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

radon 222 as a tracer for mixing in the water column and benthic exchange in the southern california borderland the concentrations of222rn and226ra in the water column and in the sediments of santa barbara and san nicolas basins have been measured semi annually over the last four years approximately one third of excess radon profiles obtained in the water column in these basins can be adequately fit with a one dimensional eddy diffusion decay model exponential profiles in the center of san nicolas basin yield a vertical eddy diffusivity of 26 16 cm2 s and 3 4 1 0 cm2 s for santa barbara basin the application of a two dimensional eddy diffusion decay model to profiles obtained in the center and on the margins of san nicolas basin produces a better fit than is found using a one dimensional vertical eddy diffusivity the two dimensional model for san nicolas basin predicts a vertical eddy diffusivity of 17 cm2 s and a horizontal eddy diffusivity of 105 cm2 s these values are in reasonable agreement with those predicted from the vertical buoyancy gradient and the horizontal length scale the vertically integrated radon excess standing crop in the water column of santa barbara basin averages 53 23 atoms m2 s this is in good agreement with the flux across the sediment water interface of 60 15 atoms m2 s calculated by measuring radon emanation in the sediments as a function of depth and applying a molecular diffusion reaction model hence one dimensional molecular diffusion accurately predicts the flux of radon from the laminated santa barbara basin sediments in san nicolas basin the integrated radon excess in the water column is 376 143 atoms m2 s but the diffusive randon flux from san nicolas basin sediments averages only 190 53 atoms m2 s this descrepancy indicates that a non diffusive process probably macrofaunal irrigation supplies much of the flux of radon from san nicolas basin sediments

effect of submarine groundwater discharge on the coastal ocean inorganic carbon cycle using radium ra isotopes we estimate that the average submarine groundwater discharge sgd flux marine plus terrestrial groundwater into the southwest florida shelf swfs was 20 6 10 3 107 and 18 6 8 3 107 m3 d21 in july and october 2009 respectively the terrestrial groundwater flux was the same order of magnitude as the local river discharge in july 2009 shelf water total alkalinity talk and dissolved inorganic carbon dic concentrations could not be explained by river inputs alone suggesting a groundwater source we estimated sgd fluxes of talk and dic using the sgd flux derived from a shelf water 226ra budget and talk and dic concentration differences between the groundwater and seawater these fluxes were also determined by the observed talk 226ra and dic 226ra relationships in the shelf water and the 226ra flux sustained by sgd these talk and dic fluxes were 11 71 times more than the combined input of local rivers suggesting that sgd was the dominant source of talk and dic to the swfs during 2009 sgd is an important component of the inorganic carbon budget for the coastal ocean

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

natural 222rn and 220rn indicate the impact of the water sediment regulation scheme wsrs on submarine groundwater discharge in the yellow river estuary china submarine groundwater discharge sgd in estuaries brings important influences to coastal ecosystems in this study we observed significant sgd in the yellow river estuary including a fresh component during the water sediment regulation scheme wsrs period we used the 222rn and 220rn isotope pair to locate sites of significant sgd within the study area three apparent sgd locations were found during a non wsrs period one of which became much more pronounced according to the remarkably elevated radon levels during the wsrs increased river discharge from 245 m3 s 1 to 3560 m3 s 1 and the elevated river water level from 11 m to 13 m during the wsrs led to a higher hydraulic head enhancing groundwater discharge in the estuary our results suggest that high river discharge 3000 m3 s 1 might be necessary for elevated fresh submarine groundwater discharging fsgd vertical profiles of salinity do and turbidity anomalies along the benthic boundary layer also indicated significant fsgd in the estuary during the wsrs nutrient concentrations had positive correlations with 222rn during a 24 h observation which indicates that sgd is a dominant nutrient pathway in this area

groundwater fluxes into a submerged sinkhole area central italy using radon and water chemistry abstract the groundwater contribution into green lake and black lake vescovo lakes group two cover collapse sinkholes in pontina plain central italy was estimated using water chemistry and a 222 rn budget these data can constrain the interactions between sinkholes and deep seated fluid circulation with a special focus on the possibility of the bedrock karst aquifer feeding the lake the rn budget accounted for all quantifiable surface and subsurface input and output fluxes including the flux across the sediment water interface the total value of groundwater discharge into green lake and black lake 540 160 l s 1 obtained from the rn budget is lower than but comparable with historical data on the springs group discharge estimated in the same period of the year 800 90 l s 1 besides being an indirect test for the reliability of the rn budget tool it confirms that both green and black lake are effectively springs and not simply water filled sinkholes new data on the water chemistry and the groundwater fluxes into the sinkhole area of vescovo lakes allows the assessment of the mechanism responsible for sinkhole formation in pontina plain and suggests the necessity of monitoring the changes of physical and chemical parameters of groundwater below the plain in order to mitigate the associated risk

importance of geochemical transformations in determining submarine groundwater discharge derived trace metal and nutrient fluxes abstract seasonal spring and summer 2002 concentrations of dissolved 3 po 4 si and doc were determined in groundwater samples from 5 wells aligned along a 30 m shore normal transect in west neck bay long island ny results show that significant systematic changes in groundwater trace metal and nutrient composition occur along the flowpath from land to sea while conservative mixing between west neck bay water and the groundwaters explains the behavior of si and doc non conservative inputs for co and ni were observed concentration increases of 10 and 2 fold respectively and removal of po 4 and no 3 decreases to about half along the transport pathway groundwater associated chemical fluxes from the aquifer to the embayment calculated for constituents not exhibiting conservative behavior can vary by orders of magnitude depending on sampling location and season e g co 3 4 10 2 8 2 10 3 mol d 1 using measured values from different wells as being representative of the true groundwater endmember chemical composition also results in calculation of very different fluxes e g cu 6 3 10 3 mol d 1 inland freshwater well vs 2 1 10 5 mol d 1 seaward well s 17 ppt this study suggests that seasonal variability and chemical changes occurring within the subterranean estuary must be taken into account when determining the groundwater flux of dissolved trace metals and nutrients to the coastal ocean

chemical signals from submarine fluid advection onto the continental shelf we report unambiguous signals of subsurface fluid input on the continental shelf 40 80 km from shore in water depths of 20 45 m the site of this input is near the continental shelf break off the south carolina coast between 32 33 n and 78 5 79 5 w repeated transects over this area reveal enrichments of 226ra 228ra and ba by factors of 3 4 above ambient ocean concentrations the short lived 223ra and 224ra are enriched by over an order of magnitude the ra and ba enrichments are not caused by up welling of deep water as no such 226ra or ba concentrations occur in the upper 2000 m of the atlantic ocean sediments in the region are largely relic sand and do not offer a viable source for 226ra 228ra and ba enrichments we conclude that the source is the discharge of submarine fluids enriched in 226ra 228ra and ba the salinity of water in the ra ba enriched zone is diluted by 0 2 0 6 relative to water at the same depth farther offshore pronounced salinity and density anomalies characterize one site of active discharge estimates of 226ra and ba concentrations in the fluids and the replacement time of water in the enriched zone suggest the fluid flux is similar to the summertime flow of major rivers in the area the region of ra ba enrichment is also characterized by a strong fluorescence signal indicating high concentrations of chlorophyll in the water it is probable that the leaking fluids supply nutrients that stimulate productivity in the bottom waters which are within the photic zone because the fluorescence signal is restricted to depths greater than 20 m it is unlikely that the signal could be recognized by satellite or aircraft sensors

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

the effects of unconsolidated sediments upon the ground motion during local earthquakes abstract a vertical seismic array at the richmond field station on the margin of san francisco bay california has provided some excellent experimental data showing the effects of unconsolidated sediments on ground motion during local earthquakes the experiments are well controlled in that good estimates of the material properties of the sediments are available with the largest uncertainty being in the attenuation three components of acceleration have been recorded in bedrock below the sediments within the sediments and at the surface of the sediments from two local earthquakes the maximum accelerations at the surface are between 1 5 and 4 3 times those in the bedrock analytical calculations which assume vertically propagating waves and which are suitable for highly attenuating materials explain the major differences between the bedrock records and the surface records for both vertical and horizontal components maximum accelerations duration frequency content general character of the records and response spectra are all in approximate agreement some of the energy arriving late in the records can best be explained by surface waves propagating horizontally in the sediments

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

hydraulic exchange between a coral reef and surface sea water hydraulic exchange between overlying sea water and the internal structure of a patch reef in kaneohe bay oahu hawaii was studied with an array of wells 1 2 and 4 m deep two natural chemical tracers radon and salinity were used to calculate the exchange rate between surface sea water and reef interstitial waters dissolved radon concentrations are substantially higher in interstitial waters than is surface water the degree of radon enrichment is quantitatively related to the time elapsed since interstitial water had equilibrated with the atmosphere residence time estimates are 1 40 days with deeper wells having slower exchange the average residence time for 1 m deep wells was 2 1 days a rainstorm induced dilution of the salinity of kaneohe bay provides the second tracer samples of surface and reef interstitial waters following this salinity perturbation are used to calculate an average residence time of 2 6 days at a depth of 1 m and 42 days at a depth of 2 m three types of physical forces thought to cause exchange between surface and interstitial water are considered by measurement of the forcing functions and reef permeability hydraulic conductivities are about 50 m d with lower values near the seaward side of the reef more most exchange seems to be caused by high frequency wave driven oscillatory pumping and by unidirectional hydraulic head gradients of uncertain origin that are stable for at least 3 4 days wave driven mixing is probably more important shallower in the reef whereas head driven flow may dominate deeper in the reef tidal pumping does not seem to contribute to exchange all methods indicate that exchange in the upper part of checker reef is primarily through vertical exchange the best estimate for the residence time of water at a depth of 1 m is 2 days water at depths of 204 m probably has a residence time of weeks to months 49 refs 8 figs 6 tabs less

mixed convection and density dependent seawater circulation in coastal aquifers 1 density dependent circulation of seawater in coastal aquifers results in submarine groundwater discharge sgd across the seabed that is a mixture of terrestrial groundwater and former marine water in this study the controls of the relative amount of seawater to freshwater in sgd were investigated numerically using the feflow and sutra codes it was found that the key controls could be expressed in the form of a single nondimensional recirculation number that incorporates the combined effects of free convection forced convection and hydrodynamic dispersion on convective overturn within the coastal salt wedge anisotropy effects were incorporated into the recirculation number with limited success based on the principle of equivalent isotropic hydraulic conductivity the type of boundary condition employed along the seabed was shown to be important convective overturn was substantially increased if backward dispersion of salt into the aquifer from along the outflowing portion of the seabed boundary was prevented overall the results demonstrated a strong dependence of convective overturn on the aquifer dispersivities suggesting that results from numerical simulations are problematic to apply to real aquifer systems that typically exhibit uncertain scale dependent dispersion properties

radon tracing of groundwater discharge into an australian estuary surrounded by coastal acid sulphate soils summary widespread sulphidic deposits have accumulated in tropical coastal floodplains throughout the world sulphidic soils oxidize when floodplains are drained for urban and agricultural development as a result large amounts of sulphuric acid may be released to nearby waterways macropores may create excellent conditions for groundwater flow in coastal acid sulphate soils cass an automated radon 222rn measurement system was used to quantify groundwater inputs into a tidally dominated estuary that is known to be influenced by acid discharges from cass richmond river estuary australia a high resolution radon survey along a 120 km long segment of the tidal river identified two areas of preferential groundwater inputs intensive time series measurements in one of those areas the tuckean broadwater demonstrated that groundwater inputs are highly variable over hourly and seasonal time scales and inversely related to surface water ph elevated radon concentrations up to 12 dpm l and low ph as low as 3 3 were observed in surface waters at low tide a few weeks after a large rain event these results demonstrate that acidic waters are entering the estuary via tidally modulated groundwater flow pathways groundwater discharge rates into drains in the tuckean swamp were estimated from a dual assumption radon mass balance to be 0 09 0 16 and 0 56 0 89 m3 s 1 during the dry and wet season respectively or 6 10 and 37 59 cm day if the area is taken into account while surface runoff increased only 2 fold in the wet season relative to the dry season groundwater discharge rates increased 6 fold since groundwater can be a major driver of surface water quality radon can be useful in cass monitoring and management efforts

on the fate of 220rn in soil material in dependence of water content implications from field and laboratory experiments abstract to study the potential of 220 rn as a groundwater tracer we analyzed different groundwater systems with a laboratory proven radon in water detection system however with one single exception no 220 rn was detected in the groundwater although 222 rn was always present at high concentrations field observations of 220 rn and 222 rn in soil gas revealed soil water content to be the crucial control for 220 rn release from soil grains to soil pores we identified water films around and water menisci between the soil grains to impede the diffusive transport of 220 rn this finding was confirmed by the results of laboratory experiments with monazite pebbles and manganese sand which both are 220 rn sources besides the water content the laboratory experiments also identified the water flow turbulent in the experiment versus laminar in groundwater to control the 220 rn emanation the laminar flow condition in groundwater together with the soil water content set a conceptual frame to explain why 220 rn can be detected in unsaturated soil but not in groundwater

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

variability of current temperature and bottom pressure across the west florida continental shelf winter 1981 1982 observations are analyzed from four current meter moorings deployed on the broad continental shelf in the northeastern gulf of mexico from november 29 1981 to february 8 1982 71 days consistent with recent modeling studies the shelf circulation responds within an inertial period to the alternating up and down coast synoptic scale wind forcing average response to a 0 5 dyn cm 2 alongshore wind stress as measured at the coast is 20 cm s 1 off cedar key and 40 cm s 1 in the north where the shelf narrows off cape san bias lower layer currents veer counterclockwise with depth as in a bottom ekman layer e folding scale 8 m the pressure field decays offshore e folding scale 160 km and yields a geostrophic current in good agreement with the observed alongshelf flow cross shelf and vertical variations of the tidal signals compare nicely with results from barotropic theory calculations indicate that most of the shoreward propagating tidal energy must be dissipated in depths of 20 m within 50 km of shore

hydrologic forcing of submarine groundwater discharge insight from a seasonal study of radium isotopes in a groundwater dominated salt marsh estuary a seasonal study of radium derived submarine groundwater discharge sgd and associated nitrogen fluxes was carried out in a salt marsh estuary between 2001 and 2003 pamet river estuary massachusetts twelvehour time series of salinity and radium at the estuary inlet were used to determine the relative importance of fresh versus saline sgd respectively the distinct radium 228ra 226ra isotopic signature of marsh peat pore water and aquifer derived brackish groundwater was used to further partition the ra derived sgd estimate of these three groundwater sources only the marsh derived groundwater was constant across time the ratio of brackish to fresh sgd was inversely correlated with water table elevation in the aquifer suggesting that ra derived sgd was enhanced during dry periods the various sgd fluxes were responsible for an average annual dissolved inorganic nitrogen din input of between 1 7 mol m 2 yr 1 and 7 1 mol m 2 yr 1 and a soluble reactive phosphate srp flux of 0 13 0 54 mol m 2 yr 1 approximately 30 of the sgd derived din and srp flux is exported to coastal waters cape cod bay whereas 70 is retained by the salt marsh ecosystem

summertime coastal currents in the northeastern gulf of mexico abstract observations of currents and temperature at a mooring on the 18 m isobath 30 km south of the florida shoreline are discussed for the 31 day period 15 august 15 september 1978 tidal currents having average amplitudes of 10 cm s 1 account for 85 of the observed kinetic energy low frequency currents with maximum speeds of 10 cm s 1 appear to be at least partly driven by local wind stress events of magnitude 0 2 dyn cm 2 frictional effects give rise to a veering with depth in the ekman sense of both the low frequency flow and the energetic counterclockwise rotating twice daily tidal currents propagation of both the tidal signal and low frequency coastal sea level fluctuations amplitudes 5 cm is westward through the study area

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

divergent drivers of carbon dioxide and methane dynamics in an agricultural coastal floodplain post flood hydrological and biological drivers many coastal floodplains have been artificially drained for agriculture altering hydrological connectivity and the delivery of groundwater derived solutes including carbon dioxide co2 and methane ch4 to surface waters here we investigated the drivers of co2 and ch4 within the artificial drains of a coastal floodplain under sugarcane plantation and quantify the contribution of groundwater discharge to co2 and ch4 dynamics over a flood event 290 mm of rainfall high temporal resolution in situ observations of dissolved co2 and ch4 carbon stable isotopes of ch4 delta c 13 ch4 and the natural groundwater tracer radon rn 222 allowed us to quantify co2 ch4 and groundwater dynamics during the rapid recession of a flood over a five day period extreme super saturation of free co2 co2 up to 2 951 mu m 25 480 of atmospheric equilibrium was driven by large groundwater input into the drains maximum 87 cm day 1 caused by a steep hydraulic head in the adjacent water table groundwater input sustained between 95 and 124 of the surface co2 flux during the flood recession by delivering high carbonate alkalinity groundwater dic 10 533 mu m similar to ph 7 05 to acidic surface water ph 4 consequently transforming all groundwater derived dic to co2 in contrast groundwater was not a major direct driver of ch4 contributing only 14 of total ch4 fluxes a progressive increase in ch4 concentrations of up to similar to 2400 nm day 1 occurred as a combination of increased substrate availability delivered by post flood drainage water and longer residence times which allowed for a biogenic ch4 signal to develop the progressive enrichment in delta c 13 ch4 values 70 to 48 and increase in ch4 concentrations 46 2460 nm support coupled production oxidation with concentrations and delta c 13 values remaining higher 2 798 nm and 47 than pre flood conditions 534 nm and 55 parts per thousand three weeks after the flood our findings demonstrate how separate processes can drive the aquatic co2 and ch4 response to a flood event in a drained coastal floodplain and the key role groundwater had in post flood co2 evasion to the atmosphere but not ch4 c 2016 elsevier b v all rights reserved

combining isotopic tracers 222rn and δ13c for improved modelling of groundwater discharge to small rivers in regions where aquifers sustain rivers the location and quantification of groundwater discharge to surface water are important to prevent pollution hazards to quantify and predict low flows and to manage water supplies 222rn is commonly used to determine groundwater discharge to rivers however using this isotopic tracer is challenging because of the high diffusion capacity of 222rn in open water this study illustrates how a combination of isotopic tracers can contribute to an enhanced understanding of groundwater discharge patterns in small rivers the aim of this paper is to combine 222rn and 13cdic to better constrain the physical parameters related to the degassing process of these tracers in rivers the hallue river northern france was targeted for this study because it is sustained almost exclusively by a fractured chalk aquifer the isotopes 222rn 13cdic 2h and 18o were analysed along with other natural geochemical tracers a mass balance model was used to simulate 222rn and 13cdic the results of 2h and 18o analyses prove that evaporation did not occur in the river the calibration of a numerical model to reproduce 222rn and 13cdic provides a best fit diffusive layer thickness of 3 21 10 5 m this approach is particularly useful for small rivers flowing over carbonate aquifers with high groundwater dic where the evolution of river dic reflects the competing processes of groundwater inflow and co2 degassing this approach provides a means to evaluate groundwater discharge in small ungauged rivers copyright 2014 john wiley sons ltd

role of aquifer heterogeneity in fresh groundwater discharge and seawater recycling an example from the carmel coast israel 1 a case study is shown in which the pattern of submarine groundwater discharge and of seawater recycling is controlled by local hydrogeological variability the coastal aquifer in dor bay is composed of two units a partly confined calcaranitic sandstone kurkar and an overlying loose sand groundwater in the kurkar has elevated activities of 222rn 390 dpm l and relatively low 224ra 223ra activity ratios 3 4 while the sand groundwater is significantly less radiogenic 6 90 dpm l and shows higher 224ra 223ra ratios groundwater discharging from sand covered areas of the bay has salinities of 16 31 and an average 222rn activity of 168 dpm l which lies on a mixing line between rn rich kurkar fresh water and rn poor seawater another key observation is that seawater infiltrates to some extent into onshore sand groundwater while the fresh water within the submarine kurkar can be traced up to 40 m offshore this implies that while fresh water mainly discharges from the kurkar unit seawater recycling is limited to the loose sand and that the discharge from sand covered areas is a mixture of kurkar water with recycled seawater advection rates from the bay floor were calculated from rn time series and found to vary between 0 and 36 cm d correlating negatively with bay water depth the average flux was 8 1 cm d and it did not seem to change much during march may and july 2006 the average amount of fresh water discharging to the bay was 5 0 m3 d per meter of shoreline radon activity in the sand groundwater also fluctuates due to influx of kurkar type groundwater

using 222rn to identify and quantify groundwater inflows to the mundo river se spain abstract groundwater discharge to the mundo river se spain has been investigated from 2011 to 2013 by means of 222rn activities in river water and groundwater starting nearby the river source some 50 km of river channel have been studied the mundo river is located in the water stressed region of the segura river basin identifying and quantifying groundwater discharge to rivers is essential for the hydrological plan of the segura basin authority four main areas of groundwater discharge to the river have been identified by means of 222rn moreover groundwater fluxes have been quantified using radon activities and when possible have been validated with chloride mass balances the uncertainty range 2 of all water balances has also been assessed groundwater discharge qgw values estimated by radon mass balances rmb and chloride mass balances cmb were similar in the river tracts and or dates in which surface inputs from tributaries were null or negligible this adds confidence to the qgw values estimated by rmb in the reaches were cmb could not be performed due to the existence of ungauged surface inputs as is the case of the upper basin of the mundo river as well as to the applicability of the method to similar situations quantification of groundwater discharge allowed identifying ayna zone as the main gaining reach of the studied area with up to 29 553 8667 m3 day 1 in year 2011 overall the total qgw estimated by means of rmb for the studied area was 8 16 of the total river flow the results are coherent with the meteorological conditions of the study period average rainfall around 450 mm y and also with the undisturbed situation of the aquifers discharging to the mundo river in the considered area

tidal variability of salinity and velocity fields related to intense point source submarine groundwater discharges into the coastal ocean velocity and hydrography measurements were used to determine the tidal variability and detailed structure of an intense 43 200 m3 d 1 point source submarine groundwater discharge from a spring located in the coastal ocean of the yucatan peninsula mexico measurements were obtained during a dry season with a combination of towed profiling and fixed instrumentation the goal of these observations was to understand the effects of tides on the velocity and salinity structure of the water column that determine mixing and dispersion processes at spatial scales from meters to kilometers tidally averaged flows were characterized by an upward jet flanked by asymmetric downdrafts the asymmetry was caused by a 0 1 m s 1 ambient horizontal flow and by the 40 angle relative to the vertical of discharge the spatially averaged salinity distributions exhibited lowest values at low tides and highest values at high tides this was attributed to tidal variations of hydrostatic pressure acting on the spring outflow which allowed 1 m s 1 vertical flows at low tides and 0 05 m s 1 vertical velocities at high tides the vertical momentum balance consisted of upward accelerations produced by buoyancy and inertia from the spring and downward accelerations from gravity on the basis of this balance and of energetic considerations the vertical extent of the spring discharge likely depends on the density contrast between ambient and discharge waters buoyancy forces the upward speed of the spring inertia forces and the depth of the water column hydrostatic pressure force all of which vary with tides

a broadband study of the 13 august 1978 santa barbara earthquake the santa barbara earthquake of 13 august 1978 provides an opportunity to perform a broadband investigation of body waves for a well recorded moderate size m l 5 1 event the long and short period teleseismic body waves are modeled in the time domain to construct a source time function which is consistent in the period range of 1 to 20 sec the long period records indicate an overall duration of 6 sec while the short period records reveal the fine scale character of the slip history consisting of two sharp pulses separated by about 1 sec the source mechanism determined from this analysis is a moderately dipping 30 ne thrust with significant left lateral slip the moment was determined to be 1 1 10 25 dyne cm the earthquake was also reasonably well recorded on accelerographs in the near field the modeling of the strong motion displacements was a two step procedure 1 the displacements were modeled alone and 2 in an attempt to achieve consistency between the local and far field time functions the qualitative features of the teleseismic short period time function were used to predict the displacements if the two sources in the short period time function are allowed to have different mechanisms the displacements can be modeled quite well this suggests that the overall faulting process was rough and the multiple source character suggested at high frequencies is due to high stress drop asperities the two sources are modeled as asperities separated by 1 5 km the first source has a mechanism consistent with the teleseismic solution while the second source is more steeply dipping the total moment determined from the strong motion data is 3 5 10 24 dyne cm or one third the long period moment this is consistent with other recent studies which suggest that the high frequency strong ground motion is controlled by the distribution of asperities even though the sum of their moments may be small compared to the overall moment this study also shows the importance of teleseismic short periods in predicting the local displacements

uranium geochemistry on the amazon shelf chemical phase partitioning and cycling across a salinity gradient abstract the size distribution of u was examined in surface waters of the amazon shelf water samples were collected during a low discharge river stage across a broad salinity gradient 0 3 35 4 and fractionated by planar filtration and tangential flow ultrafiltration into 1 solution u s c 10 000 mw 0 4 m 3 dissolved u d p 0 4 m phases concentrations of colloidal u comprise up to 92 of the dissolved u fraction at the river mouth and attain highest values 0 45 g l in the productive biogenic region of the amazon shelf salinities above 20 u d and u c distributions are highly nonconservative relative to ideal dilution of river water and seawater indicating extensive removal at salinities below 10 the distribution of u s also shows some nonconservative behavior yet removal if any is minimal saltwater induced precipitation and aggregation of riverine colloidal material is most likely the dominant mechanism of u removal in the low salinity terrigenous region of the amazon shelf there is evidence of a substantial colloidal u input 245 of the riverine u c flux into surface waters above 5 such u c enrichment most likely is the result of colloidal u rich porewater diffusion advection from the seabed and fluid muds or shelf wide particle colloid disaggregation removal of solution and dissolved phase u via a colloidal intermediate and u c aggregation was examined in terms of coagulation theory the highly reactive nature of all u phases on the amazon shelf suggests that remobilization and fractionation of u may also occur in other river influenced coastal environments

nutrient biogeochemistry in a gulf of mexico subterranean estuary and groundwater derived fluxes to the coastal ocean we hypothesize that biogeochemical processes in a subterranean estuary in the northeastern gulf of mexico significantly alter nutrient concentrations that are discharged into the ocean via submarine groundwater discharge sgd this subterranean estuary is a site of steep gradients over small spatial scales so selecting the appropriate groundwater endmember for flux calculations is difficult two endmember mixing models typically applied to investigate biogeochemical processes in surface estuaries are not useful in this case because of aquifer heterogeneity and complex solid fluid interactions groundwater residence times redox potential source strength and aquifer matrix appear to be the most important drivers for dissolved organic carbon doc and nutrient concentrations in this pristine coastal plain aquifer the distribution of dissolved species was consistent with a sequence of reactions in a narrow 2 m surface layer in which nitrate is initially exhausted likely because of denitrification organic nitrogen is remineralized releasing ammonium and some doc remains on the basis of a 222rn derived non steady state box model total terrestrial marine sgd rates were estimated to oscillate around 11 cm d21 the sgd is composed almost entirely of recirculated seawater accounting for 95 of total sgd fluxes conservative estimates of groundwater derived nitrogen inputs into the coastal ocean were 8 2 6 1 2 mmol m22 d21 consisting of ammonium 58 organic nitrogen 28 and nitrate 14 we suggest that these mainly represent recycled rather than new nutrient additions when extrapolated to the florida gulf coast the nitrogen and doc fluxes were comparable to the main regional rivers supporting the proposition that sgd plays a major role in coastal biogeochemistry the biogeochemical implications of submarine groundwater discharge sgd into coastal environments are becoming increasingly recognized globally groundwater discharge has been estimated to be only a few percent of the total freshwater flux to the oceans burnett et al 2006 in spite of that small fraction the input of nutrients to coastal environments via groundwater pathways could be globally more important because nutrient concentrations in groundwater are often much higher than those in river water in addition high dissolved n p ratios in groundwater relative to surface waters might drive the coastal ocean toward p limitation within the coming decades perhaps changing the present n limited coastal primary production slomp and van cappellen 2004

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

radon and radium isotopes as tracers of submarine groundwater discharge results from the ubatuba brazil sgd assessment intercomparison abstract we determined groundwater flow rates shortly after the wet season into an embayment near ubatuba brazil as part of an international intercomparison experiment for submarine groundwater discharge sgd assessment techniques our estimated rates were determined by the combined use of continuous radon measurements and assessment of radium isotope patterns the spatial distribution of the short lived radium isotopes 223ra and 224ra provided the means for independent evaluations of radon losses by mixing and atmospheric evasion we were thus able to construct a well constrained mass balance for radon that included a groundwater flux term our results showed that the groundwater discharge into this embayment from the fractured crystalline rock aquifer is not steady state but varies with tidal modulation and rain induced forcing tidally modulated and rain induced flow rates were comparable during this period the sgd rates estimated from radon ranged from 1 cm day to 29 cm day cm3 cm2 day with a mean and standard deviation of 13 6 cm day these estimates were mostly similar to a dye dilution automatic seepage meter 15 19 cm day and were within the broad ranges estimated by manual and continuous heat seepage meters but lower than indicated by an artificial tracer test performed nearshore

nutrient inputs through submarine groundwater discharge in an embayment a radon investigation in daya bay china abstract daya bay a semi closed bay of the south china sea is famous for its aquaculture agriculture and tourism although routine environmental investigations in the bay have been conducted since the early 1980s evaluations of submarine groundwater discharge sgd an important process in exchange between groundwater and coastal seawater and its environmental impacts have never been reported in this study naturally occurring radon isotope 222 rn was measured continuously at two sites north west and middle east sites and used as a tracer to estimate sgd and associated nutrient inputs into the bay the sgd rates estimated based on the 222 rn mass balance model were on average 28 2 cm d at north west site and 30 9 cm d at middle east site the large sgd rate at middle east site may be due to the large tidal amplitude and the sandy component with high permeability in sediments the sgd driven nutrient fluxes which were calculated as the product of sgd flux and the difference of nutrient concentrations between coastal groundwater and seawater were 3 28 10 5 mol d for dissolved nitrates no 3 n 5 84 10 3 mol d for dissolved inorganic phosphorous dip and 8 97 10 5 mol d for reactive silicate si these nutrient inputs are comparable to or even higher than those supplied by local rivers in addition these sgd driven nutrients have a nitrogen phosphorous ratio as high as 43 which may significantly affect the ecology of coastal waters and lead to frequent occurrence of harmful algal blooms

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

geothermal springs of the west florida continental shelf evidence for dolomitization and radionuclide enrichment abstract on the sea bed of the west florida continental shelf about 45 km ssw of ft myers florida an 85 km 2 area has been discovered in which six thermal springs discharge warm chemically altered seawater from vents and seepage zones the spring water apparently originates in the subsurface ocean around the florida platform and penetrates the highly porous strata of the platform about 500 1000 meters below sea level it percolates toward the interior of the platform and is geothermally heated to about 40 c en route then it rises along more vertical flow channels and is discharged in warm submarine springs beneath the platform several chemical processes alter the percolating seawater one process seems to be a secondary dolomitization of the limestone of the platform because in the discharging seawater magnesium is lower by 2 7 mmole kg and calcium higher by 3 6 mmole kg than in normal seawater with the same chlorinity other reactions within the sediments of the platform enrich the spring effluents 1000 fold in 226 ra 10 000 fold in 222 rn and 90 fold in 228 ra compared to the seawater surrounding the platform thus the springs may be important sources of radionuclides for the gulf of mexico the percolating seawater also loses all of its oxygen and nitrate to reduction processes loses most of its phosphate and 40 of its 238 u and roughly quadruples its silica content coastal carbonate platforms are fairly common geological features thus processes like those beneath the west florida shelf may function on a world wide basis to play an important role in the diagenesis of carbonate sediments

groundwater inflow to a shallow poorly mixed wetland estimated from a mass balance of radon summary radon activity within a shallow wetland in southern australia has been measured on three occasions between may and october 2006 measured activities within the surface water display a similar pattern of spatial variability on each occasion suggesting that it is related to the locations of groundwater inflow and mixing processes the mean groundwater inflow rate has been estimated from the mean radon activity using a mass balance approach the components of the radon budget are i contribution from groundwater inflow ii diffusive flux from wetland bottom sediments iii loss due to gas exchange iv loss due to radioactive decay v loss due to groundwater or surface water outflow also required to complete the water balance are the surface water inflow rate direct precipitation on the wetland and evaporation rate the radon diffusive flux has been estimated from measurements of radon production within the sediments and a diffusive transport model calibrated by measurements of radon activity in sealed chambers that can receive radon only from diffusion and lose it only by radioactive decay radon loss due to gas exchange is inferred from the loss rate of sf6 following its injection into isolated areas of the wetland while the rate of radioactive decay is known the radon activity in groundwater inflow is measured from sampling piezometers surrounding the wetland steady state and transient mass balance approaches yield similar results with groundwater inflow rates varying between 12 and 18 m3 day estimated groundwater inflow rates are most sensitive to the radon activity of groundwater inflow the gas exchange velocity surface water area and the accuracy with which the mean radon activity in the wetland can be measured importantly it is relatively insensitive to the surface water inflow rate which is poorly known

submarine groundwater borne nutrients in a tropical bay maowei sea china and their impacts on the oyster aquaculture submarine groundwater discharge sgd has been recognized as an important pathway for nutrients into estuaries coasts and the adjacent seas in this study 222rn was used to estimate the sgd associated nutrient fluxes into an aquaculture area in a typical tropical bay maowei sea china the sgd into the maowei sea during june of 2016 was estimated to be 0 36 0 33 m d 1 and was associated with sgd derived dissolved inorganic nitrogen din dissolved inorganic phosphorus dip and dissolved silicon dsi fluxes mol d 1 of 4 5 5 5 106 5 3 9 1 104 and 9 4 9 3 106 respectively the sgd derived nutrients i e din dip and dsi were more than 1 9 0 9 and 3 6 times the amounts in the local river input and served as dominant sources in the nutrient budgets in the maowei sea moreover the n p ratios in the sgd around the maowei sea were high mean 64 and these ratios likely exceeded the environmental self purification capacity thereby enhancing the biomass and changing the phytoplankton community structure therefore sgd processes with derived nutrients may affect the biogeochemical cycles and marine ecological environment in the maowei sea furthermore the n p ratios 67 in oysters are very close to those in the sgd in the maowei sea this coincidence suggests that the high n p ratios in the sgd are likely to be one of the most important sources that support oyster aquaculture which might weaken the burden of water eutrophication in the maowei sea

quantification of point source groundwater discharges to the ocean from the shoreline of the big island hawaii aerial thermal infrared imaging has revealed that submarine groundwater discharge sgd along the western coast of the big island of hawaii is often focused as point source discharges that create buoyant groundwater plumes that mix into the coastal ocean we quantified the sgd fluxes associated with several plumes using natural geochemical tracers offshore transects of 222rn and 224ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area using a series of simultaneous mass balance equations for water salt and radon we determined the groundwater fluxes of six plumes near kona hawaii the average sgd fluxes ranged from 1100 m3 d21 to 12 000 m3 d21 of total fresh saline sgd the fresh meteoric groundwater equivalents for the same flows modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition ranged from 630 m3 d21 to 8600 m3 d21 these fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh sgd rates in this region

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

submarine groundwater discharge in a subsiding coastal lowland a 226ra and 222rn investigation in the southern venice lagoon several recent studies have suggested that submarine groundwater discharge sgd occurs in the venice lagoon with discharge rates on the same order or larger than the surface runoff as demonstrated previously in several other coastal zones around the world here the first set of 222rn data along with new 226ra data are reported in order to investigate the occurrence and magnitude of sgd specifically in the southern basin of the lagoon the independent connection with the adriatic sea at the chioggia inlet in addition to the relative isolation of the water body from the main lagoon make this area an interesting case study there is probably only minimal fresh groundwater flux to the lagoon because the surrounding aquifer is subsiding and mainly has a lower hydraulic head than seawater the data show that the ra and rn activities are in slight excess in the lagoon compared to the open sea with values on the same order as those observed in the northern and central basins taking into account the water exchange rate between the lagoon and adjacent seawater provided by previous hydrodynamic numerical modelling it is shown that this excess cannot be supported at steady state by only riverine input and by diffusive release from the sediment interstitial water high activities observed in groundwater samples collected from 16 piezometers tapping into the shallow aquifer over the coastal lowland substantiate that the excess radioactivity in the lagoon may indeed be due to the advection of groundwater directly into the lagoon bottom water through the sediment interface however the data show that the groundwater composition is extremely heterogeneous with high ra activities concentrated within a narrow coastal strip where the contact between fresh and saline water takes place while rn strongly decreases when approaching the lagoon shore across the 20 km coastal plain assuming that the average groundwater activities measured in the coastal strip are representative of the sgd composition a sgd flux of 7 7 3 5 105 and 2 5 2 106 m3 d is calculated using a 226ra and 222rn budget respectively i e about 1 3 times the surface runoff substantially lower than in previous studies the influence of all assumptions on sgd estimates groundwater heterogeneity diffusive sediment flux one box versus multi boxes model calculations is discussed and a sensitivity analysis of the influence of imperfect exchange and mixing at the lagoon outlets that affects the lagoon composition is provided finally the results confirm that the sgd flux calculated with these assumptions is largely 80 composed of saline lagoon water circulating through the sediment under the lagoon margin and that the fresh water discharge associated with sgd is at most a minor term in the lagoon hydrologic balance