characterizing groundwater lake interactions and its impact on lake water quality summary geochemical tracers were used to investigate groundwater lake interactions and to map nutrient concentrations within georgetown lake a 1219 ha lake situated at 1960 m above sea level between two mountain ranges in western montana radon 222 was used to identify locations and relative amounts of groundwater inflow to the lake and nutrients were sampled to investigate the role of groundwater on nutrient dynamics occurring within the lake sampling primarily took place during late winter and early spring when the lake was frozen stratified and relatively anoxic and all lake samples were collected near the bottom of the lake radon concentrations in the lake varied spatially from less than 3 5 194 0 pci l radon results show that groundwater enters the lake through fractured paleozoic karst limestone situated near a major thrust fault no groundwater flows were noted on the western side of the lake which is underlain by west dipping precambrian metasedimentary rocks the western two thirds of the lake is anoxic near the bottom of the water column with h2s and nh 4 concentrations as high as 1 99 mg l and 4 0 mg l respectively along the eastern side of the lake h2s was absent and nh 4 was generally low suggesting that groundwater inflows improve water quality pore water diffusion samplers show that there is an internal source of nh 4 h2s and po 4 3 to the lake originating from decay of organic carbon in the lake sediments

methane transport through submarine groundwater discharge to the north pacific and arctic ocean at two alaskan sites here we quantify the flux of methane to the coastal arctic and north pacific oceans via submarine groundwater discharge sgd by use of naturally occurring radium isotopes as groundwater tracers combined with methane concentration measurements of coastal groundwater our findings indicate the flux of methane through this process is much greater in the coastal north pacific 35 6 27 mg m 21 d 21 than the arctic ocean 4 1 6 0 6 to 11 8 6 3 9 mg m 21 d 21 the dominant controls on methane flux through sgd were not methane concentrations in the aquifer but rather the hydrologic characteristics of each site that mitigated or intensified the sgd water volume flux 120 6 50 m 3 m 21 d 21 in the north pacific compared to 12 6 4m 3 m 21 d 21 in the arctic tidal pumping was observed to be an especially important control on sgd flux at the north pacific site

dynamics of submarine groundwater discharge and associated fluxes of dissolved nutrients carbon and trace gases to the coastal zone okatee river estuary south carolina abstract multiple techniques including thermal infrared aerial remote sensing geophysical and geological data geochemical characterization and radium isotopes were used to evaluate the role of groundwater as a source of dissolved nutrients carbon and trace gases to the okatee river estuary south carolina thermal infrared aerial remote sensing surveys illustrated the presence of multiple submarine groundwater discharge sites in okatee headwaters significant relationships were observed between groundwater geochemical constituents and 226 ra activity in groundwater with higher 226 ra activity correlated to higher concentrations of organics dissolved inorganic carbon nutrients and trace gases to the okatee system a system level radium mass balance confirmed a substantial submarine groundwater discharge contribution of these constituents to the okatee river diffusive benthic flux measurements and potential denitrification rate assays tracked the fate of constituents in creek bank sediments diffusive benthic fluxes were substantially lower than calculated radium based submarine groundwater discharge inputs showing that advection of groundwater derived nutrients dominated fluxes in the system while a considerable potential for denitrification in tidal creek bank sediments was noted in situ denitrification rates were nitrate limited making intertidal sediments an inefficient nitrogen sink in this system groundwater geochemical data indicated significant differences in groundwater chemical composition and radium activity ratios between the eastern and western sides of the river these likely arose from the distinct hydrological regimes observed in each area groundwater from the western side of the okatee headwaters was characterized by higher concentrations of dissolved organic and inorganic carbon dissolved organic nitrogen inorganic nutrients and reduced metabolites and trace gases i e methane and nitrous oxide than groundwater from the eastern side differences in microbial sulfate reduction organic matter supply and or groundwater residence time likely contributed to this pattern the contrasting features of the east and west sub marsh zones highlight the need for multiple techniques for characterization of submarine groundwater discharge sources and the impact of biogeochemical processes on the delivery of nutrients and carbon to coastal areas via submarine groundwater discharge

the behavior of u and th series nuclides in the estuarine environment rivers carry the products of continental weathering and continuously supply the oceans with a broad range of chemical constituents this erosional signature is however uniquely moderated by biogeochemical processing within estuaries estuaries are commonly described as complex filters at land sea margins where significant transformations can occur due to strong physico chemical gradients these changes differ for different classes of elements and can vary widely depending on the geographic location u and th series nuclides include a range of elements with vastly different characteristics and behaviors within such environments and the isotopic systematics provide methods for investigating the transport of these nuclides and other analog species across estuaries and into the coastal ocean there are numerous types and definitions of estuaries see dyer 1973 in this paper it is simply considered to be a region where freshwater and seawater mix to emphasize the chemical focus of the issues involved here this region can either be contained within a river channel or extend onto the shelf with effects often extending well into an adjoining ocean basin fairbridge 1980 these are complex ecological biogeochemical and hydrodynamic systems with strong gradients in the concentrations and composition of micro and macro particulate matter as well as dissolved organic and inorganic species particle reactive radionuclides and trace elements being transported across estuaries are subject to partitioning between the dissolved colloidal and particulate phases the variable chemical nature of the u and th series radionuclides is evident in their distributions in an estuarine environment such radionuclides can effectively serve as tracers to identify the sources fate and transport of particles and colloids as well as other pollutants that behave similarly to these nuclides these nuclides also have a wide range of half lives that can be used to examine processes over various time scales for example th and ra daughter isotopes have

rainfall infiltration derived submarine groundwater discharge from multi layered aquifer system terminating at the coastline this article investigates the quantity of submarine groundwater discharge sgd from a coastal multi layered aquifer system in response to constant rainfall infiltration the system comprises an unconfined aquifer a leaky confined aquifer and an aquitard between them and terminates at the coastline an approximate analytical solution is derived based on the following assumptions i flow is horizontal in the aquifers and vertical in the aquitard and ii flow in the unconfined aquifer is described by nonlinear boussinesq equation the analytical solution is compared with numerical solutions of the strictly two dimensional nonlinear model to validate the model assumptions used for the analytical solution the sgd from the leaky confined aquifer increases with the inland rainfall infiltration recharge and the specific leakage of aquitard the maximum sgd ranges from 1 87 to 10 37 m3 per day per meter of shoreline when rainfall infiltration ranges from 18 2 to 182 mm year and the specific leakage of aquitard varies from 10 9 to 10 1 l day copyright 2011 john wiley sons ltd

intercomparison of submarine groundwater discharge estimates from a sandy unconfined aquifer summary recent studies suggest that chemical loading from submarine groundwater discharge sgd may rival other major sources such as rivers in many coastal areas sgd can occur as terrestrially derived typically fresh groundwater discharge or by seawater circulation through aquifer sediments because both terrestrial and recirculated seawater sgd can be significant sources of chemical loading to coastal waters appropriate methods are needed to properly assess and quantify the rates and distribution of these different inputs although many techniques exist to quantify sgd each method samples different components of sgd e g fresh versus saline discharge over different temporal and spatial scales the result is that confusion exists about how to use the different methods in this study we investigate the applicability of a variety of techniques for estimating sgd from an unconfined sandy coastal aquifer physical methods are first used to understand the spatial variability of discharge this information is then used with physical and geochemical data to estimate sgd investigative methods include direct measurement via seepage meters hydrogeologic estimation using darcy s law and tracer based estimates using radon and radium isotopes at our field site on cape cod massachusetts nearshore landward topography appears to exert a significant control on the spatial variability of fresh groundwater discharge presumably through its effects on evapotranspiration and hence recharge rates the darcy estimate of fresh sgd 4 0 m 3 m 1 d 1 is similar to a previous estimate made using a seepage meter transect that spans the seepage face radon serves as a valuable estimator of total sgd fresh plus saline 5 6 m 3 m 1 d 1 the difference between the total and fresh sgd estimates is in good agreement with the radium based sgd estimate 0 56 m 3 m 1 d 1 which primarily measures saline circulation through coastal sediments thus we conclude that the hydrogeologic estimate and radon and radium techniques are complimentary for estimating different components of total sgd at our field site

dynamic temporal patterns of nearshore seepage flux in a headwater adirondack lake abstract although seepage in lakes is known to vary as a function of precipitation and watershed characteristics temporal patterns of seepage flux over daily and weekly time scales have not been extensively studied with a concentrated effort of direct measurement of seepage in nearshore areas in this study seepage was intensively measured with seepage meters over two summers and during snowmelt in lower sylvan pond a small lake in the adirondack mountains region of new york state usa a consistent pattern of slight discharge never exceeding 105 ml m 2 h 1 was observed at three stations along a segment of the shoreline near the inlet stream a distinct temporal pattern of seepage was observed at three stations along another portion of the shoreline seepage discharged 400 ml m 2 h 1 for a portion of the summer in 1998 and then shifted to recharge 2 h 1 for the remainder of the summer a similar temporal pattern was observed again in 1999 but the transition to recharge occurred earlier and higher rates of discharge 610 ml m 2 h 1 and recharge 608 ml m 2 h 1 were recorded additionally seepage at these three stations increased after large rainfall events and a pronounced episodic increase of seepage was measured during snowmelt distinct seepage patterns along portions of the shoreline show that seepage can vary considerably within seasons and suggests a need to consider changes of seepage over time periods of days to weeks as well as among seasons and years this study demonstrates that the resolution of temporal seepage data can be important to the understanding of water fluxes to aquatic ecosystems

use of tritium and helium to define groundwater flow conditions in everglades national park the concentrations of tritium 3 h and helium isotopes 3 he and 4 he were used as tracers of groundwater flow in the surficial aquifer system sas beneath everglades national park enp south florida from ages determined by 3 h 3 he dating techniques groundwater within the upper 28 m originated within the last 30 years below 28 m waters originated prior to 30 years before present with evidence of mixing at the interface interannual variation of the 3 h 3 he ages within the upper 28 m was significant throughout the 3 year investigation corresponding with varying hydrologic conditions in the region of taylor slough bridge younger groundwater was consistently detected below older groundwater in the biscayne aquifer suggesting preferential flow to the lower part of the aquifer an increase in he with depth in the sas indicated that radiogenic 4 he produced in the underlying hawthorn group migrates into the sas by diffusion higher 4 he values in brackish groundwaters compared to fresh waters from similar depths suggested a possible enhanced vertical transport of 4 he in the seawater mixing zone groundwater salinity measurements indicated the presence of a wide 6 28 km seawater mixing zone comparison of groundwater levels with surface water levels in this zone indicated the potential for brackish groundwater discharge to the overlying everglades surface water

a multi level pore water sampler for permeable sediments abstract the construction and operation of a multi level piezometer multisampler designed to collect pore water from permeable sediments up to 230 cm below the sediment water interface is described multisamplers are constructed from 1 inch schedule 80 pvc pipe one quarter inch flexible pvc tubing leads from eight ports at variable depths to a 1 inch tee fitting at the top of the pvc pipe multisamplers are driven into the sediment using standard fence post drivers water is pumped from the pvc tubing with a peristaltic pump field tests in banana river lagoon florida demonstrate the utility of multisamplers these tests include collection of multiple samples from the permeable sediments and reveal mixing between shallow pore water and overlying lagoon water

pathways and processes associated with the transport of groundwater in deltaic systems summary rivers are considered to be the primary means driving hydrological and geochemical fluxes between the continents and the ocean however it is unclear how well surface water fluxes represent total fluxes or whether more diffuse subterranean fluxes of river water to the coastal ocean occur this question is important in light of research demonstrating that submarine groundwater discharge sgd is important for geochemical and hydrological fluxes here we examine the pathways and potential magnitude of the role that sgd plays in the mississippi river delta mrd the largest delta in north america we present multiple independent lines of evidence demonstrating a hydrological connection between the mississippi river mr and the mrd evidence includes hydrological budgets demonstrating downstream water losses from the mr which are unexplained and are of the same magnitude as water sources to adjacent coastal bays of the mrd well data indicating a correlation between groundwater height and the stage of the mr and excess 222 rn inventories exceeding that expected from in situ production implying an advective i e groundwater source to coastal bays sgd likely flows from the mr to its delta via paleochannels and other buried sand bodies seismic data indicates that such features are common whereas resistivity data suggest the intrusion of low salinity water to coastal bays adjacent to the river these results may be applicable to other deltas worldwide as many of the world largest rivers have deltas with numerous abandoned distributaries that could act as conduits for groundwater

using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off crescent beach florida abstract a spectacular submarine spring is located about 4 km east of crescent beach fl in the atlantic ocean the single vent feature of crescent beach spring provides a unique opportunity to examine onshore offshore hydrogeologic processes as well as point source submarine ground water discharge the floridan aquifer system in northeastern florida consists of tertiary interspersed limestone and dolomite strata impermeable beds confine the water bearing zones under artesian pressure miocene and younger confining strata have been eroded away at the vent feature enabling direct hydrologic communication of eocene ground water with coastal bottom waters the spring water had a salinity of 6 02 which was immediately diluted by ambient seawater during advection mixing the concentration of major solutes in spring water and onshore well waters confirm a generalized easterly flow direction of artesian ground water nutrient concentrations were generally low in the reducing vent samples and the majority of the total nitrogen species existed as nh 3 the submarine ground water tracers rn 222 1174 dpm l 1 dpm methane 232 nm and barium 294 5 nm were all highly enriched in the spring water relative to ambient seawater the concentrations of the reverse redox elements u v and mo were expectedly low in the submarine waters the strontium isotope ratio of the vent water 87 sr 86 sr 0 70798 suggests that the spring water contain an integrated signature indicative of floridan aquifer system ground water additional sr isotopic ratios from a series of surficial and lower floridan well samples suggest dynamic ground water mixing and do not provide clear evidence for a single hydrogeologic water source at the spring vent in this karst dominated aquifer such energetic mixing at the vent feature is expected and would be facilitated by conduit and fractured flow radium isotope activities were utilized to estimate flow path trajectories and to provide information on potential travel times between an onshore well and the spring using either 223 ra and 224 ra or 228 ra and qualifying this approach with several key assumptions estimates of water mass travel times from an upper floridan well in crescent beach to the submarine vent feature distance 4050 m are in the order of 0 01 0 1 m min 1

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

geochemical behaviour of radium isotopes and radon in a coastal thermal system balaruc les bains south of france abstract the behaviour of the four ra isotopes measured by gamma spectrometry and 222 rn measured with an alphaguard ionisation chamber has been investigated in nacl rich thermal waters of balaruc les bains on the mediterranean coast south of france this study allows identification of the deep thermal water signature and reveals the influence of seawater or karst water inflows on ra isotopes and 222 rn the deep thermal water has 226 ra and 222 rn activities of 840 and 1900 mbq l respectively a 228 ra 226 ra activity ratio of 0 59 and low 224 ra 228 ra and 223 ra 226 ra ratios of 0 67 and 0 025 respectively several arguments suggest a dominant role of radioactive decay for short lived ra isotopes and rn during the relatively rapid ascent of thermal water through wide open fractures and drains the low 223 ra 226 ra ratio constrains the maximum ascent velocity of thermal water to 8 10 m h seawater inflow into the hydrothermal system results in an enrichment in short lived ra isotopes and 222 rn the high 223 ra 226 ra ratio 0 23 suggests that 223 ra 224 ra and 222 rn produced by alpha recoil in the upper jurassic limestone are entrained by seawater percolation through the coastal basement due to active pumping in one of the near shore production well this process would be enhanced by a low water rock ratio i e in a low porosity micro fractured limestone mixing of this enriched seawater with thermal water induces barite precipitation with co precipitation of a large fraction of ra short lived ra isotopes may thus be useful tracers of seawater flux towards the continent conversely the inflow and mixing of karst groundwater result in a general dilution of all dissolved elements only a small enrichment in 224 ra and 223 ra but a large enrichment in 222 rn up to 26 bq l the combination of ra isotopes and 222 rn data provides a good way to trace the dynamics of different water masses along coastal areas

tracing anthropogenically driven groundwater discharge into a coastal lagoon from southern brazil summary we investigated the distribution of naturally occurring geochemical tracers 222 rn 223 ra 224 ra 226 ra ch 4 18 o and 2 h in the water column and adjacent groundwater of mangueira lagoon as proxies of groundwater discharge mangueira lagoon is a large 90 km long shallow 4 5 m deep fresh and non tidal coastal lagoon in southern brazil surrounded by extensively irrigated rice plantations and numerous irrigation canals we hypothesized that the annual intense irrigation for rice agriculture creates extreme conditions that seasonally change groundwater discharge patterns in the adjacent lagoon we further supposed that dredging of irrigation canals alters groundwater fluxes while the activities of 222 rn in shallow groundwater were 2 3 orders of magnitude higher than in surface water ch 4 and radium isotopes were only 1 order of magnitude higher therefore 222 rn appears to be the preferred groundwater tracer in this system radon concentrations and conductivities were dramatically higher near the pump house of rice irrigation canals consistent with a groundwater source modeling of radon inventories accounting for total inputs groundwater advection diffusion from sediments and decay of 226 ra and losses atmospheric evasion horizontal mixing and decay indicated that groundwater advection rates in the irrigation canals 25 cm d are over 2 orders of magnitude higher than along the shoreline 0 1 cm d nearly 75 of the total area of the canals is found in the southern half of the lagoon where groundwater inputs seem to be higher as also indicated by methane and stable isotope trends in spite of the relatively small area of the canals we estimate that they contribute nearly 70 of the total 57 000 m 3 d groundwater input into the entire mangueira lagoon we suggest that the dredging of these canals cut through aquitards which previously restricted upward advection from the underlying permeable strata the irrigation channels may therefore represent an important but previously overlooked source of nutrients and other dissolved chemicals derived from agricultural practices into the lagoon

terrestrial originated submarine groundwater discharge through deep multilayered aquifer systems beneath the seafloor a large quantity of submarine groundwater discharge sgd of about 1000 m3 day 1 m 1 of the 600 km long shoreline of south atlantic bight has been estimated by moore global biogeochemical cycles 2010b 24 gb4005 doi 10 1029 2009gb003747 however there is great uncertainty in estimating the percentage of net land originated groundwater recharge of sgd moreover most previous studies considered the homogeneous case for the coastal superficial aquifers here we investigated the terrestrial originated sgd through a multilayered submarine aquifer system which comprises two confined aquifers and two semi permeable layers the inland recharge includes a constant part representing the annual average and a periodical part representing its seasonal variation an analytical solution was derived and used to analyse the distributions of the terrestrial originated sgd from the multilayered aquifers along the winyah bay transect south atlantic bight it is found that the width of the zone of sgd from the upper aquifer ranges from 0 8 to 8 0 km depending on the leakance of the seabed semi permeable layer a head of the upper aquifer at a coastline 1 0 m higher than the mean sea level will cause a sgd of 1 82 18 3 m3 day 1 m 1 from that aquifer as the seabed semi permeable layer s leakance varies from 0 001 to 0 1 day 1 providing considerable possibility for considerable land originated sgd seasonal terrestrial originated sgd variations predicted by the analytical model provide consistent explanation of the seasonal variation of 226ra observed by moore journal of geophysics 2007 112 c10013 doi 10 1029 2007jc004199 the contribution of the lower aquifer to sgd is only 1 2 12 of that of the upper aquifer copyright 2014 john wiley sons ltd

linking regional sources and pathways for submarine groundwater discharge at a reef by electrical resistivity tomography 222rn and salinity measurements 1 submarine groundwater discharge sgd is an important component of the hydrologic cycle connecting terrestrial to marine environments sgd in fringing reefs and its consequences on biogeochemistry and ecology remain mostly unexplored the 222rn activity and salinity of seawater indicate a substantial groundwater contribution throughout most of the 20 km2 studied tropical reef in pangasinan philippines over 30 km of electrical resistivity profiles with a penetration depth of 12 5 m shows widespread zones within the reef that are much more resistive than porous reef rocks or sediment saturated with typical seawater some discrete resistive areas are located close to where seawater has 222rn peaks and where geologic lineaments are likely located suggesting that these are preferential pathways for fresher groundwater discharging to the reef sgd at the site could be a major ecological factor connecting the reef to the subsurface environment which in turn may lead to connections to land

seismic evidence for fluid escape from mesozoic cuesta type topography in the skagerrak abstract gas and fluid dynamic processes in the mesozoic to recent strata of the southern slope and center of the norwegian trench skagerrak have been analyzed by high resolution multi channel seismic data collected with a watergun as the seismic source on board of rv heincke in spring 2003 three profiles across the southern slope and the center of the trench and four profiles cover the north eastern termination of the trench the data resolve the quaternary succession and the subcropping mesozoic strata the separating unconformity shows a typical cuesta topography caused by glacial erosion on the slope contourite drifts are present above a water depth of approximately 400 m internal reflections of the quaternary are obscured by acoustic turbidity particularly phase reversed bright reflections occurring in the entire lower jurassic to upper cretaceous succession suggest the presence of fluids therein sea floor pockmarks have been observed on the southern slope and in the center of the trench both slope and trench pockmarks are vertically correlated with the sub crop of fluid charged mesozoic rocks beneath which indicate lateral fluid escape from porous mesozoic rocks fluids that migrate towards a slope pockmark are capable to wash out gas from the quaternary leaving gas free patches behind since no thermogenic gas has ever been measured in core samples from the slope and trench freshwater seepage is a possible explanation in this case the water outflow might represent artesian springs

significant groundwater input to a coastal plain estuary assessment from excess radon a submarine groundwater discharge zone was identified through the investigation of persistent excess radon in the delaware river and bay estuary this zone the excess radon maximum erm was located approximately 82 km upstream from the mouth of the delaware bay water column radon activity at the erm was elevated relative to the radon activity observed outside of this zone and was as high as 2 73 dpm l 1 a radon budget model developed to assess the contribution of multiple radon sources to the erm indicated that simple molecular diffusion from sediments could not support the observed excess radon activity an additional source of radon is required to sustain the excess radon activity in the erm a groundwater flux of 14 to 29 m 3 s 1 from the two aquifers that subcrop on the delmarva peninsula immediately west of the erm can support the excess radon observed in the water column the stratigraphy and hydrology of these aquifers makes them likely sources of the groundwater discharge that results in the erm the calculated submarine groundwater discharge flux is equivalent to the surface water discharge of the second and third largest tributary rivers of the delaware estuary 2003 elsevier science b v all rights reserved

the importance of groundwater discharge to the methane budgets of nearshore and continental shelf waters of the northeastern gulf of mexico methane concentrations in groundwater wells sinkholes and springs averaged 61 9 mu m while concentrations in nearshore and continental shelf waters within the study area averaged 62 7 nm and 27 5 nm respectively we tested the hypothesis that the three orders of magnitude difference between groundwater and seawater concentration would make ch sub 4 an indicator of submarine groundwater discharge to surficial waters methane budgets for nearshore and continental shelf water columns were consistent with the hypothesis that groundwater seepage or seawater recirculation through the seabed is the dominant source of ch sub 4 relative to benthic diffusive flux riverine flux and in situ water column production seepage recirculation appears to account for approximately 83 99 of the total ch sub 4 input into the water column within the study area utilizing measured porewater ch sub 4 concentrations the calculated amounts of seepage required to support the observed benthic fluxes were comparable to seepage rates measured in the field nearshore seepage meter transacts showed a strong and direct correlation between the integrated quantity of groundwater seepage along a shoreline and the inventory of ch sub 4 in those waters our study further showed a similar correlation between sup 222 rn another potential groundwater tracer andmore ch sub 4 in offshore waters supporting the hypothesis of a common benthic source for these constituents 67 refs 10 figs 2 tabs less

methanotrophy controls groundwater methane export from a barrier island abstract methane concentrations can be high in coastal groundwater resulting in methane export driven by submarine groundwater discharge however the magnitude of this methane flux depends significantly on the rate of methanotrophy the often overlooked process of microbial methane consumption that occurs within coastal aquifer sediments here we describe a zone of methanogenesis within the freshwater lens of a barrier island aquifer and investigate the methane source sink behavior of the barrier island system as a whole the median concentration of methane dissolved in fresh groundwater beneath the center of the island was 0 6 mm supported by high rates of potential methanogenesis 22 mmol m 2 day 1 however rates of microbial methane consumption were also elevated in surrounding sediments 18 mmol m 2 day 1 groundwater flowing from the zone of methanogenesis to the point of discharge into the ocean had a long residence time within methanotrophic sediments 195 days such that the majority of the methane produced within the barrier island aquifer was likely consumed there

methodological study of submarine groundwater discharge from a karstic aquifer in the western mediterranean sea summary a multiproxy approach of complementary techniques is applied to localise and quantify submarine groundwater discharge sgd from el maestrazgo jurassic aquifer an example of widespread carbonate coastal aquifer of the western mediterranean sea castellon spain unconventional water resources are critical in this area where highly populated resorts have been developed the aquifer has two main features of particular interest a karstic system with a deep saturated zone reaching 450 m and with no significant surface discharge occurring within the continental area on the other hand sgd can alter the condition of coastal marine environments reducing salinities and providing nutrients that can cause eutrophication and algal blooms the applied combined techniques make it possible to detect groundwater outflows using airborne thermal infrared tir images to monitor physico chemical anomalies in the sea and to quantify the submarine groundwater discharges by means of direct measurements and radium isotopic analyses three main coastal areas affected by sgd and a submarine spring located at 3 km from the coast which seems to be associated with tectonic discontinuities were localised the calculated fresh sgd from ra isotopes 375 mm 3 y 1 is in agreement with the mean aquifer recharge obtained by hydrogeological methods 394 mm 3 y 1

application of 222rn and ch4 for assessment of groundwater discharge to the coastal ocean groundwater discharge is a neglected source of freshwater and dissolved constituents to the ocean it can occur via diffuse seepage and point source spring discharge two naturally occurring trace gases 222 rn and ch 4 are present in groundwater at concentrations that are elevated by several orders of magnitude relative to seawater and they may be useful in tracing groundwater inputs to surface waters water samples collected near a submarine spring in the northeastern gulf of mexico displayed radon and methane concentrations inversely related to salinity and considerably greater than those found in surrounding waters coastal water 222 rn and ch 4 inventories varied directly with groundwater seepage rates the integrated quantities of 222 rn and ch 4 in the nearshore waters overlying a seepage meter transect showed a significant positive