Special Issue "Submarine Groundwater Discharge and Its Effects"

A special issue of Hydrology (ISSN 2306-5338).

Deadline for manuscript submissions: closed (31 January 2019).

Special Issue Editors

Guest Editor
Dr. Alanna L. Lecher Website E-Mail
Department of Natural and Applied Science, Lynn University, 2519 N Military Trail, Boca Raton, FL 33431, USA
Interests: biogeochemistry; marine pollution; groundwater; chemical oceanography; isotopes
Guest Editor
Dr. Karen Knee Website E-Mail
Department of Environmental Science, American University, Washington, DC, USA
Interests: submarine groundwater discharge (SGD); anthropogenic influences on water quality; pollutant transport; freshwater and coastal marine systems
Guest Editor
Dr. Kimberly Null Website E-Mail
Moss Landing Marine Laboratories, San Jose State University, Moss Landing, CA, USA
Interests: coastal groundwater; water quality; nutrient dynamic in estuaries; treatment wetlands

Special Issue Information

Dear Colleagues,

Submarine groundwater discharge (SGD) is an important source of biologically-active solutes to the coastal ocean that has been widely studied since its discovery in the late 20th century. SGD can be comprised of point source (submarine spring) or non-point source (diffuse) seepage. The literature pertaining to SGD has been dominated by studies that quantify the flux of SGD and associated solutes. Less commonly, studies focus on qualitatively and quantitatively describing processes in the coastal aquifer, also called the subterranean estuary, which affect SGD-associated solute fluxes to the coastal ocean, introducing new techniques, upscaling SGD fluxes to the basin and global scales, and evaluating the impact of SGD on coastal ecology.

This Special Issue invites articles describing novel research, technical notes pertaining to methods, and reviews on all topics pertaining to SGD. However, we especially invite studies that explore new methods relevant to SGD, that evaluate the relative contributions of fresh groundwater and recirculated seawater, or that document the impact of SGD on the coastal ocean.

Dr. Alanna L. Lecher
Dr. Karen Knee
Dr. Kimberly Null
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • biogeochemistry
  • subterranean estuary
  • SGD methods
  • marine impacts
  • coastal zone impacts
  • submarine springs
  • diffuse seepage

Published Papers (7 papers)

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Research

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Open AccessArticle
Evidence for Pathways of Concentrated Submarine Groundwater Discharge in East Antarctica from Helicopter-Borne Electrical Resistivity Measurements
Hydrology 2019, 6(2), 54; https://doi.org/10.3390/hydrology6020054 - 20 Jun 2019
Cited by 1
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Open AccessArticle
Freshening of a Coastal Karst Aquifer Revealed by the Temporal Changes in a Spring Water Composition (La Palme, Southern France)
Hydrology 2019, 6(2), 45; https://doi.org/10.3390/hydrology6020045 - 03 Jun 2019
Abstract
Coastal karst aquifers are vulnerable to sea level rise and seawater intrusion. Knowledge of aquifer hydrological characteristics is therefore essential to managing this water resource. Long-term aquifer monitoring may not always be possible, especially in areas that humans frequent for recreational purposes. However, [...] Read more.
Coastal karst aquifers are vulnerable to sea level rise and seawater intrusion. Knowledge of aquifer hydrological characteristics is therefore essential to managing this water resource. Long-term aquifer monitoring may not always be possible, especially in areas that humans frequent for recreational purposes. However, hydrological information can be deduced from the chemical composition of periodically sampled groundwaters. We characterized the complete chemical composition (temperature, pH, salinity, ORP, O2, Na-K-Ca-Mg-Ba-Sr-Si-Cl-SO4-DIC, and DOC) of a brackish karstic spring located along the French Mediterranean coast (La Palme). The salinity of the spring water varied between 4 and 9 during the 2.5 year period of observation. Chemical analyses revealed that the spring is modified from modern seawater, as shown by Na-normalized dissolved element concentrations. Thermodynamic calculations of mineral saturation states (PHREEQC) point to aragonite and barite saturation and elevated equilibrium CO2 partial pressure. The simultaneous salinity minima and oxygen maxima coincide with extreme values of dissolved element concentrations. This indicates that variation in salinity and water chemistry in La Palme coastal aquifer is primarily driven by infiltration of fresh rainwater. This study shows that geochemical investigations can provide an alternative approach to characterizing the hydrological properties of coastal karst aquifers when wells or boreholes are not readily available. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Open AccessArticle
Modeling the Potential of Submarine Groundwater Discharge to Facilitate Growth of Vibrio cholerae Bacteria
Hydrology 2019, 6(2), 39; https://doi.org/10.3390/hydrology6020039 - 18 May 2019
Abstract
Submarine groundwater discharge (SGD), the discharge of terrestrial groundwater to the ocean, can govern the coastal benthic environment. Bacteria such as Vibrio cholerae inhabit coastal waters and sediments, whose growth can be influenced by SGD. In particular, salinity changes introduced by SGD could [...] Read more.
Submarine groundwater discharge (SGD), the discharge of terrestrial groundwater to the ocean, can govern the coastal benthic environment. Bacteria such as Vibrio cholerae inhabit coastal waters and sediments, whose growth can be influenced by SGD. In particular, salinity changes introduced by SGD could have a positive effect on the abundance but also virulence of non-halophilic V. cholera bacteria dwelling in coastal waters and shallow marine sediments. Here we assess potential effects of SGD on the environmental properties that favor V. cholerae in a numerical modeling study representing multiple scenarios. Approaching natural systems, simulation results reveal a high sensitivity of non-halophilic Vibrio cholerae growth to SGD and its primary driving factors. This dependency leads to highest growth potential at high groundwater inflow and low hydraulic conductivity of the aquifer as well as for steep sea-side boundary slopes. Besides its minor impact on the extent of SGD in our model, dispersion is a crucial limiting factor for V. cholerae habitat. We conclude that there is a close connection between the driving factors of SGD and low salinity zones along a coastal slope, and recommend taking these into consideration for evaluating local V. cholerae outbreaks. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Open AccessArticle
Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa
Hydrology 2019, 6(1), 18; https://doi.org/10.3390/hydrology6010018 - 16 Feb 2019
Cited by 1
Abstract
Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This [...] Read more.
Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ15N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. In addition to sampling in situ macroalgae, pre-treated macroalgal specimens were deployed throughout each embayment to uptake ambient nutrients and provide a standardized assessment of differences between locations. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ15N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Open AccessArticle
Submarine Groundwater Discharge Differentially Modifies Photosynthesis, Growth, and Morphology for Two Contrasting Species of Gracilaria (Rhodophyta)
Hydrology 2018, 5(4), 65; https://doi.org/10.3390/hydrology5040065 - 02 Dec 2018
Abstract
On many tropical reefs, submarine groundwater discharge (SGD) provides a substantial and often overlooked nutrient source to nearshore ecosystems, yet little is known about the impacts of SGD on the biology of reef organisms. To address this, the physiological responses of the endemic [...] Read more.
On many tropical reefs, submarine groundwater discharge (SGD) provides a substantial and often overlooked nutrient source to nearshore ecosystems, yet little is known about the impacts of SGD on the biology of reef organisms. To address this, the physiological responses of the endemic rhodophyte Gracilaria coronopifolia and an invasive congener, Gracilaria salicornia, were examined across an SGD gradient in the field and laboratory. Tissue samples of both species were cultured for 16 days along an onshore-offshore SGD gradient at Wailupe, Oahu. G. salicornia tolerated the extremely variable salinity, temperature, and nutrient levels associated with SGD. In marked contrast, half of G. coronopifolia plants suffered tissue loss and even death at SGD-rich locations in the field and in laboratory treatments simulating high SGD flux. Measurements of growth, photosynthesis, and branch development via two novel metrics indicated that the 27‰ simulated-SGD treatment provided optimal conditions for the apparently less tolerant G. coronopifolia in the laboratory. Benthic community analyses revealed that G. salicornia dominated the nearshore reef exposed to SGD compared with the offshore reef, which had a greater diversity of native algae. Ultimately, SGD inputs to coastal environments likely influence benthic community structure and zonation on otherwise oligotrophic reefs. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Open AccessArticle
Fresh and Recirculated Submarine Groundwater Discharge Evaluated by Geochemical Tracers and a Seepage Meter at Two Sites in the Seto Inland Sea, Japan
Hydrology 2018, 5(4), 61; https://doi.org/10.3390/hydrology5040061 - 01 Nov 2018
Cited by 1
Abstract
Submarine groundwater discharge (SGD) consists of fresh submarine groundwater discharge (FSGD) and recirculated submarine groundwater discharge (RSGD). In this study, we conducted simultaneous 25-hour time-series measurements of short-lived 222Rn and 224Ra activities at two sites with differing SGD rates in the [...] Read more.
Submarine groundwater discharge (SGD) consists of fresh submarine groundwater discharge (FSGD) and recirculated submarine groundwater discharge (RSGD). In this study, we conducted simultaneous 25-hour time-series measurements of short-lived 222Rn and 224Ra activities at two sites with differing SGD rates in the central Seto Inland Sea of Japan to evaluate SGD rates and their constituents. At both sites, we also quantified the total SGD, FSGD, and RSGD using a seepage meter to verify the water fluxes estimated with 222Rn and 224Ra. SGD rates estimated using 222Rn and 224Ra at the site with significant SGD approximated the total SGD and RSGD measured by the seepage meter. However, SGD rates derived using 222Rn at the site with minor SGD were overestimated, since 222Rn activity at the nearshore mooring site was lower than that in the offshore area. These results suggest that the coupling of short-lived 222Rn and 224Ra is a powerful tool for quantification of FSGD and RSGD, although it is important to confirm that tracer activities in coastal areas are higher than those in offshore. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Review

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Open AccessReview
Synthesizing the Effects of Submarine Groundwater Discharge on Marine Biota
Hydrology 2018, 5(4), 60; https://doi.org/10.3390/hydrology5040060 - 19 Oct 2018
Cited by 8
Abstract
Submarine groundwater discharge (SGD) is a global and well-studied geological process by which groundwater of varying salinities enters coastal waters. SGD is known to transport bioactive solutes, including but not limited to nutrients (nitrogen, phosphorous, silica), gases (methane, carbon dioxide), and trace metals [...] Read more.
Submarine groundwater discharge (SGD) is a global and well-studied geological process by which groundwater of varying salinities enters coastal waters. SGD is known to transport bioactive solutes, including but not limited to nutrients (nitrogen, phosphorous, silica), gases (methane, carbon dioxide), and trace metals (iron, nickel, zinc). In addition, physical changes to the water column, such as changes in temperature and mixing can be caused by SGD. Therefore SGD influences both autotrophic and heterotrophic marine biota across all kingdoms of life. This paper synthesizes the current literature in which the impacts of SGD on marine biota were measured and observed by field, modeling, or laboratory studies. The review is grouped by organismal complexity: bacteria and phytoplankton, macrophytes (macroalgae and marine plants), animals, and ecosystem studies. Directions for future research about the impacts of SGD on marine life, including increasing the number of ecosystem assessment studies and including biological parameters in SGD flux studies, are also discussed. Full article
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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