between surface water and groundwater the chemical characteristics of the groundwater in farmland exclude the possibility of seawater intrusion the wetland is vulnerable to pollution by groundwater discharge from farmland and to secondary salinization caused by rising water tables the salinity values of groundwater at coast sites likely reflect the presence of seawater trapped in the clay sediments a premise corroborated through measurements of groundwater levels stable isotopes and major ion signatures our delta d delta o 18 two dimensional graphic plot demonstrated that groundwaters of farmland and wetland changed toward more depleted isotopic compositions following water diversion but this was not the case in the coast sites where the water table varied little year round a hydrochemical facies evolution diagram hfe d demonstrated that freshening is taking place in the largest portions of the aquifers and that without sustained water diversion recharge these underground water bodies may switch from freshening to salinization on a seasonal time scale thus the qualities of waters in coastal aquifers in the yellow river delta are substantially influenced by the process of ecological water diversion and also by land use practices and by the lithological properties of the drainage landscape c 2014 elsevier ltd all rights reserved

saltwater intrusion as potential driver of phosphorus release from limestone bedrock in a coastal aquifer abstract an important but often overlooked consequence of saltwater intrusion is the potential increase of groundwater soluble reactive phosphorus concentrations the phosphorus sorption dynamics of two limestone rocks of different composition were investigated by simulating seawater intrusion over a wide range of mixing ratios between freshwater and saltwater both rocks exhibited a logarithmic loss of sorption efficiency in mixtures containing more than approximately 3 mm cl concentration 100 mg cl l about

hydrodynamic analysis of a mediterranean aquifer system with the use of hydrochemical and isotopical analysis as supporting tools the management of groundwater resources in coastal environments within the mediterranean basin has become of paramount importance especially in the light of global changes a typical example of such a hydrosystem is the lavrio basin in greece this research site involves two aquifer types granular and karstic formations that are hydraulically interconnected furthermore the proximity to the sea and the abstractions for irrigation and drinking water supply have led to the phenomenon of seawater intrusion the present study aims at analyzing the hydraulic hydrological and hydrogeological conditions of the area by means of hydrochemical and isotopical data interpretation as supporting tools which will inform and support the development of an integrated conceptual hydrogeological model of the area field investigations were conducted in order to collect piezometric and chemical data and use them to retrieve the quantitative and qualitative status of the local aquifer units new interpretation of an older dataset gave an insight into how the karstic aquifer behaves in terms of hydraulics the results have also demonstrated that there is a hydraulic connection between the different aquifers and the mediterranean sea while natural recharge was quantified for both aquifer types

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

factors controlling mechanisms of groundwater salinization and hydrogeochemical processes in the quaternary aquifer of the eastern nile delta egypt in this study combining interpretations of conservative dissolved ions and environmental isotopes in water were used to investigate the main factors and mechanisms controlling groundwater salinization and hydrogeochemical processes in the eastern nile delta egypt hydrogeochemical and isotopic study has been carried out for 61 water samples from the study area total dissolved solid tds contents of groundwater are highly variable rising along flowpath from the south 410 mg l to the north 14 784 mg l implying significant deterioration and salinization of groundwater based on tds and ionic ratios groundwater samples were classified into three groups in low saline groups water chemistry is greatly influenced by cation exchange mineral dissolution precipitation anthropogenic pollutants and mixing with surface water whilst in high saline groups water chemistry is affected by salt water intrusion reverse cation exchange and evaporation the chemical constituents originating from saline water sources reverse ion exchange and mineral dissolution are successfully differentiated using ionic delta and saturation index approaches the 18o 2h relationship plots on a typical evaporation line suggesting potential evaporation of the recharging water prior to infiltration isotope evidence concludes that the groundwater have been considerably formed by mixing between depleted meteoric water recharged under different climatic conditions and recently infiltrating enriched surface water and excess of irrigation water the 18o data in conjunction with chloride concentrations provide firm evidence for impact of dissolution of marine origin evaporite deposits during past geologic periods on groundwater salinity in the northern region moreover the relation between 14c activities and cl concentration confirms this hypothesis

tidal dynamics in the south china sea summary the tidal dynamics of the south china sea are examined by the use of a two dimensional non linear hydrodynamic finite difference model which has been run separately for the m2 and k1 tidal constituents the models are tuned through the open boundary conditions to fit the observed coastal tides cotidal charts for the two constituents are presented and compared with earlier charts based on coastal observations alone the flow of tidal energy is studied and it is concluded that the strength of the diurnal tide in the sea is due largely to the resonant diurnal response of the gulfs of tonkin and thailand an energy budget reveals that for both constituents direct tidal forcing within the sea is significant and that tidal energy which enters through the open boundary is in fact lost back to the earth moon orbital system by this means

comment on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 recently schopf and kudryavtsev 2012 have published an exhaustive review on the biogenicity of the most controversial evidence of ancient life on earth to date an assemblage of carbonaceous filaments found in the 3465 ma apex chert of northwestern australia schopf and packer 1987 schopf 1993 the morphology of the filaments their carbon isotopic composition and the sedimentary environment interpreted as shallow marine suggested to schopf 1993 that these filaments were fossilized cyanobacteria this discovery sparkled a large controversy among the scientific community that lasted for more than 25 years see pinti and altermann 2011 for a review on the subject in the synopsis of the controversy page 762 schopf andkudryavtsev 2012 wrote the apex fossils have subsequently been suggested to be inorganic silica or clay mineral needle like crystals pinti et al 2009 again at page 769 the authors reported that needles composed of halloysite al2si2o5 oh 4 a clay mineral and of quartz sio2 have been compared with the apex fossils pinti et al 2009 these are two serious misstatements because we never compared any of the pseudofossils that we observed in apex chert to the microfossils of schopf 1993 schopf and kudryavtsev 2012 themselves report at

on the modification of tides in shallow water regions by wind effects 1 the influence of non linear effects upon tides in shallow coastal regions due to the presence of a significant storm surge is examined using a two dimensional model of the west coast of britain the model has an unstructured grid designed to have a high resolution mesh in the near coastal region of the eastern irish sea the area chosen as the focus of this study the influence of tide surge interaction upon the m2 m4 and m6 components of the tide due to surges produced by steady uniform wind stresses is examined in detail calculations show that in deep regions the tide is unaffected by the surge however in shallow coastal regions there is significant modification of tidal elevations and currents this arises because of changes in bottom stress and the non linear interaction term in the hydrodynamic equations in addition the locations of regions that wet and dry are changed during the tidal cycle due to the influence of the surge this gives rise to significant spatial variations and changes in magnitude of the tide and its higher harmonics depending upon wind stress direction and water depth these results explain why tidal energy remains in the surge residual in shallow water when it is computed by de tiding the total signal using a tide only calculation an effect often found in observed surge residuals

tidal characteristics in bass strait south east australia abstract we used a two dimensional barotropic numerical model to examine the complex behaviour of the tides in bass strait bass strait located in south east australia between the australian continent and tasmania has the appropriate dimensions to create a half wave tidal resonance for the m 2 tides the m 2 tidal wave amplitude m 2 tidal amplitude towards the central northern tasmanian coast to a maximum of 1 1 m the tidal phases and current ellipses in the strait showed the m 2 tides resembled a half wavelength resonance in a curved open basin the semidiurnal s 2 and diurnal k 1 and o 1 tidal amplitudes were comparatively small m 2 amplitudes by 10 15 in the strait s central region when obt and direct gravitational tidal dgt forcing were included the model accurately reproduced the observed tidal amplitudes dgt forcing was used to generate resonantly amplified m 2 tides amplitudes of 0 1 0 3 m locally with destructive interference between the obt forced and dgt forced tides occurring in the centre of the strait the model simulations also revealed that storm systems propagating west to east attenuated the m 2 tidal amplitudes in the strait the greatest decrease in the tidal amplitudes occurred along the central northern tasmanian coast and was attributed to tide surge interaction and resonance behaviour in the strait

response of the mediterranean and dead sea coastal aquifers to sea level variations 1 the present study examines the response of groundwater systems to expected changes in the mediterranean sea rise of 1cm yr and dead sea levels decline of 1 m yr a fast response is observed in the dead sea coastal aquifer exhibited both in the drop of the water levels and in the location of the fresh saline water interface no such effect is yet observed in the mediterranean coastal aquifer as expected numerical simulations using the feflow software show that the effect of global sea level rise depends on the coastal topography next to the shoreline a slope of 2 5 is expected to yield a shift of the interface by 400 m after a rise of 1m 100 years whereas a vertical slope will yield no shift reduced recharge due to climate change or overexploitation of groundwater also enhances the inland shift of the interface

the effect of salinization and freshening events in coastal aquifers on nutrient characteristics as deduced from column experiments under aerobic and anaerobic conditions summary this study experimentally quantified the effect of seawater intrusion salinization and freshening events in coastal aquifers on nutrient n p and dsi dynamics across the fresh saline groundwater interface laboratory column experiments were conducted under aerobic and anaerobic conditions in order to simulate the processes occurring in the fresh saline interface they were performed with aquifer sediments simulating the natural conditions during alterations of natural fresh groundwater to seawater and vice versa the salinization and freshening experiments showed that nh4 and po43 and dsi were affected mainly by ion exchange processes while microbial activity controlled the nitrogen species no3 and no2 due to the cation exchange salinization generated enrichment above the expected conservative behavior of nh4 up to 80 mol l 1 an order of magnitude higher than in seawater or fresh groundwater under anaerobic conditions no3 was removed by denitrification as demonstrated by the decrease in no3 concentrations the increase in no2 concentrations and the increase in 15n by 15 25 clear evidence was shown for anion exchange of po43 which competes with hco3 and boron on adsorption sites dsi seems to take part in the exchange process similar to po43

geochemical and palaeohydrological controls on the composition of shallow groundwater in the netherlands with the exception of the south of the country the netherlands has a strong bipartite hydrogeology the holocene part with a coastal dune belt and confining top layer of clay and peat further inland and the pleistocene where thick phreatic aquifers dominate this research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions close to 6000 groundwater analyses were grouped and interpreted in terms of 1 salinity 2 redox status 3 acid base and carbonate status and 4 natural nutrients nh4 and po4 the a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians even for geologically or geographically related data groups the compound specific interpretation indicates that there are geogenically controlled systematic differences in groundwater composition at the regional scale the imprint of the geological sediments on the groundwater composition decreases in the order marine estuarine via limnological fluvial to aeolian the imprints with respect to ph and carbonate status natural nutrients and redox status are not necessarily interrelated the vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive holocene confining top layer or temporal changes in contamination in the holocene part the salinity is controlled by the palaeoenvironmental conditions during the holocene and by the recharge origin the average cl concentration decreases from estuarine via lagoonal to the former zuider sea which was a bay the most reduced states and also the highest nutrient concentrations and highest co2 pressure are related to the presence of holocene marine sediments in the confining top layer degradation of marine derived organic matter as a nutrient source is likely more intense in the holocene deposits than that of peat and sedimentary remnants of terrestrial plants a broad range in ph carbonate status and redox status is encountered in the pleistocene part here the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in ph calcite saturation and silicate weathering one region with late pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the holocene part of the netherlands furthermore reactive fe is not abundant in all pleistocene fluvial sediments nor is it maximally mobilised as not all anoxic groundwater in these sediments is siderite saturated this leads to considerable intra and inter region variability 2013 elsevier ltd

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

late holocene depositional environments and coastal evolution of the mekong river delta southern vietnam abstract the mekong river delta in southern vietnam is a tide dominated delta and has been formed by the mekong river system the sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre existing deposits in the south china sea and gulf of thailand around 6000 to 5000 yr bp maximum holocene transgression occurred and seawaves surrounded uplands of the late pleistocene terrace basement rock and weathered land in the northern parts of the delta double notches were undercut by seawaves on the limestone hill in hatien at about 4 5 and 2 5 m above present sea level marine deposits prevailed throughout the delta during the highstand and regressions of relative sea level over the last 4550 yr bp delta progradation has produced a great flat plain of 62 520 km 2 this extremely fast progradation could be due to a very high sediment supply depositing in the slight inclination of the receiving basin b neotectonic movements and relative sea level changes c widespread mangrove forests playing an important role to enhance sediment accumulation former mangrove marshy deposits were significantly developed in the plain of reeds and longxuyen quadrangle mangrove marshes have also been developing well in the camau peninsula and present coastlines moreover regressions over the last 4550 yr bp have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta

14c excess in deep sea sediments porewater driven by diffusionߞsoutheast mediterranean core profiles in the deep se mediterranean sea revealed a significant 14 c excess in the total dissolved inorganic carbon dic of porewater as compared to the 14 c of the sediments below the bioturbation zone down to core bottom 2 m the main observation was that the age difference between porewater and sediments as calculated from the excess was not constant but rather increasing with depth the porewater apparent age was younger by 10 than the age of the sediment at the core top and gradually became younger by about 70 at the bottom of the core flux calculations and mass balances of the chemical and isotopic data suggest that this 14 c excess stems from a downward diffusive flux of 95 15 atoms of 14 c dic m 2 s 1 from the bioturbation zone and overlying bottom water into the sediment the 14 c dic flux is opposite in direction to the dic flux out of the sediment it is suggested here that the 14 c dic flux may severely interfere with age determination of small submarine brine lakes formed in the deep mediterranean in addition the 14 c excess should show up in authigenic carbonate phases precipitating within the sediment and hence may serve as a tool to identify the extent and duration of authigenic carbonate precipitation

holocene delta evolution and sediment discharge of the mekong river southern vietnam abstract evolutionary changes delta progradation and sediment discharge of the mekong river delta southern vietnam during the late holocene are presented based on detailed analyses of samples from six boreholes on the lower delta plain sedimentological and chronostratigraphic analyses indicate clearly that the last 3 kyr were characterized by delta progradation under increasing wave influence southeastward sediment dispersal decreasing progradation rates beach ridge formation and steepening of the face of the delta front estimated sediment discharge of the mekong river for the last 3 kyr based on sediment volume analysis was 144 36 million t yr 1 on average or almost the same as the present level the constant rate of delta front migration and stable sediment discharge during the last 3 kyr indicate that a dramatic increase in sediment discharge owing to human activities as has been suggested for the yellow river watershed did not occur although southeast asian rivers have been considered candidates for such dramatic increases in discharge during the last 2 kyr the mekong river example although it is a typical large river of this region does not support this hypothesis therefore estimates of the millennial scale global pristine sediment flux to the oceans must be revised

study of shallow groundwater quality evolution under saline intrusion with environmental isotopes and geochemistry evolution of the shallow groundwater quality under saline intrusion in porous aquifer system has been studied with environmental isotopes and geochemistry in the laizhou bay area china two campaigns of water sampling from various sources were carried out in spring and winter for environmental isotopic and chemical analyses the origin of groundwater salinity from intrusion of both modern seawater and deep brine water was identified by analysing the correlations between 18o d t cl so 4 2 and electrical conductivity the results indicate that the brine is originated from evaporating and concentrating of intruded seawater and its d and 18o are different from modern seawater but similar to those of mixture of seawater with fresh groundwater it is hard to distinguish the salinity origin in this area by the d 18o relationship alone the relations between 18o and conductivity cl and so 4 2 have been used to identify the salinity origin due to the distinct difference in salinity between the brine and seawater conjunctively with use of t a threshold of t 12 tu was adopted to identify the origin of saline groundwater