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Submarine Groundwater Discharge (SGD) is a hydrological process which commonly occurs in coastal areas. It is described as submarine inflow of fresh-, and brackish groundwater from land into the sea. Submarine Groundwater Discharge is controlled by several forcing mechanisms, which cause a hydraulic gradient between land and sea.〔William C.Burnett, Bokuniewicz, Henry, Huettel, Markus, Moore, Willard S., Taniguchi, Makoto. "Groundwater and pore water inputs to the coastal zone", ''Biogeochemistry'', Volume 66, 2003, Page 3–33.〕 Considering the different regional settings the discharge occurs either as (1) a focused flow along fractures in karst and rocky areas, (2) a dispersed flow in soft sediments, or (3) a recirculation of seawater within marine sediments. Submarine Groundwater Discharge plays an important role in coastal biogeochemical processes and hydrological cycles such as the formation of offshore plankton blooms, hydrological cycles, and the release of nutrients, trace elements and gases.〔Claudette Spiteri, Caroline P. Slomp, Matthew A. Charette, Kagan Tuncay, Christof Meile. "Flow and nutrient dynamics in a subterranean estuary (Waquoit Bay, MA, USA): Field data and reactive transport modeling", ''Geochimica et Cosmochimica Acta'', Volume 72, Issue 14, 15 July 2008, Pages 3398–3412.〕〔Caroline P. Slomp, Philippe Van Cappellen. "Nutrient inputs to the coastal ocean through submarine groundwater discharge: controls and potential impact", ''Journal of Hydrology'', Volume 295, Issues 1–4, 10 August 2004, Pages 64–86.〕〔Willard S. Moore. "Large groundwater inputs to coastal waters revealed by 226Ra enrichments", ''Nature'', Volume 380, 1996〕〔Matthew A. Charette, Edward R. Sholkovitz. "Trace element cycling in a subterranean estuary: Part 2. Geochemistry of the pore water", ''Geochimica et Cosmochimica Acta'', Volume 70, Issue 4, 15 February 2006, Pages 811–826.〕 ==Forcing mechanisms== In coastal areas the groundwater and seawater flows are driven by a variety of factors. Both types of water can circulate in marine sediments due to tidal pumping, waves, bottom currents or density driven transport processes. Meteoric freshwaters can discharge along confined and unconfined aquifers into the sea or the oppositional process of seawater intruding into groundwater charged aquifers can take place.〔 The flow of both fresh and sea water is primarily controlled by the hydraulic gradients between land and sea and differences in the densities between both waters and the permeabilities of the sediments. According to Badon-Ghijben (1888)〔Badon-Ghijben W., 1888. Nota in verband met de voorgenomen putboring nabij Amsterdam (Notes on the probable results of well drilling near Amsterdam). Tijdschrift van het Koninklinjk Instituut van Ingenieurs. The Hague 1888/9: 8–22〕 and Herzberg (1901)〔Herzberg, B. 1901. Die Wasserversorgung einiger Nordseebader. Gasbeleuchtung und Wasserversorgung 44: 815–819, 842–844〕 the thickness of a freshwater lens below sea level (z) corresponds with the thickness of the freshwater level above sea level (h) as: z= ρf/((ρs-ρf)) *h With z being the thickness between the saltwater–freshwater interface and the sea level, h being the thickness between the top of the freshwater lens and the sea level, ρf being the density of freshwater and ρs being the density of saltwater. Including the densities of freshwater (ρf = 1.00 g •cm-3) and seawater (ρs = 1.025 g •cm-3) equation (2) simplifies to: z=40 *h Together with Darcy's Law, the length of a salt wedge from the shoreline into the hinterland can be calculated: L= ((ρs-ρf)Kf m)/(ρf Q) With Kf being the hydraulic conductivity, m the aquifer thickness and Q the discharge rate.〔Domenico, E. P. & Schwartz, F. W.; 1998. Physical and chemical hydrogeology. 2nd ed. New York. John Wiley & Sons Inc.: 506〕 Assuming an isotropic aquifer system the length of a salt wedge solely depends on the hydraulic conductivity, the aquifer thickness and is inversely related to the discharge rate. These assumptions are only valid under hydrostatic conditions in the aquifer system. In general the interface between fresh and saline water forms a zone of transition due to diffusion/dispersion or local anisotropy.〔Stuyfzand, P. J.; 1993. Hydrochemistry and Hydrology of the Coastal Dune area of the Western Netherlands. PhD thesis, Vrije Universiteit Amsterdam: 367.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Submarine groundwater discharge」の詳細全文を読む スポンサード リンク
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