geochemical evolution of groundwater beneath mexico city abstract the geochemical evolution of groundwaters along a 24 km flow beneath central mexico city path from the sierra de las cruces towards lake texcoco has been investigated using stable isotopes radiocarbon and major and trace elements to determine the natural baseline conditions the extent of any contamination and the effectiveness of the overlying aquitard seal modern groundwaters of low salinity 1 are found up to 11 km from the outcrop area and groundwater ages of up to 6000 yr bp occur in the middle part of the section groundwater stable isotope ratios 18 o and 2 h lie close to the global meteoric water line indicating that the groundwater originates from local rainfall the groundwater chemistry may be interpreted as the result of inputs from the source area with progressive water rock interaction down the horizontal flow gradient a redox boundary is found at 9 km along the line of section coincident with the start of the confined section relatively low nitrate concentrations below 9 mg l 1 no 3 n are found in the aerobic waters low concentrations of no 3 in the aerobic waters and low cl reflect inputs prior to the modern development some elements cr u as se sb increase their concentration with distance time as far as the redox boundary but low concentrations occur in the reducing aquifer section the chemistry of several major ions mg na cl k as well as trace elements such as li rb ba reflect the weathering of the basaltic mineral assemblage feldspars and mafic minerals and their increases are generally proportional to residence time phosphate f and i concentrations indicate a probable source from apatite in the basaltic or rhyolitic rocks a borehole in the east of the city some 17 km downgradient intercepted thermal water si geothermometry indicates 163 c at depth this water gives a distinctive composition indicating possible addition of metamorphic co 2 which has then reacted with the igneous rocks increases in b and cl are derived from volatiles trapped in the glass or vesicular basalt a thermal anomaly found in the middle section of the heavily pumped aquifer is interpreted as the up coming of warmer water from medium to greater depth mainly from basalts rhyolites and possibly limestones the geochemistry indicates that groundwater beneath mexico city is of good quality and there is no obvious evidence of leakage of inorganic compounds from surface sources of contamination through the aquitard the younger groundwater drawn from the western outcrop area is generally of good inorganic quality increased drawdowns in the confined aquifer have induced flow of warmer water with higher cl from depth the resources in the aquifer represent an important reserve of good quality water which need to be properly managed as a high quality resource as part of integrated plans for the city s future supplies

hydrochemical characteristics and salinity of groundwater in the ejina basin northwestern china a hydrochemical investigation was conducted in the ejina basin to identify the hydrochemical characteristics and the salinity of groundwater the results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area the ionic ration plot and saturation index si calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area most of the stable isotope 18o and d compositions in the groundwater is a meteoric water feature indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation based on radioactive isotope tritium 3h analysis the groundwater ages were approximately estimated in different aquifers the groundwater age ranges from less than 5 years between 5 years and 50 years and more than 50 years within 1 km of the river water influence zone the groundwater recharges from recent heihe river water and the groundwater age is about less than 5 years in shallow aquifer from 1 km to 10 km of the river water influence zone the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer the groundwater age is more than 50 years in deep confined aquifer

high frequency internal wave observations in the marginal ice zone three thermistor chains extending from 15 to 65 m were deployed from ice floes in the marginal ice zone north of svalbard in a triangle with sides of 500 800 m for a period of 7 days vertical displacement spectra indicate that the internal wave energy level is lower than the garrett and munk spectrum by a factor of 2 3 but higher than other observations in the arctic a group of internal waves a wave train with frequency of 2 3 cph was observed to propagate at 0 05 m s through the triangle in a west southwesterly direction during a 4 to 6 hour period a case study of this wave train where the horizontal phase differences between the three thermistor chains were analyzed showed wavelengths of 100 200 m and phase velocities of 0 10 0 15 m s observation of the density field and the velocity field indicated that stratification dominated over vertical shear consequently the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean the estimated wavelengths and phase velocities agree with the dispersion relation for first mode internal waves the generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle or ice keels moving in relation to the water creating lee waves in the pycnocline

transport of soluble salts in a large semiarid basin river murray australia median annual concentrations of cl so4 hco3 na k mg and ca increase greatly downstream in the river murray along its 2500 km route to the sea chloride increases from less than 2 mg l 1 near the headwaters to about 170 mg l 1 near the downstream end of the main channel water near the head of the river has hco3 balanced by similar equivalents of na ca and mg while higher salinity water in the downstream half of the river is dominated by na and cl sources of these dissolved ions include a sea derived airborne salts contributing essentially all of the cl br and 80 of the na and b rock derived ions from weathering of sedimentary rock and soil minerals contributing most of the observed hco3 80 of the ca and 20 25 of the mg and so4 much of the change in chemistry along the axis of the murray is due to influx of saline groundwater which has a major ion composition similar to sea water inflows of irrigation drainage water also enhance downstream transport of salts especially hco3 the stable isotope composition of the river murray 2h and 18o begins with relatively depleted heavy isotope abundances 47 8 in the uplands of the southeastern margin of the murray darling basin increasing steadily by 30 and 6 respectively due to evaporative enrichment from river surfaces and influx of drainage returned from irrigation diversions despite the similarity of groundwater major ion chemistry to that of sea water stable isotope compositions of groundwaters clearly demonstrate that water molecules from past marine incursions have been completely flushed from the system similarly the cl br ratios of groundwaters are not appreciably different from seawater values indicating that dissolution of fossil evaporites does not contribute significant salt to the groundwaters or the river

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

hydrogeochemical controls and usability of groundwater in the semi arid mayo tsanaga river basin far north province cameroon deuterium 18o major ions and dissolved silica in groundwater from semi arid mayo tsanaga river basin in the far north province cameroon were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water electrical conductivity ranges from 57 2 581 s cm with alternating low and high values along the hydraulic gradient waters from piedmont alluvium show low concentrations in major cations which peak in mg within basalt na within plain alluvium and ca within basalt and the sandy limani yagoua ridge the initial dominant groundwater composition is cahco3 which did not evolve within the basalt and piedmont alluvium but evolved to nahco3 in the granite and plain alluvium the main processes controlling the major ions composition include the following 1 dissolution of silicates and fluorite 2 precipitation of fluorite and carbonate 3 cation exchange of ca in water for na in clay 4 and anthropogenic activities the d and 18o ratios vary from 35 to 0 7 and 5 3 to 1 1 respectively the lowest and highest isotope ratios are observed in groundwater within the downstream sandy limani yagoua ridge and the upstream graintes respectively variation in isotope ratios depends on altitude effect of 0 48 per 100 m between 600 and 850 m asl and on evaporation which had insignificant effect on the water salinity seventy percent of the groundwater shows poor drinking quality and 90 is suitable for irrigation

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

sensitivity of post hurricane beach and dune recovery to event frequency the recovery of santa rosa island in northwest florida is characterized following hurricane katrina september 2005 which was preceded by hurricanes ivan 2004 and dennis 2005 beach and dune recovery were quantified to the east and west of pensacola beach through a comparison of lidar data collected immediately following hurricane katrina and in july 2006 after almost a year of recovery east of pensacola beach the santa rosa unit the shoreline retreated by an average of 64 m during the 2004 2005 hurricane season and recovered by an average of 19 m to the west of pensacola beach the fort pickens unit the shoreline retreated by an average of 30 m and while no significant shoreface recovery was observed the presence of vegetation on low profile dunes promoted backshore accretion it is found that beachface recovery in the santa rosa unit and backshore accretion in the fort pickens unit occurred at the widest sections of the island where the pre storm profile volume had been relatively large and overwash penetration was at a minimum the narrow sections of the island between cuspate headlands had a smaller profile volume before the storms leading to greater overwash penetration and in some cases island breaching in both sections which limited the volume of sediment available for shoreface recovery the alongshore variation in recovery is not only related to the island width but also the offshore bathymetry height of the pre storm dunes and the overwash penetration if sufficient time is allowed for the return of vegetation and the recovery of the dunes the variations in storm impact observed during hurricane ivan will be reinforced during subsequent storms in this respect the level of impact during subsequent storms and the ability of the island to recover will depend on the frequency of storm events copyright 2009 john wiley sons ltd

post storm beach and dune recovery implications for barrier island resilience abstract the ability of beaches and dunes to recover following an extreme storm is a primary control of barrier island response to sea level rise and changes in the frequency and or magnitude of storm surges whereas erosion of the beach and dune occurs over hours and days it can be years to decades before the beach and dune are able to recover to their pre storm state as a consequence there are numerous descriptions of near instantaneous beach and dune erosion due to storms the immediate onshore transport of sand and the initial phases of beach and dune recovery following a storm but a paucity of data on long term beach and dune recovery a combination of previously published data from galveston island texas and new remotely sensed data from santa rosa island florida is used in the present study to quantify the rate of dune recovery for dissipative and intermediate beach types respectively recovery of the dune height and volume on galveston island was observed within two years following hurricane alicia 1983 and was largely complete within six years of the storm despite extensive washover in contrast the dunes on santa rosa island in northwest florida began to recover four years after hurricane ivan 2004 and only after the profile approached its pre storm level and the rate of vegetation recovery regrowth was at a maximum results show that complete recovery of the largest dunes in height and volume will take approximately 10 years on santa rosa island which suggests that these sections of the island are particularly vulnerable to significant change in island morphology if there is also a change in the frequency and magnitude of storm events in contrast the areas of the island with the smallest dunes before hurricane ivan exhibited a rapid recovery but no further growth in profile volume and dune height beyond the pre storm volume and height despite continued recovery of the largest dunes to their pre storm height a change in storm magnitude and or frequency is a potential threat to barrier island resilience particularly for those sections of the island where dune recovery has historically taken the longest time further study is required to determine how and why dune recovery varies for the dissipative and intermediate beaches of galveston island and santa rosa island respectively

assessment of shallow groundwater in lake nyos catchment cameroon central africa implications for hydrogeochemical controls and uses in 1986 carbon dioxide gas exploded from lake nyos and killed about 1 800 people after that disaster various administrative and research activities have been conducted to mitigate subsequent disasters however none of those endeavors have characterized the groundwater chemistry to identify hydrogeochemical processes that control the water chemistry and the quality of the water for domestic and agricultural uses that support the lives of un official resettlers around lake nyos conventional hydrochemical techniques coupled with statistical and graphical analysis were therefore employed to establish the baseline hydrochemical conditions assess processes controlling solutes distribution in shallow groundwater in the lake nyos catchment and explore its usability groundwater samples were analyzed for their physical and chemical properties the wide ranges of electrical conductivity and total dissolved solid values reveal the heterogeneous distribution of groundwater within the watershed the relative abundance of major dissolved species was ca mg na k for cations and hco3 cl so4 no3 for anions piper diagram classified almost all water samples into mixed camg hco3 water type major ion geochemistry reveals that in addition to silicates weathering water rock interaction ion exchange processes regulate the groundwater chemistry principal component analysis supports the occurrence of water rock interaction hierarchical cluster analysis showed that the chemistry of groundwater in the study area is controlled by three main factors and suggests no hydraulic connectivity between deep lake water and groundwater in the catchment the quality assessment of the groundwater showed that groundwater parameters are within the acceptable limit of the world health organization and nigeria guidelines for drinking and domestic uses and water found to be good for irrigation

stable isotopic and geochemical characteristics of groundwater in kherlen river basin a semi arid region in eastern mongolia summary inorganic solute ion concentrations and stable isotopes of oxygen and hydrogen in groundwater river water and precipitation were investigated to gain insight into the groundwater recharge process in the kherlen river basin a semi arid region in eastern mongolia the solute constituents in the river water main stream were of ca hco3 type spatially invariant and low in concentration groundwater in the upstream region was also characterized by a ca hco3 type though all ion concentrations were higher than in the river water on the other hand the chemical composition of the groundwater in the midstream region southern and eastern was spatially variable and the na mg2 cl and hco 3 concentrations were considerably higher than in the river water and upstream groundwater the stable isotopic compositions showed an evaporation effect on the groundwater and river water as well as an altitude effect in the precipitation and river water preferential recharge by relatively large rainfall events is thought to have caused the depleted isotopic ratio in the groundwater in the dry regions the stable isotope chemical and hydrological data suggest that the main stream water of the kherlen river is recharged by precipitation that falls in a headwater region at an altitude of more than 1650 m and that the interaction between the groundwater and river water is not dominant in the midstream and downstream regions of the river basin

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

stratification and sedimentation in complex vegetated coastal dunes sable island nova scotia abstract a descriptive code for analysing the internal structure of vegetated coastal dunes is presented the code is based upon three elements grain size stratification and the nature of plant remains it is used in an analysis of the dunes on sable island nova scotia a description of the stratification within the older dunes of the island provides the basis for a genetic interpretation of the processes operating throughout their history particular importance is attached to the role of vegetation in deposition four phases of dune development each with distinct styles of stratification are recognized in the sable island dunes the first consists of tractional and grainfall deposition within very sparse vegetation the second phase is dominated by grainfall deposition through increasingly dense vegetation the third phase is represented by a paleosol finally the fourth phase consists of horizontal parallel and wavy laminated beds of loosely compacted finer sand which result from grainfall deposition through dense vegetation

impact of storm tides and inundation frequency on water table salinity and vegetation on a juvenile barrier island abstract freshwater lenses are generally of major interest for drinking water supply in coastal environments knowledge of the interrelations between ground surface elevation sea level inundation frequency groundwater salinity and vegetation is also vital to understand coastal ecosystem functioning this study provides an integrated analysis of these parameters at a barrier island in the north sea that is currently developing under highly dynamic processes but remains largely unaffected by humans this study is particularly relevant in view of predicted sea level rise and increasing storm frequencies as the analysis of groundwater salinities at the water table water level data and ground surface elevation reveal the pronounced influence of storm tides and inundation frequency on the water table salinity at the eastern part of the barrier island spiekeroog the so called ostplate located off the northwest coast of germany the shallow freshwater is restricted to the elevated dune areas and shows spatial and temporal variations depending on the time passed since the last storm tide the water table salinities depend on inundation frequencies whereby more than three flooding events in the year prior to sampling led to brackish water table salinities inundation frequency and water table salinity are both largely a function of ground surface elevation and the dependence of water table salinity on the ground surface elevation can be quantified with an exponential function combining this function with digital elevation models enables the extrapolation and reconstruction of present and past water table salinity distributions within the study area which overall show decreasing salinities with increasing ground surface elevation since the vegetation zonation also depends on the inundation frequency an identified match between water table salinities and vegetation zones suggests that water table salinities may be inferred from vegetation maps in the future

groundwater recharge environments and hydrogeochemical evolution in the jiuquan basin northwest china the groundwater recharge environments and hydrogeochemical characteristics in the quaternary aquifer of jiuquan basin was investigated using a combination of chemical indicators stable isotopes and radiocarbon dating the d excess values of winter precipitation and surface water revealed that the meltwater from snow and ice played the dominant role in the basin s surface water supply the unconfined groundwater showed gradual enrichment of heavy isotopes along the flow path but delta o 18 and delta h 2 values were similar to those of surface water suggesting recent recharge as a result of rapid seepage along rivers combined with the effects of high evaporation the c 14 pmc values of unconfined groundwater was between 71 5 and 90 9 and since 80 modern carbon probably represents the upper limit of initial c 14 activity this suggests that the groundwater is relatively young the confined groundwater was depleted in heavy isotopes coupled with low c 14 values similar to 20 53 indicating that the groundwater was mainly recharged as palaeowater during the late pleistocene and holocene epochs under a cold climate the surface water and most groundwater samples were fresh rather than saline with tds 490 and 1000 mg l 1 respectively the chemistry of unconfined groundwater changed from hco3 dominated to no dominant ions and then to so42 dominated moving along the flow path from the jiuquan jiayuguan basin to the jinta basin and the confined water was so42 dominated the results have important implications for groundwater management in the basin where a high proportion of the water being used is in effect being mined i e extracted faster than its replacement rate thus significant changes are urgently needed in the regional water use strategy c 2012 elsevier ltd all rights reserved

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

vertical sedimentation units in a barrier island washover fan overwash is a major component of a barrier island s response to high energy conditions examination of the 19 20 march 1975 storm deposits at assateague island showed that an overwash sequence could be divided into sedimentation units interpretation depends upon defining textural and mineralogical combinations that can be logically ordered as a vertical sequence if the sequence is depositional and formed from a single material normal grading usually results if polymineralogical and erosionally truncated inverse grading with a top layer of heavy minerals can be formed via an in situ sorting process dependent on disturbance depth and overwash influence

chemical characteristics of groundwater in parts of mountainous region alvand hamadan iran eighty seven groundwater samples have been collected from a mountainous region alvand iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater most water quality parameters are within world health organization acceptable limits set for drinking water the least mineralized water is found closest to the main recharge zones and the salinity of water increased towards the north of the basin the most prevalent water type is ca hco3 followed by water types ca no3 ca cl ca so4 and mg hco3 the ca no3 water type is associated with high nitrate pollution agricultural and industrial activities were associated with elevated level of no3 mineral dissolution weathering of evaporites dominates the major element hydrochemistry of the area chemical properties of groundwater in alvand region are controlled both by natural geochemical processes and anthropogenic activities

coastal geomorphology and restoration abstract increases in human development of the coastal zone sea level rise and intensity of coastal storms will test the resilience of coastal systems an integrated approach is needed to describe geomorphic biologic dependencies feedbacks between processes and responses and determine how coastal systems can be maintained or restored the 2013 binghamton geomorphology symposium focused on three themes in these research areas 1 the geomorphic response of coastal landforms to changes in sea level and episodic storms 2 the way these stressors alter geomorphic biotic interactions and reduce the resilience of coastal environments and 3 the way natural and human processes are being integrated to restore or maintain dynamic geomorphic and biologic linkages this issue contains eighteen papers presented at the symposium six papers are devoted to each of these themes the papers point to the importance of ecological systems in modulating the responses to natural physical processes and in turn responding to geomorphic change and the role of humans in assisting natural processes

water and gas chemistry of lake nyos and its bearing on the eruptive process abstract the isotopic and chemical composition of water samples collected from lake nyos some two and eight weeks after the eruption of august 21 1986 point to the existence of three distinct mixing regimes involving three water components an essentially homogeneous unmixed body of water at depths 100 m overlain by water increasingly affected by surface evaporation and a 5 10 m layer containing recent but pre eruption rain water the cationic constituents na k mg ca mn fe of the lake water correspond to the dissolution of around 0 1 g of local rock the waters are close to saturation with respect to siderite the composition of the gas dissolved in the deep lake waters 0 65 b w of co2 pco2 4 4b corresponds in mmol mol 1 to 996 co2 2 0 ch4 2 0 n2 0 05 ar 0 004 he 0 0002 h2 0 0001 ne co 2 13 c 3 4 and of he rair 5 5 suggest deep magmatic origins the 13c and 2h content of ch4 organic sedimentary origin the presence of aromatic hydrocarbons indicates very high temperatures of hydrocarbon formation exsolution of gas will first lead to the precipitation of siderite then iron hydroxide the chemistry of the lake waters points to a loss of some 240 000 t of co2 from the upper 100 m of the lake their isotopic composition is consistent with the assumption that the eruption was triggered by the accumulation of cold rain waters at the lake surface prior to the eruption inducing partial convective overturn there is no need to invoke addition of chemical or isotopic constituents from deeper levels during the eruption

ecomorphodynamic feedbacks and barrier island response to disturbance insights from the virginia barrier islands mid atlantic bight usa abstract ecomorphodynamic feedbacks play an important role in the susceptibility and response of barrier islands to disturbance by overwash dune building grasses like ammophila breviligulata can help to restore areas of high relief after overwash events i e resist disturbance if overwash recurs before dunes have reestablished however overwash adapted maintainer species like spartina patens upright variety may preferentially survive maintainer species help to preserve low flat topography thereby increasing the likelihood of future overwash i e reinforcing disturbance under frequent disturbance conditions this positive feedback may lead to overwash persistence we explore the potential influence of the maintainer feedback on two morphologically distinct barrier islands in the virginia coast reserve vcr located in the mid atlantic bight of the u s east coast combined topographic and vegetation surveys show that on hog island high relief rotating where dunes dominated by a breviligulata are ubiquitous overwash zones are currently limited in extent and related to beach width rather than dominance by s patens historical aerial photos and stratigraphic evidence ground penetrating radar cores indicate that gradual recovery has taken place following overwash events on hog island except where the beach is narrow and eroding conversely on metompkin island low relief transgressing overwash is widespread and dominated by s patens particularly along the rapidly migrating northern half of the island where shell armoring is also common overwash has generally been more prevalent and persistent here than on hog island we present a new conceptual model of the response of barrier islands to disturbance incorporating ecological and physical processes our findings suggest that in barrier systems where both dune building grasses and overwash adapted maintainer species are common like the vcr the maintainer feedback is likely to be a more important dynamic on islands already susceptible to frequent disturbance because of physical factors the maintainer feedback therefore has the potential to accelerate large scale shifts from dune dominated to overwash dominated barrier morphologies as the effects of climate change increased storm intensity sea level rise cause overwash to become more frequent

rapid dune changes associated with overwash processes on the deltaic coast of south louisiana abstract the caminada moreau barrier headland of south louisiana is a low profile beach and dune coastline that is transgressing rapidly over the surfaces of the abandoned lafourche delta complex with the passage of cold fronts 10 30 times per year and hurricanes once every 4 yrs overwash events occur year round with varying degrees of frequency intensity and geomorphological modification this coastline consists of washover and dune surfaces that respond rapidly to overwash impact the fine sand stored in washover deposits is easily reworked by aeolian processes into a variety of dune forms in the shore zone that are vegetated rapidly geomorphological changes vary according to the position ground elevation and surface stability of the dunes independent factors are overwash surge elevations beach gradient and the presence of pre existing landforms for ten years detailed surveys supplemented by aerial photographs and videotape surveys have recorded these changes the analysis of these information sources provides insight into both the general evolution of this distinctive coastline and also the geomorphological interaction of dunes beaches and washover deposits in different physiographic settings

using hydrochemical and isotopic data to determine sources of recharge and groundwater evolution in an arid region a case study in the upper middle reaches of the shule river basin northwestern china understanding sources of recharge and mechanisms for hydrogeochemical evolution of groundwater in the shule river basin an arid inland river basin in northwestern china is essential for successful water resource management sources of water and associated groundwater recharge processes were investigated using hydrogeological hydrogeochemical and isotopic methods the study area was divided into three parts changma the shule valley and the beishan area the hydrogeochemical and isotopic analysis results show that groundwater in changma mainly originated from precipitation in the qilian mountains lateral flow from changma is the primary recharge mechanism while direct recharge by infiltration of precipitation can be neglected in the shule valley minerals within the aquifer material e g halite calcite dolomite and gypsum dissolve into water that recharges the groundwater system therefore strong linear relationships were found between na and cl and between ca2 mg2 and so42 hco3 with stoichiometry ratios of approximately 1 1 in both cases groundwater quality in the region is generally good with low salinity and hardness local precipitation is the only source of recharge for groundwater in the beishan area low groundwater velocity and dry climatic conditions suggest that dissolution of minerals from the aquifer material controls hydrogeochemical evolution water rarely travels from the beishan area to the shule valley therefore almost all the groundwater in the shule valley originates from changma global climate change and loss of glaciers in the qilian mountains may lead to a reduction of recharge therefore the groundwater resources of the shule valley must be managed to sustain water supply

geochemical evolution of ground water in smith creek valley a hydrologically closed basin in central nevada u s a abstract smith creek valley is a hydrologically closed basin in which ground water is recharged by subsurface inflow from sorrounding mountains and infiltration of streamflow into alluvial fan deposits near the mountains ground water is discharged by evapotranspiration from shallow ground water areas in the central part of the basin dominant ions in the dilute recharge water are na ca and hco 3 dissolved solids concentration increases during flow through the basin fill sediments with na becoming increasingly dominant in the discharge area a bare soil playa sorrounded by phreatophytic vegetation ground water salinity dominated by na and cl increases markedly the main processe controlling geochemical evolution of ground water in the basin fill aquifer were identified using major ion chemistry mass balance calculations thermodynamic calculations stable isotopes and mineral identification these processes are 1 dissolution of volcanic tuff and tuff derived basin fill deposits 2 cation exchange of ca and mg in the water for na in clay minerals 3 weathering of plagioclase to montmorillonite 4 precipitation of zeolite minerals 2 concentration of dissolved constituents by evapotranspiration 6 dissolution of cl and so 4 evaporative salts 7 precipitation of calcite

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

dissolution of fluoride in groundwater a water rock interaction study fluoride rich groundwater is well known in granite aquifers in india and the world although its presence is necessary chances of health risk become high if the fluoride concentration is more than the permissible limit of 1 5 mg l world health organization who in drinking water fluoride mainly occurs in groundwater as a natural constituent results of a laboratory study on water rock interaction at normal temperature pressure and different chemical conditions indicate that the specific conductivity ph ca and hco3 are important chemical parameters for the dissolution of fluoride to groundwater from fluoride rich minerals e g fluorite experimental results indicate that an alkaline medium ph 7 6 to 8 6 high hco3 concentration ranging from 350 450 mg l and moderate specific conductivity ranging from 750 1 750 s cm are favourable for fluoride dissolution no significant correlation existed between fluoride and cahco3

internal wave generation by ice floes moving in stratified water results from a laboratory study a series of tests has been conducted to investigate the increased ice water drag exhibited by ice floes in two layer salinity stratified water scaled model tests are used to quantify the additional drag due to internal wave creation at the fresh water salt water interface this additional drag is shown to have a peak value five times the drag in similar unstratified conditions and to have a strong dependence on a few well defined nondimensional parameters describing the ice and water characteristics

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

stability and bistability in a one dimensional model of coastal foredune height on sandy coastlines foredunes provide protection from coastal storms potentially sheltering low areas including human habitat from elevated water level and wave erosion in this contribution we develop and explore a one dimensional model for coastal dune height based on an impulsive differential equation in the model coastal foredunes continuously grow in a logistic manner as the result of a biophysical feedback and they are destroyed by recurrent storm events that are discrete in time modeled dunes can be in one of two states a high resistant dune state or a low overwash flat state the number of stable states equilibrium dune heights depends on the value of two parameters the nondimensional storm frequency the ratio of storm frequency to the intrinsic growth rate of dunes and nondimensional storm magnitude the ratio of total water level during storms to the maximum theoretical dune height three regions of phase space exist 1 when nondimensional storm frequency is small a single high resistant dune attracting state exists 2 when both the nondimensional storm frequency and magnitude are large there is a single overwash flat attracting state 3 within a defined region of phase space model dunes exhibit bistable behavior both the resistant dune and the low overwash flat states are stable comparisons to observational studies suggest that there is evidence for each state to exist independently the coexistence of both states i e segments of barrier islands consisting of overwash flats and segments of islands having large dunes that resist erosion by storms as well as transitions between states

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

hydrogeochemical evaluation of groundwater in the lower offin basin ghana alumino silicate mineral dissolution cation exchange reductive dissolution of hematite and goethite oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the offin basin the main aim of this study was to characterise groundwater and delineate relevant water rock interactions that control the evolution of water quality in offin basin a major gold mining area in ghana boreholes dug wells springs and mine drainage samples were analysed for major ions minor and trace elements major ion study results show that the groundwater is principally ca mg hco3 or na mg ca hco3 in character mildly acidic and low in conductivity groundwater acidification is principally due to natural biogeochemical processes though acidic the groundwater has positive acid neutralising potential provided by the dissolution of alumino silicates and mafic rocks trace elements loading except arsenic and iron of groundwater is generally low reductive dissolution of iron minerals in the presence of organic matter is responsible for high iron concentration in areas underlain by granitoids elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation approximately 19 and 46 of the boreholes have arsenic and iron concentrations exceeding the who s guidelines for drinking water quality final task group meeting who press world health organization geneva 2004 maximum acceptable limits of 10 g l 1 and 0 3 mg l 1 for drinking water

seasonal variation of groundwater quality in a part of guntur district andhra pradesh india the area in guntur district andhra pradesh india is selected to discuss the impact of seasonal variation of groundwater quality on irrigation and human health where the agriculture is the main livelihood of rural people and the groundwater is the main source for irrigation and drinking granite gneisses associated with schists and charnockites of the precambrian eastern ghats underlie the area groundwater samples collected seasonally pre and post monsoons during three years from forty wells in the area were analyzed for ph ec tds ta th ca2 mg2 na k co 3 2 hco 3 cl so 4 2 no 3 and f the chemical relationships in piper s diagram chebotarev s genetic classification and gibbs s diagram suggest that the groundwaters mainly belong to non carbonate alkali type and cl group and are controlled by evaporation dominance respectively due to the influence of semi arid climate gentle slope sluggish drainage conditions greater water rock interaction and anthropogenic activities a comparison of the groundwater quality in relation to drinking water quality standards proves that most of the water samples are not suitable for drinking especially in post monsoon period us salinity laboratory s and wilcox s diagrams and na used for evaluating the water quality for irrigation suggest that the majority of the groundwater samples are not good for irrigation in post monsoon compared to that in pre monsoon these conditions are caused due to leaching of salts from the overlying materials by infiltrating recharge waters a management plan is suggested for sustainable development of the area

interdependence of geomorphic and ecologic resilience properties in a geographic context abstract ecology and geomorphology recognize the dynamic aspects of resistance and resilience however formal resilience theory in ecology has tended to deemphasize the geomorphic habitat template conversely landscape sensitivity and state and transition models in geomorphology downweight mechanisms of biotic adaptation operative in fluctuating spatially explicit environments adding to the interdisciplinary challenge of understanding complex biogeomorphic systems is that environmental heterogeneity and overlapping gradients of disturbance complicate inference of the geographic patterns of resistance and resilience we develop a conceptual model for comparing the resilience properties among barrier dunes the model illustrates how adaptive cycles and panarchies the formal building blocks of resilience recognized in ecology can be expressed as a set of hierarchically nested geomorphic and ecological metrics the variance structure of these data is proposed as a means to delineate different kinds and levels of resilience specifically it is the dimensionality of these data and how geomorphic and ecological variables load on the first and succeeding axes that facilitates the delineation of resistance and resilience the construction of dune topographic state space from observations among different barrier islands is proposed as a way to measure the interdependence of geomorphic and ecological resilience properties

virginia barrier island configuration a reappraisal the 12 virginia barrier islands are divided into three groups on the basis of historical retreat rates and characteristics the growth and reversal of inlet offsets is a long term event that results from the operation of known coastal processes both geomorphic evidence and wave refraction analyses indicate that shoreline irregularity will diminish with time there is no basis for the prediction or expectation that cape like features will evolve along this shoreline

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

downward lee wave radiation from tropical instability waves in the central equatorial pacific ocean a possible energy pathway to turbulent mixing turbulent mixing in the equatorial pacific ocean is an important process that controls diapycnal heat transport and hence affects the air sea interactions and global climate it is recently shown that in the eastern equatorial pacific strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves tiws which propagate westward along the equator at a speed of 0 5 m s 1 with a wavelength of 1000 km in this study using a high resolution ocean general circulation model we show that the tiws can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial pacific although the thermocline is too deep to be directly affected by the vertical shear of the tiws the front of the tiw is clearly manifested as a narrow strip of strong convergence of horizontal surface flow from which area downward and westward propagating internal waves are intermittently emanated these internal waves can be interpreted as lee waves generated by the surface flow convergence zone which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow the associated downward energy flux below the surface mixed layer increases as the tiw structure becomes deeper toward the central equatorial pacific so that the energy pathway to turbulent mixing in the thermocline can be created the downward energy flux integrated over the entire equatorial pacific and averaged during january 2011 amounts to 8 1 gw occupying a significant fraction of the energy input to the tiws

morphological barrier island changes and recovery of dunes after hurricane dennis st george island florida abstract during the summer of 2005 hurricane dennis overwashed the eastern portion of st george island part of the northwest barrier island chain located along the florida panhandle in this paper lidar based morphological changes of the barrier island are analyzed along with the short term post storm recovery of secondary dunes results show that overwash from the storm surge removed nearly the entire foredune complex and the initial breaching probably occurred where the complex was either low or discontinuous in these locations beach widening was less in contrast approximately 10 m of beach widening occurred where foredunes were higher and continuous implying that more sediment was available for seaward transport during storm conditions the secondary dunes recovered at an average linear rate of 3 4 cm per month in the presence of vegetation although monthly averages varied from 1 5 to 1 4 m3 m and total volume changes varied from 17 9 to 16 4 m3 m for the duration of the study furthermore vegetation deterred dune migration thus favoring dune growth and reducing erosion due to wind in contrast the absence of vegetation inhibited dune growth insignificant changes in elevation occurred in areas of storm debris or lag deposit finally distributions of topographic gradients and curvature calculated numerically from pre and post storm lidar data are introduced as a potential tool in determining the relative post storm recovery of the dune field

erosional and depositional characteristics of regional overwash deposits caused by multiple hurricanes regional scale washover deposits along the florida gulf and atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring trenching ground penetrating radar imaging aerial photography and prestorm and poststorm beach profile surveys erosional and depositional characteristics in different barrier island sub environments including dune field interior wetland and back barrier bay were examined over the eroded dune fields the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward dipping stratification over the marshes in the barrier island interior the washover deposits are characterized by steep tabular bedding with no erosion at the bottom overwash into the back barrier bay produced the thickest deposits characterized by steep prograding sigmoidal bedding no significant erosional feature was observed at the bottom washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding the washover deposits caused by hurricanes frances 2004 and jeanne 2004 along the southern florida atlantic coast barrier islands are substantially different from those along the northern florida barrier islands caused by ivan 2004 and dennis 2005 in terms of regional extension erosional features and sedimentary structures these differences are controlled by different overall barrier island morphology vegetation type and density and sediment properties the homogeneity of sediment along the northern florida coast makes distinguishing between washover deposits from ivan and dennis difficult in contrast along the atlantic coast barrier islands the two overwash events as demonstrated by two phases of graded bedding of the bimodal sediments are easily distinguishable

recent shifts in coastline change and shoreline stabilization linked to storm climate change since cuspate coastlines are especially sensitive to changes in wave climate they serve as potential indicators of initial responses to changing wave conditions previous work demonstrates that cape hatteras and cape lookout north carolina which are largely unaffected by shoreline stabilization efforts have become increasingly asymmetric over the past 30 years consistent with model predictions for coastline response to increases in atlantic ocean summer wave heights and resulting changes in the distribution of wave approach angles historic and recent shoreline change observations for cape fear north carolina and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment produce comparable differences in shoreline change rates in response to changes in wave climate results suggest that the effect of beach nourishment is to compensate for and therefore to mask natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone therefore this case study suggests that the effects of wave climate change on human modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities similar analyses of cuspate features in areas where the change in wave climate is less pronounced i e fishing point maryland virginia and where local geology appears to exert control on coastline shape i e cape canaveral florida suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave dominated coastlines where the change in wave climate has been most pronounced however if hurricane generated wave heights continue to increase large scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger scale coastline shape comes into equilibrium with changing wave conditions copyright 2014 john wiley sons ltd

stratigraphy of washover deposits in florida implications for recognition in the stratigraphic record abstract twelve washover deposits were cored on the west central gulf coast of florida to provide data to permit development of a model to help identify washover facies in the stratigraphic record typical modern washover stratigraphy displays landward dipping plane beds comprised of well sorted sand with distinct laminae of shells and heavy minerals five subfacies are delineated which show variations in composition texture and bioturbation throughout the washover facies these subfacies represent differences in flow conditions during overwash position relative to sea level and variable degrees of reworking after deposition three shell assemblages aid in identification of washover deposits backbarrier sediments composed of shoreface open water species or mixed shoreface backbarrier species may potentially be washover in origin sediments with purely backbarrier quiet water shell species are likely to have been deposited independently of washover activity examination of washover deposits of differing ages reveals that preservation of washover stratigraphy is not exclusively a function of time reworking of small scale stratification can occur in as short as a decade however this same stratification was found to be preserved in deposits several hundred years old destruction of original washover signatures is related to the position of the deposits relative to sea level and the rate and depth of burial even after the destruction of small scale stratigraphic features washover deposits may still be identified as such due to their texture composition and shell assemblages key features in recognizing the facies after bioturbation and reworking are 1 the presence of clean sand in otherwise muddy backbarrier sediments 2 the landward thinning of the facies and 3 the presence of shoreface shells or mixed shoreface backbarrier shells on landward portions of the barrier island system if reworking is severe and or there are limited subsurface data distinguishing washovers from genetically similar deposits e g flood tidal deltas and spillover deposits in the stratigraphic record is difficult and when considered out of stratigraphic context may not be recognizable

characterization of groundwater chemistry under the influence of lithologic and anthropogenic factors along a climatic gradient in upper cauvery basin south india hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin semi arid 500 800 mm of mean annual rainfall sub humid 800 1 200 mm year and humid 1 200 1 500 mm year are the climatic zones chosen along the granito gneissic plains of kabini basin in south india for the present analysis data on groundwater chemistry is initially checked for its quality using nicb ratio 40 of pollution and eliminated for the characterization piper s diagram with mean concentrations indicates the evolution of canahco3 semi arid from cahco3 humid zone along the climatic gradient carbonates dominate other anions and strong acids exceeded weak acids in the region mule hole sew an experimental watershed in sub humid zone is characterized initially using hydrogeochemistry and is observed to be a replica of entire sub humid zone with 25 wells extension of the studies for the entire basin 120 wells showed a chemical gradient along the climatic gradient with sub humid zone bridging semi arid and humid zones ca na molar ratio varies by more than 100 times from semi arid to humid zones semi arid zone is more silicaceous than sub humid while humid zone is more carbonaceous ca cl 14 along the climatic gradient groundwater is undersaturated humid saturated sub humid and slightly supersaturated semi arid with calcite and dolomite concentration depth profiles are in support of the geological stratification i e 18 m of saprolite and 25 m of fracture rock with parent gneiss beneath all the wells are classified into four groups based on groundwater fluctuations and further into deep and shallow based on the depth to groundwater higher the fluctuations larger is its impact on groundwater chemistry actual seasonal patterns are identified using recharge discharge concept based on rainfall intensity instead of traditional monsoon non monsoon concept non pumped wells have low na cl and ca cl ratios in recharge period than in discharge period dilution few other wells which are subjected to pumping still exhibit dilution chemistry though water level fluctuations are high due to annual recharge other wells which do not receive sufficient rainfall and are constantly pumped showed high concentrations in recharge period rather than in discharge period anti dilution in summary recharge discharge concept demarcates the pumped wells from natural deep wells thus characterizing the basin

ionic exchange in groundwater hydrochemical evolution study case the drainage basin of el pescado creek buenos aires province argentina the phreatic aquifer beneath the pampean plain in eastern central argentina constitutes a relevant source of water supply in the area the objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer based on a study case located in the middle and upper basin of the el pescado creek results indicate that ca2 na exchange is the main process determining the evolution of groundwater from the recharge areas ca hco3 towards the local discharge areas na hco3 as well as representing a source of na contribution to the water in the aquifer this hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally the ion exchange capacity of these discharge areas has environmental importance due to its influence on groundwater quality and potential groundwater uses these results may be applied to any aquifer sharing similar hydrogeological characteristics

coupled topographic and vegetation patterns in coastal dunes remote sensing observations and ecomorphodynamic implications vegetation plays a key role in stabilizing coastal dunes and barrier islands by mediating sand transport deposition and erosion dune topography in turn affects vegetation growth by determining local environmental conditions however our understanding of vegetation and dune topography as coupled and spatially extensive dynamical systems is limited here we develop and use remote sensing analyses to quantitatively characterize coastal dune ecotopographic patterns by simultaneously identifying the spatial distribution of topographic elevation and vegetation biomass lidar derived leaf area index and hyperspectral derived normalized difference vegetation index patterns yield vegetation distributions at the whole system scale which are in agreement with each other and with field observations lidar derived concurrent quantifications of biomass and topography show that plants more favorably develop on the landward side of the foredune crest and that the foredune crestline marks the position of an ecotone which is interpreted as the result of a sheltering effect sharply changing local environmental conditions we conclude that the position of the foredune crestline is a chief ecomorphodynamic feature resulting from the two way interaction between vegetation and topography

generation of internal waves by sea ice observations in the greenland sea marginal ice zone suggest that when strong stratification occurs near the surface momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift since energy is radiated away by the internal waves turbulent mixing and heat flux are also affected we investigate the downward flux of momentum and energy by internal waves in an ice covered ocean with an idealized model comprising a mixed layer overlying a deep uniformly stratified layer a buoyancy jump separates the mixed layer from the pycnocline drag from a single wave number component of the under ice roughness spectrum is derived as the product of a drag coefficient based on ice speed under ice roughness wave number and amplitude and uniform stratification to the ice ocean interface times an attenuation factor that depends additionally on mixed layer depth and the buoyancy jump at the base of the mixed layer the model is extended to a plausible spectrum of under ice roughness by integration over wave number space internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for 1 decreased ice velocity relative to the wind 2 decreased heat exchange coefficient between the ice and ocean and 3 lack of mixed layer deepening all of which were observed during the last week of the 1984 marginal ice zone experiment

overwash and aeolian processes on a u s northeast coast barrier abstract a field investigation of overwash aeolian processes and vegetative response was undertaken to obtain the first quantitative data of this kind for the new england area the new england blizzard of 1978 february 6 7 resulted in massive overwashing of nauset spit cape cod massachusetts volumetric determinations showed that as much as 400 m3 of overwash sand per meter of dune breach was transported across the barrier during this event with deposition thicknesses of 1 65 m above the living salt marsh although considerable amounts of sand were deposited by overwash much of this sediment was redistributed through aeolian processes during interstorm periods approximately half the sediment deposited by the 1978 northeaster was blown back to the beach by offshore winds and an equal amount accumulated in the peripheral dunes at distinct fan features large barren washover flats can remain unvegetated for long periods of time where the substrate is continually affected by overwash and aeolian transport these areas eventually become the loci of new major barrier dunes through the revegetation process initiated by drift line deposits