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Assessing methodologies for measuring groundwater discharge to the Ocean
Abstract
The direct discharge of groundwater into the coastal zone has received
increased attention in the last few years. We now know that this process
represents an important pathway for material transport between land and
sea. Groundwater discharge often contains higher concentrations of
dissolved nutrients and other components than does river water; thus, it
can play an important role in the health of coastal ecosystems.
... Several studies have attempted to characterize coastal groundwater discharge by direct measurement using seepage meters (Bokuniewicz 1980;Whiting and Childers 1989;Bokuniewicz and Pavlik 1990;Cable et al. 1997a;Burnett 2002;Taniguchi et al. 2003). The challenges in using point measurements have included a large variability in discharge as well as a lack of sample density in both space and time. ...
... Seepage meters have been widely used to measure groundwater discharge into lakes, rivers and coastal waters (Bokuniewicz 1980;Capone and Bautista 1985;Whiting and Childers 1989;Cable et al. 1997a;Portnoy et al. 1998;Burnett et al. 2003). When used correctly, and where fluxes are large, seepage meters have been shown to give reproducible flux estimates Burnett 2002). Where flows are small, seepage meters may overestimate flux, perhaps due to effects of currents and waves (Shinn et al. 2002), although underestimation has also been reported (Belanger and Montgomery 1992). ...
... The waves and currents in Waquoit Bay are minimal, however, and measured flow rates are up to three orders of magnitude greater than those described in Shinn et al. (2002). A recent study (Burnett 2002) found that groundwater discharge measured by seepage meters agreed with total discharge estimated by natural tracers (Ra, Rn), although the tracer method does not describe the spatial pattern or salinity of discharge. ...
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.
... Submarine groundwater discharge (SGD) is being acknowledged as an important flux of materials to the coastal ocean [1,2,3,4,5,6]. Several components of SGD are recognized: (1) fresh water flowing directly from an aquifer to the ocean, (2) mixtures of fresh water and sea water cycling through surficial unconfined aquifers, and (3) inputs of freshwater-seawater mixtures from deeper semiconfined aquifers. ...
... In August 2000 a SGD intercomparison experiment was organized by members of Scientific Committee on Oceanic Research (SCOR) Working Group 112 and the Land-Ocean Interaction in the Coastal Zone (LOICZ) project of IGBP [6]. The objective of this experiment was to compare estimates of SGD obtained from seepage meters (manual, heat pulse, and ultrasonic), geochemical tracers ( 226, 228, 223, 224 Ra, 222 Rn, 3 H, 3 He, 4 He, and 14 C), and hydrologic modeling. ...
... Seepage m eters and 222 Rn modeling in the nearshore zone estimated discharge rates of 1.6 to 2.5 m 3 min -1 for the 2 x 10 4 m 2 study area (Burnett et al, 2002). The near-shore SGD fluxes estimated from the radium isotope measurements agree well with these estimates. ...
Submarine groundwater discharge (SGD) is being acknowledged as an important flux of materials to estuaries and the coastal ocean Several components of SGD are recognized: (1) fresh water flowing directly from an aquifer to the estuary or ocean, (2) mixtures of freshwater and seawater cycling through surficial unconfined aquifers, (3) inputs of freshwater-seawater mixtures from deeper semiconfined aquifers. These components may interact and mix before they enter the ocean. Ideally we would like to know the total SGD flux and the fraction of this flux attributable to each of these three components. Naturally-occurring radionuclide tracers, especially the four radium isotopes, offer promise in realizing this goal. In August 2000 a SGD intercomparison experiment was organized on a small embayment on the northeast Gulf of Mexico to compare estimates of SGD obtained from seepage meters, geochemical tracers, and hydrologic modeling. Ra isotope samples were collected from seepage meters, piezometers, and surface waters. The two long-lived Ra isotopes, 228 Ra and 226 Ra, provide convincing evidence that there are two sources of SGD to the study area: shallow seepage from the surficial aquifer and input from a deeper aquifer. A three endmember mixing model can describe the Ra distribution in all samples.
... Such techniques rely on the enrichment of the tracer in groundwater relative to seawater, and require measurements of tracer activity (or chemical concentration) in both groundwater and seawater. The most commonly used tracers are 222 Rn and four radioisotopes of Ra ( 224 Ra, 223 Ra, 228 Ra, 226 Ra) (Cable et al., 1996;Moore, 1996a;Moore and Arnold, 1996;Burnett et al., 2002). SGD can be estimated using mass balance models that quantify sources and sinks of the tracers while assuming a groundwater endmember concentration (Moore, 1996a). ...
... Thus, in the case of Ra, total SGD is not easily quantifiable using a single endmember activity. Additional factors such as geologic heterogeneity, sorption processes, complex flow patterns, and reactions can also introduce errors and uncertainty into tracer-based SGD estimates (e.g., Burnett et al., 2002;Lambert and Burnett, 2003;Mulligan and Charette, 2006;Dulaiova et al., 2008;Michael et al., 2011;Schutte et al., 2016). ...
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.
... Such techniques rely on the enrichment of the tracer in groundwater relative to seawater, and require measurements of tracer activity (or chemical concentration) in both groundwater and seawater. The most commonly used tracers are 222 Rn and four radioisotopes of Ra ( 224 Ra, 223 Ra, 228 Ra, 226 Ra) (Cable et al., 1996;Moore, 1996a;Moore and Arnold, 1996;Burnett et al., 2002). SGD can be estimated using mass balance models that quantify sources and sinks of the tracers while assuming a groundwater endmember concentration (Moore, 1996a). ...
... Thus, in the case of Ra, total SGD is not easily quantifiable using a single endmember activity. Additional factors such as geologic heterogeneity, sorption processes, complex flow patterns, and reactions can also introduce errors and uncertainty into tracer-based SGD estimates (e.g., Burnett et al., 2002;Lambert and Burnett, 2003;Mulligan and Charette, 2006;Dulaiova et al., 2008;Michael et al., 2011;Schutte et al., 2016). ...
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.
... The submarine groundwater delivery of certain dissolved constituents such as select radionuclides, trace metals, and nutrient species to coastal bottom waters has often been overlooked [Krest et al., 2000;Valiela et al., 1990;Reay et al., 1992;Simmons, 1992]. This omission from coastal hydrologic and mass balance budgets by both hydrologists and oceanographers alike is largely due to the difficulty in accurately identifying and quantifying submarine groundwater discharge [Burnett et al., 2001a, b;Burnett et al., 2002]. ...
... Artesian or pressurized aquifers can extend for considerable distances from shore, and where the confining units are breached or eroded away, groundwater can flow directly into the sea [Manheim and Paull, 1981]. While the magnitude of this submarine groundwater discharge is often less than direct riverine runoff, recent studies have shown that coastal aquifers may contribute significant quantities of freshened water to coastal bottom waters in ideal hydrogeologic strata [Zektzer et al., 1973;Burnett et al., 2001a, b;Burnett et al., 2002]. Although it is quite unlikely that submarine groundwater discharge plays a significant role in the global water budget [Zektzer and Loaiciga, 1993], there is strong evidence that suggests that the geochemical signature of many redox sensitive constituents is directly affected by the exchange of subsurface fluids across the sediment-water interface Swarzenski et al., 2001]. ...
Approximately 70% of the world's population lives in coastal areas, and the majority of these people depend on coastal aquifers for freshwater. The fragility of these aquifers and their sensitivity to human activity demand informed, competent management to guarantee their survival. Significant knowledge and new technologies related to the subject have accumulated in the last two decades, and a need has emerged for a comprehensive reference that gathers and disseminates crucial information to engineering practitioners and policymakers. Coastal Aquifer Management-Monitoring, Modeling, and Case Studies provides the most advanced and up-to-date methods and tools for the study and protection of coastal aquifers. This "how-to" volume presents a worldwide perspective with contributions from an international panel of experts. They address topics such as geohydrology, optimization, uncertainty analysis, and GIS as they relate to geographically-specific case studies; knowledge from these examples can be applied to aquifer issues in other regions. A companion CD-ROM supplements the text with programs and graphics, making this overview an indispensable reference and tool for the analysis of critical freshwater resources.
... Fluxes of SGD estimated from groundwater flow models are typically one to several orders of magnitude smaller than those measured using field instruments or chemical tracers (Moore, 1996). These differences indicate that meteoric water originating as a recharge to onshore aquifers represents only a fraction of total SGD, with the remainder composed of seawater that is mixed with the shallow porewater (Bokuniewicz, 1992;Burnett et al., 2000;Burnett and Dulaiova, 2003). ...
... As seepage measurements give information on SGD fluxes on local scale only, isotopic tracers have been applied to estimate integrated SGD fluxes over the coast. Isotopic methods of SGD studies using stable ( 2 H, 13 C, 15 N, 18 O) as well as radioactive ( 3 H, 14 C, Ra isotopes, radon) isotopes have recently been developed, and SGD investigations have been carried out in several coastal regions (Moore, 2000;Burnett et al., 2000Burnett et al., , 2001aDe Oliveira et al., 2003Aggarwal et al., 2004;Moore and Wilson, 2005;Moore, 2006;Moore and de Oliveira, 2008;Povinec et al., 2006a,b;Weinstein et al., 2006). Especially deuterium and 18 O are effective conservative tracers of mixing processes at the groundwatereseawater interface, because there is clear isotopic distinction between on-shore meteoric groundwater and seawater. ...
In summary, the papers in this volume present research by those working from the marine and the terrestrial sides of issues related to SGD and groundwater-seawater interactions. The first part of this paper provides an introduction and background information on the subject of SGD and groundwater-seawater interactions. The second part of this paper provides an overview of the 38 symposium papers and places them in context according to the methods used to quantify SGD. The papers presented in this volume describe important contributions to the literature and document a variety of investigative approaches applied over a range of conditions at locations across the globe.
... Fluxes of SGD estimated from groundwater flow models are typically one to several orders of magnitude smaller than those measured using field instruments or chemical tracers (Moore, 1996). These differences indicate that meteoric water originating as a recharge to onshore aquifers represents only a fraction of total SGD, with the remainder composed of seawater that is mixed with the shallow porewater (Bokuniewicz, 1992;Burnett et al., 2000;Burnett and Dulaiova, 2003). ...
... As seepage measurements give information on SGD fluxes on local scale only, isotopic tracers have been applied to estimate integrated SGD fluxes over the coast. Isotopic methods of SGD studies using stable ( 2 H, 13 C, 15 N, 18 O) as well as radioactive ( 3 H, 14 C, Ra isotopes, radon) isotopes have recently been developed, and SGD investigations have been carried out in several coastal regions (Moore, 2000;Burnett et al., 2000Burnett et al., , 2001aDe Oliveira et al., 2003Aggarwal et al., 2004;Moore and Wilson, 2005;Moore, 2006;Moore and de Oliveira, 2008;Povinec et al., 2006a,b;Weinstein et al., 2006). Especially deuterium and 18 O are effective conservative tracers of mixing processes at the groundwatereseawater interface, because there is clear isotopic distinction between on-shore meteoric groundwater and seawater. ...
A new technology based on in situ underwater gamma-ray spectrometry of radon daughter products in water has been applied for groundwater-seawater interaction studies in the coastal regions of SE Sicily (offshore Donnalucata) and SE Brazil (offshore Ubatuba). The continuous monitoring carried out at the Donnalucata (and Ubatuba) site have revealed an inverse correlation between the 222Rn concentration versus the tides and salinity, as 222Rn concentrations in seawater varied from 2 kBq m-3 (1 kBq m-3) during high tide to 5 kBq m-3 (5 kBq m -3) during low tide. The observed variations in 222Rn concentrations are likely caused by sea level changes, as tidal effects induce variations of hydraulic gradient, which can increase 222Rn concentrations during a falling tide, while during a high tide, 222Rn concentrations decrease.
... The interest in SGD has increasingly grown within the scientific community as it is now recognized as an important pathway for the transport of chemical compounds between land and ocean, which can strongly affect marine biogeochemical cycles at local, regional and global scales (e.g., Cho et al., 2018;Luijendijk et al., 2020;Rahman et al., 2019;Rodellas et al., 2015a;. SGD is also recognized to provide a wide range of ecosystem goods and services (Erostate et al., 2020;Alorda-Kleinglass et al., 2021) The definition of SGD has been discussed in several review papers in the marine geosciences field (e.g., Burnett et al., 2002;Burnett et al., 2001;Burnett et al., 2003;Church, 1996;Moore, 2010;Santos et al., 2012;Taniguchi et al., 2019;Taniguchi et al., 2002). Here, we will adopt the most inclusive definition, where SGD represents "the flow of water through continental and insular margins from the seabed to the coastal ocean, regardless of fluid composition or driving force" (Burnett et al., 2003;Taniguchi et al., 2019). ...
Submarine groundwater discharge (SGD) is now recognized as an important process of the hydrological cycle worldwide and plays a major role as a conveyor of dissolved compounds to the ocean. Naturally occurring radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra) are widely employed geochemical tracers in marine environments. Whilst Ra isotopes were initially predominantly applied to study open ocean processes and fluxes across the continental margins, their most common application in the marine environment has undoubtedly become the identification and quantification of SGD. This review focuses on the application of Ra isotopes as tracers of SGD and associated inputs of water and solutes to the coastal ocean. In addition, we review i) the processes controlling Ra enrichment and depletion in coastal groundwater and seawater; ii) the systematics applied to estimate SGD using Ra isotopes and iii) we summarize additional applications of Ra isotopes in groundwater and marine studies. We also provide some considerations that will help refine SGD estimates and identify the critical knowledge gaps and research needs related to the current use of Ra isotopes as SGD tracers.
... These data can provide some preliminary information about the saline/freshwater interface, but mapping of the spatial variability of the salinization front may fail in areas where sampling points are sparse and/or the geological complexity is high. Therefore, to clearly understand the mechanism of saltwater intrusion and define the salinization front, the integration of geophysical, hydrogeological and hydrogeochemical data must be applied (Burnett et al. 2002;Samsudin et al. 2008;Capizzi et al. 2010;Akpan et al. 2013;Kura et al. 2014;Redhaounia et al. 2015;Himi et al. 2017;Goebel et al. 2017). ...
Saltwater intrusion and its spatial distribution using a multidisciplinary approach were investigated on the northeast coast of Bafra Plain, which is one of the most important delta plains in Turkey. Intensive agricultural activity in the study area, which supplies the local and international market with agricultural products, is increasing the importance of this ecosystem. Even the groundwater potential and supply are high; the main problem is the groundwater degradation due to salinization. Moreover, local lithological, tectonic and hydrological complexities increase the uncertainty in the interpretation of the collected (chemical, geophysical, etc.) data, providing an inaccurate geomodel. Specifically, in the study area, there are mixtures of freshwater/saltwater aquifers and geological units containing clay lenses/thin layers and fine-grained alluvium. At the same time, these geological formations have similar resistivity responses, and the ambiguity of the collected electric and electromagnetic geophysical data is high. Therefore, a third geophysical method (seismic refraction), which is sensitive to different physical parameters to constrain the uncertainty in the interpretation, was used. In this study, the salinization of Bafra Plain and complex aquifer system was revealed with the combined use of direct-current resistivity and transient electromagnetic data constrained by seismic refraction data and guided by hydrogeological and hydrochemical data. Using information obtained from a multidisciplinary study, we inferred that the intrusion is monitored inland up to 3.5 km. The intrusion is traced after approximately the first 10 m depth in the central part of the plain. Additionally, in some areas, it was concluded that the intrusion is interrupted by clay lenses. Also, drainage channels constructed in the plain have brought soil salinization under control but have not completely succeeded in controlling the saltwater intrusion into the deeper aquifer. The saltwater intrusion can move more inland if groundwater pumping is not controlled, especially in areas close to the river.
... Continuous monitoring of groundwater flow velocities provides insights into, e.g., groundwater recharge, movement of solutes (contaminants as well as salts), the rates of interaction between groundwater and surface water, and interference between Aquifer Thermal Energy Systems [1,2]. However, quantitative groundwater flow measurements can be challenging [3] and various methods for the monitoring of groundwater flow are available that all have their strengths and weaknesses. ...
Active Heating-Distributed Temperature Sensing (AH-DTS) has the potential to allow for the measurement of groundwater flow velocities in situ. We placed DTS fiber-optic cables combined with a heating wire in direct contact with aquifer sediments in a laboratory scale groundwater flow simulator. Using this setup, we empirically determined the relationship between ΔT, the temperature difference by constant and uniform heating of the DTS cable and the background temperature of the groundwater system, and horizontal groundwater flow velocity. Second, we simulated the observed temperature response of the system using a plan-view heat transfer flow model to calibrate for the thermal properties of the sediment and to optimize cable setup for sensitivity to variation in groundwater flow velocities. Additionally, we derived an analytical solution based on the heat flow equation that can be used to explicitly calculate flow velocity from measured ΔT for this specific AH-DTS cable setup. We expect that this equation, after calibration for cable constitution, is valid for estimating groundwater flow velocity based on absolute temperature differences measured in field applications using this cable setup.
... Yet, quantifying SGD is important, as concentrations of dissolved constituents in SGD are often greater than in surface waters, resulting in significant groundwater-derived solute contributions [10,14]. One potential means of evaluating groundwater pathways and fluxes into the coastal zone more accurately is through the use of natural tracers, where 222 Rn is an excellent tracer [3,[15][16][17][18]. The very large enrichment of 222 Rn concentration in groundwaters over surface waters (usually 1000-fold or greater), and its unreactive nature and short half-life (t 1/2 = 3.83 days) make 222 Rn an excellent tracer to identify areas of significant groundwater discharge [3,19]. ...
Gaza Strip has suffered from seawater intrusion during the past three decades due to low rainfall and high abstraction from the groundwater resource. On a yearly basis, more than 170 million m3 of groundwater is abstracted, while the long-term average recharge from rainfall is 24.4 million m3/year. Submarine groundwater discharge (SGD) has never been studied in the Gaza Strip, due to lack of experience in this field, next to the ignorance of this subject due to the seawater intrusion process taking place. Continuous radon measurements were carried out in six sites along the Gaza Strip to quantify the SGD rate. The final result shows SGD to occur in all sampled sites. The range of SGD rates varies from 0.9 to 5.9 cm·day−1. High values of SGD are found in the south (Rafah and Khan Younis governorates). The high values are probably related to the shallow unconfined aquifer, while the lowest values of SGD are found in the middle of Gaza Strip, and they are probably related to the Sabkha formation. In the north of Gaza Strip, SGD values are in the range of 1.0 to 2.0 cm·day−1. Considering that SGD would occur with the measured rates in a strip of 100 m wide along the whole coast line, the results in a quantity of 38 million m3 of groundwater being discharged yearly to the Mediterranean Sea along Gaza coast. Nutrient samples were taken along Gaza Strip coastline, and they were compared to the onshore wells, 600 m away from the Mediterranean Sea. The results show that SGD has higher NO3− + NO2− than nutrient-poor seawater, and that it is close to the onshore results from the wells. This confirms that the source of SGD is groundwater, and not shallow seawater circulation. In a coastal strip of 100 m wide along the Gaza coast, a yearly discharge of over 400 tons of nitrate and 250 tons of ammonium occurs from groundwater to the Mediterranean Sea.
... 222 Rn a natural radioactive element present in sediment pores and aquifers that are used as tracers for SGD due to its greater magnitude in groundwater than surface water. The concentration of radon in ocean water body is mainly due to significant contribution from groundwater sources [7,10,[12][13][14][15]. Even though radon variations in coastal waters are also due to processes like sediment re-suspension, long shore currents [7] we have made out study considering that advective transport of groundwater through radon rich sediments are the dominant process. ...
... Tidal fluctuation will cause hydraulic head fluctuation and pore water salinity oscillation (Erskine, 1991;Abdollahi-Nasab et al., 2010;Heiss and Michael, 2014;Elad et al., 2017). Tide-induced hydraulic gradients can result in a transient increase of the solute transfer rate more than 20 times higher than the average rate in the aquifers that undergo saltwater intrusion ( Li et al., 1999) and likely contribute to fluctuations in submarine seepage rates (Burnett et al., 2002). However, the transient behaviour of solute migration and the associated mixing processes under highly variable groundwater flow have remained lar- gely unexplored so far. ...
... Burnett W.C. et al., 2002; Landsberger S. et al., 2013)[12] ...
An assessment of radiologically enhanced residual materials generated during oil and gas production in near Baku, Azerbaijan, was conducted. Distribution of the 228Ra/226Ra Activity Ratio (AR) with depth in a sediment core from radium lake was examined. The dashed line represented ingrowth assuming that 228Ra was below equilibrium with 232Th in the young sediments near the top and reached equilibrium at a depth around 10 cm. In this study the radium isotopic data are used to provide estimates of the age of formation of the radiobarite contaminant and age of oil field lake. The results indicate that, the upper two layers in the core (up to 4 cm) contain fallout 137Cs so at least these layers are no older than about 40 yrs. Formation waters that are sent to disposal ponds may consist of accumulated heavy hydrocarbons, paraffin, inorganic solids, and heavy emulsions. We report here results of chemical and radiochemical measurements from formation waters separated from oil pumped from approximately 700 m below ground near Baku, Azerbaijan. Our results also include data from a formation water storage pond (“radium lake”) where the waters are temporarily stored after oil is separated and then eventually disposed of by pumping into the Caspian Sea. We also analyzed the associated sediment for radiochemical components. Our study was intended to investigate how radium fractionated between the pond water and sediments.
... budget is generally small, it represents an important source of nutrients and other 70 contaminants that affect the ecology of the estuaries and coastal fresh water bodies 71 (Andersen et al. 2007;Black et al. 2009;Boehm et al. 2005;Chen and Wang 1999;72 Charette 2007; Kontar and Burnett 1999;Kontar et al. 2002a, b;Kroeger and 73 Charette 2008; Leote et al. 2008;Li et al. 1999;Niencheski et al. 2007;Nowicki 74 et al. 1999;Paytan et al. 2006;Portonoy et al. 1998;Santos et al. 2009;Simmons 75 1992; Slomp and Van Cappellen 2004;Smith et al. 2002;Spiteri et al. 2008;76 Swarzenski et al. 2006b76 Swarzenski et al. , 2007aUchiyama et al. 2000;Weiskel and Howes 1992; 77 Winter et al. 1998). There are reports that SGD may also be an important source of 78 alkalinity and carbon to shelf waters (Lin et al. 2010;Wang et al. 2008Wang et al. , 2009. ...
The submarine groundwater discharge (SGD) transports a significant amount of various contaminants into the coastal zone especially in tsunami affected areas. An assessment of the impact of intruded pollutants in the coastal ecosystems requires understanding the fate of the pollutants and processes of their dispersal in ambient waters. In this paper, we proposed a methodology for SGD data collection and data assessment, using different methods, technology, techniques and instruments as well as the 3-D coupled ocean circulation/particle-tracking model for assessment and predicting the transport and dispersal of pollution-containing SGD into a coastal environment. Among the proposed methods to use for data collection and the SGD assessment primary attention was paid to geophysical, hydrologic, remote sensing and hydro-geologic measurements, using natural radiotracers, measurements by seepage meters and benthic chambers, biogeochemical and biological measurements. Also, several new modeling approaches were considered in particular those which use the particle-tracking model. The particle-tracking model takes currents and turbulent diffusivities predetermined by the ocean circulation model and uses the Lagrangian approach to predict the motion of individual droplets, the sum of which constitutes a contaminant plume which is the result of discharge of contaminant-rich submarine groundwater. Presently, we limited our simulations to elucidate the effect of tides on the SGD/nitrate plume formation. The model predicts behaviour of a nitrate plume, its shape and variation during a tidal cycle in the shallow waters. The model can be used to predict contamination of coastal waters with various pollutants incoming with SGD in the aftermath of a tsunami when impact of the latter on aquifers can be significant.
... 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.
... Many studies indicate that groundwater may be a significant contributor of contaminants to coastal waters (i.e. estuaries and embayments) through submarine groundwater discharge (SGD) (Marsh, 1977;Capone and Bautista, 1985;McLachlan and Illenberger, 1986;Valiela et al., 1990;Simmons, 1992;Burnett et al., 2002;Lee and Kim, 2007) affecting the ecology of estuaries and coastal fresh water bodies (Weiskel and Howes, 1992;Portnoy et al., 1998;Nowicki et al., 1999). In particular, tracer-derived flux estimates indicate that SGD can be an important source of nutrients to bays and estuaries (Johannes, 1980;Charette and Buesseler, 2004;Burnett et al., 2007;Charette, 2007;Santos et al., 2008;Garcia-Solsona et al., 2010;Kim et al., 2011) and has been linked to coastal eutrophication and harmful algae bloom outbreaks (Hu et al., 2006;Lee and Kim, 2007;Lee et al., 2010). ...
A two-dimensional variable-density groundwater flow and transport model was developed to provide a conceptual understanding of past and future conditions of nitrate (NO3) transport and estimate groundwater nitrate flux to the Gulf of Mexico. Simulation results show that contaminant discharge to the coast decreases as the extent of saltwater intrusion increases. Other natural and/or artificial surface waters such as navigation channels may serve as major sinks for contaminant loading and act to alter expected transport pathways discharging contaminants to other areas. Concentrations of NO3 in the saturated zone were estimated to range between 30 and 160 mg · L-1as NO3. Relatively high hydraulic vertical gradients and mixing likely play a significant role in the transport processes, enhancing dilution and contaminant migration to depth. Residence times of NO3 in the deeper aquifers vary from 100 (locally) to about 300 years through the investigated aquifer system. NO3 mass fluxes from the shallow aquifers (0 to 5.7 x 104 mg · m-2 · d-1) were primarily directed toward the navigation channel, which intersects and captures a portion of the shallow groundwater flow/discharge. Direct NO3 discharge to the sea (i.e. Gulf of Mexico) from the shallow aquifer was very low (0 to 9.0 x 101 mg · m-2 · d-1) compared to discharge from the deeper aquifer system (0 to 8.2 x 103 mg · m-2 · d-1). Both model-calibrated and radiocarbon tracer-determined contaminant flux estimates reveal similar discharge trends, validating the use of the model for density-dependent flow conditions. The modeling approach shows promise to evaluate contaminant and nutrient loading for similar coastal regions worldwide. This article is protected by copyright. All rights reserved.
... Measurement techniques routinely employed to estimate submarine groundwater discharge include direct physical methods such as seepage flux meters and indirect chemical methods such as groundwater tracer tests (Burnett et al. 2002). A simple seepage flux meter consists of a chamber placed open-end down in the marine sediments that collects seepage water in a removable plastic bag that is secured to a small opening in the top. ...
... The waves and currents at our study site in Waquoit Bay are minimal, and measured flow rates are up to three orders of magnitude greater than those described in Shinn et al. [2002]. A recent study [Burnett et al., 2002] found that total discharge measured by seepage meters agreed with estimates derived from natural tracers (Ra, Rn), although the tracer method does not describe the spatial pattern or salinity of discharge. ...
... Measurement techniques routinely employed to estimate submarine groundwater discharge include direct physical methods such as seepage flux meters and indirect chemical methods such as groundwater tracer tests (Burnett et al. 2002). A simple seepage flux meter consists of a chamber placed open-end down in the marine sediments that collects seepage water in a removable plastic bag that is secured to a small opening in the top. ...
The most likely routes of introduction of human sewage into Hanalei Bay, Hawaii include [i] direct discharge via designed outfalls (treated sewage) or holding tanks aboard boats (untreated sewage), [ii] indirect surface discharge from sewage entering rivers or streams that empty into the Bay, and [iii] indirect subsurface discharge from sewage entering groundwater that discharges into the Bay. Ongoing studies designed to monitor bacterial levels in Hanalei Bay suggest that while the first two routes may contribute seasonally and/or sporadically to sewage contamination, the third route (groundwater discharge) may be the most substantial and potentially the most problematic.
... One hypothesis is that discrepancies could arise from the exchange of water between the water column and pore waters of shallowly-buried sediments (Bokuniewicz, 1992;Burnett et al., 2002;Rasmussen, 1998;Martin et al., 2004). Using multi-level piezometers called "multisamplers" developed by Martin et al. (2003), Martin et al. (2004) found rapid and significant variations in pore water Clconcentrations suggesting the presence of two flow regimes within the upper 230 cm of lagoonal sediments. ...
... Adequate characterization is difficult, however, because of the large areas involved and the spatial and temporal variability of flow. SGD is usually assessed via (1) modeling, (2) direct measurement, or (3) tracer techniques (Burnett et al. 2002, Burnett et al. 2001, Oberdorfer 2003. ...
Handheld aerial infrared imagery was used to infer submarine groundwater discharge (SGD) to a Hawaiian fish-pond and adjacent bay at Kaloko, Hawai'i, using heat as a tracer for the relatively cooler groundwater. Use of a handheld infrared camera aboard readily available, unmodified aircraft is a convenient and less expensive alternative to use of a camera mounted in the belly of a customized aircraft, although it favors taking images with an oblique view instead of the preferable nadir view. Pond-wide patterns of SGD were readily apparent in oblique images and were typically more apparent in infrared imagery than in ground truth data, due to the formation of thin (order of cm) surface strata of groundwater which could easily fail to be observed with conventional temperature probes. Absolute temperature measurement is affected by the variation of surface emissivity and reflectivity with angle of camera view; corrections based on use of Fresnel's equation were of the order of several degrees centigrade at convenient oblique aerial viewing angles. Other factors that may affect apparent water temperature include sky temperature and camera error. Surface waves may also account for variations in average surface emissivity and reflectance that were not accounted for by the aforementioned corrections. Under suitable conditions, handheld aerial infrared imagery revealed spatial patterns of groundwater inflow, detected differences in water temperature at the meter scale, and measured absolute water temperature with accuracy on the order of 2 to 3°C. © 2006, by the American Society of Limnology and Oceanography, Inc.
... Studies using multiple techniques to measure SGD, such as tracer studies, seepage meters, and groundwater flow models, show that the magnitude of SGD strongly depends on the measurement techniques (e.g., Burnett et al. 2002;Cable et al. 2004). Our results suggest that seepage meters are a reliable technique for measuring pore water advection from sediments if the environment is calm. ...
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.
... . 라듐과 라돈 동위원소들은 우라늄과 토륨의 자연적인 붕괴에 의해 생성되며, 보존성 이 뛰어나 해저로 유출되는 지하수를 측정하는데 용이한 특성을 가지며 , 특히 라돈은 중요 한 지화학적 추적자로서 해저유출수 연구에 많이 이용되 고 있다 (Burnett et al., 2002;Burnett and Dulaiova, 2003). 라돈은 지구상에 70여종이 존재하며, 암석, 퇴적층, 토양 속에 포함되어 있는 고체상태의 화합물인 226 Ra 원 자의 방사능 붕괴로부터 생성된다 (Mancini et al., 1995). ...
Groundwater which infiltrated in recharge areas discharges in the forms of evapotranspiration, baseflow to streams, groundwater abstraction and eventually flows into the sea. This study characterized radon-222 concentration and electrical conductivity (EC) in coastal groundwater discharge, well groundwater, Ilkwang Stream water, and seawater in the coastal area of Busan Metropolitan City and subsequently estimated groundwater discharge rate to the sea. The median value of Rn-222 concentration is highest in well groundwater (18.36 Bq/L), and then decreases in the order of coastal groundwater discharge (15.92 Bq/L), Ilkwang Stream water (1.408 Bq/L), and seawater (0.030 Bq/L). The relationship between Rn-222 concentration and EC values is relatively strong in well groundwater and then in seawater. However, the relationship is not visible between coastal groundwater discharge and Ilkwang Stream water. The groundwater discharge rate to the sea is estimated as /day by using radon mass budget model and /day by using Darcy's law.
... The most important tasks with regard to the management of the coastal/island aquifers are detection, quantification, and monitoring of saline and freshwater interaction (Burnett et al. 2002). Thus, setting a proper management plan for groundwater reserves is impossible without an understanding of the spatial distribution of fresh and saline groundwater as well as the processes that influenced their advancement (Glynn and Plummer 2005). ...
In this study, geophysics, geochemistry, and geostatistical techniques were integrated to assess seawater intrusion in Kapas Island due to its geological complexity and multiple contamination sources. Five resistivity profiles were measured using an electric resistivity technique. The results reveal very low resistivity <1 Ωm, suggesting either marine clay deposit or seawater intrusion or both along the majority of the resistivity images. As a result, geochemistry was further employed to verify the resistivity evidence. The Chadha and Stiff diagrams classify the island groundwater into Ca-HCO3, Ca-Na-HCO3, Na-HCO3, and Na-Cl water types, with Ca-HCO3 as the dominant. The Mg2+/Mg2++Ca2+, HCO3
−/anion, Cl−/HCO3
−, Na+/Cl−, and SO4
2−/Cl− ratios show that some sampling sites are affected by seawater intrusion; these sampling sites fall within the same areas that show low-resistivity values. The resulting ratios and resistivity values were then used in the geographical information system (GIS) environment to create the geostatistical map of individual indicators. These maps were then overlaid to create the final map showing seawater-affected areas. The final map successfully delineates the area that is actually undergoing seawater intrusion. The proposed technique is not area specific, and hence, it can work in any place with similar completed characteristics or under the influence of multiple contaminants so as to distinguish the area that is truly affected by any targeted pollutants from the rest. This information would provide managers and policy makers with the knowledge of the current situation and will serve as a guide and standard in water research for sustainable management plan.
... Li and Jiao, 2003), ocean currents and waves on continental shelf (Huettel et al., 1998;Precht and Huettel, 2003), and large storm events (Moore and Wilson, 2005) which may increase seawater-groundwater exchanges in coastal aquifers. A number of methods can be applied for measuring SGD, such as hydrological modeling based on piezomet-ric head measurements (Cherkauer and Taylor, 1990;Oberdorfer et al., 1990), direct seepage measurements (Taniguchi and Fukuo, 1993;Cable et al., 1997;Rasmussen, 1998;Taniguchi, 2002;Kim et al., 2003), geophysical tracers such as groundwater temperature or electrical tomography (Moore et al., 2002), and steadystate mass-balance models using geochemical tracers (Ellins et al., 1990;Moore, 1996Moore, , 2000Moore, , 2006Rama and Moore, 1996;Cable et al., 1996;Moore and Shaw, 1998;Hussain et al., 1999;Corbett et al., 2000;Krest et al., 2000;Charette et al., 2001Charette et al., , 2003Kelly and Moran, 2002;Kim and Hwang, 2002;Burnett et al., 2002;Crotwell and Moore, 2003;Kim et al., 2005;Boehm et al., 2006;Dulaiova et al., 2006;Breier and Edmonds, 2007). Among these methods, the radionuclide tracers are particularly powerful tools to quantify SGD on different scales of time and space. ...
Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of 226Ra and 228Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO2. Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25–2 L water samples containing as little as 20 fg of 226Ra and 0.2–0.4 fg of 228Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in 226Ra and 228Ra compared to the samples further offshore. The high precision radium measurements display a small but significant 226Ra and 228Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of 226Ra and 228Ra through SGD to be 5.2 × 1010 and 21 × 1010 dpm/d respectively. The 226Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, 228Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24–4.5 × 1010 l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 1010 l/d during the study period (1.6 to 29% of the river flow).
Submarine groundwater discharge (SGD) demarcated as a significant component of hydrological cycle found to discharge greater volumes of terrestrial fresh and recirculated seawater to the ocean associated with chemical constituents (nutrients, metals, and organic compounds) aided by downward hydraulic gradient and sediment-water exchange. Delineating SGD is of primal significance due to the transport of nutrients and contaminants due to domestic, industrial, and agricultural practices that influence the coastal water quality, ecosystems, and geochemical cycles. An attempt has been made to demarcate the SGD using thermal infrared images and radon-222 (222Rn) isotope. Thermal infrared images processed from LANDSAT-8 data suggest prominent freshwater fluxes with higher temperature anomalies noted in Cuddalore and Nagapattinam districts, and lower temperature noted along northern and southern parts of the study area suggest saline/recirculated discharge. Groundwater samples were collected along the coastal regions to analyze Radon and Physico-chemical constituents. Radon in groundwater ranges between 127.39 Bq m-3 and 2643.41 Bq m-3 with an average of 767.80 Bq m-3. Calculated SGD fluxes range between -1.0 to 26.5 with an average of 10.32 m day-1. Comparison of the thermal infrared image with physio-chemical parameters and Radon suggest fresh, terrestrial SGD fluxes confined to the central parts of the study area and lower fluxes observed along with the northern and southern parts of the study area advocate impact due to seawater intrusion and recirculated seawater influence.
Application of natural tracers such as radon isotope mass balance has been useful in estimating the submarine groundwater discharge (SGD). This study used 222Rn and evaluated the magnitude of SGD at Tiruchendur coast of southeast India in the Gulf of Mannar (Indian Ocean). Higher magnitudes of 222 Rn in the porewater and seawa-
ter in comparison with the groundwater suggest simultaneous SGD with fluxes of 0.1–0.25 m 3m −2 d−1at off-shore and 0.4–0.20 m3m−2d−1at the near shore. These baseline data would contribute to the management and protection of the Gulf of Mannar region in near future.
The present study focused on the estimation of submarine groundwater discharge (SGD) and the effects of nutrient fluxes due to the SGD process. The parameters of SGD such as magnitude, character, and nutrient flux in Punnakayal region of South East coast of India were evaluated using multiple tracers of groundwater inputs in 2018–2019. It was found that the elevated values for the tracers in the study area, displayed a gradational change in the values as move from estuarine part to the offshore. Simultaneous occurrence of fresh and saline SGD is observed on the study sites. Also, indicated that the SGD fluxes ranged from 0.04–0.12 m³ m⁻² d⁻¹ at the estuary and 0.03–0.15 m³ m⁻² d⁻¹ at the groundwater site. A substantially increased value for ²²²Rn activities is distinguished in the estuary to values over 312 dpm L⁻¹. Nutrient embellishments were generally greatest at locations with substantial meteoric elements in groundwater; however, the recirculation of saltwater through the geological formation could provide a way of transferring terrestrially-derived nutrients to the coastal zone at many places.
Submarine groundwater discharge is the main way to transfer land-based sources to the ocean. To verify the in situ monitoring capability of the multichannel electrical resistivity method for groundwater discharge in the coastal zone during tidal processes, in situ monitoring was carried out in different aquifers of Shilaoren Bay in September 2015 and May 2017. The electrodes were placed on the seabed, and the collection array was dipole-dipole. The monitoring results show that during tidal processes, seawater intrusion and submarine groundwater discharges in different sedimentary layers have different spatial and temporal evolution characteristics and they can clearly be reflected in time-series resistivity profiles. The percentage difference change in resistivity can be used to define the main groundwater discharge areas. Based on the theory of balance of salinity, the average discharge rate for different periods can also be estimated. Through monitoring, we find that the main discharge area is in the middle and lower parts of the intertidal zone and that the average discharge rate per unit area is 0.86 m³/h, which is the same as the actual values. From the monitoring results, we find that the multichannel electrical resistivity method has good in situ monitoring capability.
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.
The interaction of two of the largest hydrological systems, groundwater and seawater, takes place along the coast, either by seawater intrusion to land (SWI) or submarine groundwater discharges (SGD). Groundwater discharge from the coastal aquifers to the oceans takes place when the elevation of the water table of coastal aquifers is higher than the mean sea level, varying seasonally and tidally. SGD provides a route for escape of a large portion of the usable groundwater resource, solutes, and contaminants to sea. The chemical evolution and redox transformation of SGD are poorly understood, especially at the subsurface freshwater discharge zone. Globally, there have been several studies to understand the coastal hydrodynamics of the SGD; however, there is a serious lack of such knowledge from the coastal aquifers of the Indian subcontinent. The present chapter demonstrates the details of groundwater discharge to the Bay of Bengal, India (BOB). Our study result shows that SGD can add a huge amount of solutes and nutrients to the BOB, which is likely to have a great impact on BOB ecosystem. Hence, understanding the dynamics of SGD in coastal parts of India is an extremely interesting scientific question along with its societal importance and environmental implications. It is expected that the knowledge and information provided in this chapter would enhance the understanding of the coastal hydrodynamics in site-specific scales and extrapolated, larger scales along the BOB and would be useful in making regional coastal management plan or integrated coastal management plan.
The hydrogeologic setting and groundwater flow system in Florida and parts of Georgia, Alabama, and South Carolina is dominated by the highly transmissive Floridan aquifer system. This principal aquifer is a vital source of freshwater for public and domestic supply, as well as for industrial and agricultural uses throughout the southeastern United States. Population growth, increased tourism, and increased agricultural production have led to increased demand on groundwater from the Floridan aquifer system, particularly since 1950. The response of the Floridan aquifer system to these stresses often poses regional challenges for water-resource management that commonly transcend political or jurisdictional boundaries. To help water-resource managers address these regional challenges, the U.S. Geological Survey (USGS) Water Availability and Use Science Program began assessing groundwater availability of the Floridan aquifer system in 2009.
The current conceptual groundwater flow system was developed for the Floridan aquifer system and adjacent systems partly on the basis of previously published USGS Regional Aquifer-System Analysis (RASA) studies, specifically many of the potentiometric maps and the modeling efforts in these studies. The Floridan aquifer system extent was divided into eight hydrogeologically distinct subregional groundwater basins delineated on the basis of the estimated predevelopment (circa 1880s) potentiometric surface: (1) Panhandle, (2) Dougherty Plain-Apalachicola, (3) Thomasville-Tallahassee, (4) Southeast Georgia-Northeast Florida-South South Carolina, (5) Suwannee, (6) West-central Florida, (7) East-central Florida, and (8) South Florida. The use of these subregions allows for a more detailed analysis of the individual basins and the groundwater flow system as a whole.
The hydrologic conditions and associated groundwater budget were updated relative to previous RASA studies to include additional data collected since the 1980s and to reflect the entire groundwater flow system, including the surficial, intermediate, and Floridan aquifer systems for a contemporary period (1995–2010). Inflow to the groundwater flow system of 33,700 million gallons per day (Mgal/d) was assumed to be exclusively from net recharge (precipitation minus evapotranspiration and surface runoff). Outflow from the groundwater flow system included spring discharge (7,700 Mgal/d) and groundwater withdrawals (5,200 Mgal/d). Estimates for all components of the groundwater system were not possible because of large uncertainties associated with internal leakage, coastal discharge, and discharge to streams and lakes. A numerical modeling analysis is required to improve this hydrologic budget calculation and to forecast future changes in groundwater levels and aquifer storage caused by groundwater withdrawals, land-use change, and the effects of climate variability and change.
Radium (Ra) is a radioactive element commonly found within soils, sediments and natural waters. Elevated Ra activities arising through natural and anthropogenic processes pose a threat to groundwater resources and human health, and Ra isotope ratios are used to decipher groundwater movement, estimate submarine discharge flux, and fingerprint contamination associated with hydraulic fracturing operations. Although adsorption to metal (hydr)oxides and certain clay minerals is well established as a dominant mechanism controlling Ra transport and retention, the extent of Ra sorption to other minerals and under variable environmental conditions (e.g. pH and salinity) is limited. Accordingly, we present results of sorption studies and surface complexation modeling (SCM) of Ra to ferrihydrite, goethite, montmorillonite, and pyrite, for a range of pH values and common background cations. Ra sorption to all substrates is observed under geochemical conditions considered, but varies according to mineral, solution pH and specific competing cations. Literature derived SCMs for Ra sorption were fitted to match either sorption impacts due to pH or different background cations, but were not able to predict the impacts of different geochemical conditions. Despite this, the use of SCMs provided a more mechanistic understanding of Ra sorption as compared to commonly used distribution coefficients.
Saline intrusion has been a major source of groundwater contaminant in coastal regions. The situation has adversely affected groundwater quality. Being an essential source of freshwater for the teeming population over the world and indeed Nigeria and its suitability for various uses is largely dependent on physico-chemical quality, this study therefore selected for its quality assessment, the coastal aquifer of Buguma in rivers state Nigeria. Water samples collected from various locations using systematic random sampling were subjected to physico-chemical analysis. sodium (Na 2+) (288mg/l) chloride(Cl-)(414.7mg/l) and nitrate (N03-)(64.45 mg/l) ions dominated the major ions of sample results and also exceeded the Nigerian Standard for Drinking Water Quality NSDWQ 2007 and WHO drinking water standard 2006. Among the trace elements, Fe 2+ and As ions were above the drinking water regulatory limits of NSDWQ and WHO. Classification techniques were employed to provide an assessable information on the chemical composition of the water samples like the major ions in the analysis. The high proportion ofNa 2+ , K + and Cl-as typified by the graphs classified the water as Na-K, Cl-type which confirmed saltwater intrusion. The water therefore needs adequate treatment to raise it to portable standard.
Submarine groundwater discharge (SGD) to the Bay of Bengal is an important groundwater discharge process to southern Asia as well as to the global oceans. Water-fluxes in these regions are not very well understood. The present study demonstrates the use of sea-bed porewater temperature as a tracer for delineating seasonal SGD from a shallow coastal aquifer to the Bay of Bengal. Porewater temperature mapping along with chemical profile of porewater column were used to delineate groundwater discharge zones for different seasons in a hydrologic year. While, the temperature profiles were used to evaluate total groundwater discharge (both terrestrial and marine), the salinity and total dissolved solids profiles were used to evaluate the component due to terrestrial (freshwater) discharge. Several springs and seeps were mapped to finger-print the freshwater discharge zones and identify the terrestrial sourced-SGD temperature windows. These zones are also identified to be enriched with algal mats, and hence may indicate the pathways of nutrient–solute discharge that enhance the primary productivity in the marine ecosystem. Assuming vertical flow in the seabed, simulated rates of discharged groundwater provided a good match with measured discharge rates. The porewater fluxes were estimated by applying analytical solutions of the heat conduction–advection equations to the observed vertical temperature profiles. High resolution thermal profiles to identify T-SGD signatures and chemical profiles along mapped transects reveal the nuances of 3-D seasonal hydrodynamics of groundwater–seawater interactions. The calculated vertical porewater fluxes through the seabed ranged from negligible to 2.45 × 10−2 m3/m2/d1 within a zone extending from high tide line to 40 m offshore, and represent the vertical porewater velocity and the average vertical porewater velocity is found as 8.2 × 10−3 m3/m2/d1. Approximations suggest that in present-day condition, total average annual SGD to Bay of Bengal is about 1.16 × 107 m3/y. Seasonal estimates suggest that the averages SGD during pre-monsoon and post-monsoon seasons are ranges 0.6–0.8 × 107 m3/y for pre-monsoon and 0.8–1.5 × 107 m3/y for post-monsoon, respectively. The findings suggest that monsoonal activity result in a significant porewater displacement from tidal flat sediments by increased groundwater discharge.
This chapter discusses the radon tracing of submarine groundwater discharge (SGD) in coastal environments. Direct discharge of groundwater into the coastal zone may be an important material flux pathway from land to sea in some areas. It has been largely ignored because of the difficulty in assessing its magnitude. While measurement problems persist, there is a growing recognition that groundwater flow into the sea is important. This chapter reviews an approach, using a simple one-dimensional model, to measure SGD via use of 222Rn as a natural tracer. Radon has certain advantages over other potential geochemical tracers of groundwater discharge. Typically, it is greatly enriched in groundwater compared to seawater; it can be measured at very low concentrations, and is completely conservative. On the other hand, as a gas it is subject to losses at the air–sea interface which may limit its use in shallow water environments. The radon tracing is an excellent qualitative tool for identifying areas of spring or seepage inputs in most coastal environments. It is a good quantitative tool in shallow marine environments characterized by large amounts of SGD.
The recent drop of sea level in the Aral Sea of about 0.6 m year−1 during the last 40 years represents one of the most dramatic example globally about the possible consequences of man-induced environmental changes. This extremely strong signal, as well as the constantly changing hydrological and meteorological fluxes in this area are missing from the seaborne observations in the 1990s because the observational network developed by the Former Soviet Union has almost not been operating during one decade in the new independent states. Fortunately, the Aral Sea level has been regularly monitored from space, in particular by satellite altimetry. In this study, we present observations of the Aral Sea level and analyze the observed trends and shorter term variability based on TOPEX/Poseidon altimeter data. This data set (available since early 1993) is complemented by hydrometeorological data and gauge data (since 1950) allowing to quantify the evolving water balance of the Aral Sea. It is shown that even though the river runoff almost ceased recently, the rapid drawing of the Aral Sea is substantially reduced by the compensating discharge of ground water. The analysis of the available data makes it possible to address the changing salt balance and to identify the major control on this balance exerted by ground water discharge. The major event of ground water discharge is identified in the period 1993–1994 and resulted in a substantial increase of the salt content. The rapid drop of salt content thereafter could indicate an increase of salt precipitation.
Understanding groundwater-seawater interactions may provide estimates of groundwater discharges to the sea. The present study is carried out to delineate the groundwater discharge zones in the inter-tidal sea bed of an aquifer adjoining the Bay of Bengal in eastern coast of India (Chandipur), by using groundwater temperature as a physical tracer. Following several river/lake water-groundwater interaction studies, it has been assumed that discharging groundwater would reflect the mean annual air temperature, which would be reasonably insulated from the diurnal and seasonal variable sea water temperature. Temperature mapping (seabed and pore water) by use of thermal sensor and digital thermometer, along with measurement of salinity, total dissolve solid and conductivity profiles of the multidepth wells were used to delineate groundwater discharge zones along multiple (max. n =11) transects within an area with dimension of 165 m × 110 m for post-monsoon and pre-monsoon seasons of 2012-2013. Highly variable mean hyporheic water temperatures ranging from 24.1°C to 32.2°C at the seepage points were observed in the post monsoon sampling season. Temperature of pore water interpolated in 2D profiles and 3D voxel models indicate dominant groundwater discharge zones at a vertical depth of 0.45m to 1.05m, extending from high tide line upto 110 m offshore, horizontally. Multidepth profiles of conductivity, salinity and TDS are showing that there is a prominent presence of freshwater groundwater plume in the seabed, upto 40m offshore, at a vertical extent of 0.2 m to 1m depth, during the post-monsoon season. The seabed was observed under continuous discharge condition while there is a spatial variation of the discharge throughout the transect. Results indicate that majority of the pore water samples collected from the multidepth wells are composed of freshwater mixed with circulated brackish water. The thermal profile suggests that even there is a positive groundwater discharge observed for the vertical depth 0.1m to 0.45m, this discharging water may also contain the circulated sea water, which recently infiltrated the seawater-groundwater mixing zone.
Submarine groundwater discharge (SGD) is a potential pathway for nutrients and anthropogenic pollutants that flow from the land into the coastal ocean, and probably influences the aquatic ecosystem in tidal areas. This paper focused on surveying possible groundwater locations around the coastal area. The possible location, pathway and discharge of SGD in the Ping-Tung Shelf of southwestern Taiwan were described by oceanographic measurements. During the field surveys of the study area, onboard surface to bottom CTD (conductivity, temperature, depth) profiling, ADCP (Acoustic Doppler Current Profiler) measurements, and fluorescence profiling were carried out at 25 different stations. The collected hydrographic data were used to identify a suspected SGD site in the central part of the study area, where a local drop of salinity by up to 0.06 psu has been observed in the lowermost 0.2 similar to 1.5 m of the water column. Thanks to explicit evidence for a possible pathway and locations, seepage meters were deployed on the sea bed to measure the SGD rate at about 6.0 ml h(-1) m(-2) in the dry season. Based on the surveyed data, the likely locations of the SGD sources in the study area were specified, all of which were restricted to the inner shelf at a depth less than 8 m. Copyright (c) 2013 John Wiley & Sons, Ltd.
In majority of the arid and dry regions of the world and in monsoon-dependent countries in Asia, groundwater is a major freshwater resource for drinking and other uses. The coastal regions, which support maximum density of population, mainly depend on the ground water. Due to the population growth and the fact that about 50% of the world population now already live in coastal regions, the groundwater issues in the coastal areas are increasingly becoming crucial (UNWWDR, 2009). Over-exploitation of groundwater in these areas can potentially lead to saltwater intrusion, land subsidence, permanent damage to the ability of an aquifer to store and transmit water, and reduced discharges to rivers, streams, and critical aquatic habitat areas (Fig. 1). Further, coastal groundwater plays an important role in nutrient flux to the ocean. The influence of submarine groundwater discharge (SGD) on the coastal water quality, their biogeochemical process and their ecology are very significant in most of the coastal regions. Investigations of interactions between groundwater and coastal seawater have been restricted mainly to the case of water movement from sea to the land, i.e. saltwater intrusion (Segol and Pinder, 1976; Reilly and Goodman, 1987) while submarine groundwater discharge (SGD) considers the water output from a basin-scale hydrological cycle, representing an input into the ocean (Fig. 2).
Open image in new windowFigure 1:A compilation of processes affecting coastal groundwater.Open image in new windowFigure 2:Schematic depiction of processes associated with SGD (modified after Taniguchi et al., 2002). Arrows indicate fluid movement.
In this paper groundwater formation conditions in the upper hydrodynamic zone of the northern coast of European part of Russia are considered. This groundwater discharges directly into the Barents and White Seas. The values of submarine discharge from European Russia into Arctic Seas, by passing river network, are estimated. Estimates of subsurface dissolved-solids discharge are given. Specific and integral characteristics of submarine discharge are analyzed. The major regularities in the formation and distribution of submarine discharge into Seas of the Arctic Ocean are described.
A study was conducted from July 2002 through June 2006 in order to assess the significance of submarine groundwater discharge (SGD) to Sarasota Bay (SB), Florida. The assessment approaches used in this study included manual seepage meters, geochemical tracers (radon, 222Rn and methane, CH4), and subseafloor resistivity measurements. The estimated SGD advection rates in the SB system were found to range from 0.7 to 24.0 cm/day, except for some isolated hot spot occurrences where higher rates were observed. In general, SGD estimates were relatively higher (5.9–24.0 cm/day) in the middle and south regions of the bay compared to the north region (0.7–5.9 cm/day). Average dissolved inorganic nutrient concentrations within the SB water column ranged: 0.1–11 μM (NO2+NO3), 0.1–9.1 μM (NH4) and 0.2–1.4 μM (PO4). The average N/P ratio was higher in the north compared to the middle and south regions of the bay. On average, we conservatively estimate that about 27% of the total N in the SB system was derived via SGD. The prevalence of shallow embayed areas in the SB system and the presence of numerous septic tanks in the surrounding settlements enhanced the potential effects of nutrient rich seepages. Statistical comparison of the quantitative approaches revealed a good agreement between SGD estimates from manual seepage meters and those derived from the 222Rn model (p=0.67; α=0.05; n=18). CH4 was found to be useful for qualitative SGD assessments. CH4 and 222Rn were correlated (r2=0.31; α=0.05; n=54). Large scale resistivity surveys showed spatial variability that correlates more clearly with lithology than with SGD patterns.
The objective of this work was to assess the groundwater discharge component of the hydrological budgets of several small lakes in north and central Florida using 222Rn (radon, t1/2 = 3.8 days) as a quantitative groundwater tracer. Methane gas and conductivity were also used as secondary natural tracers to help locate active sites of seepage. We present results based on a steady-state radon mass balance model developed to assess groundwater discharge into shallow unstratified lakes. Model assumptions include a constant 222Rn input flux over relatively short (days–weeks) periods and a well-mixed water column. Detailed surveys in several Florida lakes using continuous 222Rn measurements supported these assumptions. In five of the seven studied lakes a high to moderate groundwater inflow was detected using this technique, while in two of them the discharge was very low to not detectable. Based on these results and the size of the lakes the calculated water-renewal times based on groundwater inflows were in a range between 3 and 40 months. Close 2-year examination of the groundwater dynamics at two of the lakes that showed substantial discharge, did not show great seasonal groundwater discharge variations. These radon-derived groundwater seepage fluxes agreed well with seepage meters and water budget calculations performed independently for some of the lakes. The approach proved to be very efficient, relatively inexpensive, and should be able to be applied as a routine procedure for estimating groundwater discharge for similar lakes elsewhere. The ultimate purpose of our efforts is to use this method in obtaining important information for the hydrological budget of these lakes that will allow evaluating nutrient loadings and TMDLs (Total Maximum Daily Loads) calculations.
Determination of sedimentary fluxes of222Rn via diffusion was required as an input for a mass balance model of radon in a freshwater lake. We obtained these fluxes
by: (1) direct measurement in the laboratory using a simulated sediment bed and water column; (2) a “sediment equilibration”
technique; and (3) porewater modeling. The first method, analogous to an in situ benthic chamber approach, uses direct observation
of the increasing222Rn activity in water overlying a sediment bed packed in plastic columns. This allows one to directly measure the fluxes and
determine the effective wet bulk sediment diffusion coefficient (D
s). Radon flux estimates using these three techniques agreed to within approximately 10–15%.
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.
Radon-222 is a good natural tracer of groundwater flow into the coastalocean.
Unfortunately, its usefulness is limited by the time consuming natureof collecting
individual samples and traditional analysis schemes. We demonstratehere an automated
system which can determine, on a “continuous”basis, the radon activity in coastal
ocean waters. The system analyses 222Rn from a constant
stream of water passing through an air-water exchangerthat distributes radon from
the running flow of water to a closed air loop.The air stream is feed to a
commercial radon-in-air monitor which determinesthe concentration of
222Rn by collection and measurement of theemitting
daughters, 214Po and 218Po,
via a charged semiconductordetector. Since the distribution of radon at equilibrium
between the air andwater phases is governed by a well-known temperature dependence,
the radonconcentration in the water is easily calculated.
People have been curious about offshore springs and seeps since at least
the days of the Romans. In spite of many centuries of both casual and
serious observations, there has been relatively little scientific study
concerning the magnitude and effects of groundwater flow into the sea.
Rather, studies were performed mostly to address water resource issues.
Investigations over the past decade or so have now shown that
groundwater discharge, at least in some cases, may be important for
geochemical budgets and ecological effects.The Scientific Committee on
Oceanic Research (SCOR) and the Land-Ocean Interactions in the Coastal
Zone (LOICZ) Project of the International Geosphere-Biosphere Program
have recently established a working group of experts to examine
questions relating specifically to groundwater discharge in the coastal
zone. Direct groundwater flow into the ocean is known to occur as
springs and seeps in near-shore areas in many parts of the world.
Submarine springs, for example, are well known off both coasts of
Florida; Mexico's Yucatan Peninsula; in several areas around the Pacific
rim including Chile, Hawaii, Guam, American Samoa, and Australia; in the
Persian Gulf near Bahrain; in the Mediterranean Sea off Spain, France,
Italy, Greece, Syria, Lebanon, Israel, and Libya; and in many other
locations.
An automatic seepage meter using a heat pulse method was developed to obtain a continuous measurement of ground-water seepage rates. According to calibrations of the automatic seepage meter fitted with a 50 cm diameter collection funnel, seepage rates from 2 X 10-5 to 5 X 10-4 cm/sec can be obtained by measuring the time when the temperature as measured by a thermistor peaks after applying a heat pulse. The automatic seepage meter was used to measure continuous seepage rates into Lake Biwa, Japan. The ground-water seepage rate measured by the automatic seepage meter in Lake Biwa changed by six times within 12 hours. The automatic seepage meter is useful for surface-/ground-water studies, because a continuous seepage rate can be obtained without errors caused by the resistance of a collection bag to water flow.
Coastal waters contain elevated dissolved activities of four radium isotopes. These elevated activities arise through desorption of Ra from particle surfaces and the input of submarine groundwaters enriched in Ra. The input of Ra near the coast is balanced by a flux of each Ra isotope toward the open ocean. Two of the Ra isotopes decay almost completely before they reach the edge of the continental shelf; the other two decay hardly at all. These differences in decay rates provide a powerful constraint on models of water movement and mixing on the shelf. These models are used to assess the factors that control the export of radium. Understanding the factors that control the export of radium allows an assessment of physical processes that regulate fluxes of other dissolved constituents in the coastal ocean. In this paper I use observations that were made during vertically stratified conditions in the South Atlantic Bight. Offshore transects of the long-lived 226Ra and 228Ra indicate that eddy diffusion controls their distributions within 50 km of shore. The short-lived 223Ra and 224Ra distributions in this region yield an eddy diffusion coefficient of 360–420 m2 s−1. The offshore fluxes of 226Ra and 228Ra derived from their across-shelf activity gradients and the eddy diffusion coefficient require a substantial volume of groundwater discharge to balance Ra removal.
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.
THE flow of ground water directly into the coastal ocean has been studied previously by in situ measurements, seep meters and diffusion gradient models1. Although these techniques provide ample evidence that such flows occur, they do not provide a means of quantifying the groundwater flux on a regional scale. Here I report large enrichments of 226Ra in coastal waters of the South Atlantic Bight, and demonstrate that groundwater discharge is the main source of the 226Ra surplus. Using 226Ra data for brackish ground waters with estimates of residence times of nearshore waters, I conclude that the groundwater flux to these coastal waters must be about 40% of the river-water flux during the study period. Besides Ra, other metals, nutrients and organic compounds are expected to be enriched in brackish ground waters, so these findings require an upward revision of terrestrial fluxes of dissolved materials to these coastal waters, and perhaps a re-evaluation of such fluxes to the global ocean. These fluxes may be sensitive to hydrological factors, groundwater usage, dredging and sea-level change.
Submarine ground water discharge can influence significantly the near-shore transport and flux of chemicals into the oceans. Quantification of the sources and rates of such discharge requires a ground water seepage meter that provides continuous measurements at high resolution over an extended period of time. An ultrasonic flowmeter has been adapted for such measurements in the submarine environment. Connected to a steel collection funnel, the meter houses two piezoelectric transducers mounted at opposite ends of a cylindrical flow tube. By monitoring the perturbations of fluid flow on the propagation of sound waves inside the flow tube, the ultrasonic meter can measure both forward and reverse fluid flows in real time. Laboratory and field calibrations show that the ultrasonic meter can resolve ground water discharges on the order of 0.1 microm/sec, and it is sufficiently robust for deployment in the field for several days. Data from West Neck Bay, Shelter Island, New York, elucidate the temporal and spatial heterogeneity of submarine ground water discharge and its interplay with tidal loading. A negative correlation between the discharge and tidal elevation was generally observed. A methodology was also developed whereby data for the sound velocity as a function of temperature can be used to infer the salinity and source of the submarine discharge. Independent measurements of electrical conductance were performed to validate this methodology.
Lane-Smith, A continuous radon monitor for use in coastal ocean waters
- Burnett