224ra 228ra and226ra in winyah bay and delaware bay the first224ra t1 2 3 64days measurements from mixing zones of estuarine systems are presented for the pee dee river winyah bay and delaware bay estuaries high resolution gamma ray spectrometry was used to determine224ra 228ra t1 2 5 7years and226ra t1 2 1622years activity ratios desorption and diffusion from suspended and bottom sediments contributes to the non conservative increases of the three isotopes in each systems in delaware bay224ra concentrations were nearly constant over the 2 5 to 15 salinity range where two turbidity maximum zones are located 228th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of224ra in this system samples collected on the ebb and flood tide from a salt marsh along delaware bay have a 5 fold increase in224ra from flood to ebb and 3 and 2 fold increases for228ra and226ra respectively indicating salt marshes are another source of radium to estuarine waters

the importance of submarine groundwater discharge to the near shore nutrient supply in the gulf of aqaba israel we used two short lived radium isotopes 223ra 224ra and a mass balance approach applied to the radium activities to determine the nutrient contribution of saline submarine groundwater discharge to the coastal waters of the northern gulf of aqaba israel radium isotope activities were measured along transects during two seasons at a site that lacked any obvious surficial water input an onshore well and an offshore end member were also sampled for all samples nutrients and salinity data were collected radium isotope activities generally decreased with distance offshore and exhibited significant tidal variability which is consistent with a shorederived tidally influenced source submarine groundwater contributes only 1 2 of the water along this coast but this groundwater provides 8 46 of the nutrients this saline groundwater is derived predominately from tidally pumped seawater percolating through the unconfined coastal aquifer and leaching radium and nutrients this process represents a significant source of nutrients to the oligotrophic nearshore reef

the role of a heterogeneous inclusion during continental collision abstract we study a simple model of the deformation due to collision between two continental plates the model is patterned after the geometry of the india asia collision but it may be applicable to more general situations the collision is modelled by the indentation of a viscoplastic plate asia by a rigid punch india a finite element approach capable of dealing with finite deformation heterogeneity and non linear rheologies is used to study the role of an inclusion of increased rigidity on the viscoplastic flow of the plate the heterogeneous zone was chosen to approximate the shape and position of the tarim basin behind tibet the lateral boundaries of the plate were defined so as to approximate those that are believed to apply for the asian plate i e fixed boundaries to the west and north free boundaries to the west and south several geometries and contrasts of rheology were analyzed to verify the general validity of our results the purpose was to determine the main kinematic features of the flow not to model the particular case of tarim it is found that the heterogeneity affects the flow in a drastic way even for small contrasts of rigidity and for small size heterogeneities the main effect of the heterogeneity is to create two important shear zones or internal boundary layers the most important is in front of the inclusion separating the main flow from the inclusion as the flow proceeds the inclusion rotates and the shear zone progressively bends in qualitative agreement with the bending of the large strike slip faults like the altyn tagh that separates the tarim from tiber our model of continuous deformation does not allow for the formation of faults or fractures but the shear zones may be understood as the initial stages for the generation of fractures or velocity discontinuities another shear zone develops to the left of the inhomogeneity near the fixed boundary and in the wake of the punch the role of these shear zones is to isolate the heterogeneity from the main flow to facilitate its rigid rotation inside the flow of the softer plate a final observation is that in the presence of the heterogeneity the lower left hand corner rotates almost like a rigid block producing a sharp bend on the left hand side of the plate as the inclusion rotates pushed by the punch this rigid block rotates clockwise to open up the space necessary for the homogeneity

horizontal dispersion of ocean tracers in internal wave shear 1 the horizontal dispersion of ocean tracers due to the interaction of vertical diffusion and the vertical shear from internal waves is examined using a lagrangian particle tracking model for idealized sinusoidal horizontal velocity profiles of unbounded vertical extent the irreversible horizontal dispersion of particle clouds is maximal when the timescale of particle diffusion across the velocity variations and the period of shear oscillation are comparable for measured velocity profiles from the thermocline in the gulf of aqaba red sea the total dispersion and irreversible dispersion of particle clouds both tend to increase with vertical diffusion cloud height and cloud age the total and irreversible horizontal cloud variances typically grow with time t like t0 to t3 and t1 to t3 respectively estimates of the irreversible horizontal dispersivity from an existing analytical model based on vertically constant oscillating shear agree remarkably well with estimates from the particle tracking model with differences dependent on the vertical variability in vertical diffusion and shear that are not incorporated in the analytical model

fluid flow in fractured reservoirs estimation of fracture intensity distribution capillary diffusion coefficient and shape factor from saturation data abstract naturally fractured carbonate reservoirs which possess most of the remaining oil in the world can fulfill the needs of widely nowadays energy demand most of the oil remains in the matrix block during production from naturally fractured reservoirs water flooding is a technique implemented in naturally fractured reservoirs to recover additional amounts of oil from the matrix blocks in this paper for the first time an analytical model for water flooding in the naturally fractured carbonate reservoirs is developed that describes the transient behavior of the imbibition mechanism in the dual porosity models using the fracture matrix fluid transfer of the dual porosity model the presented analytical model takes the account of viscous capillary and capillary imbibition mechanisms in fracture and matrix system respectively the analytical solution is validated using both laboratory data and a numerical solution in order to consider the effect of the heterogeneity in fractured reservoirs the proposed analytical model is developed for various distributions of block sizes in addition a graphical method is developed to estimate capillary diffusion coefficient and matrix block size distribution based on the water saturation data in the monitoring well during water injection the monitoring well is used to monitor and evaluate reservoir during water flooding the proposed methodology which is based on water saturation data in the monitoring well does not call for a specific test in the reservoir moreover the relating shape factor is calculated with the aid of dual porosity model equipped with variable fracture intensity distribution the findings imply that the fluid transfer is highly dependent on the distribution of matrix block size

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

submarine groundwater discharge as a source of dissolved nutrients to an arid coastal embayment la paz mexico submarine groundwater discharge sgd was investigated in the southeastern portion of la paz bay baja california mexico using radon 222rn as a natural tracer in the absence of permanent surface flows in this arid region we hypothesize sgd is a major regional source of dissolved nutrients four spatial surveys showed higher radon and nutrient nh4 no3 no2 po4 and sio4 values in the winter than summer lagging rainfall by 3 4 months the surveys revealed two sites balandra and merito with a stronger radon signal intensive time series 12 24 h measurements at those sites were used to estimate sgd fluxes using a radon mass balance approach in balandra sgd was estimated to be 0 18 m3 m 2 day 1 and significant correlations between radon and nutrients no3 and sio4 were observed in merito sgd rates were estimated to be 0 10 m3 m 2 day 1 and no correlations between nutrients and 222rn were observed the difference between the two sites was interpreted to be related to different components dominating sgd i e fresh sgd in balandra and saline sgd in merito the estimated sgd derived nutrients fluxes were 2 52 0 04 0 94 7 164 mmol m2 day 1 for dissolved inorganic nitrogen phosphate and silicate respectively these fluxes could explain between 5 and 20 of the regional marine primary productivity values

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

high fluxes of radium and barium from the mouth of the ganges brahmaputra river during low river discharge suggest a large groundwater source the annual flux of sediment from the ganges brahmaputra river is among the highest in the world the desorption of226ra and ba from this sediment produces a major point source of226ra and ba input to the ocean highest226ra and ba fluxes are expected to occur during high river flow june september when most of the sediment is discharged surprisingly during low discharge of the ganges brahmaputra river fluxes of226ra and ba to the northern bay of bengal are comparable to expected river derived fluxes during peak river discharge a large non riverine source of ra and ba is required to explain the high fluxes during low river discharge i suggest that this source is submarine discharge of groundwater containing high concentrations of226ra and ba total annual fluxes of226ra and ba to the ocean from this system are significantly greater than estimated previously

thermally driven exchanges between a coral reef and the adjoining ocean abstract in this paper hydrographic observations made over a fringing coral reef at the northern end of the gulf of aqaba near eilat israel are discussed these data show exchange flows driven by the onshore offshore temperature gradients that develop because shallow regions near shore experience larger temperature changes than do deeper regions offshore when subjected to the same rate of heating or cooling under heating conditions the resulting vertically sheared exchange flow is offshore at the surface and onshore at depth whereas when cooling dominates the pattern is reversed for summer conditions heating and cooling are both important and a diurnally reversing exchange flow is observed during winter conditions heating occupies a relatively small fraction of the day and only the cooling flow is observed when scaled by v the observed profiles of the cross shore during cooling velocity collapse onto a single curve the value of v depends on the convective velocity scale uf and the bottom s

application of tracer injection tests to characterize rock matrix block size distribution and dispersivity in fractured aquifers the complexity of mass transfer processes between the mobile and immobile zones in geohydrologic settings and the limitations that currently exist in the characterization of contaminated sites demand the development of improved models in this work we present a model that describes the mass transfer in structured porous media this model considers divergent radial advective dispersive transport in fractures and diffusive mass transfer inside rock matrix blocks the heterogeneous nature of fractured formations is included with the integration of various distributions of rock matrix block sizes into the transport model breakthrough curves generated based on the developed model are analyzed to investigate the effects of the rate of injection dispersivity and the immobile to mobile porosity ratio on mass transfer between mobile and immobile zones it is shown that the developed model in conjunction with tracer data collected from a monitoring well can be used to estimate the dispersivity and fracture intensity results reveal that the dispersivity is independent of the rock matrix block size distribution for dispersion dominant transport in fractures these findings are used to develop a methodology to characterize rock matrix block size distribution in fractured aquifers and to estimate dispersivity based on a tracer test which will improve our decisions concerning the remediation of contaminated sites

radium isotopes reveal seasonal groundwater inputs to cockburn sound a marine embayment in western australia summary the mass balance and activity ratios of naturally occurring radium ra iso topes 223 ra 224 ra 226 ra 228 ra were investigated in cockburn sound western australia to further understand submarine groundwater discharge sgd into these coastal waters water samples from 11 marine stations and 20 groundwater sites encompassing threeaquifer layers were analysed for ra at four times at the end of winter september2003 early summer december 2003 late summer march 2004 and mid winter july2004 variable isotopic signatures of groundwater suggested that vertical mixing mayoccur between different aquifer layers and two isotopically different water sources wereidenti ed in marine waters both inside and outside of cockburn sound a mass balance ofthe long lived radium isotopes 228 ra and 226 ra produced a range of discharge estimatesfrom 0 8 10 7 l day 1 in late summer to 2 7 10 7 l day 1 at the end of winter signaturesof radium isotopes in the coastal waters suggested that groundwater discharge was notcon ned to the shoreline and may have occurred from a number of aquifer sources at atemporally variable scale a 2007 elsevier b v all rights reserved

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

relating estuarine geology to groundwater discharge at an oyster reef in copano bay tx abstract coastal bays with fresh submarine groundwater discharge sgd have been found to provide a favorable environment to shellfish e g oysters significant variability in the spatial distribution and magnitude of sgd may occur because of subsurface heterogeneity we investigated the relationship between stratigraphic controls i e paleovalley systems and the spatial distribution of sgd in relation to oyster reefs in copano bay south texas major oyster reefs have been shown to be oriented perpendicular to shore along interfluves and near paleovalley margins a novel combination approach of radioactive geochemical tracers stable isotopes geophysical and petrophysical techniques were used to identify estuarine depositional environments for individual hydrogeologic characterization and evaluation of sgd distribution with implications to ecological features such as oyster reefs a 1 km2 area within a paleovalley system in copano bay yielded discernible differences in sediment type apparent resistivity and sgd rates among four different depositional environments paleovalley paleovalley margin oyster reef and interfluve electrical resistivity tomography revealed a direct connection between the oyster reef and the underlying more permeable interfluve and the presence of a fresher sgd component in the subsurface measurements of sgd from stationary and mobile continuous radon 222 surveys across each depositional environment showed that by and large areas in proximity to reefs have larger sgd rates 62 6 11 3 cm d in january and 28 7 10 8 cm d in july when compared to paleovalleys 31 9 8 9 cm d in january and 19 5 7 2 cm d in july the role of depositional environments as hydrologic controls on sgd to oyster reefs revealed in this study is further confirmed by significant differences in stable and radioactive isotopes observed over small spatial scales offshore when compared to the entire estuary although constant mixing and radon 222 degassing of bay waters are likely altering the relationships between the different depositional environments and magnitude of sgd this study provides an improved understanding of possible pathways of freshwater and solute inputs to oyster reefs for more informed decisions on reef restoration efforts

using ra isotopes to examine transport processes controlling benthic fluxes into a shallow estuarine lagoon measurements of the benthic flux of four naturally occurring radium isotopes in a shallow lagoon in the bega river estuary has provided information on the types and rates of transport processes operating in the lagoon sediments the measurement techniques included ra mass budgets of the lagoon ra fluxes into benthic chambers and modelling of the pore water and solid phase ra profiles in a sediment core the sediment profile of 210pb and the solid phase and pore water profiles of the longer lived ra isotopes 228ra half life 5 7 years and 226ra half life 1600 years indicate bioturbation to a depth of 10 cm a diffusion bioturbation model has been used to assess the relative importance of molecular diffusion and bioturbation as transport processes controlling the benthic flux of ra the flux of the shortest lived isotope 224ra half life 3 7 days is not significantly enhanced by bioturbation and its flux is consistent with diffusion controlled release however bioturbation enhances the 228ra flux by a factor of more than two over the flux due to molecular diffusion alone modelled pore water profiles and flux calculations are consistent with a bioturbation time scale between 0 5 and 2 years the measured benthic flux of 226ra is much greater than can be accounted for by the modelled profile and may be due to slow 226ra desorption from the sediment variable sediment accumulation rates or groundwater flow based on 226ra pore water and flux measurements at the time of this study groundwater flow has an upper limit of 0 3 cm d 1

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

breathing of a coral cay tracing tidally driven seawater recirculation in permeable coral reef sediments 1 coral reefs are characterized by high gross productivity in spite of low nutrient concentrations this apparent paradox may be partially reconciled if seawater recirculation in permeable sediments over large meters and long hours to days scales is an important source of recycled nitrogen and phosphorus to coral reefs in this paper we use radon 222rn a natural tracer to quantify tidally driven pore water or groundwater exchange between 1 an offshore coral cay island and its fringing reef lagoon and 2 a reef lagoon and the surrounding ocean as seawater infiltrates heron island at high tide it acquires a radon signal that can be detected when pore waters emerge from carbonate sands at low tide a nonsteady state model indicated that vertical pore water upwelling rates or saline submarine groundwater discharge were 40 cm d within the reef lagoon and 100 cm d outside the lagoon at low tide within the lagoon tidal pumping and temperature driven convection were the main driving forces of pore water advection at low tide the reef lagoon level is about 1 m higher than the surrounding ocean as a result a steep hydraulic gradient develops at the reef edge driving unidirectional filtration through the reef framework groundwaters were highly enriched in nitrate average of 530 mol likely influenced by bird guano relative to lagoon waters 1 9 mol rough but conservative estimates indicated that groundwater derived nitrate fluxes 7 9 mmol m2 d can replace the entire lagoon nitrate inventory every 19 days we speculate that as offshore coral islands breath inhale seawater at high tide and exhale groundwater at low tide they release nutrients that lead to sustained productivity within coral reefs

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

submarine groundwater discharge into the coast revealed by water chemistry of man made undersea liquefied petroleum gas cavern summary the occurrence of submarine groundwater discharge sgd as well as its supply of many nutrients and metals to coastal seawaters is now generally known however previous studies have focused on the chemical and radiological analysis of groundwater surface seawater shallow marine sediments and their pore waters as well as the measurement of upward flow through the marine sediments as end members of the discharge process in this study chemical and isotopic analysis results of marine subsurface waters are reported these were obtained from deep boreholes of an undersea liquefied petroleum gas lpg storage cavern located about 8 km off the western coast of korea the cavern is about 130 150 m below the sea bottom which is covered by a 4 8 19 5 m silty clay stratum an isotopic composition 2h and 18o of the marine subsurface waters falls on a mixing line between terrestrial groundwater and seawater vertical ec profiling at the cavern boreholes revealed the existence of a fresh water zone an increase in the contents of ferrous iron and manganese and a decrease in levels of nitrate bicarbonate and cavern seepage were recorded in august 2006 indicating a decreased submarine groundwater flux originating from land mainly caused by an elevated cavern gas pressure it is suggested in this study that the main source of fresh waters in the man made undersea cavern is the submarine groundwater discharge mainly originating from the land

localization and fault growth in layered brittle ductile systems implications for deformations of the continental lithosphere we present experiments and numerical simulations dealing with the growth of faults in thin brittle ductile systems to understand deformation modes in the continental lithosphere experiments were uniaxial shortening of layers of dry sand and silicone putties of various viscous resistances for large strength ratios between the brittle and ductile layers r 5 10 the deformation localizes into two shear bands the fault pattern is created before reaching 10 shortening and has fractal dimensions varying between 1 6 and 1 8 for small strength ratios r 5 10 deformation never localizes the fault pattern is homogeneous with a trivial dimension of 2 and grows continuously during deformation the transition between localized and homogeneous deformation occurs when the mechanical resistance of brittle layers is 5 10 times larger than the resistance of ductile layers this transition was also investigated by means of electrical analog simulations a fuse network which represents an elasto brittle layer is coupled with a capacitor layer which models strain rate dependent fluids an ac potential is applied and the fuses progressively burned out until they form a connected network the ac potential frequency is a tuning parameter similar to the applied strain rate in experiments a critical frequency is obtained marking a transition between a localization mode where the density of burned fuses decreases as the system size increases and a delocalization mode where the density of burned fuses remains constant with increasing system size the scaling dependency of the fracture process as well as the critical frequency are consistent with experimental results available information on the rheology of the continental lithosphere shows that this mechanical transition is bracketed by the possible range of brittle to ductile strength ratios

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

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

evidence of submarine groundwater nutrient supply to an oligotrophic barrier reef detailed hydrographic survey revealed patches of high nutrients and low salinity in the surface waters over a submerged limestone barrier reef in the oligotrophic coastal waters of the southeast indian ocean the nutrient patches exist throughout the year and represent concentrations that are more than 10 times those in the surrounding water numerical model results show that the nutrients originate from the reef and that the patchiness is caused by changes in water circulation the limestone in the region is known to be solution riddled and submarine seeps of nutrient rich groundwater on the reef are a likely source underground conduits represent major routes by which groundwater nutrients can be transported over several kilometers and supplied to barrier reef ecosystems resulting in islands of high productivity

an analytical solution for transient radial flow through unsaturated fractured porous media this paper presents analytical solutions for one dimensional radial transient flow through horizontal unsaturated fractured rock formation in these solutions unsaturated flow through fractured media is described by a linearized richards equation while fracture matrix interaction is handled using the dual continuum concept although linearizing richards equation requires a specially correlated relationship between relative permeability and capillary pressure functions for both fractures and matrix these specially formed relative permeability and capillary pressure functions are still physically meaningful these analytical solutions can thus be used to describe the transient behavior of unsaturated flow in fractured media under the described model conditions they can also be useful in verifying numerical simulation results which as demonstrated in this paper are otherwise difficult to validate

use of radium isotopes to examine pore water exchange in an estuary the measured distributions of four isotopes of ra along the estuary of the bega river are used to examine sediment water column exchange ra is created in estuarine sediments by the radioactive decay of insoluble th parents residing close to or on the surfaces of the sediment grains ra desorbed into the pore water is continuously lost to the water column due to the cyclical draining and filling of the sediments by the tides the distribution of ra in the estuary is governed by its rate of loss from the sediments its advection along the estuary resulting from river discharge into the estuary s head tidal mixing and radioactive decay these processes are all described in a model matching of model predicted ra concentrations with measurements allows an estimate of the effective depth in the sediments to which the pore water is exchanged every tidal cycle this depth is large 15 cm but it is shown to be reasonable for the bega estuary

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

evaluation of salt marsh hydrology using radium as a tracer abstract radium isotopes provide unique and important information concerning water exchange in a salt marsh tidal creek system seasonal radium data collected over five tidal cycles from a creek draining a south carolina salt marsh radium and thorium data from the adjacent marsh sediments and interstitial water radium data from the drainage basin are modeled to yield residence times of water in the upper 10 cm of the marsh sediments ranging from less than one to twenty six hours water residence times derived from chambers which directly measure the flux of ra isotopes to the creek waters agree well with these calculated interstitial water turnover times dissolved radium activities in the tidal creek were greater during the summer than during other times of the year we suspect that seasonal changes in the storage of organic carbon and rates of bioturbation lead to net reduction of radium carrier phases in the marsh sediments during the summer