No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Importance of submarine groundwater discharge (SGWD) and seawater cycling to material flux across sediment/water interfaces in marine environments
Abstract
Data on SGWD from sites in the Florida Keys and on the southeastern continental shelf of the US indicate that water movement across sediment/water interfaces is a common occcurrence at least to water depths of 30 to 35m. Discharge values from the Florida Keys were 8.9l m-2d-1 for depths <27m and 5.4 l m-2d-1 for depths of c27 to 39m. On the southeastern continental shelf, discharge ranged between c6 and 20 l m-2d-1. One site was found in 20m depth where there was a persistent negative hydraulic head and mean influx of seawater to the sediments (c10.8 l m-2d-1). Even though geohydrological models would predict coupling of SGWD with landbased hydraulic heads, definitive lower salinity SGWD could not be detected. The driving force seems to be subtidal pumping and much of the discharge measured was probably recycled seawater. SGWD serves to move dissolved solutes into the water column, and could be an important link in benthic-pelagic coupling in continental shelf ecosystems. -from Author
... Karstic features like conduits or volcanic lava tubes provide these conditions. 6−13 While it has been shown that submarine springs can have flow rates in the m 3 s −1 range, 14 only a few direct discharge flow rate measurements exist 7,15 and especially deep SGD sites have been little described so far. ...
... However, radon concentrations in groundwater from sediment, meta-sediment or granitic aquifers, which are all found in the study area, show a wide range of possible values ranging typically from 10,000 to over 1,000,000 Bq m −3 . 15 Outlook. This study presents an approach to detect and quantify SGDs based on field observations ( 222 Rn, T, S) at the sea surface and cheap, broadly available water column measurements (CTD profile and bathymetry). ...
Groundwater discharge into the sea occurs along many coastlines around the world in different geological settings and constitutes an important component of global water and matter budget. Estimates of how much water flows into the sea worldwide vary widely and are largely based on onshore studies and hydrological or hydrogeological modeling. In this study, we propose an approach to quantify a deep submarine groundwater outflow from the seafloor by using autonomously measured ocean surface data, i.e., 222Rn as groundwater tracer, in combination with numerical modeling of plume transport. The model and field data suggest that groundwater outflows from a water depth of ∼100 m can reach the sea surface implying that several cubic meters per second of freshwater are discharged into the sea. We postulate an extreme rainfall event 6 months earlier as the likely trigger for the groundwater discharge. This study shows that measurements at the sea surface, which are much easier to conduct than discharge measurements at the seafloor, can be used not only to localize submarine groundwater discharges but, in combination with plume modeling, also to estimate the magnitude of the release flow rate.
... Groundwater discharge from aquifers as well as infiltration of saline water into sediment is induced by tidal activity in other estuarine ecosystems such as in the Chesapeake Bay and the Swan-Canning estuary (Robinson et al 1998, Smith and Turner 2001, Acworth and Dasey 2003. Groundwater discharge is also recognized as a significant source of nutrients such as for nitrogen and phosphorus into coastal systems (Simmons, 1992, Krest et al 2000, Moore et al 2002, Hwang et al 2005. Moreover, nitrogen flux from submarine groundwater discharge to local rivers has been reported in the literature (e.g. ...
... Moreover, nitrogen flux from submarine groundwater discharge to local rivers has been reported in the literature (e.g. Georgio shelf by Simmons 1992). Groundwater may also be a significant source of nutrients, including nitrate to surface waters (Valiela et al 1990, LaRoche et al 1997. ...
The Bay of Bengal receives nitrogen inputs from multiple sources and the potential role of nitrogen-metabolizing microbial communities in the surface water is not well understood. The nitrogen budget estimate shows a deficit of 4.7 ± 2.4 Tg N yr-1, suggesting a significant role of dissolved organic nitrogen remineralization in fuelling ecosystem processes. Unravelling the process of remineralization leading to increasing concentrations of dissolved inorganic nitrogen (DIN) in coastal ecosystems such as mangroves require a better understanding of the composition of functional resident bacterioplankton communities. Bacterioplankton communities were elucidated from eight stations along different estuaries spanning west to east of northeast coastal Bay of Bengal to understand the influence of DIN on shaping these communities. The eight stations were differentiated into ‘low’ and ‘high’ DIN stations based on a DIN concentration, with five stations with High DIN concentration (>45 µM) and three stations with Low DIN concentration (<40µM). The V3-V4 region of 16S rRNA was amplified and sequenced to elucidate resident bacterioplankton community structure from environmental DNA. Proteobacteria, Bacteroidetes, and Firmicutes were the dominant bacterioplankton phyla across all stations. Nitrogen-fixing groups such as Nitrospirae, Lentisphaerae, Chloroflexi, and Planctomycetes make up about 1% of the bacterioplankton communities. Abundances of Spirochaetes and Tenericutes showed a positive correlation with DIN. Pseudomonadales, Alteromonadales, and Desulfovibrionales were found to distinctly vary in abundance between low and High DIN stations. Predicted metagenomic profiles from taxonomically derived community structures indicated bacterial nitrate-nitrite reductase to be negatively correlated with prevalent DIN concentration in High DIN stations but positively correlated in Low DIN stations. This trend was also consistent for genes encoding for nitrate/nitrite response regulators and transporter proteins. This indicates the need to delineate functional bacterioplankton community structures to better understand their role in influencing rates and fluxes of nitrogen within mangroves.
... The discharge of coastal groundwater has become increasingly important as industry and populations continue to migrate toward fragile coastal zones. The submarine groundwater delivery of certain dissolved constituents such as select radionuclides, trace metals, and nutrient species to coastal bottom waters has often been overlooked [Krest et al., 2000;Valiela et al., 1990;Reay et al., 1992;Simmons, 1992]. This omission from coastal hydrologic and mass balance budgets by both hydrologists and oceanographers alike is largely due to the difficulty in accurately identifying and quantifying submarine groundwater discharge [Burnett et al., 2001a, b;Burnett et al., 2002]. ...
... SGWD consists of both groundwater flow from upland regions and water exchange at the aquifer-ocean interface [Simmons, 1992]. While the upland groundwater flow can be estimated based on the aquifer recharge [Zekster and Loaiciga, 1993], it is difficult to quantify the rate of water exchange across the seabed, which is influenced by near-shore processes [Li et al., 1997a;Turner et al., 1997;. ...
Approximately 70% of the world's population lives in coastal areas, and the majority of these people depend on coastal aquifers for freshwater. The fragility of these aquifers and their sensitivity to human activity demand informed, competent management to guarantee their survival. Significant knowledge and new technologies related to the subject have accumulated in the last two decades, and a need has emerged for a comprehensive reference that gathers and disseminates crucial information to engineering practitioners and policymakers. Coastal Aquifer Management-Monitoring, Modeling, and Case Studies provides the most advanced and up-to-date methods and tools for the study and protection of coastal aquifers. This "how-to" volume presents a worldwide perspective with contributions from an international panel of experts. They address topics such as geohydrology, optimization, uncertainty analysis, and GIS as they relate to geographically-specific case studies; knowledge from these examples can be applied to aquifer issues in other regions. A companion CD-ROM supplements the text with programs and graphics, making this overview an indispensable reference and tool for the analysis of critical freshwater resources.
... Groundwater discharges to the sea (SGD) from coastal aquifers is considered as a potential source for transport of solutes, anthropogenic contaminants and nutrients to seawaters. Discharging groundwater from coastal aquifers may adversely affect the coastal ecosystems and marine biota (Johannes, 1992;Simmons, 1992). Freshwater inputs to the ocean by groundwater discharge will vary from region to region based on the local geology, climate, and geomorphology of the area and the subsurface structure of the aquifer. ...
... Both the T-SGD and M-SGD, while discharging, may influence the geochemistry and redox behavior of the groundwater-seawater (GW-SW) interaction zone (Kohout, 1960;Michael et al., 2003). Since groundwater is enriched in solute and nutrients, discharge groundwater via SGD can lead to a large solute flux and nutrient flux to the coastal ecology (Simmons, 1992;Corbett et al., 1999;Slomp and Van Cappellen, 2004;. In some coastal areas, SGD is identified as the major source of nutrient flux to the ocean which further suggested to be the primary process of eutrophication (Paerl, 2009;Valiela et al., 2002;Null et al., 2012). ...
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.
... When flow instability occurs, it alters the migration path and residence time of land-sourced solute plumes in the nearshore aquifer, pushing them deeper and causing the discharge zone to shift over time (Shen et al., 2019). The altered groundwater flow dynamics modify pathways of land-derived nutrients and promotes dynamic and enlarged seawater-freshwater mixing in the beach aquifer, affecting transformation of land-derived nutrients, metals and pollutants, and thus, their mass fluxes from the terrestrial to the marine ecosystem (Johannes, 1980;Simmons, 1992;Moore, 1999;Anschutz et al., 2009;Robinson, et al., 2007a;Robinson, et al., 2007b;Anwar et al., 2014;Robinson et al., 2018). Moreover, if the USP becomes unstable, fingering flow likely results in multiple freshwater discharge locations along the beach face and variable freshwater discharge volumes over time (Greskowiak, 2014;Röper et al., 2014;Robinson et al., 2018). ...
... Russoniello et al. 2016), hydraulic heads (Moore 2010;Mulligan et al. 2006;Oberdorfer 2003), tidal amplitudes (e.g. Abarca et al. 2013;Robinson et al. 2007;Simmons 1992), wave amplitudes (e.g. Xin et al. 2010), and anthropogenic activity (irrigation or pumping of fresh water, modifications of surface water flow paths -to mention a few; Knee and Paytan 2011). ...
Submarine groundwater discharge (SGD) at the interface of land and sea is likely an important part of the global hydrological cycle and has started to attract the attention of a growing interdisciplinary scientific community. While before the year 2000 only a few papers about that topic are listed in the ISI Web of Science, by now about 100 publications per year address the topic. Submarine groundwater discharge has been defined as ‘direct groundwater outflow across the ocean-land interface into the ocean’ (Church, 1996), later refined to ‘any and all flow of water on continental margins from the seabed to the coastal ocean’ (Burnett et al., 2003), consisting of fresh terrestrial groundwater of modern origin (‘meteoric water’), connate water, and recirculated seawater (Fig.1). Although the majority of the SGD flux is derived from recirculated seawater, the term “groundwater discharge” often tends to be misleadingly reduced on its fresh terrestrial groundwater proportion. Additional confusion may also be caused by the use of different synonyms for this proportion which comprise “freshwater discharge”, “submarine spring” (if discharge occurs in spatially focused form, such as in karst environments), “freshwater spring” or “Vrulja” (Bögli, 1980; Milne, 1897; Kohout, 1966; Fleury et al., 2007; d´Elia et al., 1981). The processes controlling the fluxes of SGD belong to topic 13 of the currently unsolved problems in hydrology (Blöschl et al., 2019).
... Los cambios de salinidad y de temperatura y el aporte de solutos pueden ser importantes condicionantes de los procesos químicos y biológicos litorales y de la productividad orgánica (Johannes, 1980;Simmons, 1992;Moore, 2010;Slomp y van Cappellen, 2004;Li et al., 1999). En las formaciones volcánicas es especialmente importante el aporte de sílice y de potasio. ...
Las rocas volcánicas son el resultado de la salida al exterior de magma, que está formado por silicatos y sílice y contiene substancias disueltas que se separan como vapores y como gases no condensables. El volcanismo es un aporte de materia al exterior y por lo tanto edifica estructuras y crea formaciones, pero también se produce un aumento de la erosión en esos relieves y fenómenos tectónicos que hunden parte de lo edificado o que está en sus proximidades. Los aspectos de destrucción de los relieves creados también son una parte importante del volcanismo y de su relevancia hidrogeológica. La creación y destrucción de los edificios volcánicos se hace en sucesivos eventos localizados, frecuentemente rápidos a escala geológica, a veces violentos, y en eventos sucesivos cada uno de duración de escala humana, con parte del material de las erupciones como lava y parte como tefra, con distribución espacial variable. Esto origina formaciones muy heterogéneas, cuyo comportamiento hidrogeológico puede ser complejo y su entendimiento requiere un buen conocimiento de los procesos geológicos y geoquímicos involucrados. Los clásicos principios de la geología sedimentaria no son directamente aplicables o debe utilizarse con notables precauciones. Bajo un punto de vista hidrogeológico hay aspectos distintos entre las formaciones volcánicas continentales y las de las pequeñas islas volcánicas, en general de menos de 5000 km2. En el continente o en grandes islas hay otras formaciones geológicas y un relieve e hidrografía que ponen en relación aspectos influenciados por el volcanismo, con otros que no lo están. En ellos, las formaciones volcánicas pueden ser hidrogeológicamente dominantes o estar supeditadas y con variaciones espaciales importantes. En pequeñas islas, las formaciones volcánicas y derivadas de las mismas suelen ser dominantes, el relieve puede tener un papel clave, no hay redes fluviales alóctonas y el nivel del mar y sus variaciones son un condicionante muy específico del comportamiento. Bajo un punto de vista geoquímico, cabe distinguir entre componentes mayoritarios, a concentraciones ponderales del orden porcentual, otras minoritarias a concentraciones del orden de partes por millón y componentes traza. Son de interés hidrogeológico aquellos elementos que pueden dar lugar a iones y compuestos solubles en el agua subterránea o que facilitan su incorporación. Los elementos químicos de los componentes mayoritarios son Si, Al, Mg, Ca, Na, K, Fe (con mayor proporción de Fe-II) y P. En las rocas básicas, como el basalto, el Si está únicamente como silicato, pero una parte del mismo forma sílice libre en las rocas ácidas, como la riolita y las intermedias como las andesitas. El Mg y Ca son más abundantes en rocas básicas comunes que en las ácidas, mientras que el contenido en Na y K tienden a ser mayor en las rocas ácidas comunes, pero con relación Na/K menor, aunque hay frecuentes desviaciones de esta tendencia. El Mg, Ca, Na y K pueden pasar al agua subterránea al alterarse la roca por aportes de acidez, con una parte que queda absorbida en los minerales resultantes de la alteración, según sean las condiciones ambientales. Lo mismo puede decirse del Li y Sr.
... Groundwater has been recognized as one of the key factors affecting coastal marine ecological and biogeochemical processes [Johannes, 1980;Simmons Jr, 1992;Miller and Ullman, 2004;Santos et al., 2008;Kim et al., 2017]. Submarine groundwater discharge (SGD) provides a significant transport pathway for land-derived chemicals (e.g., nutrients, contaminants, and trace elements) to enter nearshore marine ecosystems [Burnett et al., 2003;Slomp and Van Cappellen, 2004;Defeo et al., 2009]. ...
Studies of coastal groundwater dynamics often assume two‐dimensional (2D) flow and transport along a shore‐perpendicular cross‐section. We show that along‐shore movement of groundwater may also be significant in heterogeneous coastal aquifers. Simulations of groundwater flow and salt transport incorporating different geologic structure show highly three‐dimensional (3D) preferential flow paths. The along‐shore movement of groundwater on average accounts for 40%–50% of the total flowpath length in both conduit‐type (e.g., volcanic) heterogeneous aquifers and statistically equivalent (e.g., deltaic) systems generated with sequential indicator simulation (SIS). Our results identify a critical role of three‐dimensionality in systems with connected high‐permeability geological features. 3D conduit features connecting land and sea cause more terrestrial groundwater flow through the inland boundary and intensify water exchange along the land‐sea interface. Therefore, conduits increase the rate of SGD compared to equivalent homogeneous, SIS and corresponding 2D models. In contrast, in SIS‐type systems, less‐connected high‐permeability features produce mixing zones and SGD nearer to shore, with comparable rates in 3D and 2D models. Onshore, 3D heterogeneous cases have longer flowpaths and travel times from recharge to discharge compared to 2D cases, but offshore travel times are much shorter, particularly for conduit‐type models in which flow is highly preferential. Flowpath lengths and travel times are also highly variable in 3D relative to 2D for all heterogeneous simulations. The results have implications for water resources management, biogeochemical reactions within coastal aquifers, and subsequent chemical fluxes to the ocean.
... Submarine groundwater discharge (SGD) flows through the pore space of sediments or along fluid conduits such as karst structures. The relevance of SGD for the transport and release of nutrients, trace elements or gases such as methane or radon from sediments into the groundwater of coastal regions or lakes has already been emphasized by Johannes (1980), Zimmermann et al. (1985), Shaw and Prepas (1990), Simmons (1992) and Bugna et al. (1996). ...
To quantify submarine groundwater discharge, we developed an inexpensive automated seepage meter that applies a tracer injection and the computation of the mean residence time. The SGD-MRT is designed to measure a wide range of discharge rates from about 30 to 800 cm³/min and allows minimizing backpressures caused by pipe friction or flow sensors. By modifying the inner volume of the flow-through unit, the range of measurement is adjustable to lower or higher discharge rates. For process control and data acquisition, an Arduino controller board is used. In addition, components like temperature, conductivity, and pressure sensors or pumps extend the scope of the seepage meter. During field tests in the Wadden Sea, covering tidal cycles, discharge rates of more than 700 cm³/min were released from sand boils. Based on the measured discharge rates and numerical integration of the time series data, a water volume of about 400 dm³ with a seawater content of less than 12% was released from the sand boil within 7 h.
... Basically, SGD is composed of terrestrial freshwater and circulated seawater driven by various forces such as convection, tidal pumping, wave set-up, terrestrial hydraulic gradient and density gradient. A significant part of SGD is of marine origin, i.e. seawater-groundwater circulation across the aquifer-sea interface (Li et al. 1999;Moore 1996;Simmons 1992). The amount of SGD varies spatially and temporally because of variations in recharge, tides, density, hydraulic gradient, complexity and heterogeneity of aquifer formation (Bokuniewicz et al. 2003). ...
A three-dimensional variable-density finite element model was developed to quantify the impact of groundwater over use on submarine groundwater discharge (SGD). The model was applied to the Arani-Korttalaiyar river basin, north of Chennai, India. This region has an upper unconfined and lower semi-confined aquifer extending up to 30 km inland from the coast and beyond this distance; the two aquifers merge and become a single unconfined aquifer. The model simulated that during the period from 2000 to 2012, the flux of seawater to the aquifer has increased from 17,000 to 24,500 m3/day due to over-exploitation of groundwater from the semi-confined aquifer. Where as in the unconfined aquifer, SGD has been taking place. Scenarios showing the impact of newly constructed managed aquifer recharge structures, 10% additional increase in rainfall recharge, and termination of pumping from five well-fields on the groundwater conditions in the area were studied. The model predicted a SGD of 85,243 m3/day from the unconfined aquifer and 22,414 m3/day from the semi-confined aquifer by the end of 2030. By adopting managed aquifer recharge methods, seawater intrusion (rate of 4,408 m3/day) can be reduced and SGD (rate of 22,414 m3/day) increased. The rate of SGD increase and the movement of seawater to aquifer can be completely prevented in the semi-confined aquifer by adopting these management options by 2030. Findings from this study have enhanced the understanding of SGD and water budget, which can be used by decision-makers for the sustainable management of groundwater resources in coastal aquifers.
... In general, the main driving forces of SGD were affected by hydraulic gradients between the land and ocean, tidal and wave pumping, convection-driven processes, and precipitation 1,5,44 . In particular, during storms and typhoons, wave pumping rates can increase by orders of magnitude exceeding the rates of fresh water inputs from runoff and SGD 7 . ...
We examined the residence time, seepage rate, and submarine groundwater discharge (SGD)-driven dissolved nutrients and organic matter in Hwasun Bay, Jeju Island, Korea during the occurrence of a typhoon, Kong-rey, using a humic fluorescent dissolved organic matter (FDOM H )-Si mass balance model. The study period spanned October 4–10, 2018. One day after the typhoon, the residence time and seepage rate were calculated to be 1 day and 0.51 m day ⁻¹ , respectively, and the highest SGD-driven fluxes of chemical constituents were estimated (1.7 × 10 ⁶ mol day ⁻¹ for dissolved inorganic nitrogen, 0.1 × 10 ⁶ mol day ⁻¹ for dissolved inorganic phosphorus (DIP), 1.1 × 10 ⁶ mol day ⁻¹ for dissolved silicon, 0.5 × 10 ⁶ mol day ⁻¹ for dissolved organic carbon, 1.6 × 10 ⁶ mol day ⁻¹ for dissolved organic nitrogen, 0.4 × 10 ⁶ mol day ⁻¹ for particulate organic carbon, and 38 × 10 ⁶ g QS day ⁻¹ for FDOM H ). SGD-driven fluxes of dissolved nutrient and organic matter were over 90% of the total input fluxes in Hwasun Bay. Our results highlight the potential of using the FDOM H -Si mass balance model to effectively measure SGD within a specific area (i.e., volcanic islands) under specific weather conditions (i.e., typhoon/storm). In oligotrophic oceanic regions, SGD-driven chemical fluxes from highly permeable islands considerably contribute to coastal nutrient budgets and coastal biological production.
... Saline SGD is clearly a global phenomenon (Kwon et al., 2014;Moore et al., 2008), but most direct evidence for SGD far from shore comes from the South Atlantic Bight, offshore of the southeastern United States. For example, seepage meters deployed for up to 5 days near the boundary between North and South Carolina reported greater SGD 37 km offshore than 0.5 km offshore (Simmons, 1992). In the same region, thermal data from wells installed 20 km offshore revealed tidally driven exchange at one site (Moore et al., 2002) but constant saline groundwater discharge (1 cm/day) at another (Moore & Wilson, 2005). ...
Marine tracer studies indicate that large volumes of saline groundwater discharge to the ocean in passive margin settings. These results have not found widespread recognition because the location and cause(s) of this submarine groundwater discharge (SGD) are unclear. Here we report observations from a new long‐term seafloor monitoring network in the South Atlantic Bight that support large‐scale SGD far from shore. In the study area near Charleston, South Carolina, we determined hydrostratigraphy via vibracoring and chirp seismic surveys, collected water samples from seafloor wells, and used heat as a tracer to monitor SGD. We detected significant pulses of saline SGD issuing from the seafloor 10–15 km from shore. These pulses coincided with abrupt sea level declines of up to 30 cm. Based on an analysis of marine conditions at the time, we propose that upwelling‐favorable winds depressed sea level in the region, causing saline groundwater to discharge from confined coastal aquifers that connect land and ocean. The combination of stacked confined aquifers and variations in sea level are nearly ubiquitous in passive coastal margins. This previously overlooked combination can explain a wide range of other published observations and promotes more dynamic flows than simple tidal fluctuations. This new mechanism may explain Ra tracer signals in the coastal Atlantic Ocean and supports significant nutrient inputs to the ocean. These large natural geochemical fluxes may be sensitive to groundwater usage on land.
... SGD contributed dissolved solutes/nutrients to coastal ecosystems may often have harmful eAects on coastal ecosystem (Johannes 1980;Zektser et al. 2006;Beck et al. 2015). SGD derived nutrient Cux may cause eutrophication leading to growth of algal blooms (Simmons 1992;Valiela et al. 2002;Hwang et al. 2005;Null et al. 2012). ...
The present study is undertaken in the eastern coast of India, along the coastal tract of Bay of Bengal (BoB), to delineate the submarine groundwater discharge (SGD)-borne nutrient flux at temporal scale and their impact to coastal ecology and biogeochemical processes. Solutes chemistry, seepage meter study, stable-isotopic signature, and geophysical techniques were used to identify the surface water–groundwater interaction zone, SGD rate and nutrient flux. The estimated rate of major annual discharge of nutrient fluxes were 240 and 224 mM m⁻² day⁻¹ for NO3⁻ and Fetot. The variation of solute and nutrient fluxes was depending on the load of terrestrial water masses, which is triggered by the local monsoonal meteoric recharge. The ecohydrological response to this solute flux results in spatio-temporal patterns of N and P-sensitive algal blooms in the intertidal zones. Most algae were identified as dinoflagellates and some haptophytes, with greenish and brownish hue that provides a distinct look to the coastal landscape. The algal blooms were found to be substantially influenced by the seasonal-nutrients flux and discharge location. Our study is expected to increase the understanding of a rarely reported eco-hydrological response to terrestrial–marine water interactions and their implications in the tropical ocean adjoining the Indian Subcontinent.
... As such, fresh groundwater discharges in a freshwater tube between the USP and the saltwater wedge ( Figure 1; Abarca et al., 2013;Boufadel, 2000;Buquet et al., 2016;Dale & Miller, 2007;Heiss & Michael, 2014;Kuan et al., 2012;Robinson, Gibbes, et al., 2007;Robinson et al., 2006;Vandenbohede & Lebbe, 2007). Tide-induced circulation across the aquifer-sea interface has been shown to contribute greatly to the total SGD (Li et al., 1999;Moore et al., 2008;Robinson, Li, & Barry, 2007;Robinson et al., 2018;Yu et al., 2019) and influences the transport pathway and fate of land-sourced chemicals in the aquifer prior to discharge to the ocean (Anwar et al., 2014;Burnett et al., 2003;Charette & Buesseler, 2004;Heiss et al., 2017;Heiss & Michael, 2014;Moore, 1999;Robinson et al., 2009;Santos et al., 2008;Santos et al., 2014;Simmons, 1992). Furthermore, tides also affect the location of the lower saltwater wedge interface and thickness of the saltwater-freshwater mixing zone. ...
Tides and seasonally varying inland freshwater input, with different fluctuation periods, are important factors affecting flow and salt transport in coastal unconfined aquifers. These processes affect submarine groundwater discharge (SGD) and associated chemical transport to the sea. While the individual effects of these forcings have previously been studied, here we conducted physical experiments and numerical simulations to evaluate the interactions between varying inland freshwater input and tidal oscillations. Varying inland freshwater input was shown to induce significant water exchange across the aquifer‐sea interface as the saltwater wedge shifted landward and seaward over the fluctuation cycle. Tidal oscillations led to seawater circulations through the intertidal zone that also enhanced the density‐driven circulation, resulting in a significant increase in the total SGD. The combination of the tide and varying inland freshwater input, however, decreased the SGD components driven by the separate forcings (e.g., tides and density). Tides restricted the landward and seaward movement of the saltwater wedge in response to the varying inland freshwater input in addition to reducing the time delay between the varying freshwater input signal and landward‐seaward movement in the saltwater wedge interface. This study revealed the nonlinear interaction between tidal fluctuations and varying inland freshwater input will help to improve our understanding of SGD, seawater intrusion, and chemical transport in coastal unconfined aquifers.
... warranting reasonable approaches to production such that any development can satisfy current needs as well as those of future generations (van der Gun and Lipponen 2010). The understanding of mechanisms behind emplacement and subsequent preservation of these freshwater reservoirs have been the subject of many studies e.g., Povinec et al. 2006;Simmons 1992;Dinnel and Wiseman 1986), which signifies a broadening of the hydrogeological domain to encompass the offshore environment. However, the dynamic preservation and lifetime of freshwater in the offshore environment remains an open hydrogeological problem (Fig. 1). ...
The existence of submarine fresh groundwater has been recorded at continental shelves worldwide. The dynamic preservation and lifetime of fresh groundwater in the offshore environment remains an open hydrogeological problem. The mechanisms and time scales of fresh groundwater preservation are examined using numerical simulations based on a geologically representative model of the New Jersey shelf, USA. Utilizing two-dimensional depth-migrated seismic and well data, a detailed hydrogeological model is built, with a vertical resolution of 10 m. The model captures the highly heterogeneous shelf environment and accounts for porosity compaction trends derived from core data. The results show transient coupled simulations of groundwater flow and heat and salt transport from the late Pleistocene until present day and projected 18,000 years into the future. They reveal freshwater preservation patterns and yield simulated borehole salinity profiles broadly consistent with field observations. The simulations show that freshwater intervals of a thickness of 200–300 m and lateral extent of tens of kilometers may have been preserved from the Last Glacial Maximum until today. It was found that approximately 30–45% of the initial freshwater volume remains preserved after 12,000 years, depending on the recharge boundary condition. The preserved volume ranges between 15 and 30% after 30,000 years. These results improve the understanding of submarine preservation of fresh groundwater through an interdisciplinary approach which integrates seismic imaging, hydrogeological modeling and high-performance numerical simulation.
... The intruded salt water is subsequently returned to the ocean with the fresh water discharging, thereby forming a salt-fresh water circulation near the coastline. Especially, the fresh water discharge into the ocean provides a transport pathway for chemicals from adjacent aquifers to the marine environment (Simmons Jr 1992;Church 1996;Taniguchi et al. 2002;Moore et al. 2008). The aforementioned processes are therefore expected to be susceptible to temporal flow fluctuations, such as tidal oscillations. ...
This study employed a coupled water‐air two‐phase flow and saltwater transport model to analyze the behaviors of generated airflow in unsaturated zones and the fluctuations of salinity at the salt‐freshwater interface in a two‐layered unconfined aquifer with a sloping beach surface subjected to tidal oscillations. The simulation results show that as the new dynamic steady‐state including effects of tidal fluctuations is reached through multiple tidal cycles, the dispersion zone in the lower saltwater wedge is broadened because freshwater/saltwater therein flows continuously landward or seaward during tidal cycles. The upper salt‐freshwater interface exhibits more vulnerable to the tidal fluctuations, and the variation of salinity therein is periodic, which is irrelevant to the hydraulic head but is influenced by the direction and velocity of surrounding water‐flow. With the tidal level fluctuating, airflow is mainly concentrated in the lower permeable layer due to the restraint of the upper semi‐permeable layer, and the time‐lag between the pore‐air pressure and the tidal level increases with distance from the coastline. The effect of airflow in unsaturated zones can be transmitted downward, causing both the magnitude of salinity and its amplitude in the upper salt‐freshwater interface to be smaller for the case with airflow than without airflow due to the resistance of airflow to water‐flow. Sensitivity analysis reveal that distributions of airflow in unsaturated zones are affected by the permeability of the upper/lower layer and the van Genuchten parameter of the lower layer, not by the van Genuchten parameter of the upper layer, whereas the salinity fluctuations in the salt‐freshwater interface are affected only by soil parameters of the lower layer. This article is protected by copyright. All rights reserved.
... Submarine Groundwater Discharge (SGD) is broadly defined as the flow of water from the seafloor to the ocean, regardless of its origin as terrestrial or marine water, or a mixture thereof [1]. It is increasingly apparent that SGD is a process of significant ecological importance in the world's oceans, as a major transport mechanism for both nutrients and contaminants [2,3]. SGD is generated through three main pathways [1]: ...
The Southern Ocean receives limited liquid surface water input from the Antarctic continent. It has been speculated, however, that significant liquid water may flow from beneath the Antarctic Ice Sheet, and that this subglacial flow carries that water along with dissolved nutrients to the coast. The delivery of solutes, particularly limiting nutrients like bioavailable iron, to the Southern Ocean may contribute to ecosystem processes including primary productivity. Using a helicopter-borne time domain electromagnetic survey along the coastal margins of the McMurdo Dry Valleys region of Southern Victoria Land, Antarctica, we detected subsurface connections between inland lakes, aquifers, and subglacial waters. These waters, which appear as electrically conductive anomalies, are saline and may contain high concentrations of biologically important ions, including iron and silica. Local hydraulic gradients may drive these waters to the coast, where we postulate they emerge as submarine groundwater discharge. This high latitude groundwater system, imaged regionally in the McMurdo Dry Valleys, may be representative of a broader system of Antarctic submarine groundwater discharge that fertilizes the Southern Ocean. In total, it has the potential to deliver tens of gigagrams of bioavailable Fe and Si to the coastal zone.
... Researchers found that episodic processes such as wind-driven upwelling (Andrews and Gentien 1982), internal waves (Andrews 1983), or terrestrial discharge events (Wolanski and van Senden 1983) could transport large amounts of 'new' nutrients to reefs. Additionally, evidence of direct inputs of nitrogen from groundwater discharge (Simmons Jr 1992) or nitrogen fixation (Larkum et al. 1988) on the reef flat were found in particular systems. More recently, researchers found that the smallest plankton (pico-and nanoplankton, < 2 µm) had been overlooked in earlier studies due to sampling protocols. ...
Tide-dominated reefs experience mean tidal ranges in excess of local mean significant wave heights. Despite being common (~one third of reefs worldwide), almost no studies have focused on how the large tidal forcing of these systems controls the physical and biogeochemical properties of overlying waters and, thus, community ecological processes. This study was conducted in the remote and near-pristine Kimberley region of northwest Australia at Tallon Island. A one-dimensional control volume approach was used to estimate: 1) community production and respiration; 2) chlorophyll a and particulate nutrient fluxes: and 3) dissolved nutrient uptake and release on the reef platform.
... The combined error associated with our assumptions is difficult to quantify for the near-global coast. However, in a comparison of 10 sites from the continental United States (Bokuniewicz, 1980;Bokuniewicz et al., 2004;Hays & Ullman, 2007;Mulligan & Charette, 2006;Reay et al., 1992;Russoniello et al., 2013;Santos et al., 2009;Simmons, 1992;Uddameri et al., 2014;Zimmermann et al., 1985), our water budget analysis yields similar estimates of fresh SGD as seepage meter studies (Sawyer et al., 2016), other water budget calculations, and validated three-dimensional groundwater flow models (Befus et al., 2017;Zhou et al., 2018; supporting information Figure S1). Our estimates tend to be lower than field-based estimates, likely because of our conservative approach for delineating coastal recharge areas, which would tend to exclude groundwater imports from upland basins. ...
The flow of fresh groundwater to the ocean through the coast (fresh submarine groundwater discharge or fresh SGD) plays an important role in global biogeochemical cycles and coastal water quality. In addition to delivering dissolved elements from land to sea, fresh SGD forms a natural barrier against salinization of coastal aquifers. Here we estimate groundwater discharge rates through the near‐global coast (60°N to 60°S) at high resolution using a water budget approach. We find that tropical coasts export more than 56% of all fresh SGD, while midlatitude arid regions export only 10%. Fresh SGD rates from tectonically active margins (coastlines along tectonic plate boundaries) are also significantly greater than passive margins, where most field studies have been focused. Active margins combine rapid uplift and weathering with high rates of fresh SGD and may therefore host exceptionally large groundwater‐borne solute fluxes to the coast.
... At individual sites, there was generally little agreement between fresh SGD flux estimates from groundwater flow models and water budgets (Figure 4b). To explore the widely ranging flux discrepancies, fresh SGD flux estimates were compared with measurements from seepage meters or other shore-based approaches for 10 sites along the U.S. Atlantic and Gulf Coasts (Bokuniewicz, 1980;Bokuniewicz et al., 2004;Hays & Ullman, 2007;Mulligan & Charette, 2006;Reay et al., 1992;Russoniello et al., 2013;Santos et al., 2009;Simmons, 1992;Uddameri et al., 2014;Zimmermann et al., 1985). The studies were chosen because they used direct near-shore measurements of SGD that were likely to capture flow from the unconfined aquifer, analogous to our computational estimates. ...
The fresh component of submarine groundwater discharge (fresh SGD) transports nutrient and contaminant loads from land to sea. Fresh SGD fluxes are poorly known but depend on geology, topography, climate, and land use. Here we assess two general approaches for quantifying the magnitude of fresh SGD over regional to continental scales—water budgets (lumped parameter models) and groundwater flow models—focusing on the U.S. Atlantic and Gulf Coasts as a large-scale case study. Estimates of fresh SGD fluxes from groundwater flow models are more variable than estimates from water budgets, and both are often less than field-based estimates. Both approaches predict the volume of fresh SGD within approximately 50% of 12.3 km³/year, in line with previous estimates, and differences are largely driven by hydrographic data inputs. The simplified water budget approach, while computationally cheap, cannot resolve flow paths or continuous flux distributions and may neglect groundwater flow from deep aquifers or distal recharge zones. Conversely, three-dimensional groundwater flow models can resolve flow paths and fresh SGD contributions from heterogeneous aquifer systems but are computationally expensive and require more parameterization. Ultimately, multiple models and integrated field data are needed to improve our estimates of fresh SGD fluxes over a wide range of scales.
... The increase in discharge detected at the more offshore locations may be induced by the action of waves generating benthic exchange or recirculation flow (Simmons, 1992;Li, Barry, Stagnitti, & Parlange, 1999;Michael et al., 2003) (Figure 8, C). Wave pumping should generate a net flux of zero due to the same amount of flow going in and out (Santos, Eyre, & Huettel, 2012). ...
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.
... Both T-SGD and M-SGD play important roles in nutrient cycling (Li et al. 1999;Michael et al. 2005). Nutrient flux via SGD may cause eutrophication (Simmons 1992;Valiela et al., 2002;Paerl 2009;Null et al., 2012) leading to harmful algal blooms (Hwang et al., 2005). ...
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.
... Namun pada penelitian tersebut belum ada yang mempelajari tentang dampaknya terhadap habitat dimana KALP tersebut berada. Meskipun beberapa penelitian seperti Bakti et al. (2012) menyatakan bahwa KALP dapat bermanfaat bagi karang seperti mengontrol kadar salinitas, juga dapat menjaga habitat ekologi laut karena dapat sebagai sumber nutrisi dalam menjaga keseimbangan nitrogen pada lingkungan terumbu karang (D'Elia et al., 1981;Umezawa et al., 2002), namun secara umum Simmons (1992) menyatakan KALP selain berpengaruh positif terhadap lingkungan di sekitar, bisa juga menjadi ancaman bagi karang karena membawa kondisi kualitas air yang tidak cocok bagi pertumbuhan karang. ...
Researches related to Submarine Groundwater Discharge (SGD) still rare in Indonesia and research to look at the impact of SGD on coral reefs for the first time carried out primarily related to the condition of reefs in the area. This study aimed to examine the impact of SGD to the condition of coral reefs using line transect method as much as 3 replicates with a length of 20 m. Belt transect width of 2 m and a length of 20 m with a repeat 3 times used to see an abundance of coral diseases in a location about 1.5 km from the SGD/spring source. The results showed there were differences between the groups category coral conditions of SGD location that is lower than 50%, which included bad condition (18.18% location 1 and 45.79% location 2) with a predominance of dead coral cover 30.85% and coral rubble 10:53%. At the location far from SGD source, have good
coral conditions since it has live coral cover over 50% (51.37%). The existence of coral disease “Yellow Syndrome” and “Black Band Disease” was not found in either location SGD, but there is at location 3 that are far from SGD source, found with high abundance.
Keywords : Submarine Groundwater Discharge, coral condition, changed indicator, North Lombok.
... Thus, our groundwater models estimated that CGWD for the eastern U.S. was up to twice as large as the previous model calculated for both coastlines. Despite having much larger integrated fluxes, our models often predicted smaller magnitude CGWD fluxes for specific coastal areas when compared to both the contiguous U.S. water budget analysis and field studies (Figure 2c) (Bokuniewicz, 1980;Bokuniewicz et al., 2004;Cambareri & Eichner, 1998;Hays & Ullman, 2007;Kroeger et al., 2007;Mulligan & Charette, 2006;Reay et al., 1992;Russoniello et al., 2013;Santos et al., 2009;Simmons, 1992;Thompson et al., 2007;Uddameri et al., 2014;Zimmermann et al., 1985). ...
Fresh groundwater discharge to coastal environments contribute to the physical and chemical conditions of coastal waters, but the roles of coastal groundwater at regional to continental scales remains poorly defined due to diverse hydrologic conditions and the difficulty of tracking coastal groundwater flow paths through heterogeneous subsurface materials. We use three-dimensional groundwater flow models for the first time to calculate the magnitude and source areas of groundwater discharge from unconfined aquifers to coastal waterbodies along the entire eastern U.S. We find 27.1 km3/yr (22.8-30.5 km3/yr) of groundwater directly enters eastern U.S. and Gulf of Mexico coastal waters. The contributing recharge areas comprised ~175,000 km2 of U.S. land area, extending several kilometers inland. This result provides new information on the land area that can supply natural and anthropogenic constituents to coastal waters via groundwater discharge, thereby defining the subterranean domain potentially affecting coastal chemical budgets and ecosystem processes.
... There are two major components of SGD: the submarine fresh groundwater discharge (SFGD) and the recirculated saline groundwater discharge (RSGD) (Li et al., 1999;Taniguchi et al., 2002). Many studies have indicated that SGD may carry large quantities of nutrients and trace metals to the ocean (Krest et al., 2000;Moore, 1996;Simmons, 1992), and can be the principal mechanism for eutrophication including the outbreak of red tides in many coastal embayments (e.g., Hu et al., 2006;Lee et al., 2010;Luo and Jiao, 2016). SGD is usually characterized by high N: P ratios due to the rapid removal of DIP from groundwater (Slomp and van Cappellen, 2004). ...
In Jiaozhou Bay, there are four wetland types, including sandy beaches, mud flats, tidal marshes, and estuarine intertidal zones. Four typical transects representing each of the wetland types were selected to investigate the flow dynamics, seawater-groundwater exchange and nutrients carried by submarine groundwater discharge (SGD). Based on field measurements of groundwater heads and salinity along each transect, the SGD averaged over the observation period was estimated using generalized Darcy's law. The SGD along the four transects ranges from 3.6 × 10⁻³ to 7.6 cm/d with the maximum occurring at the sandy beach. The SGD rate has a good correlation with the hydraulic conductivities of the wetland sediments. There is a positive correlation between the ratio of NO3-N/DIN and SGD rates. The SGD-associated nutrient output rate ranges from 3.3 × 10⁻² to 9.5 mmol/m²/d for DIN (dissolved inorganic nitrogen), and from 6.2 × 10⁻⁵ to 1.8 × 10⁻² mmol/m²/d for DIP (dissolved inorganic phosphorus). Compared to the nutrients delivered by the river, nutrients carried by SGD provide a more important source for the phosphate-limited environment to plankton in Jiaozhou Bay.
... Furthermore, we did not observe any significant release of alkalinity (A T ) from the sediments to the overlying water column, providing further insight into the dominant reactions taking place within 1 Introduction 20 A fraction of the particulate organic matter (POM) generated photosynthetically in the euphotic zone settles to the sediment where microbes utilize a variety of electron acceptors to respire this organic material producing dissolved inorganic carbon (DIC) and nutrients. As a result, sediment pore waters become highly concentrated in many chemical constituents relative to the overlying water column (Moore et al., ments (Colbert and Hammond, 2008;Hancock et al., 2006;Simmons Jr., 1992), and modelling the biogeochemistry of chemical fluxes across the sediment-water interface (Fennel et al., 2009). While the relative magnitude of the benthic fluxes can vary greatly over regional scales, balancing of biogeochemical budgets in oceanic environments requires the consideration of sediment-water column interac-15 tions. ...
Exchanges between sediment pore waters and the overlying water column play a significant role in the chemical budgets of many important chemical constituents. Quantification of such benthic fluxes requires explicit knowledge of the sediment properties and biogeochemistry. Alternatively, changes in water column properties near the sediment-water column interface can be exploited to gain insight into the sediment biogeochemistry and benthic fluxes. Here, we apply a 1-D diffusive mixing model to near-bottom water column profiles of 224Ra activity in order to yield vertical eddy diffusivities (KZ), based upon which we assess the diffusive exchange of inorganic carbon (DIC), nutrients and oxygen (O2), across the sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia, Canada. Near-bottom observations of DIC, O2 and nutrients provide flux ratios similar to Redfield values, suggesting that benthic respiration of primarily marine organic matter is the dominant driver. Furthermore, we did not observe any significant release of alkalinity (AT) from the sediments to the overlying water column, providing further insight into the dominant reactions taking place within sediments: the respiration of organic matter occurs largely under aerobic conditions or products of anaerobic processes are reoxidized quickly in oxygenated layers of the sediments. Finally, comparison with other carbon sources reveal the observed benthic DIC release as a significant contributor to the Bedford Basin carbon system.
... Este processo é importante para a produtividade biológica e até mesmo em processos de remineralização geológica (Simmons, 1992). Em 2006, Mulligan & Charette descreveram este processo como fonte principal de nutrientes em diversos estuários e baías, de considerável efeito ecológico, enquanto que Corbett et al. (1999) estimaram que essa contribuição chega a ser aproximadamente igual à contribuição via escoamento superficial em alguns locais. ...
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.
... As demand for freshwater is expected to increase due to population growth (Postel, 1998), impacts on freshwater releases and reduced riverine flows are anticipated to be substantial, especially in arid and semi-arid regions where climate change will simultaneously reduce precipitation and increase evaporation (Kirtman et al., 2013). Studies in these areas indicate that elevated salinity levels in subsurface discharge to coastal waters are associated with recirculated seawater (Moore and Church, 1996;Simmons et al., 2001;Simmons, 1992). However, high evaporation rates characteristic to arid and semi-arid areas that increase the salt content in soils and bottom sediments of surface waters could play a significant role in salinization of surficial aquifers (Bighash and Murgulet, 2015;Schmidt and Garland, 2012). ...
Hydrologic alterations in coastal rivers and semi-arid climates affect water chemistry. • Stable isotopes of δ 18 O and δD constrain well the magnitude of groundwater contribution. • Variable degrees of groundwater discharge occur downstream and upstream of the dam. • Electrical resistivity methods show sources and quality of groundwater discharge. • Evaporation effects significantly alter surface water and groundwater quality. There is a lack of understanding and methods for assessing the effects of anthropogenic disruptions, (i.e. river fragmentation due to dam construction) on the extent and degree of groundwater-surface water interaction and geochemical processes affecting the quality of water in semi-arid, coastal catchments. This study applied a novel combination of electrical resistivity tomography (ERT) and elemental and isotope geochemistry in a coastal river disturbed by extended drought and periodic flooding due to the operation of multiple dams. Geochemical analyses show that the saltwater barrier causes an increase in salinity in surface water in the downstream river as a result of limited freshwater inflows, strong evaporation effects on shallow groundwater and mostly stagnant river water, and is not due to saltwater intrusion by tidal flooding. Discharge from bank storage is dominant (~ 84%) in the downstream fragment and its contribution could increase salinity levels within the hyporheic zone and surface water. When surface water levels go up due to upstream freshwater releases the river temporarily displaces high salinity water trapped in the hyporheic zone to the underlying aquifer. Geochemical modeling shows a higher contribution of distant and deeper groundwater (~40%) in the upstream river and lower discharge from bank storage (~13%) through the hyporheic zone. Recharge from bank storage is a source of high salt to both upstream and downstream portions of the river but its contribution is higher below the dam. Continuous ERT imaging of the river bed complements geochemistry findings and indicate that while lithologically similar, downstream of the dam, the shallow aquifer is affected by salinization while fresher water saturates the aquifer in the upstream fragment. The relative contribution of flows (i.e. surface water releases or groundwater discharge) as related to the river fragmentation control changes of streamwater chemistry and likely impact the interpretation of seasonal trends.
... Menurut Simmons (1992), keseimban gan habitat ekologi laut dapat terjaga den gan adanya kehadiran suplai air tawar ke wilayah laut melalui KALP. KALP ini juga berperan sebagai sumber nutrisi dalam men jaga ke seimbangan nitrogen pada lingkung an te rumbu karang (D'Elia et al.,1981dan Umezawa et al., 2002dalam Taniguchi et al., 2005, sumber nutrisi dan spesies terlarut lain nya, termasuk pencemaran ke laut dan ekosis temnya (Unesco, 2004;2005, dan Burnett et al., 2006. ...
... SGD has potential to create estuarine conditions near the SGD locations, which can alter local benthic habitats and ecology. The movement of water across the sediment/water interfaces is very important to the ecology of aquatic habitats (Simmons 1992) because the groundwater might deliver contaminants to coastal waters. According to Barlow (2003), coastal groundwater systems have been contaminated by numerous chemical pollutants, however, the major concern is excessive nutrient loads, particularly due to nitrogen transport to the coastal environments, which occurs as a consequence of activities such as wastewater disposal from septic tanks and agricultural and urban use of pesticides and fertilizers. ...
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.
... Saline SGD is clearly a global phenomenon (Kwon et al., 2014;Moore et al., 2008), but most direct evidence for SGD far from shore comes from the South Atlantic Bight, offshore of the southeastern United States. For example, seepage meters deployed for up to 5 days near the boundary between North and South Carolina reported greater SGD 37 km offshore than 0.5 km offshore (Simmons, 1992). In the same region, thermal data from wells installed 20 km offshore revealed tidally driven exchange at one site (Moore et al., 2002) but constant saline groundwater discharge (1 cm/day) at another (Moore & Wilson, 2005). ...
... At some sites with little or no surface flow, SGD is the only pathway by which terrestrial nutrients are transported to the sea. These sites include volcanic islands such as Hawai`i (Kay et al., 1977;Oki, 1999) and Jeju Island, Korea (Kim et al., 2003), karst environments such as the Yucatan Peninsula of Mexico Young et al., 2008), Florida (Brooks, 1961;Simmons, 1992;Corbett et al., 1999), and Jamaica (D'Elia et al., 1981), and arid locations such as Eilat, Israel . In some locations where rivers are present, groundwater nutrient loads are comparable to, or greater than, river-borne loads (e.g., Crotwell and Moore, 2003;Garrison et al., 2003;Burnett et al., 2007); however, in other locations, SGD is likely to be a negligible contributor to the nutrient budget (Burnett et al., 2001). ...
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.
... It has been recognized over the last two decades that variation of submarine groundwater discharge (SGD) would significantly affect a costal region's physical, chemical and ecological environments (Moore 1996;Li et al. 1999;Bokuniewicz 2001;Simmons 1992;Taniguchi et al. 2002, Burnett et al. 2003. Thus, the discharge location and quantification of SGD have become important research issues for marine scientists, coastal geologists and hydrologists. ...
There are many factors affecting submarine groundwater discharge (SGD). However, systematic study of the influences of these factors is still limited. In this study, numerical modeling is performed to quantitatively explore the influences of various factors on SGD in a coastal aquifer. In such locations, tidal and terrestrial hydraulic gradients are the primary forces driving fresh and salt water movement. Unlike steady-state flow, dynamic fresh and salt water mixing at the near-shore seafloor may form an intertidal mixing zone (IMZ) near the surface. By constructing a general SGD model, the effects of various model components such as boundary conditions, model geometry and hydraulic parameters are systematically studied. Several important findings are obtained from the study results: (1) Previous studies have indicated there will be a freshwater discharge tube between the classic transition zone and the IMZ. However, this phenomenon may become unclear with the increase of heterogeneity and anisotropy of the medium’s conductivity field. (2) SGD and IMZ are both more sensitive to the vertical anisotropy ratio of hydraulic conductivity (Kx/Kz) than to the horizontal ratio (Kx/Ky). (3) Heterogeneity of effective porosity significantly affects SGD and IMZ. (4) Increase of the storage coefficient decreases fresh water discharge but increases mixing salt water discharge and total SGD. The increase will also change the shape of the IMZ. (5) Variation of dispersivities does not affect SGD, but significantly changes the distributions of the IMZ and the whole mixing zone. These findings will be helpful to the sampling design of field studies of SGD and to the application of dynamic SGD models to field sites for model development and calibration.
... Seawater circulation in coastal aquifers, which is a major component of submarine groundwater discharge (SGD), has been recognized as a process that affects trace element and nutrient mass balances of coastal areas (e.g. Simmons, 1992;Moore et al., 2008;. SGD was shown to contribute Ca, Ba and Sr to the Bengal Basin in the same order of magnitude as river fluxes (Basu et al., 2001;Dowling et al., 2003). ...
Radium isotopes in the Dead Sea Lake and the surrounding aquifer were studied in order to define the processes controlling their activities in the lake and in the groundwater. 226Ra activities in the groundwater show a significant removal of 226Ra from the lake water as they enter the aquifer. Short-lived radium isotopes show a nonlinear relation with salinity which is caused by the effect of salinity on the adsorption of radium. Simulations of radium distribution in the aquifer, using the code of SUTRA-MS, were done in order to estimate the adsorption distribution coefficient of radium in the aquifer. 228Ra activities in the Dead Sea water are much higher than the expected activities according to the radium sources to the Dead Sea. These observations together with the removal of 226Ra in the Dead Sea groundwater may indicate a large-scale saline water circulation in the aquifer.
Meteoric groundwater discharge (MGD) to coastal regions transports terrestrial freshwater and nutrients that may alter coastal ecosystems by supporting harmful algal blooms. Estimation of MGD-driven nutrients is crucial to assess potential effects on coastal zones. These estimates require a reliable assessment of MGD rates and pore water nutrient concentrations below subterranean estuaries. To estimate nutrient delivery into a subterranean estuary in the Indian River Lagoon, FL., pore water and surface water samples were collected from nested piezometers along a selected transect on five sampling episodes. Groundwater hydraulic head and salinity were measured in thirteen onshore and offshore piezometers. Numerical models were developed, calibrated, and validated using SEAWAT to simulate MGD flow rates. Lagoon surface water salinity exhibits no spatial but mild temporal variation between 21 and 31. Pore water salinity shows tremendous variation in time and space throughout the transect except in the middle region of the lagoon which exhibits uniform but elevated salinities up to 40. Pore water salinity as low as that of freshwater happens to occur in the shoreline regions during most of the sampling episodes. Both pore water and surface water show remarkably higher total nitrogen TN than total phosphorus TP concentrations and most TN is exported as NH4, reflecting the effect of mangroves on the geochemical reactions that reduce NO3 into NH4. Nutrient contributions of pore water and lagoon water exceed the Redfield TN/TP molar ratio in all sampling trips by up to a factor of 48 and 4, respectively. Estimated TP and TN fluxes receives by the lagoon via MGD are 41-106 and 113-1478 mg/d/m of shoreline. The molar TN/TP ratio of nutrient fluxes exceeds the Redfield ratio by a factor of up to 3.5 which indicates the potential of MGD-driven nutrients to alter the lagoon water quality and support harmful algal blooms.
The influx of fresh groundwater and re-circulated sea water into coastal ecosystem occurs through the submarine groundwater discharge (SGD). Measurement of salinity, radium tracers (²²⁴Ra, and ²²⁶Ra isotopes) and nutrients in estuarine water, coastal surface water and groundwater during December 2019 estimated the SGD and associated nutrient fluxes near the Karameniyar estuary (Gulf of Mannar) and surroundings of the Manapad region at southern part of Tamil Nadu state in India. The presence of excessive radium tracers revealed that the SGD was contributing to Ra desorption from the sediments and enrichment in the coastal waters. We estimated SGD of approximately 0.03–0.59 m³ m⁻² d⁻¹ for the Manapad region and relatively more homogeneous but comparatively less values in the Karameniyar estuary (0.03–0.34 m³ m⁻² d⁻¹). Higher average values of dissolved inorganic nitrogen (DIN; 43.62 μmol L⁻¹) and soluble reactive phosphate (SRP; 1.848 μmol L⁻¹) suggested greater influence of SGD on the overall coastal water nutrient budget. This study also indicated simultaneous occurrence of fresh and saline SGD in this region.
The comment by Julian (2020) criticizes aspects of our paper, “Nitrogen enrichment, altered stoichiometry, and coral reef decline at Looe Key, Florida Keys, USA.” The comment begins by misrepresenting our extensive literature review, while providing no justification for the claim of a “skewed reading.” Julian’s critique focused on methods of data handling, statistics, and spatial awareness, which we demonstrate in every case to be either irrelevant or incorrect. We provide additional supporting data that refute these claims. For example, Julian criticized the removal of data points below the method detection limits (MDLs), but when these points are included, the results do not change. Further, Julian criticized our removal of outliers, but so few points were excluded that it did not change the results of the statistical analyses. Julian also misinterpreted the methods of our correlation and stepwise regression analyses but did not dispute the Kruskal–Wallis tests of our 30-year dataset that revealed significant decadal changes. Julian’s closing paragraph is replete with misinformation and demonstrates a lack of understanding as to how increased freshwater flows associated with Everglades Restoration have led to a worsening of algal blooms and coral decline in the Florida Keys National Marine Sanctuary (FKNMS). This comment represents a smokescreen to confuse the scientific community about the physical connectivity of the Everglades basin and the FKNMS. Past water management policies based on politics, not sound science, have caused irreparable and ongoing environmental damage to sensitive coral reef communities in the FKNMS.
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.
Saltwater intrusion and the recirculation of seawater that occur at the seacoast in coastal aquifers are investigated for vertically isotropic and anisotropic aquifers as dependent functions of two independent dimensionless ratios, i.e., the ratio of the freshwater inflow relative to the vertical density-driven buoyancy flux (az) and the ratio of the vertical hydraulic conductivity relative to the horizontal hydraulic conductivity (rK). Values of az are varied over a range from 0.10 to 10.0 for three cross sections in which rK = 0.01, 0.10, and 1.00. The maximum values of saltwater intrusion and recirculation occur at the smallest values of az = 0.10 and rK = 0.01, and the minimum values occur at the largest values of az = 10.0 and rK = 1.00. Numerical experiments are performed first for the uncoupled condition, in which the flow and transport equations are solved for a constant-density flow field, and then for the coupled condition, in which the flow and transport equations are solved for a variable-density flow field. For all three hydraulic conductivity ratios, saltwater intrusion is significantly greater and the recirculation of seawater is significantly less for the coupled condition than for the uncoupled condition at the smaller values of az. The results of this investigation clearly demonstrate that saltwater intrusion and recirculation in coastal aquifers increase at the smaller values of az as the degree of vertical anisotropy increases, and that variable-density numerical codes should be used to obtain accurate solutions for saltwater intrusion and recirculation in both isotropic and vertically anisotropic coastal aquifers in which the freshwater inflow is small relative to the vertical density-driven buoyancy flux.
A methodology based on γ-spectrometry measurements of untreated coastal water samples is proposed for the direct estimation of coastal residence time of submarine discharged groundwater. The method was applied to a submarine spring at Stoupa Bay covering all seasons. The estimated residence time exhibited an annual mean of 4.6±1.7 d. An additional measurement using the in situ underwater γ-spectromerty technique was performed, in the same site. The in situ method yielded a value of 2.8±0.2 d that was found consistent with the corresponding value derived using the developed lab-based method (3.4±2.0 d) for the same period.
Water dissolving and water removing
Not all groundwater ends up flowing into rivers. Some is discharged directly into the ocean along the coast. Although much lower in volume than water transported by rivers, such submarine groundwater discharge can be a hidden source of dissolved ions, nutrients, or contaminants from human activities. Sawyer et al. performed a high-resolution continental-scale analysis of fresh groundwater discharge along the coastline of the United States. In total, more than one-fifth of coastal waters are vulnerable to groundwater-borne contamination.
Science , this issue p. 705
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 submarine groundwater discharge (SGD) transports a significant amount of various contaminants into the coastal zone especially in tsunami affected areas. An assessment of the impact of intruded pollutants in the coastal ecosystems requires understanding the fate of the pollutants and processes of their dispersal in ambient waters. In this paper, we proposed a methodology for SGD data collection and data assessment, using different methods, technology, techniques and instruments as well as the 3-D coupled ocean circulation/particle-tracking model for assessment and predicting the transport and dispersal of pollution-containing SGD into a coastal environment. Among the proposed methods to use for data collection and the SGD assessment primary attention was paid to geophysical, hydrologic, remote sensing and hydro-geologic measurements, using natural radiotracers, measurements by seepage meters and benthic chambers, biogeochemical and biological measurements. Also, several new modeling approaches were considered in particular those which use the particle-tracking model. The particle-tracking model takes currents and turbulent diffusivities predetermined by the ocean circulation model and uses the Lagrangian approach to predict the motion of individual droplets, the sum of which constitutes a contaminant plume which is the result of discharge of contaminant-rich submarine groundwater. Presently, we limited our simulations to elucidate the effect of tides on the SGD/nitrate plume formation. The model predicts behaviour of a nitrate plume, its shape and variation during a tidal cycle in the shallow waters. The model can be used to predict contamination of coastal waters with various pollutants incoming with SGD in the aftermath of a tsunami when impact of the latter on aquifers can be significant.
Benthic flux is the rate of flow across the bed of a water body, per unit area of bed. It is forced by component mechanisms, which interact. For example, pressure gradients across the bed, forced by tide, surface gravity waves, density gradients, bed-current interaction, turbulence, and terrestrial hydraulic gradients, drive an advective benthic flux of water and constituents between estuarine and coastal waters, and surficial aquifers. Other mechanisms also force benthic flux, such as chemical gradients, bioturbation, and dispersion. A suite of component mechanisms force a total benthic flux at any given location, where each member of the suite contributes a component benthic flux. Currently, the types and characteristics of component interactions are not fully understood. For example, components may interact linearly or nonlinearly, and the interaction may be constructive or referred to, in some literature, as submarine groundwater discharge. Benthic flux is important in characterizing water and constituent budgets of estuarine and coastal systems. Analytical models to characterize selective benthic flux components are reviewed. Specifically, these mechanisms are for the component associated with the groundwater tidal prism, and forced by surface gravity wave setup, surface gravity waves on a plane bed, and the terrestrial hydraulic gradient. Analytical models are applied to the Indian River Lagoon, Florida; Great South Bay, New York; and the South Atlantic Bight in South Carolina and portions of North Carolina.
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.
To address the issue of human sewage reaching corals along the main reef of the Florida Keys, samples were collected from surface water, ground-water and coral [surface mucopolysaccharide layers (SML)] along a 10 km transect near Key Largo, FL. Samples were collected semi-annually between July 2003 and September 2005 and processed for faecal indicator bacteria (faecal coliform bacteria, enterococci and Clostridium perfringens) and human-specific enteric viruses (enterovirus RNA and adenovirus DNA) by (RT)-nested polymerase chain reaction. Faecal indicator bacteria concentrations were generally higher nearshore and in the coral SML. Enteric viruses were evenly distributed across the transect stations. Adenoviruses were detected in 37 of 75 samples collected (49.3%) whereas enteroviruses were only found in 8 of 75 samples (10.7%). Both viruses were detected twice as frequently in coral compared with surface water or groundwater. Offshore, viruses were most likely to be found in groundwater, especially during the wet summer season. These data suggest that polluted groundwater may be moving to the outer reef environment in the Florida Keys.
SHALLOW near-shore ocean waters support high primary production because
of the availability of inorganic nutrients. The availability is usually
attributed to the proximity of fresh-water runoff or to coastal
upwelling and deep water advection1,2.
The freshwater aquifer at Discovery Bay, Jamaica, produces subterranean springs and seeps near the reef at the mouth and along the southern and western shorelines of the bay. A strong inverse correlation exists between salinity and N concentration. Undiluted spring-water typically contains 80 μg at N per liter or more, primarily as nitrate, but is essentially devoid of P. Input from the springs is enough to reduce the salinity by one to several parts per thousand near these sites and appears to produce a significant enrichment of nitrogen to the bay.
Several new techniques were used to identify zones of groundwater and contaminant inflow to the headwaters area of a small stream draining an agricultural watershed in southwestern Ontario. Along a 3 km length of stream, seepage meters were used to measure and collect seepage flux and mini-piezometers were used to measure piezometric head relative to the stream and to collect pore water 0.6 m below the streambed.
Measurement of seepage flux at 43 locations along a 3 km segment of Hillman Creek showed that most of the study section was a groundwater discharge zone. Spatial differences in seepage flux ranged from less than 0.001 to nearly 9 cm m s 1. During the growing season there was a marked diurnal change in seepage rate at several locations and this was also reflected by a corresponding change in stream discharge.
Paired samples, one from a piezometer 0.6 m below streambed and one from the adjacent seepage meter, were significantly correlated (P < 0.01) with respect to specific conductance, chloride and inorganic carbon concentration. This suggested that in many instances site-specific estimates of chemical inputs from groundwater to surface water can be estimated quickly without the necessity of allowing natural groundwater flow to flush out the water initially trapped within the seepage container. Seepage meters can be used to measure seepage flux and the small piezometers can be used to obtain samples. The concentrations of non-conservative solutes (organic carbon, nitrate + nitrite nitrogen, and phospate) in seepage meter samples were not significantly correlated with the concentrations in corresponding mini-piezometer samples.
In situ measurements of inorganic nitrogen fluxes and riverbed oxygen consumption were made on sediments in 3, 9, and 16 m of water at the mouth of the York River during stratified and destratified water conditions. Ammonia was regenerated, the rate of which increased with depth and oxygen concentration in the overlying water. Nitrate and nitrite fluxes from the sediment were minimal or non-existent during stratification at the 16-m station but increased and the nutrients were taken up by the sediments under destratified conditions. At the 3-m station, which is above the halocline when developed, nitrate and nitrite appeared to be the major forms of nitrogen being released by the sediments. Oxygen consumption by the riverbed at the 16 and 9-m stations was higher during the increased oxygen tensions associated with vertical destratification. The 3-m station maintained the highest rates of oxygen consumption throughout the sampling period. The in situ incubation of bottom water alone at all three stations indicated negligible rates of oxygen uptake.
: The construction and irrigation of permanent tube-dwellings by sedentary infaunal benthos result in complex patterns of chemical reactions and diffusion gradients in sedimentary deposits. These patterns are reflected in the three-dimensional distribution of pore water constituents, diagenetically mobile solid phases, biogeochemically important microorganisms, and meiobenthos. The quantitative effect of burrows on transport-reaction processes in sediments is analogous to the effect of roots on terrestrial soils. In contrast to factors which cause heterogeneity, mobile infauna rapidly homogenize sediment and presumably simplify internal gradients. The activities of both mobile and sedentary benthos increase the rates of certain metabolic reactions, such as sulfate reduction, which take place below the sediment-water interface. These same activities increase the flux of dissolved material between sediment and the overlying water to a greater degree than that accounted for by one-dimensional molecular diffusion. Increased exchange rates may obscure the presence of some reactions in sediments by preventing the depletion of reactants or buildup of reaction products. Because biogenic influences on particle and fluid transport in sedimentary deposits reflect the types of organisms present, bottom areas which are inhabited by macrobenthos of varying mobility and feeding type differ in their chemical characteristics. In environments having a large seasonal temperature range, biogenic control of sedimentary chemistry is replaced by abiogenic reaction-diffusion controls during winter periods.
This paper summarizes the hydrogeology of the thick carbonate-evaporite sequence that extends from land surface to the oil horizons at depths of about 11,500 feet below sea level in southern Florida. It sets forth the few known facts about the hydrology of the deep water-bearing rocks and discusses a hypothesis concerning the cyclic flow of salt water related to geothermal heating in the Floridan aquifer. Meinzer (1923, p. 30) defined an aquifer as a "formation, a group of formations, or part of a formation that is water bearing." The connotation of quantity was included by the statement: "Few if any formations are entirely devoid of gravity ground water, but those that do not contain enough to be of consequence as a source of supply are not rated as water bearing." The quality of the water does not enter the definition, for if it did, a change in quality (as by salt-water encroachment) would correspondingly convert aquifers to nonaquifers. This paper treats permeable water-bearing beds as aquifers even though the contained water might be a brine seven times as salty as sea water and, therefore, normally not considered a source of supply.
Ahs tract Benthic fluxes of dissolved nutrients and manganese from biologically disturbed, relatively unpolluted sediment in Narragansett Bay, Rhode Island, have been measured. Analyses of the vertical gradients of chemical species dissolved in port waters and the uptake of 22Na from the overlying water permits evaluation of the contribution of biological advection and molecular diffusion to the transport of dissolved materials across the sediment-water interface. The activity of bottom-dwelling organisms appears to be about as important as molecular diffusion in most cases. The sum of the independently estimated contributions by both mechanisms is in good agreement with integrated benthic fluxes measured in situ. Sulfate and oxygen oxidize comparable amounts of organic matter in these sediments.
ABSTRACT Axiorygmanethertoni is described from material collected in about 30 m of water off the Key Largo area of the Florida Keys, and from 52-58 m in the Gulf of Mexico off the west coast of Florida. The genus is characterized by the possession of sexually dimorphic chelipeds, and by the absence of an appendix masculina in the male. The species burrows in sand flat areas around coral heads, with densities of up to 80/m2. The burrows, usually about 15 cm long, are often blocked by debris such as calcareous algal fragments. The species is considered to play an important role in the transfer of material across the sediment-water interface.
The movement of water across the sediment/water interface in a marine habitat can have an important effect on benthic communities and those communities in the overlying water. Regardless of its source, the fact that water flushes the sediment/water interface represents an important pathway for the movement of chemical ions into the open sea. The purpose of this study was to measure the quantity and quality of submarine groundwater discharge into a deep coral reef habitat using seepage meters and submarine piezometers. Four sites were investigated in the vicinity of Key Largo, Florida. The data from both types of sampling units showed the groundwater had a different chemical composition than ambient seawater. Rates of discharge were independent of tidal action and depth. Use of a manometer demonstrated the presence of a positive hydraulic head on both sampling units. While salinity varied in the sampling units with respect to ambient seawater, the data suggest that a mechanism exists for moving nutrients and trace minerals across the sediment/water interface which may be global in its nature and which may transcend regional or localized effects of groundwater influx through confined aquifers.
In a coastal aquifer a steady flow of fresh water toward the sea can limit the encroachment of the salt water into the aquifer. This action is treated on the assumptions that the flow is steady and two-dimensional, that the salt and fresh water are immiscible, and that there is no fingering. Theoretical equations for the shape and location of the interface and for the boundary velocities are derived for several sets of boundary conditions. The uncertainty of the location of the interface is circumvented by use of a hodograph plane. In addition, a complex potential is employed and related to the hodograph by conformal mapping. Certain boundary conditions represent inversions of gravity seepage through dams for which solutions already exist. Numerical computations are also presented for a semi-infinite aquifer having a vertical seepage face and one having a horizontal seepage face.
The dispersion of salts produced by reciprocative motion of the salt-water front in a coastal aquifer induces a flow of salt water from the floor of the sea into the zone of diffusion and back to the sea. The head losses that accompany the landward flow tend to lessen the extent to which the salt water occupies the aquifer.
Observations over a period of nearly 20 years confirm the fact that the salt-water front in the Biscayne aquifer along the coast of the Miami area, Florida, is dynamically stable at a position seaward of that computed according to the Ghyben-Herzberg principle. During periods of heavy recharge the fresh-water head is high enough to cause the fresh water, the salt water, and the zone of diffusion between them to move seaward. In addition to this bodily movement of the system, there is a seaward flow of diluted salt water in the zone of diffusion. When the fresh-water head is low, salt water in the lower part of the aquifer intrudes inland, but some of the diluted sea water in the zone of diffusion continues to flow seaward. Cross sections showing equipotential lines in terms of equivalent fresh-water head show that the sea water flows inland, becoming progressively diluted with fresh water, to a line along which there is no horizontal component of flow, after which it moves upward and returns to the sea. The cyclic flow acts as a deterrent to the encroachment of sea water because of return to the sea of a part of the inland flow. Introduction. The basic premise of the Ghyben-Herzberg principle is that the position of the interface between fresh water and salt water incoastal aquifer will be governed by a hydrostatic equilibrium between fresh water and the more dense sea water. Hubbert (1940, pp. 924-926) showed, however, that because fresh water was known to flow seaward, the position of the interface would be governed by a dynamic equilibrium between flowing fresh water and static salt water. This concept is shown in Figure i where the depth to a point on the interface (z) would be equal to the head of fresh water (h) with reference to sea level at the point on the interface multiplied by the ratio of the tween the densities of sea water (p,) and fresh water. Observations over a period of nearly 20 years indicate that the salt front in the Biscayne aquifer of the Miami, Florida, area is dynami- cally stabilized seaward of the theoretical posi- tion given by either concept (Fig. 2). Recent studies indicate that the lack of agreement re- sults from the fact that two assumptions in- herent in the above developments are not ful-
Formulas are developed for the flow pattern followed by the seaward-moving fresh ground water as it nears a beach. It is found that, under steady flow conditions, a sharply defined interface is formed between the fresh and salt water. Along the interface the pressure of the static salt water, owing to its greater density, is counterbalanced by the pressures which drive the fresh water seaward. The fresh water escapes through a gap between this interface and the shore line. An increase in the flow of fresh water widens the gap. Tidal action causes a diffusion of salt water across the interface. This salt is carried back to sea with the fresh-water flow.
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.
Darcy Law was used to calculate fluid flow, and sampling of water to determine the water quality was performed in an attempt to estimate groundwater input to Great Sippewissett Marsh in the Falmouth area of Cape Cod, Massachusetts. Estimates of nutrient input were compared to previously published data. (JR)
The composition of any environment or object is determined by a particular balance between material transport processes and chemical reactions within and around it. In the case of marine sedimentary deposits, the dominant agents of mass transport are often large bottom-dwelling animals that move particles and fluids during feeding, burrowing, tube construction, and irrigation. Such biogenic material transport has major direct and indirect effects on the composition of sediments and their overlying waters. In this chapter I review some of what is presently known about these effects, their implications for both chemical and biological properties of a deposit, and how they can be conceptualized in quantitative models.
The diffusion coefficients of sulfate, ammonium, and phosphate ions were determined directly in the laboratory by placing two samples of homogenized, anoxic mud from Long Island Sound in contact with one another across a planar interface. After 141 h concentration profiles were dctcrmined and from them, values of effective diffusion coefficients (which incorporntc the effects of adsorption) were calculated. Correction of these values for adsorp- tion, using independently determined linear adsorption constants for the same sediments, gave the following values (X lo-" cm2. s- r, 20°C errors 22~): D,(SO,), 5.Ok1.2; D,(NII,), 9.8k2.0; U,(POJ, 3.6kl.l. These values agree well with values calculated for the same scd- iments from estimates of formation factors plus data for diffusion coefficients at infinite di- lution.
Nonlithified, dome‐shaped deep‐water stromatolite analogs grow at a depth of 36 m and a light intensity of 100 Es−1m−2 off French Reef in the Key Largo National Marine Sanctuary. The only other modern deep‐water stromatolite analogs known to occur in the world are in antarctic freshwater lakes and these structures exist at light levels ≤ 1% of surface values (<1.0 Es−1m−2). Even though the two habitats are very dissimilar, they share the commonality of nonlithified, laminated stromatolite analogs growing in low‐light environments. The Key Largo formations exist on a carbonate sand substrate and have a low chlorophyll a:biomass ratio in comparison to the antarctic stromatolite analogs. The dominant cyanobacteria in the majority of antarctic habitats and in the Key Largo habitat are members of the genus Phormidium. The cyanobacterium in the Key Largo stromatolite analogs has been tentatively identified as Phormidium nov. sp. Reasons for the ability of the Key Largo structures to exist in areas of potential metazoan bioturbation present a biological enigma that remains to be explained.
An apparatus is described which allows groundwater discharge through lake beds to be measured directly. On transects at right angles to-the shore-line of Lake Taupo, New Zealand, discharges Mere found to decrease rapidly with distance from the shore. The potential use of this technique in the construction of nutrient budgets for lakes is outlined.
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.
Water movement is probably the most important factor influencing life in the interstices of sandy beaches. In order to better understand this ecosystem, e.g. the distribution and migration of interstitial fauna and overall energy transfer, measurements of water flow through high energy beaches were made on the Atlantic coast of the USA. Special hot thermistor-probes and associated electronic circuits were built, capable of measuring water-flow velocity down to less than 10 m/sec. These were buried in the sand at various depths and locations in the intertidal zone and the flow velocity recorded continuously for one or more tidal cycles. In addition, an orientation sensor was constructed and used together with the flow probe so that a picture of the flow patterns in the intertidal zone of a beach and their changes during a tidal pattern could be developed and defined quantitatively.
Sandy subtidal sediments are part of the earth's largest filter system. Water flow through bottom sediments is driven by wave action on the sea surface. The mechanisms involved are described, including a theoretical deduction and field measurements. As an example, the total water exchange through part of the West Atlantic shelf is computed and the influence of the phenomenon is discussed from a biological point of view and with regard to its importance for the world's oceans.
Theoretical diffusive flux rates for dissolved reactive phosphate (DRP) were determined for sediments in a small area of the
Indian River, Florida for the period March–May 1982. Flux rates from the sediment varied from 29 to 70 × 10−6g per m2 per day in seagrass associated sediments to 3–25 × 10−6g per m2 per day for an area devoid of seagrass. Simultaneous measurements of groundwater seepage velocities indicated greater velocities
in seagrass associated sediments (1.03 × 10−6m per sec) than an area devoid of grass (0.77 × 10−6m per sec). Measured seepage flux accounted for more than 99% of the combined estimated diffusive and seepage flux of DRP
for nearshore seagrass sediments. Also noted was an apparent direct relationship between tidal height, DRP and seepage velocity
in nearshore sediments (25 m from shore) which further demonstrates the importance of hydrogeologic variables to these areas.
The flux of ammonia, phosphate, silica and radon-222 from Potomac tidal river and estuary sediments is controlled by processes occurring at the sediment-water interface and within surficial sediment. Calculated diffusive fluxes range between 0·6 and 6·5 mmol m−2 day−1 for ammonia, 0·020 and 0·30 mmol m−2 day−1 for phosphate, and 1·3 and 3·8 mmol m−2 day−1 for silica. Measured in situ fluxes range between 1 and 21 mmol m−2 day−1 for ammonia, 0·1 and 2·0 mmol m−2 day−1 for phosphate, and 2 and 19 mmol m−2 day−1 for silica. The ratio of in situ fluxes to diffusive fluxes (flux enhancement) varied between 1·6 and 5·2 in the tidal river, between 2·0 and 20 in the transition zone, and from 1·3 to 5·1 in the lower estuary. The large flux enhancements from transition zone sediments are attributed to macrofaunal irrigation. Nutrient flux enhancements are correlated with radon flux enhancements, suggesting that fluxes may originate from a common region and that nutrients are regenerated within the upper 10–20 cm of the sediment column.The low fluxes of phosphate from tidal viver sediments reflect the control benthic sediment exerts on phosphorus through sorption by sedimentary iron oxyhydroxides. In the tidal river, benthic fluxes of ammonia and phosphate equal one-half and one-third of the nutrient input of the Blue Plains sewage treatment plant. In the tidal Potomac River, benthic sediment regeneration supplies a significant fraction of the nutrients utilized by primary producers in the water column during the summer months.
Although much progress has been made toward the mathematical description of saltwater-freshwater relationships in groundwater systems since the late 19th century, the advective and dispersive mechanisms involved are still incompletely understood. This article documents the major historical advances in this subject and summarizes the major direction of current studies.From the time of Badon Ghyben and Herzberg, it has been recognized that density is important in mathematically describing saltwater-freshwater systems. Other mechanisms, such as hydrodynamic dispersion, were identified later and are still not fully understood. Quantitative analysis of a saltwater-freshwater system attempts to mathematically describe the physical system and the important mechanisms using reasonable simplifications and assumptions. This paper, in developing the history of quantitative analysis discusses many of these simplifications and assumptions and their effect on describing and understanding the phenomenon.
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.
Green turtles, Chelonia mydas, make lengthy, regular migrations from Brazil to their nesting grounds on Ascension Island, 1400 miles away. The navigational systems used by Chelonia are unknown; but recent measurements of visual acuity in green turtles suggest that they cannot use stars for guidance. In this paper, we evaluate the possibility that orientation is based, in part, on the detection of some chemical substance originating at Ascension Island.Calculations based on the turbulences and structure of the oceanic currents in the South Atlantic Ocean show that the concentration of any substance emanating from the island would be only 100- to 1000-fold lower in the Brazilian coastal region than in the upstream waters in the immediate vicinity of the island. In order to use this chemical trail as a cue in navigation, the turtles would have to be able to follow the gradient of increasing concentration to the center of the stream and then travel against the current in an easterly direction.The potential problems of sensory receptor habituation, of the determination of polarity in a shallow chemical gradient, of the detection of compass direction or the direction of current flow, and of the maintenance of a straight course in the open sea, are discussed. The potential advantage of having the hatchlings imprinted by the taste or odor of the waters near their birthplace, in terms of reducing the amount of genetic information needed for successful orientation, is also considered.
Assessing submarine groundwater discharge in relation to land use
- G M Simmons
- Jr
- W Reay
- S Smedley
- M Willlams
Simmons, G. M., Jr, Reay, W., Smedley, S.. Willlams, M.
(1990). Assessing submarine groundwater discharge in
relation to land use. In: Mihursky, J. A., Chaney, A. (eds.)
The Chesapeake Bay's hidden tributary: submarme groundwater discharge In: Proc. Groundwater Issues and Solutions in the Potomac h v e r Basin/Chesapeake Bay Region. CO-Sponsored by the Assoc. of Ground Water Scientists and Engineers
- G M Simmons
Simmons, G. M., Jr (1989) The Chesapeake Bay's hidden
tributary: submarme groundwater discharge. In: Proc.
Groundwater Issues and Solutions in the Potomac h v e r
Basin/Chesapeake Bay Region. CO-Sponsored by the
Assoc. of Ground Water Scientists and Engineers, et al.,
George Washington University, Washington, D.C., p. 9-30
This manuscript was submitted to the editor New perspectives in the Chesapeake system
This manuscript was submitted to the editor
New perspectives in the Chesapeake system. Proceedings
of the Chesaveake Bav Research Conference, Dec. 4-9,
1990, Baltimore, MD: CRC Publ. 137. Chesapeake
Research Consortium, Solornons, MD, p. 6 3 5 4 4 4
Dolomitizat~on by groundwater-flow systems in carbonate platforms
- M Simrns
Simrns, M. (1984). Dolomitizat~on by groundwater-flow systems in carbonate platforms. Trans. Gulf Coast Ass. Geol.
Soc. 34: 41 1
Nitrogen fixation potent~al in a deep coral reef habitat and ~ t s importance to submarine groundwater discharge
- G Im Simmons
- Jr
- J Neal
- N Simrnons
- D Lacy
- R Chadduck
- K Elliott
Simmons, G. IM., Jr, Neal, J., Simrnons, N., Lacy, D, Chadduck, R., Elliott, K. (1987). Nitrogen fixation potent~al in a
deep coral reef habitat and ~ t s
importance to submarine
groundwater discharge. Virginia Water Resources Forum,
April 6-7 Virginia Water Resources Research Center,
Blacksburg, VA (Abstr.)
Water quality of newly discovered groundwater discharge into a deep coral reef habitat
- G M Simmons
- Jr
- F G Love
Simmons, G M,, Jr, Love, F. G. (1987). Water quality of newly
discovered groundwater discharge into a deep coral reef
habitat. In. Cooper, R. A.. Shepard, A. N. (eds.) Science
applications of current diving technology on the U.S. continental shelf. NOAA Symposium Series for Undersea
Research 2(2): 155-163. NOAA Undersea Research Program, Rockville, MD
Quantitative observations on salinity
- Fcl B Robblee
- J T Tilmant
- J Emerson
Robblee, Fcl. B., Tilmant, J. T., Emerson, J. (1989). Quantitative
observations on salinity. Bull mar. Sci. 44: 523
Introduction to statistical analysis Sediments and transfer a t and in the bottom interfacial layer Pollutant transfer and transport in the sea
- W J Dixon
- Massey
- F J E K Jr
- M Smies
Dixon, W. J., Massey, Jr, F. J. (1969). Introduction to statistical
analysis, 3rd edn. McGraw-Hill, New York
Duursma, E. K., Smies, M. (1982). Sediments and transfer a t
and in the bottom interfacial layer. In: Kullenberg, G. (ed.)
Pollutant transfer and transport in the sea, chap. 3. CRC
Press, Inc., Boca Raton, p. 101-139
Characteristics of the groundwater seepage into Great South Bay. Marine Science Research
- H Bokuniewicz
- M Zeithin
Bokuniewicz, H.. Zeithin, M. (1980). Characteristics of the
groundwater seepage into Great South Bay. Marine
Science Research Center, S.U.N.Y Stony Brook, Spec.
Rpt. 35
The role of sediment-water column interactions in the continental shelf ecosystem
- L Cahoon
Cahoon, L. (1987) The role of sediment-water column interactions in the continental shelf ecosystem. In: Mitchell, C. T.
(ed.) Proc. Amer. Assoc. Underwater Sci., 947 Newhall St.,
Costa Mesa, CA 92627, p. 171-180
The Permian reef complex of the Guadalupe Mountains region, Texas and New Mexico Phosphorus regeneration and the n~etabolism of coastal marine bottom communities
- N D Newell
- J K Rigby
- A G Fischer
- A J Whiteman
- J E Hllcox
- J S Bradley
Newell, N. D., Rigby, J. K., Fischer, A G., Whiteman, A. J.,
Hllcox, J. E., Bradley, J. S. (1953). The Permian reef complex of the Guadalupe Mountains region, Texas and New
Mexico. W H. Freeman Co., Salt Ldkc ('ity
N ~ x o n,
S. W., Ktlley. J. R., Furmas, B. N.. Oviatt. C. A., Hale,
S. S. (1979). Phosphorus regeneration and the n~etabolism
of coastal marine bottom communities. In: Tenore, K. R.,
Cuull, B. C. (eds.) Marine b e n t h ~ c dynamics. Cniv. of South
Carolina Press, Columbia, p. 219-242
(1.980) Quantifying solute distributions in the bioturbated zone of marine s e d i m ~ n t s hy deflniny an average microenvironment
- R C Aller
Aller, R C. (1.980). Quantifying solute distributions in the
bioturbated zone of marine s e d i m ~ n t s hy deflniny an average microenvironment. Geochim. cosmoch~m. Acta 44.
1955-1965