We define submarine groundwater discharge (SGD) to consist either of fresh groundwater, re-circulated seawater, or a composite thereof. We evaluate and present SGD in terms of a vector for nutrient delivery to coastal waters.
Submarine groundwater discharge (SGD) is an ubiquitous coastal process that is driven by a composite of climatologic, hydrogeologic, and oceanographic processes. For example, terrestrial hydraulic gradients that reflect both short and long term climatic conditions almost always transport both surface and ground water toward the coast. In coastal waters, physical oceanographic processes such as wave set-up, tidal pumping, and density-driven circulation impact these hydraulic gradients and thus affect rates of SGD. Although only fresh groundwater discharge has traditionally been accounted for in numerical simulations of coastal water budgets, the discharge of recirculated saline groundwater may be equally or even more important in terms of material transport (for example, nutrients, metals, organics) across land/sea margins. For the purposes of this site, we therefore define SGD to consist either of fresh groundwater, re-circulated seawater, or a composite thereof, and will evaluate and present SGD in terms of a vector for nutrient delivery to coastal waters.
Until the mid-1990s, studies on SGD did not receive widespread attention, because it was generally thought that SGD rates were not large enough to be a direct influence on ocean water budgets. This omission may in part be due to the inherent difficulty in identifying sites and quantifying rates of SGD, because most SGD occurs as diffusive flow, rather than discrete spring flow. This is in sharp contrast to studies of river discharge or river chemistry, which are obviously more easily sampled and quantified. However, there is a growing recognition that the submarine discharge of fresh, brackish, and marine ground water into coastal oceans is just as important as river discharge in some areas of the coastal ocean. This site will thus review the progress made in SGD science (with particular emphasis on new applications of geochemical tracers and novel geophysical tools), provide links to many SGD projects and study sites, and present an inclusive list of relevant publications. The eventual goal of our SGD science is to develop some forecasting or predictive capability based on being able to de-couple climatic and seasonal signatures from SGD rates.
Modernizing our Approach
Increasing population density and changing agricultural practices in coastal areas have led to releases of nutrients (and other contaminants) into the coastal environment from fertilizer use, industrial practices, and wastewater discharge. These increased nutrient releases have led to eutrophication in many coastal waters, which is a widespread concern. Yet, the role that groundwater-derived nutrients has played in coastal eutrophication is not well understood in many areas. The ecological and economic impacts of eutrophication have been substantial in many coastal regions, which demands a better understanding of the contribution of groundwater-derived nutrient fluxes. Management of wastewater treatment practices in coastal regions critically depends on accurate estimates of the flux and quality of ground water in the coastal zone. In addition, informed resource management requires an improved understanding of the geological framework of coastal aquifers, the pathways by which ground water travels to the coastal zone, the specific locations and dimensions of submarine discharge zones, and the geochemical transformations that take place prior to discharge.
Basic science questions related to how fluid flux across ocean margins and fluid recirculation through ocean margin sediments affects elemental cycling at all scales are also scientific priorities of this research effort. Experiments that address more applied aspects of nutrient delivery can also yield information that is valuable for developing a more general understanding of land-ocean aquifer interactions.
While previously, our focus was to examine geologic control on coastal aquifers and groundwater discharge, today it is apparent that knowledge of land–sea exchange must also encompass interplay among ecosystems science including ecosystems health and climate-change-related processes, as well as natural geohazards.
Research Locations
- American Samoa
- Barter Island, Alaska
- Hawaiʻi
- Big Island
- Maui
- Oʻahu
- Malibu Lagoon, California
- Puget Sound, Washington
- Roi-Namur Island, Kwajalein Atoll, Republic of the Marshall Islands
- San Francisco, California
- Santa Barbara, California
- Younger Lagoon, Santa Cruz, California
- Overview
We define submarine groundwater discharge (SGD) to consist either of fresh groundwater, re-circulated seawater, or a composite thereof. We evaluate and present SGD in terms of a vector for nutrient delivery to coastal waters.
Sources/Usage: Public Domain. Visit Media to see details.Submarine groundwater discharge (SGD) is an ubiquitous coastal process that is driven by a composite of climatologic, hydrogeologic, and oceanographic processes. For example, terrestrial hydraulic gradients that reflect both short and long term climatic conditions almost always transport both surface and ground water toward the coast. In coastal waters, physical oceanographic processes such as wave set-up, tidal pumping, and density-driven circulation impact these hydraulic gradients and thus affect rates of SGD. Although only fresh groundwater discharge has traditionally been accounted for in numerical simulations of coastal water budgets, the discharge of recirculated saline groundwater may be equally or even more important in terms of material transport (for example, nutrients, metals, organics) across land/sea margins. For the purposes of this site, we therefore define SGD to consist either of fresh groundwater, re-circulated seawater, or a composite thereof, and will evaluate and present SGD in terms of a vector for nutrient delivery to coastal waters.
Until the mid-1990s, studies on SGD did not receive widespread attention, because it was generally thought that SGD rates were not large enough to be a direct influence on ocean water budgets. This omission may in part be due to the inherent difficulty in identifying sites and quantifying rates of SGD, because most SGD occurs as diffusive flow, rather than discrete spring flow. This is in sharp contrast to studies of river discharge or river chemistry, which are obviously more easily sampled and quantified. However, there is a growing recognition that the submarine discharge of fresh, brackish, and marine ground water into coastal oceans is just as important as river discharge in some areas of the coastal ocean. This site will thus review the progress made in SGD science (with particular emphasis on new applications of geochemical tracers and novel geophysical tools), provide links to many SGD projects and study sites, and present an inclusive list of relevant publications. The eventual goal of our SGD science is to develop some forecasting or predictive capability based on being able to de-couple climatic and seasonal signatures from SGD rates.
Modernizing our Approach
Sources/Usage: Public Domain.USGS scientists install a thermal imaging system in the National Park of American Samoa off the south shore of Ofu, Manua. The system detects temperature variations, like a colder freshwater plume that emanates from the shore. Increasing population density and changing agricultural practices in coastal areas have led to releases of nutrients (and other contaminants) into the coastal environment from fertilizer use, industrial practices, and wastewater discharge. These increased nutrient releases have led to eutrophication in many coastal waters, which is a widespread concern. Yet, the role that groundwater-derived nutrients has played in coastal eutrophication is not well understood in many areas. The ecological and economic impacts of eutrophication have been substantial in many coastal regions, which demands a better understanding of the contribution of groundwater-derived nutrient fluxes. Management of wastewater treatment practices in coastal regions critically depends on accurate estimates of the flux and quality of ground water in the coastal zone. In addition, informed resource management requires an improved understanding of the geological framework of coastal aquifers, the pathways by which ground water travels to the coastal zone, the specific locations and dimensions of submarine discharge zones, and the geochemical transformations that take place prior to discharge.
Basic science questions related to how fluid flux across ocean margins and fluid recirculation through ocean margin sediments affects elemental cycling at all scales are also scientific priorities of this research effort. Experiments that address more applied aspects of nutrient delivery can also yield information that is valuable for developing a more general understanding of land-ocean aquifer interactions.
While previously, our focus was to examine geologic control on coastal aquifers and groundwater discharge, today it is apparent that knowledge of land–sea exchange must also encompass interplay among ecosystems science including ecosystems health and climate-change-related processes, as well as natural geohazards.
Research Locations
Sources/Usage: Public Domain.Image produced from a thermal imaging system shows a submarine (cold and fresh) groundwater discharge plume emanating from the shoreline and propagating over the reef flat. - American Samoa
- Barter Island, Alaska
- Hawaiʻi
- Big Island
- Maui
- Oʻahu
- Malibu Lagoon, California
- Puget Sound, Washington
- Roi-Namur Island, Kwajalein Atoll, Republic of the Marshall Islands
- San Francisco, California
- Santa Barbara, California
- Younger Lagoon, Santa Cruz, California
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