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Magnitude and variations of groundwater seepage along a Florida marine shoreline
Abstract
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.
... Studies involving seepage meters have reached the following general conclusions: (1) many seepage meters are needed because of the natural spatial and temporal variability of seepage rates [Shaw and Prepas, 1990a,b]; (2) the resistance of the tube [Fellows and Brezonik, 1980] and bag [Shaw and Prepas, 1989; Belanger and Montgomery, 1992] should be minimized to prevent artifacts; (3) use of a cover for the collection bag may reduce the effects of surface water movements due to waves, currents or streamflow activities [Libelo and Maclntyre, 1994]; and (4) caution should be applied when operating near the seepage meter detection limit [Cable et al., 1997]. The influence on seepage measurements of frictional resistance in the tube connecting the drum to the collector bag produces inaccurate seepage rates. ...
... Covering the collection bag with a bucket to isolate it from overlying surface water flow significantly reduces this error. Although the application of manual type seepage meters has had some problems as mentioned above, a recent field evaluation of the "Lee-type" seepage meters showed that consistent and reliable results can be obtained if one accounts for these potential problems [Cable et al., 1997]. Time-series experiments with empty collection bags demonstrated that the short-term anomalous influx reported by Shaw and Prepas [1989] was significant and could seriously affect the results, particularly at low seepage rates (Figure 2). ...
... (b) seepage rate (mL min x m "2) vs. time to demonstrate seepage meter response relative to collection time interval. Individual pre-filled bag measurements in (b) are shown together with the mean (arrow) [Cable et al., 1997]. Perhaps the most serious disadvantage of using manual seepage meters in coastal zone studies is that they are very labor intensive. ...
... In locations were freshwater is a significant component of SGD composition, nutrient concentrations in SGD may be orders of magnitude higher than receiving coastal waters (Beusen et al., 2013;Blanco et al., 2011;Bowen et al., 2007;Moore, 2010). Some studies suggest the SGD may contribute nutrient loads that are equal to or greater than that of rivers and streams (Cable et al., 1997;Garrison et al., 2003;Kim et al., 2005). Although the global contribution of SGD may be 0.01 % to 10 % of surface runoff, nutrient concentrations are typically greater; this implies SGD is an important source of N to many ecosystems at local and regional scales (Taniguchi et al., 2002;Zhang and Mandal, 2012). ...
... This typically produces physical and chemical gradients associated with distance from shore and water column depth (Johannes, 1980;Johnson et al., 2008). While discharge at most locations is likely a large-scale diffuse, yet spatially variable occurrence (Cable et al., 1997;Garrison et al., 2003;Michael et al., 2003;Taniguchi et al., 2006;Taniguchi et al., 2008), distinct artesian springs with high flux rates can create extreme changes in the physical and chemical parameters of the adjacent waters Dimova et al., 2012;Swarzenski et al., 2013). ...
... Although, this may be the most direct measurement approach, high variability at small spatial scales often confounds the interpretation of results at the regional level (Garrison et al., 2003;Michael et al., 2003) (Cable et al., 1997;Taniguchi et al., 2006;Taniguchi et al., 2008). The use of geochemical groundwater tracers, that are more concentrated in SGD than coastal waters, provide an extremely effective method to quantify SGD flux on multiple spatial scales Moore, 2010). ...
Submarine groundwater discharge (SGD) is a ubiquitous process that delivers significant amounts of nutrients and other solutes to coastal ecosystems worldwide. Although the quality and quantity of SGD has been characterized at many sites, the biological implications of this process remain poorly understood. The objective of this work was to compare the physiological response of macroalgae and benthic community structure across gradients of SGD and nutrient loading in Hawai‘i. Common marine algae were collected and/or deployed at several sites on O‘ahu, and Maui. Selection of sites was informed by adjacent land use, known locations of wastewater injection wells, and previous estimates of environmental risk due to onsite sewage disposal systems (OSDS). For deployed samples, initial values of algal tissue nitrogen (N) parameters were determined after pretreatment in low nutrient conditions. At all locations, algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with the N parameters (δ15N and N concentration) of coastal groundwater , marine surface water, or groundwater simulations. Algal tissue N was highest (> 2 %) in samples located nearshore at sites adjacent to coastal aquifers enriched with anthropogenic sources of N. The lowest tissue N values (< 1 %) were found offshore or at relatively unimpacted sites. In general, the δ15N values of algal tissues and water samples were highest (9 - 18 ‰) at sites adjacent to high-volume wastewater injection wells and high densities of OSDS; lowest values (< 4 ‰) were observed in samples adjacent to sugarcane fields. Benthic diversity was greatest in locations with low anthropogenic impact. In contrast, highly impacted locations were dominated by opportunistic species. This work advances the use and interpretation of algal bioassays by highlighting the importance of onshore-offshore trends, and deviations from initial N parameter values, for the detection of N source and relative N availability. Wastewater was detectable and a major source of N at many locations. These results support recent studies that indicate SGD is a significant transport pathway for anthropogenic pollutants with important biogeochemical implications. Minimizing contaminant loads to coastal aquifers will reduce pollutant delivery to nearshore reefs in areas with SGD flux.
... Studies involving seepage meters have reached the following general conclusions: (1) many seepage meters are needed because of the natural spatial and temporal variability of seepage rates [Shaw and Prepas, 1990a,b]; (2) the resistance of the tube [Fellows and Brezonik, 1980] and bag [Shaw and Prepas, 1989; Belanger and Montgomery, 1992] should be minimized to prevent artifacts; (3) use of a cover for the collection bag may reduce the effects of surface water movements due to waves, currents or streamflow activities [Libelo and Maclntyre, 1994]; and (4) caution should be applied when operating near the seepage meter detection limit [Cable et al., 1997]. The influence on seepage measurements of frictional resistance in the tube connecting the drum to the collector bag produces inaccurate seepage rates. ...
... Covering the collection bag with a bucket to isolate it from overlying surface water flow significantly reduces this error. Although the application of manual type seepage meters has had some problems as mentioned above, a recent field evaluation of the "Lee-type" seepage meters showed that consistent and reliable results can be obtained if one accounts for these potential problems [Cable et al., 1997]. Time-series experiments with empty collection bags demonstrated that the short-term anomalous influx reported by Shaw and Prepas [1989] was significant and could seriously affect the results, particularly at low seepage rates (Figure 2). ...
... (b) seepage rate (mL min x m "2) vs. time to demonstrate seepage meter response relative to collection time interval. Individual pre-filled bag measurements in (b) are shown together with the mean (arrow) [Cable et al., 1997]. Perhaps the most serious disadvantage of using manual seepage meters in coastal zone studies is that they are very labor intensive. ...
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.
... Taniguchi et al., 2008). Tides, hydraulic changes, and seasonal fluctuation also affect SGD rates (Lewis, 1987;Taniguchi et al., 2002;Santos et al., 2008), particularly in areas with significant precipitation and groundwater recharge (Cable et al., 1997). Because of the enrichment of nutrients produces ecological impacts such as eutrophication and changes in phytoplankton community. ...
... By placing a cover over the bag, it is possible to minimize the influence that waves or currents have on the instruments (Libelo and MacIntyre, 1994). Utilizing a bag that holds a certain volume of water during the early phase can enable the identification of both positive and negative flow rates (Cable et al., 1997). Artefacts may be produced by the current flowing through the metre (Shin et al., 2002). ...
Submarine groundwater discharge (SGD) is the combination of fresh and saline groundwater flux to marine system through continental boundaries regardless of its chemical composition and factors influencing the flow. We have discussed the SGD studies in the Asian context; SGD has been studied in various parts of Asia, including China, Japan, South Korea, and Southeast Asia. In China, SGD has been studied in several coastal regions, including the Yellow Sea, the East China Sea, and the South China Sea. In Japan, SGD has been studied in the Pacific coast, where it has been found to be an important source of fresh water to the coastal ocean. In South Korea, SGD has been studied in the Yellow Sea, where it has been found to be an important source of fresh water to the coastal ocean. In Southeast Asia, SGD has been studied in several countries, including Thailand, Vietnam, and Indonesia. Recently the SGD studies acquired much development India, the research on SGD in India is limited, and more studies are needed to understand the SGD process, its impact on the coastal environment, and the management strategies, Groundwater extraction for irrigation, industry, and domestic use is increasing in India, which can affect the SGD process in coastal aquifers. Overall, the studies suggest that SGD is an important process in Asian coastal regions, playing a role in the supply of fresh water and the transport of pollutants and nutrients.
... There are several methods developed to trace SGD (Cable et al. 1997;Kim and Hwang 2002;Taniguchi et al. 2002Taniguchi et al. , 2005Martin et al. 2005). Integrated flux estimations of SGD at the aquifer-marine interface are only possible by environmentally occurring isotopic tracers (such as 222 Rn) (Moore 1999). ...
... To make the natural geochemical tracers applicable, it is important to recognize all sources and sinks of the tracer (Taniguchi et al. 2003;Burnett et al. 2006). There are many SGD investigations using 222 Rn in various environments such as coastal embayment and oceanic coastlines (Ellins et al. 1990;Cable et al. 1996Cable et al. , 1997Burnett et al. 2001bBurnett et al. , 2006Burnett and Dulaiova 2003;Charette et al. 2008;Stieglitz et al. 2010;Hosono et al. 2012). expressed that radon technique is a good quantitative tool to evaluate integrated SGD components flux in shallow marine environments with large amounts of SGD. ...
Submarine groundwater discharge (SGD) is a process through which groundwater and solutes are transferred from coastal aquifers into the oceans. Generally, the SGD is composed of two basic components: (1) fresh groundwater, FSGD; and (2) recirculated seawater, RSGD. Radon, a naturally occurring geochemical tracer, is a useful tool to evaluate the SGD in coastal areas. This study aims to evaluate the impact of wind waves on each components of submarine groundwater discharge. We monitored temporal fluctuations of seawater ²²² Rn concentration at Shiranui and Minamata bays, where elevated seawater ²²² Rn concentration spatial distribution observed during our previous studies. The measurements were conducted in coastal seawater where the connected coastal aquifer water table is very shallow. Additionally, a seawater model was applied to evaluate the seawater ²²² Rn concentration that originates from rivers in the study area. The ²²² Rn inventory in the study area implies that the groundwater advection is one of the major sources of ²²² Rn in the seawater. The obtained dataset suggests that the seawater ²²² Rn concentration increases, but the salinity decreases during windy periods. This means that more fresh groundwater contributes to dilute the recirculated seawater (RSGD) during windy conditions. Therefore, when the sea is windy and seawater waves propagate onshore, the fresh groundwater flux may increase where shallow coastal aquifers exist.
... Previous studies at very focused sites e.g. Indian River Lagoon (Martin et al., 2006(Martin et al., , 2007, Waquit Bay (Michael et al., 2003), Gulf of Mexico (Cable et al., 1997a), Northern part of Gulf of Mexico have helped to directly measure and determine the SGD flux at the specific coastal study sites and have been up-scaled to delineate implications to global oceans . Here, following similar philosophy, at a focused site on the eastern coast of India, we have measured the tidally influenced to SGD rates by densely gridded seepage meters and delineated its implication to the Bay of Bengal. ...
... 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.
... Seepage meters have the advantage of allowing direct measurement of discharging groundwater. In addition, manual seepage meters are relatively inexpensive and simple to construct (Cable et al., 1997). The disadvantage of seepage meters is that, while they provide an accurate measure of seepage occurring at the exact installation site, a large number are required to estimate discharge over a larger area, such as a bay or beach, because SGD can be highly heterogeneous on small spatial scales Prepas, 1990a, 1990b). ...
... Numerical modeling of SGD from a homogeneous aquifer has predicted that fresh SGD should decrease exponentially with distance offshore (McBride and Pfannkuch, 1975;Fukuo and Kaihotsu, 1988;Taniguchi et al., 2003), and most field data show the expected pattern (e.g., Attanayake and Waller, 1988;Bokuniewicz et al., 2004;Paytan et al., 2004). However, at some sites SGD does not decrease as expected with distance from shore (e.g., Connor and Belanger, 1981;Cable et al., 1997;Bokuniewicz et al., 2004). SGD fluxes may be greater at some distance offshore than at the shoreline for several reasons. ...
This chapter provides a review of the current state of knowledge on submarine groundwater discharge (SGD) and the associated fluxes of nutrients, trace metals, microbes, pharmaceuticals, and other terrestrial constituents to coastal waters. We review methods of estimating SGD, present flux estimates from different locations worldwide, and discuss how various hydrogeologic features such as topography, aquifer substrate, climate, waves, and tides affect SGD. We discuss the range of nutrient and metal concentrations observed in groundwater and their relationship to land use, and explore the chemical changes that nutrients and metals undergo during their seaward journey through the aquifer. Climate change is likely to affect both the quantity and the quality of SGD, and we investigate these effects, which are only beginning to be studied. The chapter concludes with a discussion of active areas of SGD research, including expanding the geographic scope of SGD studies; characterizing and reducing the uncertainty associated with SGD measurements; understanding the behavior of nutrients, metals, and other pollutants in the subterranean estuary; and modeling SGD on a global scale.
... Seepage meters have the advantage of allowing direct mea surement of discharging groundwater. In addition, manual seepage meters are relatively inexpensive and simple to con struct (Cable et al., 1997). The disadvantage of seepage meters is that, while they provide an accurate measure of seepage occurring at the exact installation site, a large number are required to estimate discharge over a larger area, such as a bay or beach, because SGD can be highly heterogeneous on small spatial scales Prepas, 1990a, 1990b). ...
... Numerical modeling of SGD from a homogeneous aquifer has predicted that fresh SGD should decrease exponentially with distance offshore (McBride and Pfannkuch, 1975;Fukuo and Kaihotsu, 1988;Taniguchi et al., 2003), and most field data show the expected pattern (e.g., Attanayake and Waller, 1988;Bokuniewicz et al., 2004;Paytan et al., 2004). However, at some sites SGD does not decrease as expected with distance from shore (e.g., Connor and Belanger, 1981;Cable et al., 1997;Bokuniewicz et al., 2004). SGD fluxes may be greater at some distance offshore than at the shoreline for several reasons. ...
... Submarine groundwater discharge (SGD) is a volumetrically significant component of the hydrologic cycle over both local (Bokuniewicz, 1980;Breier and Edmonds, 2007;Charette, 2007;Lee and Olsen, 1985) and regional (Cable et al., 1997;Moore, 1996) scales. As concentrations of chemical constituents in groundwater often highly exceed those of surface waters (Boehm et al., 2006;Burnett et al., 2003 and references therein;Charette et al., 2001;Slomp and Van Cappellen, 2004;Valiela et al., 1990), even small amounts of SGD can have disproportionately large effects on the chemical budgets of coastal areas. ...
... Seepage meters (e.g. Cable et al., 1997;Taniguchi et al., 2003), which measure discharge at a given point, have considerable weakness in accounting for localized discharge and spatial variation in flow. While hydraulic models invoking Darcy's Law can yield discharge estimates, these models often only deal with freshwater fluxes; the total groundwater flux at the coast is a mix of both fresh and saline discharge. ...
Submarine groundwater discharge (SGD) represents a significant flux of water and chemical constituents to coastal regions. Because 226Ra and 228Ra are highly concentrated in groundwater relative to surface water, and their signal is well-integrated throughout coastal surface waters, these isotopes have been increasingly utilized to quantify SGD over the past several decades. In this study, a combined radium and salt balance is used to yield estimates of fresh and saline SGD to four of Rhode Island's coastal ponds (Winnapaug, Quonochontaug, Ninigret, and Point Judith Ponds). Fresh SGD rates determined for each pond range between 0 and 17 L m− 2 d− 1. These values largely fall in line with previous estimates made using hydrologic models. The uncertainty of saline SGD estimates for each pond is high; minimum and maximum saline SGD estimates differ by as much as three orders of magnitude. These results echo the discrepancy between two previous radium-based studies from this location. The variability of dissolved radium in the Rhode Island coastal aquifer plays a large role in the uncertainty of these saline SGD estimates. Groundwater dissolved radium activity is dependent upon many different factors, including groundwater salinity and redox conditions, sediment thorium and radium activities, and the amount of time to which the sediment has been exposed to saline groundwater. Due to the heterogeneous nature of glacial outwash sediments, none of these parameters are likely consistent throughout the aquifer in this location. Groundwater 226Ra and 228Ra activities in the coastal ponds vary significantly both laterally and with sediment depth. For example, groundwater samples collected in Ninigret Pond separated by a vertical distance of only 5 cm differ by as much as 3 × 103 dpm 100 L− 1 for both 226Ra and 228Ra. The results from this study indicate that a single groundwater sample or suite of samples may not accurately reflect the average radium activity of the groundwater actually discharging into each pond. Targeted sampling in areas where SGD is qualitatively observed can potentially remedy this problem.
... Several studies have shown that SGD delivers a substantial quantity of nutrients and trace metals into coastal seas (Rodellas et al., 2014), even surpassing fluvial nutrient input in certain regions (Burnett et al., 2007a,b;Taniguchi et al., 2008). Tides, hydraulic changes, and seasonal fluctuation also affect SGD rates (Santos et al., 2009), particularly in areas with significant precipitation and groundwater recharge (Cable et al., 1997). The enrichment of nutrients produces ecological impacts such as eutrophication and changes in phytoplankton community. ...
Submarine Groundwater Discharge (SGD) may be a major source of chemical contaminants that go from land to sea. We initially calculated SGD at the local scale in Kayalpattinam, a typical coast with fast industrial growth, using radon (²²²Rn), radium isotopes and associated nutrient fluxes. Then, to evaluate the large-scale consequences of SGD on nutrient budgets, we summarized SGD research. The SGD hotspots corresponded with the location of polluted near-shore waters indicated. Based on radon (²²²Rn) mass balance models, the total (fresh and saline) SGD flux in was calculated to be 0.14–0.20 m³ m− 1 day− 1. We proposed the first estimate of SGD and related nutrient fluxes of the Kayalpattinam coast by integrating these findings with published data. These nutrient fluxes from SGD accounted for more than 50% of total dissolved inorganic nitrogen (DIN), Sodium Reactive phosphate (SRP), and silicate (DSi) inputs into coastal waterways, accounting for about 45% of the phosphorus needed for primary production. SGD had a considerably higher N/P ratio (78) than Redfield, which has major implications for phytoplankton growth and structure. SGD has the ability to impact water quality, control nutrient budgets, and drive primary production on a local, regional, and global scale.
... Thus, both radium and radon measurements are needed to differentiate between the fresh groundwater and recirculated seawater component of SGD. Natural radium and radon isotopes are excellent tracers for SGD because of their conservative state, higher concentration in groundwater and seawater, and relative ease to measure [17]. It has been pointed out that 222 Rn inputs to the groundwater inland may also be a point source from deep-seated fractures. ...
Submarine groundwater discharge is a pathway of fresh and recirculated groundwater to the sea. It is recently understood that this phenomenon delivers thirteen times more nutrients to the sea than the river water. This is due to the high residence time of groundwater in the coastal aquifers when compared with the river water. Studies to estimate the discharge in the field is very scarce; therefore, the real magnitude of discharge and the nutrient budget through SGD is still inconclusive. On the other hand, quantifying the SGD rates in a location would help calculate the optimal pumping rate from the coastal aquifer without leading to seawater ingress. Methods available currently to estimate SGD rates are resource intensive and needs dedicated instruments. We suggest a cost-effective methodology using the basic civil engineering survey instruments and fabricated tools to estimate the SGD rates from the coastal aquifer. This method not only estimates the discharge, but it also helps delineate the seawater-freshwater interface in the coastal aquifer and could differentiate between the fresh and recirculated SGD. The limitation of this methodology is that the SGD rates can only be estimated from the coastal unconfined aquifers, not the deeper aquifers.
... They found that the decrease in SGD with distance offshore was only observed at 7 of the sites; in contrast, 17 of the sites had offshore SGD that substantially exceeded those at some locations closer to shore. Cable et al. (1997b) observed large spatial and temporal variability of SGD along transects extending hundreds of meters offshore, located about 80 km south of Tallahassee, Florida. Charette et al. (2015) measured elevated levels of radium isotopes in the North Atlantic, indicating significant SGD along the continental shelf. ...
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.
... Numerous methods have been used to detect and quantify SGD (Burnett et al., 2006) including optical systems (Karpen et al., 2004), geochemical watercolumn investigations of tracers like the natural radionuclides radium and radon (Burnett and Dulaiova, 2003;Moore, 1996;Moore et al., 2008;Scholten et al., 2013), dissolved silicon (Oehler et al., 2019), methane and chloride (Dulaiova et al., 2010;Schlüter et al., 2004), remote sensing (Shaban et al., 2005;Tamborski et al., 2015;Wilson and Rocha, 2012) and direct investigations using cores and different types of seepage meters (Bugna et al., 1996;Burnett and Dulaiova, 2003;Cable et al., 1997;Sauter et al., 2001). Only a few geophysical methods, like geoelectric (Stieglitz, 2005;Viso et al., 2010), controlled source electromagnetic (CSEM) (Gustafson et al., 2019;Müller et al., 2011), or autonomous underwater vehicle (AUV) investigations (Sauter et al., 2003) have been used to explore SGD. ...
Fluid migration from deep sedimentary basins towards Earth’s surface has various implications for hydrocarbon accumulations and influences slope stability, climate and ecological systems. Fluids seeping from the seafloor can give insight into deep crustal and tectonic processes and can significantly change the seafloor morphology as well as the chemical composition of the overlying ocean. (...)
... Numerous methods have been used to detect and quantify SGD (Burnett et al., 2006) including optical systems (Karpen et al., 2004); geochemical water column investigations of tracers like the natural radionuclides radium and radon (Burnett & Dulaiova, 2003;Moore, 1996;Moore et al., 2008;Scholten et al., 2013), dissolved silicon (Oehler et al., 2019), methane, and chloride (Dulaiova et al., 2010;Schlüter et al., 2004); remote sensing (Shaban et al., 2005;Tamborski et al., 2015;Wilson & Rocha, 2012); and direct investigations using cores and different types of seepage meters (Bugna et al., 1996;Burnett & Dulaiova, 2003;Cable et al., 1997;Sauter et al., 2001). Only a few geophysical methods, like geoelectric (Stieglitz, 2005;Viso et al., 2010), controlled source electromagnetic (Gustafson et al., 2019;Müller et al., 2011), or autonomous underwater vehicle investigations (Sauter et al., 2003) have been used to explore SGD. ...
Submarine groundwater discharge (SGD) into coastal areas is a common global phenomenon and is rapidly gaining scientific interest due to its influence on marine ecology, the coastal sedimentary environment and its potential as a future freshwater resource. We conducted an integrated study of hydroacoustic surveys combined with geochemical porewater and water column investigations at a well-known groundwater seep site in Eckernförde Bay (Germany). We aim to better constrain the effects of shallow gas and SGD on high frequency multibeam backscatter data and to present acoustic indications for submarine groundwater discharge. Our high-quality hydroacoustic data reveal hitherto unknown internal structures within the pockmarks in Eckernförde Bay. Using precisely positioned sediment core samples, our hydroacoustic-geochemical approach can differentiate intra-pockmark regimes that were formerly assigned to pockmarks of a different nature. We demonstrate that high-frequency multibeam data, in particular the backscatter signals, can be used to detect shallow free gas in areas of enhanced groundwater advection in muddy sediments. Intriguingly, our data reveal relatively small (typically <15 m across) pockmarks within the much larger, previously mapped, pockmarks. The small pockmarks, which we refer to as “intra-pockmarks”, have formed due to the localized ascent of gas and groundwater; they manifest themselves as a new type of ‘eyed’ pockmarks, revealed by their acoustic backscatter pattern. Our data suggest that, in organic-rich muddy sediments, morphological lows combined with a strong multibeam backscatter signal can be indicative of free shallow gas and subsequent advective groundwater flow.
... Several studies found that SGD locally transports a significant amount of solutes into coastal oceans, including nutrients and trace metals ( Charette and Buesseler, 2004;Rodellas et al., 2014), even exceeding fluvial nutrient input in some areas ( Burnett et al., 2007b;Taniguchi et al., 2008). SGD rates tend to fluctuate due to tidal, hydraulic, and seasonal variability (Lewis, 1987;Santos et al., 2009;Taniguchi, 2002), especially in regions with high precipitation and groundwater recharge ( Cable et al., 1997). Spatial variation of SGD locally also affects water quality in receiving water bodies, due to the enrichment of nutrients that causes ecological effects such as eutrophication and changes in phytoplankton community ( Corbett et al., 1999;Lee et al., 2009;Niencheski et al., 2007;Valiela and Costa, 1988). ...
... They found that the decrease in SGD with distance offshore was only observed at 7 of the sites; in contrast, 17 of the sites had offshore SGD that substantially exceeded those at some locations closer to shore. Cable et al. (1997b) observed large spatial and temporal variability of SGD along transects extending hundreds of meters offshore, located about 80 km south of Tallahassee, Florida. Charette et al. (2015) measured elevated levels of radium isotopes in the North Atlantic, indicating significant SGD along the continental shelf. ...
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.
... An additional freshwater input, which is significant in Florida, is submarine groundwater discharge (SGD). Studies on these freshwater groundwater systems have shown discharge rates ranging from 0.23 to 5.3 m 3 m −2 year −1 , which is similar to smaller river and first magnitude spring discharge rates (Cable et al. 1997;Santos et al. 2008). ...
Increasing global CO2 and local land use changes coupled with increased nutrient pollution are threatening estuaries worldwide. Local changes of estuarine chemistry have been documented, but regional associations and trends comparing multiple estuaries latitudinally have not been evaluated. Rapid climate change has impacted the annual and decadal chemical trends in estuaries, with local ecosystem processes enhancing or mitigating the responses. Here, we compare pH, dissolved oxygen, temperature, and salinity data from 10 Florida shellfish estuaries and hundreds of shellfish bed stations. Over 80,000 measurements, spanning from 1980 to 2008, taken on Atlantic Ocean and West Florida coast showed significant regional trends of consistent pH decreases in 8 out of the 10 estuaries, with an average rate of decrease on the Gulf of Mexico side estuaries of Florida of 7.3 × 10⁻⁴ pH units year⁻¹, and average decrease on the Atlantic Coast estuaries of 5.0 × 10⁻⁴ pH units year⁻¹. The rates are approximately 2–3.4 times slower than observed in pH decreases associated with ocean acidification in the Atlantic and Pacific. Other significant trends observed include decreasing dissolved oxygen in 9 out of the 10 estuaries, increasing salinity in 6 out of the 10, and temperature increases in 3 out of the 10 estuaries. The data provide a synoptic regional view of Florida estuary trends which reflect the complexity of changing climate and coastal ocean acidification superimposed on local conditions. These data provide context for understanding, and interpreting the past and predicting future of regional water quality health of shellfish and other organisms of commercial and ecological significance along Florida’s coasts.
... Uma das metodologias para detecção da ocorrência da DAS é o uso do seepage meter, descrito por Lee (1977). Este método de avaliação da advecção foi empregado em diversos trabalhos (Shaw & Prepas, 1989;Cable et al., 1997a;Corbett et al., 1999), por sua facilidade de aplicação, resposta rápida e baixos cus- ...
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.
... A close relation between groundwater discharge rates and precipitation was also reported in a study off the west coast of Ireland (Smith and Cave, 2012). Other studies indicate that groundwater discharge rates from shallow aquifers can also vary seasonally due to changes in precipitation (Cable et al., 1997;Capone and Slater, 1990). Thus, it can be assumed that groundwater discharge rate in the Bay of Puck depends strongly on precipitation. ...
... According to Wilson and Rocha (2013), 222 Rn is an ideal tracer of SGD, as it behaves conservatively (as a noble gas), and is relatively easy to measure. In addition, its concentration in groundwater is several orders of magnitude higher than in seawater and its half-life of 3.82 days is comparable with the scale of coastal circulation (Cable et al. 1997;Dulaiova et al. 2008;Stieglitz et al. 2010). ...
Submarine Groundwater Discharge (SGD), which represents subsurface exchange of water between land and ocean, is a major component of the hydrological cycle. Until the mid-1990s, it was generally believed that SGD rates were not large enough to influence ocean water budgets. This thought might be due to the difficulty in quantifying rates of SGD, because most SGD occurs as diffusive flow, rather than discrete spring flow. However, there is a growing recognition that the submarine discharge of fresh groundwater into coastal oceans is just as important as river discharge in some areas of the coastal ocean. Due to growing ecological concerns about SGD, there is considerable progress on research about SGD with particular emphasis on how to quantify and trace the SGD, and to develop some forecasting or predictive capability of SGD rates based on climatic and seasonal effects.
This chapter presents a comprehensive overview of the methods used to quantify SGD to coastal areas and summarizes the previous studies on SGD. In addition, this chapter also discusses driving forces of groundwater flow through coastal aquifers, mechanism of groundwater seawater interaction and some other important issues that are necessary to understand the methods for quantifying SGD in coastal areas. The main goal of this chapter is to provide an overview of the applied methodologies to quantify SGD in coastal areas, which in turn will allow researchers, coastal zone managers, and others to choose appropriate methods that meet their specific project requirements.
... A close relation between SGD and precipitation was also reported in a study off the west coast of Ireland (Smith and Cave 2012). Other studies indicate that SGD rates from shallow aquifers can also vary seasonally due to changes in precipitation (Cable et al. 1997; Slater 1990). Thus, it can be assumed that groundwater discharge rate in the study area depend strongly on precipitation. ...
The water discharge is the most important pathway connecting land and ocean. Surface water inputs (e.g., rivers and streams) are usually easily visible and are typically large point material sources to the coastal ocean (Mulligan and Charette 2009). Hence, the contribution of surface water discharge to the ocean geochemical budgets has been well studied. The hydrodynamics and impact of terrestrial water on geochemical cycles of elements and its influence on the ocean ecosystem has been well recognised.
... The radon-derived SGD rates used in this study represent only a narrow seepage face stretch of about 200 m off the beach (Santos et al., 2009a). Therefore, our estimates should be seen as minimum values because saline and fresh SGD are likely to occur further offshore as observed near our study site (Cable et al., 1997;Moore, 2003) and elsewhere in Florida (Liu et al., 2014;Smith and Swarzenski, 2012). ...
... 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). Specific site features, such as the presence of natural embayments or anthropogenic constructions that can cut through confining units , can also result in highly heterogeneous spatial SGD patterns. ...
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.
... The large carbon fluxes in September and November 2009 can be attributed to increased SGD caused by precipitation, as Kozerski (2007) showed that the Gulf of Gdańsk hydrological system is recharged mainly by precipitation. A close relation between SGD and precipitation was reported by Smith & Cave (2012) and Cable et al. (1997), who indicated that SGD rates from shallow aquifers can vary seasonally as a result of changes in precipitation. Hence, it can be assumed that groundwater is a more significant source of DIC and DOC to the study area during summer and autumn than in winter and spring. ...
Submarine Groundwater Discharge (SGD) is an important yet poorly recognised pathway of material transport to the marine environment. This work reports on the results of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations and loads in the groundwater seeping into the southern Baltic Sea. Most of the research was carried out in the Bay of Puck (2009-2010), while in 2013 the study was extended to include several other groundwater seepage impacted areas situated along the Polish coastline. The annual average concentrations of DIC and DOC in the groundwater were equal to 64.5 ± 10.0 mg C L− 1 and 5.8 ± 0.9 mg C L− 1 respectively. The carbon specific flux into the Bay of Puck was estimated at 850 mg m− 2 yr− 1. The loads of carbon via SGD were scaled up for the Baltic Sea sub-basins and the entire Baltic Sea. The DIC and DOC fluxes via SGD to the Baltic Sea were estimated at 283.6 ± 66.7 kt yr− 1 and 25.5 ± 4.2 kt yr− 1. The SGD derived carbon load to the Baltic Sea is an important component of the carbon budget, which gives the sea a firmly heterotrophic status.
... While sources such as precipitation, river discharge, seawater exchange and nitrogen fixation are important to many coastal ecosystems, determining the contribution of nutrient delivered through SGD may also be essential (Seitzinger et al., 2010). In many temperate and tropical regions, seasonal patterns in the water cycle play an important role in controlling SGD (Cable et al., 1997;Michael et al., 2005). ...
Submarine groundwater discharge (SGD) represents a significant pathway of materials between land and sea, especially as it supplies nutrients, carbon and trace metals to coastal waters. To estimate SGD fluxes to the Godavari estuary, India, we used multiple tracers: salinity, Si, 223Ra, 224Ra, 228Ra and 226Ra. Tracer abundances were elevated in groundwater from the unconfined coastal aquifer and in surface water from the near shore zone; these enrichments decreased to low levels offshore, indicative of groundwater discharge. A model based on the decay of 224Ra relative to 228Ra was used to determine apparent water ages of various bays within the estuary. These ages ranged from 2.6 to 4.8 days during November 2011. Knowing the water age, the distribution of radium in the estuary, and the radium isotopic composition of groundwater enabled us to calculate SGD fluxes to the estuary. These fluxes (in units of 106 m3 d− 1) were on the order of 5 in the Gautami Godavari estuary, 20–43 in the Vasishta Godavari estuary, and about 300 in Kakinada bay, where enhanced ion exchange processes and redox-controlled cycling in the mangrove ecosystem may contribute to higher fluxes. These estimates of water fluxes allowed us to determine the magnitude and seasonal variability in the nutrient fluxes to the estuary associated with SGD. These nutrient fluxes (in units of mmol m− 2 d− 1) ranged from 1–19 (N), 0.6-2.6 (P), 5–40 (Si) in Gautami Godavari; 19–40 (N), 2.6-5.5 (P), 200 (Si) in Vasishta Godavari; and 120–140 (N), 10 (P), 220 (Si) in Kakinada bay. The high SGD fluxes to Kakinada bay contribute significant nutrients to this bay; considerably lower SGD fluxes to Vasishta Godavari still contribute significant nutrients to this estuary. Thus SGD represents a major source of new nutrients to these coastal ecosystems. For the entire Godavari estuarine system, SGD fluxes contribute (48–88) x 109 mol DIC y− 1 and (51–94) x 109 mol TA y− 1. These fluxes represent ~ 54 and ~ 62% of the riverine DIC and TA fluxes to the Godavari estuarine system. This study provides baseline data against which future changes in nutrient and carbon fluxes due to urbanization and economic growth over this region can be compared.
... Bars represent ± one standard deviation of the measurements taken on each day. been previously reported in a coastal system, there are studies which provide evidence of higher discharge offshore [Simmons, 1992;Cable et al., 1997]. It is possible that diagenetic changes or recent sedimentation on the bottom could create a high permeability pattern aligned with the shoreline, but slug tests show no such pattern. ...
... 2. Benthic flux estimates with manual seepage meters may be inaccurate due to pressure gradients generated by flow through and around the collection bag, the seepage chamber, and across the connection port [Fellows and Brezonik , 1980;Shaw and Prepas, 1989;Belanger and Montgomery, 1992;Shinn et al., 2002;Murdoch and Kelly, 2003]. 3. Manual seepage meters are not accurate below a 0.4 to 0.7cm/d detection limit; q bf observations near or below the detection limit must be interpreted with caution [Cable et al., 1997]. 4. Benthic organisms, such as Arenicola crusata (lugworm), Callianassa sp. ...
Coastal seas play an important role in the cycling of materials such as nutrients, influencing the productivity of marine organisms. River inflow and submarine groundwater discharge (SGD) are important pathways by which terrestrial nutrients reach estuaries. The assessment of SGD fluxes and their impact on the near-shore marine environment is essential for understanding nutrient cycling and evaluating pollution of coastal seas. SGD-derived nutrients provide positive impacts on marine productivity but other terrestrial contaminants may be harmful to coastal ecosystems. Radon-222 is applicable as a tracer of SGD as groundwater contains much higher concentrations of 222Rn than river water and seawater. This chapter introduces a general tracer method using 222Rn to evaluate SGD in coastal seas, including sampling and physical observations, and a 222Rn mass-balance model.
Coastal dynamic forces, such as waves and tides, altogether drive groundwater circulation and salt transport in the intertidal zone. However, few numerical studies have ever considered the combined effects of waves and tides. In this study, the fluctuations of wave height are integrated with tidal level together using an iterative least squares fitting method, in which the wave height can be acquired from measured sea level in the surf zone, and this fitted wave height is further verified by wind speed. Groundwater flow and salt transport were then simulated using the MARUN code to evaluate the impacts after considering wave effect. The simulated equivalent freshwater head and salinity of the model with wave effect presented less difference with the measured data compared with the simulated results of the model without wave effect. After incorporating the wave effect in a model, submarine groundwater discharge (SGD) was increased, among which recirculated SGD grew more rapidly than the fresh, leading to the proportion of the fresh SGD accounting for a small proportion (1.1%). The water influx and efflux rates increased greatly especially during the period of high wave height. Most of the influx occurred in the intertidal zone, while a considerable amount of efflux occurred in the subtidal zone. The iterative algorithm to separate the wave height from the mixed field data can be employed to identify and quantify the respective effects of tides and the combined effects of waves and tides on the density‐dependent beach groundwater flow.
This article aims to overview the previous research trends and find out the future perspective about the relationship between groundwater and ecosystems. Especially, we focused on the dynamics of microbes in groundwater which involve any material cycles and ecosystems, and seagrass/seaweed meadows and coral reefs which are categorized as Groundwater Dependent Ecosystems (GDEs) in the coastal groundwater discharge area and play important roles in the conservation of material cycles and biodiversity. Regarding the microbes, most of the studies were focused on the application of groundwater as drinking water and purification of pollutants in groundwater in the past, however, the relationship between groundwater flow and the dynamics of microbes has been studied recently. Regarding the seagrass/seaweed meadows and coral reefs, most of the research was targeted the area with a significant impact of Submarine Groundwater Discharge (SGD). Some previous studies demonstrated that SGD tends to increase the biomass of seagrass/seaweed as a nutrient source, however, it leads to a lack of their biodiversity. Some other studies reported that SGD may intensify the coral reef vulnerability due to the growth of specific algae and degradation of skeletal density and breeding potential of coral reefs if SGD-derived nutrients cause eutrophication in seawater. However, the relationship between groundwater and these ecosystems are still not fully understood in the previous research. It will be important to accumulate the results in various observation sites, apply the new techniques, and cooperate the researchers with different backgrounds (e.g. biogeochemistry, microbiology, ecology) based on groundwater hydrology for further understanding.
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.
Submarine groundwater discharge (SGD) is known to transport terrestrial nutrients and other potential pollutants to coastal areas around the world. However, SGD studies in tropical developing regions, such as Southeast Asia, are scarce, even though this area is hypothesized to be an SGD hotspot due to favorable meteorological and hydrological conditions. Jepara, a coastal city in northern Java, is characterized by a number of environmental and anthropogenic steering factors (e.g., precipitation rates, volcanic geology, coastal population density, and urban land use) that may support the notion of considerable SGD rates and its associated pollutant fluxes. Therefore, this thesis investigates SGD volumetric estimation with nutrient and microbial community composition to analyze the scale of land-based pollutants delivered by SGD to the nearshore water. Additionally, environmental and health impacts of SGD and suggested coastal water management in this region are also discussed. 222Rn was employed as a groundwater tracer in the coastal water to estimate SGD rates. Spatial and temporal 222Rn surveys were conducted in the estuaries and along the coastline of Jepara. The results indicate that terrestrial groundwater was discharged more at the estuaries than at the coastline. Fresh groundwater comprised up to 42% of total river discharge and 40% of total SGD at the coastline. SGD in this area was driven primarily by tidal pumping, with additional hydraulic gradient-driven fresh groundwater discharge at low tide. A combination of estuarine and coastal SGD results in total volumetric SGD rates of 6.6 x 105 m3 d-1. SGD rates in this area were comparable with those of other volcanic SGD studies and were higher than those in other sub-tropical or temperate region studies. SGD was confirmed to deliver terrestrial dissolved inorganic nitrogen (DIN) and dissolved silica (DSi) to the coastal system, and it also potentially acted as one of the landa ocean delivery pathways for fecal indicators and bacterial pathogens. It was also found that salinity and temperature were the most determinant variables that shaped microbial community composition in an SGD cross section. Nutrient and land-use analyses suggest that high nutrient pools in the coastal hydrological system originated from human activities, i.e., agriculture, livestock, and the sewage system. This result was also supported by microbial community analysis, where identification of fecal indicators and potential pathogens in the SGD compartment confirmed the occurrence of biological contamination. Nutrient levels and potential pathogens lead to coastal eutrophication and waterborne illnesses, which were reported from this area. From these observations, it was concluded that suitable coastal water pollution prevention at this study site should include terrestrial nitrogen containment along the riverbank and estuaries (e.g., a constructed wetland or riparian zones) and the development of a sewage system and a centralized wastewater treatment plant. Overall, this thesis shows a significant amount of contaminant discharge in the coastal area via SGD due to a combination of both environmental and anthropogenic factors. Moreover, it can be inferred that a combination of interdisciplinary geoscience research (e.g., hydrosphere, biosphere, anthroposphere) can provide a deeper understanding and assessment of SGD in a specific environment. Even though it is a local study, the methodology and results of this thesis can be replicated and thus provide assistance in other coastal urban cities in tropical regions and hence facilitate better evaluation and monitoring of tropical coastal water ecosystems in the future.
The study on sw-gw interactions had been conducted in the Upper Central plain of Thailand to investigate the recharge rate and river conductance via field measurements and the parameters derived were compared with the values used in the calibrated groundwater model in the study area.
This study explores little-recognized subject of microbiological dependencies occurring in the regions where groundwater drainage occurs. The main goal is to follow variability of prokaryotic organisms (bacteriocenosis) which inhabit the shallow littoral area of the Gulf of Puck and also to characterize the occurrence of underwater groundwater drainage in the area with the environmental conditions affecting it. There were no studies of this type in the coastal zone of the sandy beaches of the Baltic Sea so far.
On the basis of the literature data, the hydrogeological and physicochemical characteristics of the phenomenon were presented, as well as the research area, which was a shallow littoral and sandy beach zone under the influence of groundwater drainage and without this influence. The research was conducted in the vicinity of the city of Hel, located at the eastern end of the Hel Peninsula.
Using microscopic, cultivation and genetic methods, the number, size structure and biomass of prokaryotic cells were analyzed. Their metabolic activity and taxonomic differentiation were determined. Due to the recreational character of the area, special attention was given to the possible impact of groundwater drainage on sanitary quality of coastal waters. The results of the research confirm that in environmental studies auto- and allochthonous bacteriocenosis develops under the influence of numerous factors, most of which can be described as "environmental stress".
It was concluded that although the inflow of groundwater in the coastal area does not cause significant changes in the number, size and biomass of bacterial cells settling in coastal sea waters and sandbanks, it does affect their activity and diversity. The intensity of these changes is however dependent on the season (mainly temperature and oxygenation). The interdependence between the availability of oxygen the value of redox potential and biochemical processes catalyzed by microorganisms with specific life requirements has been observed. It has been demonstrated, among others, that selected groups of microbiological indicators, e.g. Archaea methanogenic, identified by genetic methods (NGS) may be a sufficiently sensitive bioindicator of the impact of groundwater drainage on the marine environment.
Recognition of the taxonomic composition of bacteriocenosis that settles pores may therefore facilitate the identification of processes occurring in the sediments in the area of underground drainage occurrence, which is particularly important due to the high variability of this phenomenon.
Based on the analysis of the number of indicator bacteria (faecal enterococci and E.coli intestinal bacteria) in seawater and pore waters, the exceedances of the limit values were found only in the summer and autumn seasons. In pore water not affected by drainage, the number of indicator bacteria was similar to or lower than that in seawater. However, the lowest values were recorded in pore water under the influence of drainage. This might be due to dilution of seawater with groundwater, changes in environmental conditions (salinity, Eh, pH, nutrient concentration, oxygen availability) or periodic presence of inhibitors (CH4, H2S). The influence of allochthonous antagonistic microflora, which may affect the partial elimination of microbial contamination of faecal origin, is also not without significance.
In the experimental part of the research, it was observed that the presence of organic substances significantly increased the lifespan of faecal bacteria, both in seawater and in porous waters under the influence of drainage. This is a crucial aspect for the sanitary quality of coastal waters. Therefore the study focused in particular on the epidemiological risk and the possibility of drug resistance occurrence in faecal bacteria.
Representatives of faecal bacteria: Enterococcus spp. and Escherichia coli, were isolated from seawater, porous waters and sandy sediments. However, detailed biochemical identification of the strains showed that the used microbiological media were insufficiently selective and e.g. besides enterococci, other bacteria were also found, mainly of the Staphylococcus genus, including Staphylococcus aureus.
Antibiograms made for Enterococcus spp. strains isolated in the area of the study were similar to clinical ones and reflected the consumption of antibiotics in Poland. The observed presence of drug-resistant bacteria could be related to their selective advantage in conditions of exposure to environmental factors (e.g. UV radiation).
The research also has revealed that the complexity of the processes between biotic and abiotic factors in the sandy beach environment and the shallow littoral zone may lead to erroneous conclusions in the short-term surveys. In order to identify and understand these correlations, cyclical and detailed monitoring is necessary.
Summarizing, the results obtained in this study will contribute to a better understanding of the potential human impact on the water resources quality. They are an important contribution to the discussion on the anthropogenic pollutants inflow from various sources, including the increasingly discussed role of groundwater drainage. Results of the survey are also of significant epidemiological importance and fall within the framework of the multi-annual monitoring programme for recreational areas. This programme, according to the requirements of the European Commission, should also take into account the natural environment sector. The issues discussed are the focus of interest of many European programmes and directives, which considered the lack of monitoring data to be the most important gap in the full implementation of tasks related to water protection.
This report describes results from activities performed in 2009 by H2H Associates for the Woodville Karst Plain Hydrologic Research Program, overseen by the Florida Geological Survey. The primary objectives of the 2009 activities were: 1) expand the hydrologic monitoring network; 2) update the online Data Portal; 3) Repeat the Lost Creek Tracer Test performed in 2008 to confirm connections ; 4) develop calibration criteria for statistical modeling in the WKP; and 5) characterize radon and methane distributions in and around Spring Creek.
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.
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.
Submarine Groundwater discharge (SGD) introduces solute and nutrients to the global oceans, resulting to considerable nutrient cycling and dynamics in the coastal areas. We have conducted a high‐resolution, spatio‐temporal, lunar‐tidal cycle patterns and variability of discharging solutes/nutrients assessment to get an overview of seasonal nutrient flux to the Bay of Bengal in eastern parts of Indian Subcontinent. While, the pre‐monsoon season SGD was found to be dominant in the marine influence (M‐SGD), the post‐monsoon season was found to be predominated by the terrestrial component of SGD (T‐SGD), extending from coast to near offshore. The solute fluxes and redox transformation were found to be extensively influenced by tidal and diurnal cycles, overlapping on seasonal patterns. We have assessed the possible role of SGD associated solutes/nutrients fluxes and their discharge mechanisms, and their associated temporal distributions have severe implications on the biological productivity of Bay of Bengal. The estimated annual solute fluxes, using the average end member concentration of the SGD associated nutrients, were found to be 240 mM m‐2d‐1 for NO3‐ and 224 mM m‐2d‐1 for Fetot. Together with huge freshwater flux from Himalayan and Peninsular Indian river, the SGD have considerable influence on the bay water circulation, stratification and solute cycling. Thus the observation from this study implies that SGD associated nutrient flux to Bay of Bengal may function as nutrient sink, which might influence the long‐term solute/nutrient flux along the eastern coast of India.
SGD has been recognized as an important pathway of material transport
from land to the marine environment. Despite numerous studies as regards hydraulic fluxes and chemical composition of groundwater seeping to the coastal ocean much remains to be done to characterize SGD impact on the coastal marine environment. The Baltic Sea
is an example of a region highly influenced by a variety of human activities that affect the ecosystem. SGD
is a source introducing dissolved substances into the Baltic Sea that has not been quantified so far. Little is known regarding the concentrations and fluxes of chemical substances in groundwater discharged to the Baltic Sea and chemical reactions that control their flux into the coastal ecosystem.
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.
Sandy sediments are now recognized as sites of high carbon turnover enhanced by porewater flow. However, it is unclear how coupling between porewater advection and benthic metabolism might permit O2-saturated areas and suboxic environments to coexist in close proximity. Field sampling campaigns, flow-through reactor (FTR) experiments and diagenetic modeling were used to study benthic O2 dynamics in surface sediments of a permeable intertidal seepage face (Ria Formosa; Southwestern Iberia). Field results demonstrated that the pressure gradient imposed by tidal oscillation at the seepage face permits seawater infiltration at high tide, and hence resupplies the benthos in O2 and organic matter (OM). Significant aerobic respiration rates (12.1–26.8 nmol cm−3 “bulk sediment” (bs) h−1) were derived from vertical O2 gradients taken from the top 28 cm of the sediment during active seepage. FTR experiments showed a vertical zonation of respiration rates following benthic OM availability (from 8.63 ± 1.88 nmol cm−3 bs h−1 at 12–32 cm depth to 53.55 ± 7.93 nmol cm−3 bs h−1 at 0–2 cm depth). Advection enhances O2 consumption rates, but respiration is ultimately limited by OM availability at high seepage rates. Diagenetic modeling of O2 distribution in the porewater suggests that even within a well-oxygenated beach aquifer, local respiration is sufficiently high to lower the porewater O2 concentration near the sediment surface during active seepage. Our results indicate that high seepage rates, OM and O2 loading promoted by tidally-driven seawater infiltration control the O2 consumption at the sediment surface, thus favoring the occurrence of suboxic biogeochemical processes near the sediment surface.
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.
The complex exchange of fluvial, subsurface and seawater within a coastal area directly affects global biogeochemical cycles and the application of isotopic tracers, mainly natural radionuclides from U and Th series, is a powerful tool to track sources and sinks of trace elements and nutrients to this systems. The unique Ra signature applied to quantify the contribution of such fluxes is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers. In the U and Th natural radioactive decay series there are four radium isotopes: 223Ra (t1/2 = 11.4 d), 224Ra (t1/2 = 3.7 d), 228Ra (t1/2 = 5.7 y) and 226Ra (t1/2 = 1,600 y). Their wide range in half-lives corresponds well with the duration of many coastal processes. All these Ra isotopes derive from decay of Th parents, which are tightly bound to particles. Because Ra is mobilized in the marine environment, sediments provide a continuous source of Ra isotopes to estuarine waters at rates set by its decay constants. The Th isotope activities in the sediments and the distribution coefficient of Ra between the sediments and water determine the potential input of each Ra isotope to the water. Because 228Ra is regenerated much faster than 226Ra, estuaries with high 228Ra/ 226Ra activity ratios in the water must have a high degree of exchange with sediments on the sea bed or with groundwater draining nearby. This information is useful to elucidate the contribution of estuarine systems to the exchange of trace elements, N, P and C in the mixing zone. The combined source functions for Ra in a coastal area include riverine particulates/ dissolved input, oceanic dissolved concentrations, input from sediments and groundwater. The relative significance of each of these sources is usually a function of the site-specific hydrogeology and where the samples are taken relative to the salinity gradient (extent of freshwater/saltwater mixing). Thus, the Ra isotopes provide fundamental information on the interaction of sediments, groundwater and estuarine waters. In this project, the distribution of natural Ra isotopes was studied in surface, groundwater and estuarine water samples collected from dry and wet seasons (2009 – 2010) campaigns performed in Ribeira Valley, Southern São Paulo State. The inventory allowed the application of Ra isotopes as tracers of fluvial and groundwater discharges to the Cananéia-Iguape estuarine complex. The exchange of groundwater/ surface water in Ribeira do Iguape River basin and related fluxes of several constituents for the Cananéia-Iguape estuarine complex mass balance is still not very well known. The results obtained in this research work evidenced that there is a prevalence of 228Ra isotope in all the set of samples analyzed. However, the activity concentrations of Ra isotopes determined from Higher Ribeira Valley through the Southern Coastal Plain of São Paulo are representative of natural background levels, showing low or minimal human intervention. In the set of samples collected along Ribeira do Iguape River, Cananéia and Iguape outlets, the higher concentrations of Ra were observed in bottom waters, indicating the diffusion of 228Ra from sediments recently deposited as a potential source of the increased concentrations of this isotope when compared with others. The activity concentrations of the short-lived Ra isotopes were negligible, lower than the limit of the detection. Fluxes of Ra for Cananéia outlet are strongly influenced by tidal oscillations, which modulate the increase and decrease of Ra concentrations in response of the respective increase and decrease of waters salinity. In Iguape outlet and in hydrochemical stations performed along Ribeira do Iguape River it was observed a linear relationship between the amount of suspended matter and the increase of 228Ra activity concentration. When we evaluate qualitatively the differences in behavior of both long-lived Ra isotopes, the concentrations of 226Ra have not shown similar distribution to 228Ra. This demonstrates negligible contribution from advective porewaters and groundwater to the studied scenario. Dominant fluxes of trace-elements, radionuclides and nutrients have their main sources centered on fluvial, sediments and suspended matter compartiments.
This chapter discusses the chemical characteristics of submarine groundwater seepage in Toyama Bay in Central Japan. There are several important sources for various materials that flow from the land to the ocean, and one of these sources is fresh water. This chapter considers and discusses the input and distribution of material to the marine environment by means of riverine inflow, atmospheric precipitation, or geothermal input due to the eruption of submarine volcanoes on mid-oceanic ridges. By the development of research techniques, the presence of submarine spring water was discovered to be a common phenomenon in continental shelf areas around the world. Spring water has been found in the northern and southern American continental shelves of California. Groundwater that seeps from the sea floor are classified into the following three patterns: the potential type, the density type, and the geothermic type. The seepage water collected off Uwozu is of the potential type. The source of the freshwater is the precipitation in the Toyama region, which is among the highest in Japan. Toyama's high precipitation is caused by high seawater temperature, which is maintained by the warm Tsushima current moving at 2.6 million m3/sec from the southwest to the northeast along the Japan Sea coast.
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.
Measurements of radon-222 activity in Carters Creek ranged from 32 to 196 disintegrations per minute per liter. A sample of ground-water from an adjacent spring contained radon-222 activity of 489 disintegrations per minute per liter. On the basis of radon-222 activities down the sampled reach of the stream, during low base-flow conditions 36% of flow leaving the reach was ground-water seepage of a point 0.5 mile downstream from the upper sampling boundary. Measurements of temperature in the water of the stream verified the point location of ground-water seepage. Subsequent measurements of radon-222 activities and streamflow at higher base-flow conditions indicated two gaining sections of stream, which were receiving about 0.3 cubic foot per second ground-water seepage in the upper reach and about 0.2 cubic foot per second ground-water seepage in the lower reach. -from Authors
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.
Rates of groundwater discharge onto coral reefs at Barbados, West Indies, were measured with seepage meters and miniature piezometers. Seepage flux varied spatially, was correlated with water depth. Groundwater nitrogen concentrations were correlated with salinity. Nitrate content of the discharge was much higher than was phosphate content. Measured fluxes were consistent with groundwater discharge estimates from aquifer models.-from Author
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 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.
The flux of groundwater through shallow-water sediments into Lake Mendota was calculated from hydrologic studies and was measured directly with seepage meters at 106 sites around the lake. Groundwater accounted for a substantial amount (around 30%) of the water budget. Pore water in seepage zones was collected for chemical analysis by two methods: (1) dialysis samplers; and (2) direct gentle suction. This pore water, which was assumed to represent seepage inflow, was considerably lower in nitrogen and phosphorus than surface inflow but was higher in phosphorus and lower in nitrogen than well water, indicating that well chemistry does not provide a good indication of the composition of groundwater entering lakes. Calculations indicated that seepage accounted for 12% of the total phosphorus loading to Lake Mendota and 2% of the total nitrogen budget. These results are interpreted in terms of the annual nutrient loading estimates that have been done on Lake Mendota involving only surface water measurements.
Seepage flux was measured with seepage meters placed along transects from the lake shore to 30–110m offshore in 10 lakes in central Alberta during May–August 1986. In the study area, the predominant surficial deposit is glacial till which is underlain by sedimentary bedrock. Seepage flux into the lakes ranged from 3 × 10−10 to 2 × 10−7 ms−1. Seepage out of the lakes was recorded at only one of 92 seepage meter sites. At one lake, seepage was measured fortnightly along transects at two locations, from May to August 1986; seepage patterns were consistent throughout that period. In the nearshore region of six of 10 lakes, seepage flux to the lakes decreased with distance from shore. Deviations from that pattern were probably a result of: (1) spatial variability of seepage flux within a small area of lakebed; (2) intertill sand and gravel lenses near the lake; (3) preglacial bedrock channels of sand and gravel underlying some of the lakes. Ground water was the major source of water (49% of total inflow) to one lake; at the other lakes, ground water was a relatively small component (10%) of total inflow.
The use of seepage meters to identify nearshore seepage patterns and to quantify seepage in lakes was evaluated with a Monte Carlo simulation model. The model simulated seepage flux as would be derived from seepage meter measurements along a transect extending from the shore of a hypothetical lake to 40 or 100m offshore. Along the transect, simulated seepage velocities decreased exponentially with distance from shore according to patterns measured at Narrow Lake, Alta., and Lake Sallie, MN. To determine statistical parameters needed in the model, seepage flux was measured in situ with closely spaced seepage meters at four different sites in Narrow Lake. Seepage velocities within a small area of lakebed were log-normally distributed, and the variance was positively correlated with mean seepage flux. The modeling indicated that the most sensitive parameter affecting the accuracy of seepage meter estimates of seepage patterns and average seepage flux along the transect was the variability in the spatial distribution of seepage flux within a small area of lakebed. There was little improvement in the accuracy of estimates of seepage patterns or transect flux when more than ten seepage meters were simulated along the transect, when the transect was “sampled” more than twice, or when seepage meters along the transect were simulated to follow a stratified rather than a systematic design.
Exchange of water between the lake and the surrounding groundwater system was computed for a permanent lake on the central Amazon floodplain (Lake Calado) from an empirical seepage model incorporating 240 direct measurements of seepage from the lakebed and seasonal changes in lake stage and morphometry. Seepage rates varied with the daily rate of change in stage height and inversely with depth of the lakebed from the water surface. The volume of seepage outflow over the rising-water period (4 × 106m3) is plausible if the rate of groundwater flow is constrained by the hydraulic conductivities expected for the soils. -from Author
Rates of groundwater discharge onto coral reefs at Barbados, West Indies, were measured with seepage meters and miniature piezometers. Seepage flux varied spatially, was correlated with water depth, and was about twice as high during the wet season as during the dry. Groundwater nitrogen concentrations were correlated with salinity but phosphate concentrations were not. Nitrate content of the discharge was much higher than was phosphate content. Measured fluxes were consistent with groundwater discharge estimates from aquifer models, but a large data set would be required to make accurate predictions of areal groundwater discharge and nutrient loading.
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.
Direct ground water seepage measurements were made in Lake Washington, Florida, to determine the importance of seepage as a water and chloride source to the lake and upper St. Johns River. Over 200 seepage measurements were made in the lake and adjoining canals from July through December 1978. Results indicated that seepage into the shore areas of Lake Washington was an insignificant water source to the lake, representing 0.6 percent of the inputs, and was nearly balanced by ground water recharge in the midlake region. Drainage canals entering Lake Washington, however, exhibited high average seepage rates (17.7 L/m2-day), over eight times the lake average (2.01 L/M2-day). Discharge from the St. Johns River was the dominant factor in the water budget of Lake Washington and represented approximately 88 percent of the inputs during the study year. Although inputs from the drainage canals represented only 6.6 percent of the St. Johns River annual discharge, these canals represented 20.4 percent of the annual St. Johns River chloride loading and 62.1 percent of the river chloride loading during the five driest months of 1978. Evidence from this study indicates that rising levels of chloride in the river in recent years are largely attributable to ground water seepage in channelized areas, particularly in the headwaters. These chloride inputs assume greater importance during low water/low flow periods.
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.
The marine angiosperms Thalassia testudinum, Syringodium filiforme, and Halodule wrightii form two of the largest reported seagrass beds along the northwest and southern coasts of Florida where they cover about 3000 square km in the Big Bend area and about 5500 square km in Florida Bay, respectively. Most of the leaf biomass in the Big Bend area and outer Florida Bay was composed of Thalassia testudinum and Syringodium filiforme which were distributed throughout the beds but which were more abundant in shallow depths. A short-leaved form of Halodule wrightii grew in monotypic stands in shallow water near the inner edges of the beds, while Halophila decipiens and a longer-leaved variety of H. wrightii grew scattered throughout the beds, in monotypic stands near the outer edges of the beds, and in deeper water outside the beds. Halophila engelmanni was observed scattered at various depths throughout the seagrass beds and in monospecific patches in deep water outside the northern bed. Ruppia maritima grew primarily in brackish water around river mouths. The cross-shelf limits of the two major seagrass beds are controlled nearshore by increased water turbidity and lower salinity around river mouths and off-shore by light penetration to depths which receive 10% or more of sea surface photosynthetically active radiation. Seagrasses form large beds only along low energy reaches of the coast. The Florida Bay seagrass bed contained about twice the short-shoot density of both Thalassia testudinum and Syringodium filiforme, for data averaged over all depths, and about four times the average short-shoot density of both species in shallow water compared with the Big Bend seagrass bed. The differences in average seagrass abundance between Florida Bay and the Big Bend area may be a consequence of the effects of greater seasonal solar radiation and water temperature fluctuations experienced by plants in the northern bed, which lies at the northern distribution limit for American Tropical seagrasses.
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.
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