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Field Evaluation of Seepage Meters in the Coastal Marine Environment
Abstract
The response of seepage meters was evaluated in a nearshore marine environment where water motion effects are more pronounced than in lake settings, where these meters have been used traditionally. Temporal and spatial variations of seepage, as well as potential artifacts, were evaluated using empty and 1000-ml pre-filled bag measurements. Time-series measurements confirmed earlier observations that anomalously high fluxes occur during the early stages (≤10min) of collection. As deployment times increased (30–60min), measured flow rates stabilized at a level thought to represent the actual seepage flux. Pre-filling the plastic measurement bags effectively alleviated this anomalous, short-term influx. Reliable seepage measurements required deployment times sufficient to allow a net volume of at least 150ml into the collection bag. Control experiments, designed by placing seepage meters inside sand-filled plastic swimming pools, served as indicators of external effects on these measurements, i.e. they served as seepage meter blanks. When winds were under 15 knots, little evidence was found that water motion caused artifacts in the seepage measurements. Tidal cycle influences on seepage rates were negligible in the present study area, but long-term temporal variations (weeks to months) proved substantial. Observed long-term changes in groundwater flux into the Gulf of Mexico correlated with water table elevation at a nearby monitoring well.
... Seepage meters, such as the ones designed by Lee [8], are the only tool to directly measure LGD and SGD [9]. The use of seepage meters to quantify SGD is often reported [7,10,11], but it is a labor intense methodology and it has certain limitations [9,12]. Other techniques (see review by Rosenberry et al. [5]) that have been extensively applied are the use of groundwater head measurements from piezometers [13] and the use of heat as a tracer [14][15][16], among others [17], that indirectly derive the horizontal/vertical flux by the application of Darcy's law or by the use of analytical solutions of the 1D heat transport equation. ...
... The measurements with seepage meters indicated that this exchange was generally from the subsurface to the lagoon (groundwater discharge) with only two locations showing groundwater recharge from the lagoon. However, seepage at those locations were negligible as the measured fluxes (−0.02 cm day −1 ) fell below the detection limit [11]. Only the discharge fluxes were inferred using the two analytical solutions for the heat transport in the lagoon bed. ...
... Water 2019, 11, 1648 ...
Surface water-groundwater interactions were studied in a coastal lagoon performing 180 seepage meter measurements and using heat as a tracer in 30 locations along a lagoon inlet. The direct seepage meter measurements were compared with the results from analytical solutions for the 1D heat transport equation in three different scenarios: (1) Homogeneous bulk thermal conductivity (Ke); (2) horizontal heterogeneity in Ke; and (3) horizontal and vertical heterogeneity in Ke. The proportion of fresh groundwater and saline recirculated lagoon water collected from the seepage experiment was used to infer the location of the saline wedge and its effect on both the seepage meter results and the thermal regime in the lagoon bed, conditioning the use of the thermal methods. The different scenarios provided the basis for a better understanding of the underlying processes in a coastal groundwater-discharging area, a key factor to apply the best-suited method to characterize such processes. The thermal methods were more reliable in areas with high fresh
groundwater discharge than in areas with high recirculation of saline lagoon water. The seepage meter experiments highlighted the importance of geochemical water sampling to estimate the origin
of the exchanged water through the lagoon bed.
... These were initially developed in the 1940's to measure loss of water from irrigation channels (Israelson and Reeve, 1944) and resurrected in the 1970's for use in small lakes and estuaries (McBride and Pfannkuch, 1975;Lee, 1977;John and Lock, 1977;Lee and Cherry, 1978). Seepage meters have since been used in numerous studies of seepage fluxes in rivers (Lee and Hynes, 1978;Libelo and MacIntyre, 1994;Cey et al, 1998;Landon et al, 2001), the near-shore marine zone (Bokuniewicz and Pavlik, 1990;Valiela et al, 1990;Cable et al, 1997;Taniguchi et al, 2003), tidal zones (Belanger and Walker, 1990;Robinson et al, 1998), coral reefs (Simmons andLove, 1984, Lewis, 1987), large lakes (Cherkauer and McBride, 1988) and water-supply reservoirs (Woessner and Sullivan, 1984). A constant-head variant of the seepage meter (the Idaho meter) has been used to measure leakage from irrigation channels into aquifers under Australian conditions (ANCID 2000; Byrnes and Webster, 1981). ...
... Allow sufficient time between initial installation of the chamber and the commencement of measurements so that hydraulic pressures inside the chamber equilibrate with those of the surface water body. Laboratory tests suggest that 80% of this equilibration occurs in the first 10 minutes (Cherkauer and McBride, 1988;Cable et al. 1997) and investigators have used stabilisation times ranging from 10-15 minutes (Landon et al. 2001) to 2-5 days (Shaw and Prepas, 1989;Shaw and Prepas, 1990); (iv.) The end of the vent tube can be fixed into position on the bank of the surface water feature using a stake or small star picket. ...
... Any change in the water volume within the control bag reflects the magnitude of these effects. Field studies in the nearshore coastal environment have also used complete control meters set up in sand-filled plastic swimming pools on the bed, specifically to measure such measurement artefacts (Cable et al. 1997); (x.) After a period of time the seepage measurement is ended by returning to the meter, turning the valve closed and recording the time that this was done. ...
The Australian Government acting through the Bureau of Rural Sciences has exercised due care and skill in the preparation and compilation of the information and data set out in this publication. Notwithstanding, the Bureau of Rural Sciences, its employees and advisers disclaim all liability, including liability for negligence, for any loss, damage, injury, expense or cost incurred by any person as a result of accessing, using or relying upon any of the information or data set out in this publication to the maximum extent permitted by law.
... On evaluating the physical and biological processes affecting marine seepage meter measurements Field or laboratory experiments are often needed with each new application to quantify potential impacts on these measurements. These impacts include hydrostatic pressure differences between the flexible bag and the rigid underlying sediments (Shaw and Prepas 1989;Cable et al. 1997a), bioirrigation/ bioturbation effects (Aller 1980;Martin et al. 2004), spatial heterogeneity and low-flow conditions (Rosenberry 2005), and effects from physical forces such as winds, waves, currents, and tides that move water across the sediments and the seepage meters (e.g., Huettel et al. 1996;Li et al. 1999;Shinn et al. 2002). These potential impacts have produced concerns about artifacts in the measured seepage rates, and researchers have refined the methodology in an attempt to improve the accuracy of the seepage measurements. ...
... These potential impacts have produced concerns about artifacts in the measured seepage rates, and researchers have refined the methodology in an attempt to improve the accuracy of the seepage measurements. For example, prefilling the seepage collection bag with 1000 mL water was found to alleviate an anomalous influx of water associated with the mechanical properties of an empty flexible plastic bag attached to a meter (Shaw and Prepas 1989;Cable et al. 1997a). The potential for artifacts of measurements has been evaluated by comparing seepage rates measured from meters with a standard deployment and a nearby seepage "blank," where a seepage meter is deployed within a child's plastic swimming pool filled with local sediment (Cable et al. 1997a;Chanton et al. 2003). ...
... For example, prefilling the seepage collection bag with 1000 mL water was found to alleviate an anomalous influx of water associated with the mechanical properties of an empty flexible plastic bag attached to a meter (Shaw and Prepas 1989;Cable et al. 1997a). The potential for artifacts of measurements has been evaluated by comparing seepage rates measured from meters with a standard deployment and a nearby seepage "blank," where a seepage meter is deployed within a child's plastic swimming pool filled with local sediment (Cable et al. 1997a;Chanton et al. 2003). Belanger and Montgomery (1992) used test-tank evaluations to compare measured seepage rates to the actual (calculated) seepage flowing through tank sand and found a 0.77 ratio between measured and actual flux. ...
Seepage meters, like most benthic flux chamber techniques, come with inherent concerns about how their presence may alter the environment and flow regimen of the benthic boundary layer and underlying sediments. Flow due to wave and current movement across topographic features induces a downward and upward flow field within the sediments surrounding the feature. We found this Bernoulli-induced flow is a real, but maybe minor, component of measured advection using seepage meters. This study was conducted in a Florida coastal lagoon to test the physical forcing mechanisms that may influence seepage measurements from sediments. Calculated Bernoulli seepage was within the measured background (∼1 to 2 cm day-1) expected from seepage meters when a plastic barrier beneath the device is used to inhibit natural seepage contributions. Nearby seepage measurements made with Lee-type seepage meters placed directly in the sediments ranged from 1 to 12 cm day -1. Thus, when seepage flow is very slow from sediments, Bernoulli-induced seepage may obscure the measurement. However, this study demonstrates that seepage in the Indian River Lagoon must be driven by forces other than Bernoulli-induced (pumped) flow. Suggestions for these forcing mechanisms highlight the uncertainty of the water source(s) in seepage measurements. In these Florida lagoon sediments, bioirrigation and terrestrial groundwater inputs are the most likely drivers, depending on distance from shore, benthic community composition, and continental recharge. Seepage measurements can be an excellent measure of advection in shallow-water marine sediments if Bernoulli-induced seepage is taken into account either experimentally or calculated based on local hydrographic and meteorological data. © 2006, by the American Society of Limnology and Oceanography, Inc.
... The adequate equilibration period varies due to sediment type, water flux rate, and installation depth (i.e., head space); salt marshes may require a longer equilibration time than sandy coastal environments due to their fine-grained sediments and potentially low water fluxes. It is important to note that seepage meter use is optimal when water fluxes exceed approximately 20 L m 2 d −1 [73,74], and along muddy marsh shorelines, SGD fluxes can be much lower. ...
... The adequate equilibration period varies due to sediment type, water flux rate, and installation depth (i.e., head space); salt marshes may require a longer equilibration time than sandy coastal environments due to their finegrained sediments and potentially low water fluxes. It is important to note that seepage meter use is optimal when water fluxes exceed approximately 20 L m 2 d −1 [73,74], and along muddy marsh shorelines, SGD fluxes can be much lower. Seepage Meter Case Study. ...
Groundwater–surface water exchange in salt marsh ecosystems mediates nearshore salt, nutrient, and carbon budgets with implications for biological productivity and global climate. Despite their importance, a synthesis of salt marsh groundwater studies is lacking. In this review, we summarize drivers mediating salt marsh hydrogeology, review field and modeling techniques, and discuss patterns of exchange. New data from a Delaware seepage meter study are reported which highlight small-scale spatial variability in exchange rates. A synthesis of the salt marsh hydrogeology literature reveals a positive relationship between tidal range and submarine groundwater discharge but not porewater exchange, highlighting the multidimensional drivers of marsh hydrogeology. Field studies are heavily biased towards microtidal systems of the US East Coast, with little global information available. A preliminary estimate of marsh porewater exchange along the Mid-Atlantic and South Atlantic Bights is 8–30 × 1013 L y−1, equivalent to recirculating the entire volume of seawater overlying the shelf through tidal marsh sediments in ~30–90 years. This review concludes with a discussion of critical questions to address that will decrease uncertainty in global budget estimates and enhance our capacity to predict future responses to global climate change.
... Benthic fluxes of radium (Ra) to the IRL were calculated using three independent methods that rely on the activities of the short-lived isotopes: (1) lagoon budget, (2) benthic flux chambers, and (3) pore water modeling. Rn-222 (Radon) and Ra-226 isotopes from previous studies provided regionally integrated estimates of seepage flux in varied coastal environments (Cable et al., 1997;Moore, 1996;Swarzenski et al., 2001). By using Rn-222 and Ra-226 as mass balance tracers of seepage flux, it is possible to obtain measurements of seepage that are independent of the short-lived Ra isotopes. ...
... The majority of data imply that groundwater discharge to Mosquito Lagoon is very important, and a review of the available hydrogeological data suggests that measurable seepage rates are possible. Although studies on flow and wave effects (water motion) on seepage meter results indicate negligible effects (Cable et al., 1997;Semmler, 2003), others believe these effects may be significant (Libelo and McIntyre, 1999;Shinn et al., 2002), or that shallow recirculating pore water derived from the overlying surface water column may represent a significant fraction of the measured groundwater input in the seepage meters (Cable et al., 2004). Possible mechanisms driving pore water advection include tides, waves, and bioturbation; bioirrigating organisms are the leading candidates (Martin et al., 2006). ...
Executive Summary
The conditions of terrestrial and estuarine resources within Canaveral National Seashore (CANA) were assessed and the threats and stresses to individual resources were identified and evaluated. With the exception of freshwater vegetation mapping, new data were not collected within CANA. Data and information derived from an intensive survey of the existing peer- reviewed and gray literature search were analyzed and synthesized to reveal the current state of each resource and to identify trends in resource quality and health.
... A large number of studies have shown that the test process data can re ect the changes of structural and functional parameters such as in ltration [8] , lateral in ltration [9] , connected porosity [10] , segregation [11] , compaction [12] , mineral gradation [13] , freeze-thaw cycle performance [14] and soil slope stability [15] . However, the photoelectric liquid level switch and the oat switch are all for the initial and nal state detection, and the water leakage, defoaming and side leakage phenomena in the test process cannot be identi ed. ...
Permeability meter plays an important role in the measurement of road seepage performance. The data deviation is easy to produce because of incorrect reading by using the manual seepage meter. Thereby, the application program based on Windows CE operating system is developed, which includes test process, data processing and battery monitoring. And the manual control, automatic delay and industry standard operation processes can be achieved by adopting the timing and event-driven modes, furthermore, it has the function of calculating standard deviation, mean value and coefficient of variation, checking out the existing data. And the recorded data can be automatically appended to the list. The software which uses the recursive median algorithm to filter the original data can monitor the dynamic change of liquid level synchronously, and can also measure the initial and final liquid level height like the manual seepage meter. It can provide a smooth curve of the seepage process. Combined with observation and data analysis, it is found that the process curve is obviously related to the phenomena of water seepage, lateral infiltration, water leakage and bubble burst, so these phenomena of water seepage process of road can be recognized through algorithm development.
... Briefly, four to seven seepage meters (Lee, 1977) with attached water collection bags (two per meter) were deployed along the beach profile each month at spring low tide and allowed to settle in for 24 h prior to sampling. Water samples were then collected at subhourly intervals, following the precautions listed in Cable et al. (1997). Sampling covered a minimum of two and a maximum of four successive tidal cycles every month. ...
Causal links between subterranean estuary (STE) dynamics, their climatological drivers, and the ecology of coastal ecosystems have remained elusive. Yet, establishing these connections is essential for fully integrated management of coastal ecosystems. We test, in a semi-arid climate, whether the composition of submarine groundwater discharge (SGD) to a lagoon can be regulated by the annual oscillation of the local STE, itself driven by groundwater recharge variability. We study STE outflow samples gathered monthly for a year in the Ria Formosa lagoon, examining the temporal dynamics of salinity, EH, pH (Total scale), dissolved oxygen and nutrient (PO43−, NO2−, NO3−, NH4+, and Si(OH)4) concentrations under the local hydrological regime. The objectives were threefold: (1) to determine the annual variability of nutrient content and N:P:Si stoichiometry in SGD into the lagoon; (2) to identify the main drivers of variability in SGD composition and stoichiometry and their interactive effects; (3) to discuss links to, and implications for, ecosystem function that could help define expectations of cause-effect relationships and be useful for environmental management of the lagoon and similar systems elsewhere.
We find that the terrestrial groundwater recharge cycle drives the expansion and contraction of the subterranean estuary on annual timescales, causing the pH of SGD to fluctuate in opposition to continental groundwater level. The annual dynamics of the STE and the resulting pH oscillation determine the annual variability of nutrient composition ratio in SGD and shape benthic primary production dynamics. When saltwater intrusion occurs, the pH within SGD increases, enhancing nitrification and desorption of exchangeable phosphorus, while silicate fluxes increase with seawater retreat. The result is that nutrient resource ratio availability for coastal primary production depends on the fresh groundwater level. This implies that ecosystem function in such systems is more tightly related to the dynamics of linked groundwater reservoirs than previously thought.
... The deployment of seepage meters involves inserting the cylinder into the sediment, and thereafter the change in the volume of water in the collection bag over a measurement period is used to determine the total fluid flux across the sediment-water interface. Seepage meters have been widely used to measure SGD across the sediment-water interface in a variety of coastal environments (Cable et al., 1997a;Michael et al., 2005;Burnett et al., 2006a;Povinec et al., 2006;Smith et al., 2009;Mejías et al., 2012). However, the utility of seepage meters is limited by their relatively small footprint that usually covers less than a square meter. ...
Coastal beach aquifers are biogeochemically active systems that mediate chemical and material fluxes across the land-sea interface. This paper provides a review of major physical stressors and geologic features that influence flow and solute fate and transport in coastal beach aquifers. We outline current understanding of the interactions between these factors and their associated impacts on water and geochemical fluxes within and across these aquifers. The physical processes that control flow, transport, and the formation and distribution of reactive zones in beach aquifers (e.g., tides, waves, density gradients, precipitation, episodic ocean events, and evaporation) operate across overlapping temporal and spatial scales, and present challenges for measuring and modeling physical flow and biogeochemical processes in coastal groundwater systems. Geologic heterogeneity introduces further complexity by modifying flowpaths, mixing patterns, and rates of biotransformation. Interactions between these physical stressors and geological controls are likely to evolve with changes in sea level, climate variability, human settlement, coastal erosion, and other natural and anthropogenic stresses, providing avenues for scientific exploration into the future role of beach aquifers as chemical mediators between the land and ocean.
... When necessary to make out the characteristics and laws of the regional SGD, a large number of measuring points must be arranged. In addition, the measurement process of seepage meter is easily disturbed or damaged by current and wave (Cable et al. , 1997). To a certain extent, these drawbacks prevent percolator from widely use. ...
... Groundwater discharge into surface-water bodies is known as submarine groundwater discharge (SGD) and groundwater recharge from surface-water bodies is known as submarine groundwater recharge (SGR) (Burnett et al. 2006;Moore 2010). Although SGD and SGR have been detected in the MRDP through geochemical tracer measurements (Cable et al. 1997(Cable et al. , 1996Kolker et al. 2013;Krest et al. 1999;Moore and Krest 2004) and river-water-discharge-rate measurements Lewis et al. 2017), due to a lack of MRD subsurface characterization, locations where surface water and groundwater exchange were seldom characterized. This study suggests that subsurface flow pathways are connecting to the estuaries at the top through shallow sands and connecting to the river channel at depth through deep sands. ...
A three-dimensional stratigraphic model was constructed of the upper 50 m of the Mississippi River Delta, southeastern USA. The model is used to understand hydrogeological connections among the Mississippi River, adjacent interdistributary bays and groundwater systems, and to understand how stratigraphic settings affect potential anthropically induced subsidence and erosion in the region. This study uses 619 geotechnical borings throughout the area along with the multiple-indicator natural neighbor (MINN) interpolation method to construct the model. Based on available data, the study focused on the Mississippi River reach from Head of Passes (river mouth) to Jesuit Bend (108 km upstream), covering an area of approximately 1,800 km2 and ranging in elevation from 3 to −46 m. The model shows typical basal coarse-grained sand bodies overlain by 10-m-thick blanket clay, which is interbedded frequently with silty and sandy sediments and occasionally with peat and organic clay. Sands are most abundant between elevations −10 and −35 m. The Mississippi River main channel incises the underlying sands, thereby providing pathways for river–groundwater exchange. Increased hydrologic loads may propagate along the flow paths potentially giving rise to high pore-water pressure and a resultant increase in land subsidence and thus local erosion of natural and local flood-control levees. This method of analysis may apply to other deltaic regions similarly subject to anthropically accelerated subsidence and erosion.
... A seaward flow of fresh groundwater requires the hydraulic potential of the onshore aquifer to be above the sea level [6]. While groundwater flow in porous media is generally controlled by aquifer permeability and inflow and thus the hydraulic head [7][8][9][10][11] as well as dispersion effects [12,13], SGD is also influenced by drivers that are specific to the coastal situation, such as tides and waves [14]. ...
Submarine groundwater discharge (SGD), the discharge of terrestrial groundwater to the ocean, can govern the coastal benthic environment. Bacteria such as Vibrio cholerae inhabit coastal waters and sediments, whose growth can be influenced by SGD. In particular, salinity changes introduced by SGD could have a positive effect on the abundance but also virulence of nonhalophilic V. cholera bacteria dwelling in coastal waters and shallow marine sediments. Here we assess potential effects of SGD on the environmental properties that favor V. cholerae in a numerical modeling study representing multiple scenarios. Approaching natural systems, simulation results reveal a high sensitivity of non-halophilic Vibrio cholerae growth to SGD and its primary driving factors. This dependency leads to highest growth potential at high groundwater inflow and low hydraulic conductivity of the aquifer as well as for steep sea-side boundary slopes. Besides its minor impact on the extent of SGD in our model, dispersion is a crucial limiting factor for V. cholerae habitat. We conclude that there is a close connection between the driving factors of SGD and low salinity zones along a coastal slope, and recommend taking these into consideration for evaluating local V. cholerae outbreaks.
... In this context it bears an enormous potential as it is possible to provide detailed and high-resolution information on SGD dynamics but also on external forces influencing it. The potential includes the high temporal resolution (sampling intervals), which differs by 1 order of magnitude from classical in situ measurement intervals of 10 1 -10 2 min (Cable et al., 1997;Mulligan and Charette, 2006;Michael et al., 2011), allowing the illumination of short-term discharge dynamics that could not be reflected with classical methods. The potential furthermore concerns the spatio-temporal continuous characteristic of the presented approach. ...
Submarine groundwater discharge (SGD) is highly variable in spatial and temporal terms due to the interplay of several terrestrial and marine processes. While discrete in situ measurements may provide a continuous temporal scale to investigate underlying processes and thus account for temporal heterogeneity, remotely sensed thermal infrared radiation sheds light on the spatial heterogeneity as it provides a continuous spatial scale.
Here we report results of the combination of both the continuous spatial and temporal scales, using the ability of an unmanned aerial vehicle (UAV) to hover above a predefined location, and the continuous recording of thermal radiation of a coastal area at the Dead Sea (Israel). With a flight altitude of 65 m above the water surface resulting in a spatial resolution of 13 cm and a thermal camera (FLIR Tau2) that measures the upwelling long-wave infrared radiation at 4 Hz resolution, we are able to generate a time series of thermal radiation images that allows us to analyse spatio-temporal SGD dynamics.
In turn, focused SGD spots, otherwise camouflaged by strong lateral flow dynamics, are revealed that may not be observed on single thermal radiation images. The spatio-temporal behaviour of an SGD-induced thermal radiation pattern varies in size and over time by up to 155 % for focused SGDs and by up to 600 % for diffuse SGDs due to different underlying flow dynamics. These flow dynamics even display a short-term periodicity of the order of 20 to 78 s for diffuse SGD, which we attribute to an interplay between conduit maturity–geometry and wave set-up.
... The deployment of seepage meters involves inserting the cylinder into the sediment, and thereafter the change in the volume of water in the collection bag over a measurement period is used to determine the total fluid flux across the sediment-water interface. Seepage meters have been widely used to measure SGD across the sediment-water interface in a variety of coastal environments (Cable et al., 1997a;Michael et al., 2005;Burnett et al., 2006a;Povinec et al., 2006;Smith et al., 2009;Mejías et al., 2012). However, the utility of seepage meters is limited by their relatively small footprint that usually covers less than a square meter. ...
Extreme storms can cause rapid morphological changes that pose high risk to society (Sallenger 2000). Semiempirical and process-based models often are used to simulate storm-induced coastal processes (Roelvink et al. 2009, Palmsten & Holman 2012, Stockdon et al. 2014, Overbeck et al. 2017). However, there are few observations of surfzone waves and currents during extreme storms. Therefore, parameterizations often are calibrated by minimizing model-data errors for pre- to post-storm bathymetric and topographic changes, and the accuracy of the simulated processes during the storm is unknown. Here, surf, swash, and dune observations collected near Duck, NC, USA, will be used to investigate wave processes and dune erosion during the passage of recent (2015-2017) Hurricanes.
... This is often an overlooked interaction, where scientific research often focuses on one of the processes and not both at the same time. Because there was an indication of higher discharge in the areas where the saltwater-freshwater interface was located, the (Bokuniewicz et al., 2004;Burnett et al., 2001;Cable, Burnett, Chanton, Corbett, & Cable, 1997;Paulsen et al., 2004;Rosenberry, 2005;Rosenberry et al., 2013). This high variability has previously been explained by sediment heterogeneities (Russoniello et al., 2013;Taniguchi, Ishitobi, & Saeki, 2005); bioirrigation (Cable et al., 2006); preferential flow paths (Kishel & Gerla, 2002); or anthropogenic alteration of the sedimentary structure (Taniguchi et al., 2006). ...
Groundwater discharge to a brackish lagoon (Ringkøbing Fjord) was quantified with seepage meters along four transects perpendicular to the shore during four seasons in one year. The objectives were to develop a conceptual model of the spatio‐temporal variability of seepage and how landscape characteristics and saltwater intrusion affect seepage fluxes. The electrical conductivity of the groundwater was measured in vertical sediment profiles up to 3 m below the lagoon bed to assess the effects of the freshwater‐salt water interface location on flux distribution. The main differences compared to existing theoretical models are a lower discharge near the shore line (0‐5 m) and two discharge peaks more off‐shore (15‐20 m and > 25 m), which allowed the development of a conceptual model that is different from the classical concepts introduced for marine or lake environments and which can be representative of other similar areas. These differences are explained by the vegetation and organic material deposition in the near shore environment reducing discharge, the presence of the saline wedge leading to upward flow and the increase of recirculation of brackish water due to wave pumping in areas off‐shore most exposed to the wind. The seasonal variability in discharge is smaller than the spatial variability between and within transects along the shoreline. Based on the conceptual model, fresh water discharge in a 20 meters wide fringe was calculated to be between 66 and 388 l/d per meter shore line, corresponding to a difference of a factor of six due to the variations in coast morphology and local characteristics of the area. The seasonal changes were responsible for changes of only 8 to 75 % depending on the location.
... Despite the short total observation time of the present study it shows a temporal discharge behaviour in the range of 101-102 seconds. Classical in-situ measurements however usually have measuring intervals of 10 1 -10 2 minutes (Cable et al., 1997;Mulligan and Charette, 2006;Michael et al., 2011) and thus differ by the order of one magnitude. These intervals could not reflect the observed short-term discharge dynamics. ...
Submarine groundwater discharge (SGD) is highly variable in spatial and temporal terms due to interplay of several terrestrial and marine processes. While discrete in-situ measurements provide a continuous temporal scale to investigate underlying processes and thus accounts for temporal heterogeneity, remotely sensed thermal infrared radiation sheds light on the spatial heterogeneity as it provides a continuous spatial scale.
Here we report results of the combination of both, the continuous spatial and temporal scales, using the ability of an Unmanned Aerial Vehicle to hover above a predefined location and the continuous recording of thermal radiation of a coastal area at the Dead Sea (Israel). With a flight altitude of 65m above the water surface resulting in a spatial resolution of 13cm and a thermal camera (FLIRTau2) which measures the upwelling long-wave infrared radiation at 4Hz resolution we are able to generate a time sequence of thermal radiation images which allows us to analyse spatiotemporal SGD dynamics. In turn, we are able to enhance focused SGD spots otherwise being camouflaged by strong lateral flow dynamics that may not be observed on single thermal radiation images. Plus, we show the spatiotemporal behavior of a SGD induced thermal radiation pattern to vary in size and over time by up to 55% for focused SGDs and by up to 600% for diffuse SGDs due to different underlying flow dynamics. These flow dynamics even display a short-term periodicity in the order of 20 to 78s for diffuse SGD which we attribute to an interplay of conduit maturity/geometry and wave setup.
... Basin-scale estimations of fresh SGD using water balance and Darcy law method have been performed in many places (Allen 1976;Muir 1968;Pluhowski and Kantrowitz 1964;Sekulic and Vertacnik 1996;Kroeger et al. 2007). Studies using various types of seepage meters to measure SGD flux have been attempted globally (Lee 1977;Taniguchi and Fukuo 1993;Cable et al. 1997;Taniguchi and Iwakawa 2001;Taniguchi et al. 2006). From the several methods attempted, seepage meter is one of the best methods to measure the groundwater discharge or inflow in locations where sediment interface and fluid fluxes are large (Winter 1981;Shaw and Prepas 1989). ...
Abstract
Submarine groundwater discharge (SGD) is described as submarine inflow of fresh and brackish groundwater from land into the sea. The release of sewages from point and non-point source pollutants from industries, agricultural and domestic activities gets discharged through groundwater to ocean creating natural disparity like decreasing flora fauna and phytoplankton blooms. Hence, to quantify fluxes of SGD in coastal regions is important. Quantification of SGD was attempted in Coleroon estuary, India, using three dissimilar methods like water budget, Darcy law and manual seepage meter. Three
seepage meters were installed at two prominent litho units (alluvium and fluvio marine) at a distance of (0–14.7 km) away from Bay of Bengal. The water budget and Darcy law-quantified submarine seepage at a rate of 6.9 × 106 and 3.2 × 103 to 308.3 × 103 m3 year−1, respectively, and the seepage meter quantified seepage rate of 0.7024 m h−1 at an average. Larger seepage variations were isolated from three different techniques and the seepage rates were found to be influenced by hydrogeological characteristics of the litho units and distance from the coast.
Keywords: Submarine groundwater discharge (SGD) · Water budget · Darcy’s law · Manual seepage meter · Coleroon
estuary
... As sediment size increases, other options such as piezometers and minipiezometers may be more practical; however, piezometers do not provide estimates of fluxes. The effects of collection bag size and type have been studied in detail (Cable et al., 1997;Isiorho and Meyer, 1999;Schincario and McNeil, 2002;Rosenberry and LaBaugh, 2008). Thick-walled, inelastic collection bags commonly suffer from relaxation error that occurs because the bag is usually compressed as it is fitted onto the seepage meter, and once it is fitted, the bag returns to its original shape due to elastic memory and draws an anomalous amount of water quickly into the bag (Schinario and McNeil, 2002). ...
... Since 1996, natural radioactive isotopes Ra and Rn were widely used as tracers to estimate SGD in large scale areas ( Gu et al., 2012;Lee et al., 2012;Moore, 1996Moore, , 2007Moore and Oliveira, 2008;Wang et al., 2015;Xu et al., 2014) . Seepage meters were also used to estimated SGD at local area, such as manual seepage instrument developed by Cable et al. ( 1997 ) , heat pulse seepage meter developed by Taniguchi and Fukuo (1993) and ultrasonic flow meter developed by Paulsen et al. (2001) . Numerical simulations usually focused on limited coastal transect, such as Guo et al. (2010) , , Xia and Li (2012) , Xia et al. (2010) . ...
There were few studies about seawater-groundwater exchange in silty, low-permeability tidal flats with very gentle slopes. This paper reports the monitoring data and preliminary analytical results on a typical transect in a silty tidal flat with large-scale seepage faces at the south coast of Laizhou Bay, China. The "pair-wells method", which was an improvement of the single-well method used by Ma et al. (2015) was used to estimate the seawater-groundwater exchange rate. We selected 14 locations along a typical transect in the intertidal zone, with a slope of 0. 4‰ and cross-shore length of 3514 m, to install pair-wells for monitoring the groundwater head, salinity and temperature at two different depths simultaneously once per hour from 20 : 00 August 10th to 23 : 00 September 12th, 2014. The vertical hydraulic conductivity measured in situ ranges from 5. 4×10⁻⁷ to 1. 1×10⁻⁵ m s⁻¹ . The salinity of the underground brine ranges from 25 to 56 g l⁻¹ . Based on the observed data and the generalized Darcy's law, the submarine groundwater discharge (SGD) and inflow along the entire transect were estimated to be 164. 0 and 6. 5 m2 d-1 , respectively. It is found that 80. 4% of the total SGD occurred between W7 and W10, where the hydraulic conductivity is one or two orders of magnitude greater than that at other wells; and 64. 6% of the total inflow occurred between W2 and W4. The single-well method, on the other hand, yields a SGD value of 223. 0 m2 d⁻¹ and inflow value of 13. 3 m² d⁻¹ . Neglecting the density effect may lead to an overestimation of the SGD by 25. 6% and underestimation of the inflow by 27. 4%.
... Resultados observados em outros trabalhos aplicados nos Estados Unidos da América com seepage meter "tipo Lee", registraram taxas na faixa de 5 a 45 cm d -1 em baías de Massachusetts (Mulligan & Charette, 2006), 0 a 20 cm d -1 na Flórida (Cable et al., 1997b), 1 a 490 cm d -1 nas Ilhas Maurício (Burnett et al., 2006) e 0 a 12 cm d -1 para zonas costeiras de Minnesota e Wisconsin (Lee, 1977), enquanto para lagoas a faixa registrada esteve entre 0 e 22 cm d -1 em Carolina do Norte e Nova Escócia (Lee, 1977). Desta forma, os resultados verificados no presente trabalho podem ser considerados baixos, mesmo havendo poucas referências para áreas lacustres. ...
The advection of groundwater in coastal lakes of southern Rio Grande do Sul State is already a well known process. This article is the first one dealing with Submarine Groundwater Discharge (SGD) in the northern coast of state to confirm and quantify the SGD in four major lakes of this region – Itapeva, Quadros, Pinguela and Barros, applying seepage meter method. In each lake two sets of sampling stations were selected. A different behavior between margins was recorded. In the margins near the hills were identified advective process; and those close to the shore line, were dominated by infiltration process. The estimated volume of the SGD reaches the order of millions of cubic meters annually toward to these lakes, accounting for 13-27% of total contributions. Furthermore, utilizing water balance it was possible to evaluate the water balance between inputs and outputs as well as the residence time in each water bodies, which ranged from 19 to 847 days.
... Since 1996, natural radioactive isotopes Ra and Rn were widely used as tracers to estimate SGD in large scale areas ( Gu et al., 2012;Lee et al., 2012;Moore, 1996Moore, , 2007Moore and Oliveira, 2008;Wang et al., 2015;Xu et al., 2014) . Seepage meters were also used to estimated SGD at local area, such as manual seepage instrument developed by Cable et al. ( 1997 ) , heat pulse seepage meter developed by Taniguchi and Fukuo (1993) and ultrasonic flow meter developed by Paulsen et al. (2001) . Numerical simulations usually focused on limited coastal transect, such as Guo et al. (2010) , , Xia and Li (2012) , Xia et al. (2010) . ...
There were few studies about seawater-groundwater exchange in silty, low-permeability tidal flats with very gentle slopes. This paper reports the monitoring data and preliminary analytical results on a typical transect in a silty tidal flat with large-scale seepage faces at the south coast of Laizhou Bay, China. The "pair-wells method", which was an improvement of the single-well method used by Ma et al. (2015) was used to estimate the seawater-groundwater exchange rate. We selected 14 locations along a typical transect in the intertidal zone, with a slope of 0.4‰ and cross-shore length of 3514 m, to install pair-wells for monitoring the groundwater head, salinity and temperature at two different depths simultaneously once per hour from 20:00 August 10th to 23:00 September 12th, 2014. The vertical hydraulic conductivity measured in situ ranges from 5.4 ×10-7 to 1.1×10-5 m s-1. The salinity of the underground brine ranges from 25 to 56 g l-1. Based on the observed data and the generalized Darcy's law, the submarine groundwater discharge (SGD) and inflow along the entire transect were estimated to be 164.0 and 6.5 m2 d-1, respectively. It is found that 80.4% of the total SGD occurred between W7 and W10, where the hydraulic conductivity is one or two orders of magnitude greater than that at other wells; and 64.6% of the total inflow occurred between W2 and W4. The single-well method, on the other hand, yields a SGD value of 223.0 m2 d-1 and inflow value of 13.3 m2 d-1. Neglecting the density effect may lead to an overestimation of the SGD by 25.6% and underestimation of the inflow by 27.4%.
... The range of groundwater fluxes reported in the literature varies significantly depending on the sediment type and other site characteristics. Extensive reviews of coastal seepage measurement studies have been performed by several researchers such as Cable et al. (1997). These reviews indicate measured seepage rates at different sites spanning from 0.01 cm/d to 124 cm/d. ...
The transport of sediment-bound contaminants to the overlying water column may occur through multiple pathways with sediment resuspension potentially being an important one. The present study considers the influence of vertical pore water flux (due to ground water discharge, for example) through the sediment bed on sediment resuspension. The investigation involved a laboratory study conducted on fine-grained cohesive sediments collected from the Anacostia River in Washington DC. Initial experiments performed on unconsolidated sediments demonstrated that preferential channels formed in the sediment through which the bulk of pore water flow migrated. Additional experiments were performed in a re-circulating flume in which resuspension rates were measured by monitoring increases in water column turbidity over time. A baseline study with no pore water flow was conducted by increasing the bed shear stress in discrete steps in order to provide a basis for comparison with the pore water flux experiments. Then, resuspension rates were quantified and a quadratic relationship was established resuspension rate and critical shear stress required to initiate resuspension. The rate constant was found to be a function of the pore water flux, but not the critical shear stress. The same conditions were studied with sediment caps applied over the bed surface. Two capping technologies were studied; a sand cap and an AquaBlok ® cap. Some of the capabilities and limitations of the two caps were identified for practical applications.
... In fact, previously compiled data [Kwon et al., 2014] show that fresh groundwater data account for almost half of the entire data set. Although we cannot separate fresh and saline groundwater in SGD, the salinity of the majority of groundwater is likely to be greater than 10 based on seepage experiments conducted throughout the world [Cable et al., 1997;Kim et al., 2003;Lewis, 1987 the fact that about 10% of SGD is composed of fresh groundwater throughout the world [Burnett et al., 2003;Kim et al., 2003;Kwon et al., 2014;Taniguchi et al., 2006]. Taniguchi et al. [2009] reported that the magnitude of total SGD is generally dependent on the distance from shore, with higher discharges and higher fresh water proportions in shallow waters. ...
Radium isotopes (228Ra and 226Ra) are excellent tracers of submarine groundwater discharge (SGD). To estimate SGD magnitudes, information on the end-member values of Ra concentrations in groundwater is critical; however, the distribution characteristics of Ra in coastal aquifers are poorly understood. In this study, we show that Ra concentrations in coastal groundwater are primarily dependent on salinity based on the data (n > 500) obtained from global coastal aquifers, although previous end-member calculations averaged all Ra concentrations without considering salinity. If we assume that SGD is composed mainly of seawater infiltrating the aquifer, previous estimates of SGD for the Atlantic Ocean and the global ocean were overestimated twofold to threefold. This may be similar for other applications using different Ra isotopes. Our study highlights that the end-members of Ra isotopes in groundwater should be carefully considered when estimating SGD using Ra isotope mass balances in the ocean.
... m 3 /m/day Simulated (Burnett and Turner, 2001;Smith and Nield, 2003;Debnath et al., 2015) Mauritius lagoon Spring 0.4-120 m 3 /m/day Seepage meter Rapaglia et al., 2006;Debnath et al., 2015) 26-56 m 3 /m/day Radon Rapaglia et al., 2006;Debnath et al., 2015) Mauritius lagoon South Beach 1-8.8 m 3 /m/day Seepage meter Rapaglia et al., 2006;Debnath et al., 2015) 5.2-9.2 m 3 /m/day Radon Rapaglia et al., 2006;Debnath et al., 2015) Florida Bay (USA) 3-35 m 3 /m/day Seepage meter (Burnett et al., 2002;Cable et al., 1997aCable et al., , 1997bDiLorenzo and Ram, 1991;Debnath et al., 2015) Shelter Island, New York (USA) 0.4-17.5 m 3 /m/day Seepage meter DiLorenzo and Ram, 1991;Schubert, 1998;Debnath et al., 2015) 0.23-1.4 m 3 /m/day Simulated DiLorenzo and Ram, 1991;Schubert, 1998;Debnath et al., 2015) Donnalucata, Sicily 10-30 m 3 /m 2 /day Seepage meter (Burnett and Dulaiova, 2006;Taniguchi et al., 2006b;Debnath et al., 2015) 30-200 m 3 /m 2 /day Radon (Burnett and Dulaiova, 2006;Taniguchi et al., 2006b;Debnath et al., 2015) Ubatuba, Brazil 5-270 cm/day Seepage meter Debnath et al., 2015) 1-29 cm/day Continuous Radon Debnath et al., 2015) Government of India (vide no. ...
Submarine groundwater discharges (SGD) play a major role in solute transport and nutrient flux to the ocean. We have conducted a spatio-temporal high-resolution lunar-tidal cycle-scale seepage meter experiment during pre-monsoon and post-monsoon seasons, to quantify the spatio-temporal patterns and variability of SGD, its terrestrial ((T-SGD) and marine components (M-SGD. The measured daily average SGD rates range from no discharge to 3.6 m3m-2d-1 during pre-monsoon season and 0.08 to 5.9 m3m-2d-1 during post-monsoon seasons, depending on the tidal pattern. The uncertainty for SGD measurement is calculated as ±0.8% to ±11% for pre-monsoon and 1.8% to 17% for post-monsoon respectively. A linear, inverse relationship was observed between the calculated T-SGD and M-SGD components, which varied along the distance from the coast and position in the tidal-cycle, Spatial and temporal (daily) variations of seepage rates within the lunar tidal cycle period distinctly demonstrate the influence of tides on groundwater seepage rate. As an instance, for the identification of the bulk discharge location, the centroid of the integrated SGD rate has been calculated and found to be near 20m offshore area. The average discharge rate per unit area further extrapolated to total SGD fluxes to the Bay of Bengal from eastern Indian coast by extrapolation of the annual and seasonal fluxes observed in the study area, which are first direct/experimental estimate of SGD to the Bay of Bengal. Approximations suggest that in present-day condition, total average annual SGD to the Bay of Bengal is about 8.98 ± 0.6 ×108 m3/y. This is suggested that the SGD input to the ocean through the Bay of Bengal is approximately 0.9% of the global input from the inter-tidal zone and that has an implication on the mass balance of discharging solutes/nutrients to the global oceans. High T-SGD input is observed for all season, which is largest toward landward direction from the delineated saltwater-freshwater interface. The high magnitude of T-SGD could play an important role in mass balance of fresh water discharge and solute transport to the global ocean, thereby influence coastal ecohydrological systems.
... Another one consists in direct measurements of groundwater seepage rates using a manual "seepage meter" (e.g. Israelsen and Reeve, 1944;Cable et al., 1997), i.e. a chamber inserted into the sediments and connected to a plastic bag. Submarine groundwater discharge can also be calculated from water balances of aquifers (e.g. ...
The Campo de Cartagena area in the Murcia region (SE Spain) is an emblematic case of the hydrological and environmental changes caused by the intensive use of groundwater for agriculture in semiarid Mediterranean areas. Agricultural development supported by the multi-layer aquifer system has led to the overexploitation of the deep layers, while irrigation return flow and the subsequent increased recharge rates increased water table levels in the unconfined layer. In addition, a large number of boreholes of the area are screened in several aquifers and allow an artificial connection between different groundwater masses. Moreover, as a consequence of the water table increase in the shallow aquifer, a permanent flow appeared in the last kilometres of the surface watershed. Together with the uncontrolled release of brines from private groundwater desalination, it induced a permanent surface flow of water to the main outlet of the system, the Mar Menor lagoon. In this context, understanding the complex evolution of the whole system and how the water balance is affected is a hard task.The first research focus aimed at collecting and reviewing all kind of existing data in order to reconstruct the evolution along one century of the multi-layer aquifer system. It highlighted an inversion of the vertical hydraulic gradient between aquifers and the decrease of water table levels up to 500 m for the deepest layer. Facing the difficult identification of the origin of groundwater samples, a method based on the Random Forest (RF) machine learning technique was developed. Despite the difficulty of an unequal dataset, accuracy over 90% was reached and 107 groundwater samples of unknown origin could be classified. Results were much better than using Linear Discriminant Analysis (LDA) or Decision Trees (CART).The second research axis was motivated by the difficulty to update the water balance of the multi-layer aquifer where irrigation return flow represents an additional source of recharge, added to the limited rainfall infiltration. Environmental tracers (14C, 13C, 2H, 18O, 3H) were combined to high-resolution temperature loggings to investigate the long-term evolution of recharge in the Campo de Cartagena aquifer system and discriminate local mixing processes (infra-boreholes) from regional mixing processes (between aquifers). Both pre-anthropization and post-anthropization recharge regime could be identified and quantified. Before the development of agriculture, recharge varied from 17 mm.a-1 in the mountain ranges to 6 mm.a-1 in the plain. In response to the increase of agricultural activity, recharge fluxes were amplified up to 210 mm.a-1 in irrigated areas.The third research axis consisted in quantifying submarine groundwater discharge (SGD). In order to decipher the influence of the different water sources on the Mar Menor, a radon (222Rn) and radium (223Ra, 224Ra) survey was combined with the hydrodynamic modeling of the lagoon. The areas of influence of a plume of radionuclides from the river were identified, the main areas of SGD were located and a location for a submarine emissary was proposed. Mass balances in winter and summer seasons provided total yearly SGD fluxes of water of 7.2-15.9 108 m3.a-1 (222Rn), 21.9-44.7 108 m3.a-1 (224Ra) and 6.9 108 m3.a-1 (223Ra, in winter). Water level effect, rather than tidal pumping, was identified as the main driver for recirculated saline groundwater, while fresh submarine groundwater discharge from the aquifer was about 1% of total SGD. As the case study is an extreme case of anthropization, these results present a wide interest that is not limited to the Murcia region or the Campo de Cartagena aquifer. The methods developed in this thesis might be used in other Mediterranean sites where groundwater exploitation seems to follow a continuous and inevitable increase.
... Although the importance of SGD has been well recognized, studies on this issue have been hampered by the lack of measurement tools on a large space and time scale. General tools for SGD assessment include hydrological considerations [4], seepage measurements [5][6], and mass balance modeling using tracers such as Ra isotopes, 222 Rn and CH 4 [7][8]. An advantage of groundwater tracers is that they present an integrated signal as they enter marine water column via various pathways in the aquifer. ...
In order to assess submarine groundwater discharge (SGD) and evaluate seasonal oscillations of such fluxes, measurements of the naturally occurring 222Rn in Ubatuba embayments were carried out from March/03 through July/2005. In this area, the main geologic/geomorphologic feature is the presence of pre-Cambrian granites and migmatites of Serra do Mar. The coastal aquifer is a fractured rock aquifer, covered by Pleistocene and Holocene sediments. The discharge pattern of this kind of aquifer is spatially heterogeneous, with preferential flow paths along rock fractures. During this investigation 222Rn in excess inventories obtained in 24 vertical profiles varied from 345 ± 24 dpm m-2 to 18,700 ± 4,900 dpm m-2. The highest inventories of 222Rn in excess were observed both in Flamengo and Fortaleza embayments, during summer campaigns. The estimated total fluxes required to support inventories measured varied from 62 ± 4 to 3,385 ± 880 dpm m-2 d-1. SGD fluxes calculated in Ubatuba embayments ranged from 0.1x10-1 to 1.9 cm d-1. Taking into account all fluxes estimated, the percentual variability was 89% (seasonal variation in 3 years period, n = 24 measurements). Although, if we consider each year of study separately, the respective percentual variabilities estimated are 72% in 2003 (n = 10 measurements), 127% in 2004 (n = 6 measurements) and 97% in 2005 (n = 8 measurements).
... estimated that SGD was -100 m 3 /d per m length of shoreline in July 1994, equivalent to 40% of river discharge and, from consideration of the regional freshwater balance, concludes that most of this discharge is seawater circulation (Moore and Church 1996). Studies that have directly measured discharge throughout the year report a total discharge that is consistently greatest during the summer and lowest in the winter months along the Atlantic coast of the United States Cable et al. 1997a;Cable et al. 1997b). Local radium fluxes measured over several years along the South Atlantic Bight indicate that SGD is larger in the summer than the winter and spring (Moore 1987;Bollinger and Moore 1993;, and monthly groundwater discharge estimated from radium fluxes in Rhode Island show a distinct pattern that peaks in the summer . ...
The fresh and saline groundwater flowing from coastal aquifers into the ocean comprise submarine groundwater discharge (SGD). This outflow is an important pathway for the transport of nutrients and contaminants, and has been shown to adversely affect coastal ecosystems in many areas of the world. The focus of this work is the characterization of SGD and the mechanisms that drive it, with a specific emphasis on seasonal forcing. Field measurements during five summers in Waquoit Bay, Massachusetts reveal the pattern and composition of submarine groundwater discharge. Flow is highly variable over small spatial and temporal scales, and the salinity and radium content of the discharge demonstrates heterogeneity in groundwater origin. Maximum discharge occurred in two alongshore bands: brackish outflow nearshore and saline discharge offshore. Most of the total flow was saline, yet net seawater inflow over a tidal cycle was negligible. Circulation mechanisms such as tides, waves, and hydrodynamic dispersion cause significant saline groundwater discharge, and are potentially important for chemical loading to estuaries. However, these mechanisms can explain only 12-30% of the observed saline outflow in Waquoit Bay. A seasonal forcing mechanism is proposed to explain the source of the remaining observed saline outflow. During periods of high inland recharge, the water table rises, forcing seaward movement of the freshwater-saltwater interface and outflow of saline groundwater; the opposite is true during times of low recharge. A series of idealized simulated systems demonstrates this process for a range of realistic aquifer parameters, and a time lag between maximum recharge and simulated peak discharge may explain the observed net discharge during times of low recharge.
... Since SGD into the coastal areas results from a composite of spatially and temporally variable physical forces interacting with the geological matrix, the magnitude and the chemical composition of SGD can vary greatly in space and time . SGD in homogeneous aquifers is expected to decrease exponentially with distance from the coast (Bokuniewicz, 1980;Cable et al., 1997b;Fukuo and Kaihotsu, 1988). However, aquifer heterogeneity can generate preferential flow paths that favor groundwater discharges offshore (Bokuniewicz et al., 2004;Burnett et al., 2001c;Cable et al., 1997a;Taniguchi et al., 2003), such as submarine springs in karst or volcanic systems (Fleury et al., 2007;Peterson et al., 2009;Swarzenski et al., 2001) or leakages of fluids from confining layers (Moore, 2010b). ...
Submarine groundwater discharge (SGD) is defined as any flow of water across the continental margin from the seabed to the coastal ocean, including fresh meteoric groundwater and seawater recirculating through coastal aquifers. SGD has been recognized as a major component of the hydrological cycle and a significant source of various dissolved terrestrial compounds (e.g. nutrients, trace metal, carbon, contaminants) to the coastal ocean. These fluxes of chemical elements via SGD may have a profound impact on the biogeochemical cycles of the receiving water bodies. This can be especially relevant in oligotrophic and semi-arid regions, such as the Mediterranean Sea. However, and despite the potential importance of SGD in regulating coastal biogeochemical cycles of the Mediterranean Sea, there is still a lack of detailed assessments on the relevance of SGD as a source of chemical constituents into this basin. Indeed, the magnitude of SGD to the entire Mediterranean basin and its associated fluxes of dissolved compounds have never been evaluated.
The main objective of this PhD Thesis is to evaluate the importance of SGD in the Mediterranean Sea by using radium (Ra) isotopes, paying attention to the role that SGD plays as a source of dissolved chemical compounds to the sea and to the use of Ra isotopes as SGD tracers. To this aim, contrasting Mediterranean coastal environments were selected, including: i) a coastal wetland nourished by groundwater inflowing from several aquifers (Peníscola marsh, Castelló); ii) a semi-enclosed embayment highly influenced by bottom sediments (Port of Maó, Minorca, Balearic Islands); and iii) a detrital bay open to the sea (Palma Bay, Majorca, Balearic Islands). Aside from these three specific sites, the first appraisal of the magnitude of SGD into the entire Mediterranean Sea was also conducted, demonstrating its significance as a source of dissolved compounds in a basin-wide scale.
Results from these studies provide new insights into the use of Ra isotopes as tracers to quantify SGD and underline their suitability in a wide range of Mediterranean hydrogeological settings. We successfully applied them to estimate SGD-driven fluxes of dissolved nutrients and, for the first time, trace metals to a coastal Mediterranean area, stressing the role SGD may play as a source of these constituents to the marine environment. We show that SGD is a volumetrically important process in the Mediterranean Sea, contributing up to (0.2–4.3)·10^12 m3/yr, a magnitude that is significantly larger than riverine discharge. SGD also represents a major source of dissolved nutrients to the basin, rivaling the conventional external sources (i.e. atmospheric deposition and river discharge). This new understanding of the magnitude of SGD and its associated chemical fluxes demonstrates the profound implications of SGD in the biogeochemical cycles of the Mediterranean Sea, emphazising the need for its consideration in coastal and basin-wide studies.
... Wave and current interactions with seepage meters can drive excess flux that would not exist in calm waters (e.g., Cable et al. 1997;Rosenberry 2008;Smith et al. 2009), leading to questions about seepage meter accuracy in dynamic surface waters (e.g., Shinn et al. 2002;King et al. 2009;Rosenberry et al. 2013). Though effects of currents on seepage meter measurements have been studied and quantified in a controlled laboratory setting (Libelo and MacIntyre 1994;Rosenberry 2008), wave impacts have not received similar attention. ...
Water exchange between surface water and groundwater can modulate or generate ecologically important fluxes of solutes across the sediment-water interface. Seepage meters can directly measure fluid flux, but mechanical resistance and surface water dynamics may lead to inaccurate measurements. Tank experiments were conducted to determine effects of mechanical resistance on measurement efficiency and occurrence of directional asymmetry that could lead to erroneous net flux measurements. Seepage meter efficiency was high (average of 93%) and consistent for inflow and outflow under steady flow conditions. Wave effects on seepage meter measurements were investigated in a wave flume. Seepage meter net flux measurements averaged 0.08 cm/h—greater than the expected net-zero flux, but significantly less than theoretical wave-driven unidirectional discharge or recharge. Calculations of unidirectional flux from pressure measurements (Darcy flux) and theory matched well for a ratio of wave length to water depth less than 5, but not when this ratio was greater. Both were higher than seepage meter measurements of unidirectional flux made with one-way valves. Discharge averaged 23% greater than recharge in both seepage meter measurements and Darcy calculations of unidirectional flux. Removal of the collection bag reduced this net discharge. The presence of a seepage meter reduced the amplitude of pressure signals at the bed and resulted in a nearly uniform pressure distribution beneath the seepage meter. These results show that seepage meters may provide accurate measurements of both discharge and recharge under steady flow conditions and illustrate the potential measurement errors associated with dynamic wave environments.
... Although the importance of SGD has been well recognized, studies on this issue have been hampered by the lack of measurement tools on a large space and time scale. General tools for SGD assessment include hydrological considerations [4], seepage measurements [5][6], and mass balance modeling using tracers such as Ra isotopes, 222 Rn and CH 4 [7][8]. An advantage of groundwater tracers is that they present an integrated signal as they enter marine water column via various pathways in the aquifer. ...
In order to assess submarine groundwater discharge (SGD) and evaluate seasonal oscillations of such fluxes, measurements of the naturally occurring 222 Rn in Ubatuba embayments were carried out from March/03 through July/2005. In this area, the main geologic/geomorphologic feature is the presence of pre-Cambrian granites and migmatites of Serra do Mar. The coastal aquifer is a fractured rock aquifer, covered by Pleistocene and Holocene sediments. The discharge pattern of this kind of aquifer is spatially heterogeneous, with preferential flow paths along rock fractures. During this investigation 222 Rn in excess inventories obtained in 24 vertical profiles varied from 345 ± 24 dpm m -2 to 18,700 ± 4,900 dpm m -2 . The highest inventories of 222 Rn in excess were observed both in Flamengo and Fortaleza embayments, during summer campaigns. The estimated total fluxes required to support inventories measured varied from 62 ± 4 to 3,385 ± 880 dpm m -2 d -1 . SGD fluxes calculated in Ubatuba embayments ranged from 0.1x10 -1 to 1.9 cm d -1 . Taking into account all fluxes estimated, the percentual variability was 89% (seasonal variation in 3 years period, n = 24 measurements). Although, if we consider each year of study separately, the respective percentual variabilities estimated are 72% in 2003 (n = 10 measurements), 127% in 2004 (n = 6 measurements) and 97% in 2005 (n = 8 measurements).
... Ground-water discharge rates to surface-water bodies in the wetland area can be calculated by the same methods as discussed in the section above. In addition, seepage meters commonly have been used to directly measure ground-water discharge rates to surface water, including lakes, streams, and coastal waters (Lee, 1977;Lee and Cherry, 1978;Woessner and Sullivan, 1984;Shaw and Prepas, 1989;Cable et al, 1997). The basic seepage meter consists of the bottom section of a 55-gallon drum or smaller bucket (depending on the area of the study site) and a plastic water collection bag, connected to the bottom of the drum with an open port. ...
... 또한, 한반도 연 안해역에서도 남해안의 여자만과 가막만 등과 같이 반폐쇄적 인 내만해역에서 만내 영양염류 중 질산염과 규산염의 약 80% 이상이 해저지하수에 의해 공급되는 것으로 밝혀지기도 하였 다 (Hwang et al., 2005a(Hwang et al., , 2010aLee et al., 2009). 이러한 해저지하수를 통한 영양염류의 유입은 연안 부영양화 를 야기하고 (Valiela et al., 1990), 조간대 저서미세조류 (Waska and , 식물플랑크톤의 기초생산(LaRoche et al, 1997;Herrera-Silveira, 1998) 및 적조발생 (Lee and Kim, 2007;Lee et al., 2010) (Cable et al., 1997;Kim et al., 2003;Taniguchi et al., 2006;Burnett et al., 2007), 지하수중에 높은 농도로 존재하는 Ra 동위원소, 222 Rn, CH 4 등과 같은 지화학적 추적자 (Moore, 1996;Charette et al., 2001;Kelly and Moran, 2002;Hwang et al., 2005b), 물수지 (water or salt balance) 및 수리·지질학적 모델(hydrogeologic assumption, Darcy's Law) 등과 같은 모델링 기법 (Oberdorfer et al., 1990;Oberdorfer, 2003) (Koh et al., 2007;Kang et al., 2008). 또한, 지층의 내부 에는 용암동굴, 용암터널의 붕괴에 의해 생성된 공동(숨골), 파 쇄대, 냉각에 의한 절리대 등과 같은 다양한 투수성의 지질구 조를 이루고 있다 (Hamm et al., 2005;Won et al., 2006;Kim et al., 2011a). ...
To examine temporal and spatial variation in salinity and nutrients in the shallow pore water of intertidal sandflats, we measured salinity and nutrient concentrations (dissolved inorganic nitrogen [DIN], phosphorus [DIP], and silicate [DSi]) in pore water of the intertidal zone along the coastline of Jeju Island at two and/or three month intervals from May 2009 to December 2010. Geochemical parameters (grain size, ignition loss [IL], chemical oxygen demand [COD], and acid volatile sulfur [AVS]) in sediment were also investigated. The surface sediments in intertidal sandflats of Jeju Island were mainly composed of sand, slightly gravelly sand and gravelly sand, with a range of mean grain size from 0.5 to 2.5 . Concentrations of IL and COD in sediment were higher along the eastern coast, as compared to the western coast, due to differences in biogenic sediment composition. Salinity and nutrient concentrations in pore water were markedly different across time and space during rainy seasons, whereas concentrations were temporally and spatially more stable during dry seasons. These results suggest that salinity and nutrient concentrations in pore water depend on the advective flow of fresh groundwater. We also observed an imbalance of the DIN/DIP ratio in pore water due to the influence of contaminated sources of DIN. In particular, nutrient concentrations during rainy and dry seasons were characterized by high DIN/DIP ratios (mean-127) and low DIN/DIP ratios (mean-10), respectively, relative to the Redfield ratio (16) in offshore seawater. Such an imbalance of DIN/DIP ratios in pore water can affect the coastal ecosystem and appears to cause outbreaks of benthic seaweed along the coastline of Jeju Island.
Direct release of fresh/recirculated groundwater to the ocean is of greater significance due to its material transfer pathways along the coastal zones. To assess the significance of submarine groundwater discharge (SGD) as a cause of chemical and dissolved fluxes to the ocean, estimation of submarine groundwater discharge, and associated dissolved nutrients and rare earth elements fluxes to the Bay of Bengal from the Sankarabarani river basin, India has endeavored. A total of 180 groundwater samples were collected from the three different locations for 30 days by considering high and low tides. The submarine groundwater discharge through the aquifer ranges from 0.75 to 2.90 m d− 1 calculated by the radon mass balance model. The SGD rate is increasing toward the coast, which is higher in location C followed by locations A and B suggesting the influence of recirculated seawater resulting in brackish SGD. From the nutrient mass balance, DIN’s average net invention was 192.00 μ mol d− 1, DIP is 4.00 μ mol d− 1, and DSi is 97.00 μ mol d− 1 suggesting SGD-derived nutrients were higher and responsible for algal blooms influencing the biodiversity of the study area. From the REE mass balance, the SGD supported REE flux was 25.70 m mol d− 1 for Nd, 5.04 m mol d− 1 for Gd, and 2.92 m mol d− 1 for Yb, respectively. The removal of LREEs in a more significant quantum in comparison with MREE and HREEs. The more excellent removal of LREEs is mainly due to increasing salinity and release of MREEs and HREEs due to its particle reactivity. The SGD-derived fluxes were influenced by tidal fluctuations, hydraulic gradient, the conductivity of the formation, groundwater extraction, and other biogeochemical influences. The sources for nutrients and REEs fluxes seem to be influenced by interaction between the fresh and bay water end members. The other dominant sources are the availability of elements, speciation, presence or absence of colloidal fragments, and various sources and sinks.
The influx of fresh groundwater and re-circulated sea water into coastal ecosystem occurs through the submarine groundwater discharge (SGD). Measurement of salinity, radium tracers (²²⁴Ra, and ²²⁶Ra isotopes) and nutrients in estuarine water, coastal surface water and groundwater during December 2019 estimated the SGD and associated nutrient fluxes near the Karameniyar estuary (Gulf of Mannar) and surroundings of the Manapad region at southern part of Tamil Nadu state in India. The presence of excessive radium tracers revealed that the SGD was contributing to Ra desorption from the sediments and enrichment in the coastal waters. We estimated SGD of approximately 0.03–0.59 m³ m⁻² d⁻¹ for the Manapad region and relatively more homogeneous but comparatively less values in the Karameniyar estuary (0.03–0.34 m³ m⁻² d⁻¹). Higher average values of dissolved inorganic nitrogen (DIN; 43.62 μmol L⁻¹) and soluble reactive phosphate (SRP; 1.848 μmol L⁻¹) suggested greater influence of SGD on the overall coastal water nutrient budget. This study also indicated simultaneous occurrence of fresh and saline SGD in this region.
This review of studies that quantified fluxes with seepage meters in marine settings in the last decades shows the historical evolution of this device and the knowledge acquired during this period. Coastal environments are differentiated from freshwater settings due to water salinity and the effects of tides and waves that have important implications for the measurement approach and generated results. The framework in which seepage meters have been used in marine settings has evolved in parallel to the understanding of submarine groundwater discharge. This review of seepage meter research shows: an uneven distribution of studies in the world with some densely-studied regions and an absolute lack of data in other regions; a dominance of studies where only seepage meters were used compared to studies that combined seepage meter measurements with values determined with radioactive tracers or hydraulic calculations; and a variety of publication outlets with different focuses (hydrology, oceanography or multidisciplinary). The historical overview of the research conducted with seepage meters shows the wide range of seepage meter applications – from simply measuring fluxes at local scales to larger studies that extrapolate local results to estimate fluxes of water, nutrients, and other solutes at regional and global scales. A variety of automated seepage meters have been developed and used to better characterize short-term groundwater-seawater exchange, including the effects of waves and tides. We present recommendations and considerations to guide seepage meter deployment in marine settings, as seepage meters are still the only method that quantifies directly the interaction between groundwater and surface water.
湿地沉积物—水界面的地表水—地下水交换通量对水环境的水文循环、水量均衡、水质变化、生化反应和生态环境效应等具有关键作用和重要意义。目前，在河流、湖泊、海洋等湿地区域的研究中，越来越多的研究者认识到地表水-地下水交互作用是不可忽略的水文循环过程，它将大大促进对区域乃至全球性水循环的深入理解。渗流仪是一种直接测量沉积物—水界面的水流通量的仪器装置，它具有构造简单、容易制作、造价便宜、操作便捷
等优点，一般适合于河流、湖泊和海洋等湿地的近岸小尺度研究。该测量方法起源于20 世纪40 年代的美国犹他州农业实验站，后来被广泛应用于世界各地的河流、河口、湖泊、滨海、渠道和水库等天然和人工湿地中地下水—地表水交换的定量研究。下面将对渗流仪的研究历程、热点前沿进行回顾与展望，以期为使用直接测量法定量研究湿地地下水—地表水交换提供一定的思路。
A regional scale modular variable-density groundwater flow model (MOCDENS3D) has been used to estimate the magnitude of submarine groundwater discharge to Manila Bay. The model area is located at the south-eastern flank of Mt. Mariveles volcano in Bataan Peninsula, Philippines. The area stretches on 12 km of coastline where preliminary SGD flux measurements were made earlier. The hydrogeologic properties of these sediments are estimated using information from pumping tests, borehole data, seismic sections and geological maps. Key features of the groundwater system include high relief in the upper slopes and narrow low relief coastal plain. The model domain incorporates both the terrestrial recharge and also the re-circulated water in the coastal sediments. Different scenarios were run to evaluate the sensitivity of SGD to changes in different input parameters. SGD rates peak during the rainy season and there’s a one month delay to the peak rainfall. SGD shows major influence of rainfall (recharge), geology and topography. Model calculations suggest that there is substantial contribution of freshwater from terrestrial origin which discharges to the bay. The presence of confining layers greatly affects the offshore extent of SGD, and therefore its potential impact on the regional environment. Model results are consistent with previously measured SGD rates using seepage meters and geochemical tracers by Taniguchi et al. (2008).
This study considers the influence of pore water flux through cohesive sediment beds on sediment resuspension. Experiments performed on unconsolidated sediments indicated that seepage occurred through preferential channels formed in the sediment. Additional experiments were performed in a re-circulating flume where the sediment bed was subjected to hydrodynamic shear stress. The resuspension rate increases as the square of the bed shear stress level above a threshold to initiate resuspension. The resuspension rate increased with increasing pore water flux. A simple relationship was established between the rate constant and the applied pore water flux. Additional tests were performed with two different cap materials to determine their effectiveness in controlling sediment resuspension. No sediment resuspension was observed with the sand cap. The AquaBlok ® cap experiences a rupture failure when the pressure head differential across the cap exceeded approximately 25 cm. INTRODUCTION Resuspension is potentially an important mechanism for mass exchange between contaminants bound to sediments and the overlying water column. Literature indicates that many potential factors can contribute to the resuspension rates for fine-grained cohesive sediments. This investigation focuses on the influence of seepage or vertical pore water flux through the sediment bed on sediment resuspension. Resuspension can potentially be controlled by placing a physical barrier (cap) to protect the contaminated sediments from erosive forces in the overlying flow. The efficacy to two potential cap materials in reducing resupsension is also investigated. Erosion of cohesive sediment beds is assumed to occur largely as a result of advective flow induced shear stress. However, there is no well-established general theory for describing the erosion of cohesive sediment beds. Berlamont, et al (1993) list 28 different factors related to sediment characteristics, bed structure, flow characteristics, etc. that may influence sediment resuspension. Among these is the degree of bed consolidation, which can be affected by pore water flux. This large number of different factors makes a systematic investigation of resuspension processes difficult. As a consequence, there has been little firm agreement about the conclusions from past experimental investigations. Laboratory and in-situ
Ein Anforderungsprofil beschreibt, welche Kriterien die Bewerber erfüllen müssen oder sollen. Ein aus der Stelle und anderen Gegebenheiten der Organisation abgeleitetes Sollprofil ist meist die unverzichtbare Basis eines fundierten, zweckgerichteten und fairen Such- und Auswahlverfahrens. In den USA ist ein stellenbezogenes Anforderungsprofil ein wichtiger Punkt bei der Verteidigung der Personalauswahl gegen Diskriminierungsklagen.1 In Deutschland kann es bei Konkurrentenklagen ein Angriffs- oder Verteidigungsmittel sein. Die Umsetzung des Anforderungsprofils in stellenrelevante Fragen im Auswahlgespräch kann die Akzeptanz der Auswahl bei den Bewerbern erhöhen. Außerdem ist das Anforderungsprofil eine Hilfe bei der Information der Bewerber über die angestrebte Stelle.
Managed sandy beach environments along developed shores often appear safe and healthy because obvious hazards such as beach erosion and flooding are considered within the purview of various mitigation programs. A range of insidious and generally unseen hazards, mostly related to pollution, often pose greater threats to the wellbeing of beach systems than do the highly visible, well publicized shoreline retreat and inundation events. Some unseen hazards, such as submarine groundwater discharge (SGD) laden with nutrients from. agro-urban activities on adjacent coastal plains,,are pervasive, processes of environmental degradation that occur so gradually that sequential impacts escape public attention. The contribution of SGDs to the coastal hydrologic regime is occasionally recognized in association with crescendo events associated with marine algal blooms that degrade water quality, bottom habitats, and coral reef ecology. Because the real dangers of SGD are probably unknown at this time, it is essential to initiate seepage meter studies of the already known high levels of nitrogen (N) and phosphorus (P) that are discharged to beach and nearshore environments. Locations of some of the larger submarine freshwater springs along the southeast Florida inner continental shelf are generally known, although volumes of flow have historically been reduced by reduction of head on the coastal plain. Submarine. groundwater provides, on a continual basis, the most direct nutrient linkage to nearshore environments. The insidious nature of the problem requires specialized detection techniques that incorporate site inspection of rock outcrop and reef morphology (for submarine springs and seeps), satellite and airborne remote sensing (coastal morphology, turbidity plumes), physical seepage measurement in situ, monitoring wells, and mini-piezometers to measure hydraulic flow. Discharges of surface water into estuaries exacerbate SGD-related pollution, as do sewage spills and outfall. pipes that discharge in the open ocean fronting beaches. Groundwater discharges for Palm Beach County are, for example, estimated at 1,659 x 10(6) m(3) a(-1). Total N in groundwater below the coastal plain adjacent to remnant Everglades averages about 1.3 mg l(-1). Groundwater nutrient fluxes to the coast are 5727 and 414 metric tons per year for N and P, respectively. Surface water contributions for N and P are respectively 2,473 and 197 metric tons per year. Nutrient delivery to beach and nearshore environments is a serious problem that threatens coastal water quality which in turn will impact beach-related activities. The full impact of the problem has yet to surface because it takes about 5 to 8 decades for groundwater from the interior parts of the coastal plain to reach the nearshore zone. Pollution of groundwaters has increased over the past five decades due to higher doses of fertilizers on croplands and runoff from expanding urban areas. The environmental quality of beach systems along this developed shore is clearly at risk from continuous pollution via nutrient-laden SGD.
This paper reviews methods available for addressing fluxes of water and nitrate, as well as the process affecting nitrate concentrations in the transition from groundwater to surface water, in a comprehensive tabular compilation. Small-scale methods, typically involving direct measurements, give the most quantitative information, while methods working on a larger scale, e.g. airborne or waterborne techniques, can give information on a larger and, in many contexts, more useful scale, but rarely with appropriate quantification. Bridging the gap may be possible by simultaneously applying large-scale measurements and small-scale direct measurements covering the range of values, using these for calibration.
Submarine groundwater discharge (SGD) in the coastal zone is recognized as a potentially significant material pathway from the land to the ocean. This chapter provides an overview on several methodologies used to estimate SGDs. Measurements of SGD using “manual seepage meters” show that consistent and reliable results can be obtained if one is aware of and careful to prevent known artifacts. New “automated seepage meters” help understand the hydrological and coastal oceanographic processes with longer-term and higher-resolution measurements. Direct measurements of SGD by seepage meters and piezometers in local areas may be scaled up to a regional basis by use of natural geochemical and geophysical tracers. Water balance estimates, although useful for rough estimates, are usually not very precise because the uncertainties in the various terms used to construct the balance are often on the same order as the groundwater discharge being evaluated. Estimates of SGD via analytical and numerical methods depend mainly on the evaluations of the thickness of the aquifers and representative hydraulic conductivities, of which well-constrained values are usually difficult to obtain.
In order to evaluate submarine groundwater discharge (SGD) rates continuously and automatically, a“continuous heat-type”automated seepage meter was newly developed, and it was applied to Tannowa, Osaka Bay, Japan. The meter is based on the measurements of the temperature gradient of the water between the downstream and upstream positions in a pipe. According to two months continuous measurements of SGD every 10 minutes, semi-diurnal periodical changes in SGD were found in Tannowa. This is attributed to the tidal effects on SGD. The time delay of the SGD from tidal records was also found to be about 5 hours. The newly developed automated seepage meter can provide longer-term and higher-resolution measurements of SGD, which helps us to understand temporal scale issues on SGD and the relevant hydrological and coastal oceanographic processes.
Submarine groundwater discharge (SGD) has been recognized as a provider for freshwater, nutrients, and dissolved constituents from continents to the oceans and paid more attention with regard to the mass balance of water or dissolved constituents on local and global scales. The submarine discharge of fresh groundwater (fresh SGD) through seepage or springs in coastal ocean may be especially important in aspects of water resource and marine environment managements in the future. Based on the worldwide compilations of observed fresh SGD, our review reveals that fresh SGD occurs in various marine environments along most shoreline of the world and the global estimates of fresh SGD were approximately 0.01-17% of surface runoff. In addition, the input of fresh SGD calculated and investigated in this study were about 50%, 57%, 89%, and 420% of total river discharge in Jeju Island, Yeongil Bay, Masan Bay, and Yeoja Bay, respectively. These inputs from fresh SGD along the shoreline of Korea Peninsula are much higher than those of the whole world, greatly vary with the region. However, since these estimates are based on the water balance method mainly used in coastal ocean, we have to perform continuous monitoring of various parameters, such as precipitation, tide, evapotanspiration and water residence time, which have an impact on the water balance in a lot of areas for evaluating the precise input of fresh SGD. In addition, since the method estimating the input of fresh SGD has brought up many problems, it is required to make an intercomparison between various methods such as hydrogeological assumption, numerical modeling, and seepage meter.
Direct groundwater inputs are receiving increasing attention as a potential source of nutrients and other dissolved constituents to the coastal ocean. Seepage into St. George Sound, Florida was measured extensively from 1992 to 1994 using seepage meters. Spatial and temporal variations were documented along a 7-km stretch of coastline and up to 1 km from shore. Measurements were made at 3 transects perpendicular to shore and 1 transect parallel to shore. The general results indicated that seepage decreased with distance from shore (2 of 3 transects), and substantial temporal and spatial variability was observed in seepage flow from nearshore sediments. In addition, trends in mean monthly integrated seepage rates were similar to precipitation patterns measured at a nearby coastal weather station. Based on these measurements, we estimate that the magnitude of groundwater seepage into the study area is substantial, representing from 0.23 to 4.4 m3 ⋅ sec-1 of flow through the sediments, approximately equivalent to a first magnitude spring. Although it is unknown how representative this region is with respect to global groundwater discharge, it demonstrates that groundwater flow can be as important as riverine and spring discharge in some cases. Our subsurface discharge rates suggest groundwater is an important hydrologic source term for this region and may be important to the coastal biogeochemistry as well.
The mutual exchange of water between lakes and contiguous permeable ground-water bodies, which are thin relative to the diameter of the lakes, was modeled digitally. A significant rate of seepage was found to extend only a relatively short distance from shore, thus forming a narrow band around the lake's perimeter. Field measurements of seepage rates through the bottom of Lake Sallie, west-central Minnesota, confirm the model results by demonstrating that both the near-shore seepage band and the exponential decrease in seepage velocity actually exist. Equations, diagrams, tables, and curves illustrate model.
Laboratory and field tests revealed that there was an anomalous, short-term influx of water into plastic bags after they were attached to seepage meters. At Narrow Lake, Alberta, the anomalous, short-term (30 min) influx of water averaged 237 ml to bags that were initially empty, but the anomaly was effectively eliminated when bags were prefilled with 1000 ml of water before they were attached to seepage meters. The impact of the anomaly on calculated seepage rates was greatest when seepage rates were low, eg. 0.3 ml m-2 min-1. The anomaly may be due to mechanical properties of the bag, and it may be alleviated by partially filling bags before they are attached to seepage meters. -from Authors
The spacial distribution of groundwater discharge into the littoral zone of Lake Rotorua (New Zealand) was determined by direct measurement. Discharges at two stations on the eastern shore were found to be 2.8 and 5.0 times greater than that at any of the other five stations gauged. On transects at right angles to the shoreline, flow rate varied inversely with depth and distance from shore. The maximum discharge recorded was 127.5 l m−2 day−1, and the minimum 2.7 l m−2 day−1. It is concluded that the technique employed could be an extremely useful tool when investigating groundwater discharge into lakes.
A device was designed to be dragged along lakebeds for locating anomalies in sediment temperature or chemistry. The drag was a density-balanced probe containing temperature transducers and an electrical conductivity cell. The drag was used successfully to detect an artificially created seepage area in soft bottom sediment below 8 m of lake water. The method may find application in estuarine or shallow ocean environments where variations in sediment properties can be used to identify anomalies, e.g., zones of groundwater flux.
Errors result in the need for meter correction factors due to flow field deflection and frictional resistance and head losses within the meter and prefilled bags to avoid short-term influx of water caused by the pulling action of deformed bags. Tank-test data indicate a ratio of measured to actual inseepage of 0.77 (at inseepage rates <20 mm h-1), with a ratio of meter to interstitial seepage flux of 0.50. Provided these precautions are observed and the adjustment factor is applied, field test "point estimates' of seepage inflow with replicate seepage meters generally have relative root-mean-square error(s) <20%. Data from measurements at single locations in tank tests indicate a constant bias and show that, once installed, the actual instrument error is even less (~5%). These errors are small compared to spatial and temporal components of sampling error typically encountered in the field. -from Authors
An integrated approach was used to quantify groundwater phosphorus flux to Narrow Lake, a smallglacial-terrain lake in central Alberta. Data from a drilling program, major ion concentrations, environmental isotopes, and computer simulations indicated that the lake gains water through the nearshore region from a small, shallow groundwater flow system; at deep offshore regions, water moves from the lake to the groundwater flow system. Seepage flux was quantified by water budget, Darcy's equation with data from wells near the lake, Darcy's equation with data from minipiezome- ters in the lake, and seepage meters. Whole-lake seepage flux determined from minipiezometer data (30 mm yr-I) was only lO-25% of the other estimates (mean, 221 mm yr-I; range, 133-332 mm yr- l from seepage meter and water budget data, respectively). Groundwater contributed - 30% of the annual water load to the lake. The P concentration, (PI, in pore water from lake sediments (mean, 175 mg m-') was 8 times higher than groundwater from wells near the lake (mean, 2 1 mg m-3). Thus, if well water was used to estimate the (P) of the seepage water, the rate of groundwater P loading to the lake would be underestimated. The rate of groundwater P loading to the lake computed from average seepage flux and average pore-water (P) was 39 mg m-2 yr-I, and ground- water may be the largest single source of P to epilimnetic water in the lake.
Great South Bay (New York) is a large lagoon on the northeast coast of the United States. The flow of groundwater across the floor of Great South Bay has been reported to account for as much as 2/3 of the total freshwater inflow. In situ measurements of this seepage flow have been made along four offshore transects in the Bay. These measurements show that the flow rate decreases rapidly offshore; within 30 m of the shoreline, the submarine outflow rates were typically 40 l (day m2)−1 and decreased to less than 10 l (day m2)−1 at a distance of 100 m from shore. The Bay floor at the study locations was sand or silty sand with vertical intrinsic permeabilities ranging from 14 to 78 darcys.The flow rate across the Bay floor may be described by an exponentially decreasing function. The flow distribution may, therefore, be specified with two parameters—the flow value at the shoreline, A, and a ‘decay’ constant, c, that governs the rate of decrease of the flow offshore. The calculated total flows along the four transects were 2·1 × 103, 1·1 × 103, 8·5 × 103 and 3·9 × 103 l (day m)−1. Between 40% and 98% of this flow enters the Bay within 100 m from shore. The total flow of groundwater across the Bay floor was calculated to be about 2 × 108 l day−1 or 10–20% of the total freshwater inflow.
The problem of groundwater discharge to the seas and oceans covers investigations of: (1) the role of submarine groundwater discharge in the world water balance; (2) the effect of groundwater on forming the water and salt balances of the seas; (3) the interrelationship between sea and groundwaters in coastal areas; (4) the effect of groundwater discharge on forming mineral deposits at sea and ocean floors; and (5) points of fresh groundwater discharge on the sea floor for water-supply purposes.The methods of investigating groundwater outflow to the seas and oceans are divided into two large groups: those based on studying coastal drainage areas and those based on studying the sea.The coastal techniques are subdivided into the hydrodynamic method, the average long-term water-balance method, the combined hydrological and hydrogeological method, and the analog-simulation method.The sea techniques include those based on studying seawater and those based on studying the sea bottom.The seawater methods incorporate investigations of the electric conductivity, the distribution of temperature, the anomalies of salt composition of seawater and the groundwater discharge studies with tracers.The sea-bottom methods include locating groundwater discharge from data on physical or chemical anomalies in bottom sediments (geothermal and geochemical techniques) and investigating structural features of the sea bottom (geophysical method, geomorphological method and observations by divers and submersibles).In conclusion, some experience in studying groundwater outflow to the seas, submarine springs investigations and results of studying groundwater discharge to the Baltic and Caspian Seas are presented.
Seepage flux can be measured and samples of groundwater flowing into lakes and estuaries collected by enclosing an area of bottom with a cylinder vented to a plastic bag. The method has the advantage of not requiring measurements of permeability of bottom sediments. Seepage velocities from −0.1–2.58 µ m s ⁻¹ were measured in Minnesota and Wisconsin lakes and in Nova Scotia and North Carolina estuaries.
Where seepage inflow was rapid (0.4–0.8 s ⁻¹ ), water collected with the seepage meter was chemically similar to water from wells on the same flow path, and the distribution and chemistry of the seepage concurred with a theoretical flow net. The rate and direction of seepage flux were correlated with water surface elevation during a tidal cycle.
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