Editor’s Message: Submarine groundwater discharge studies and the absence of hydrogeologists

Hydrogeology Journal, Jan 2008

Gholam A. Kazemi

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Editor’s Message: Submarine groundwater discharge studies and the absence of hydrogeologists

Hydrogeology Journal Editor's Message: Submarine groundwater discharge studies and the absence of hydrogeologists Gholam A. Kazemi The objective of this editor's message is to recognize marine coastal processes were unknown. Since 2000, a the current efforts, and highlight the need for the wider number of sites across the globe have been chosen for involvement, of hydrogeologists in a special field of detailed study of SGD phenomenon including sites in groundwater studies, namely “submarine groundwater Australia, Brazil, Italy, Mauritius and the USA (Burnett et discharge”. It is also intended to briefly report on the al. 2006). These studies have employed a range of participation of the author in one such study. The term techniques including seepage meters, tracers, onshore submarine groundwater discharge (SGD), or formerly and offshore CTD (conductivity, temperature, depth) SGWD, appeared in the literature during the early 1970s profiling and hydrogeological modeling approaches. New (e.g. Zektser et al. 1973) or even earlier (e.g. Manheim methodologies such as LandSat satellite imagery are now 1967; Glover 1964). However, universal adoption of this being tested. expression was not very quick. Bokuniewicz (1980), for Annually, about 2,400 km3 of freshwater discharges into instance, used phrases like “submarine outflow of ground- the world's seas and oceans in the form of SGD, which is water” or “groundwater flow across the sea floor” to defined as any type of flow of water upwards across the sea describe the same phenomenon. Long after those early floor, from the ocean bottom into the overlying water publications, a couple of articles in the high prestige (SCOR-LOICZ 2004). This amounts to only 6% of the journal Nature (Moore 1996; Younger 1996) and the annual river input into oceans. However, due to its higher improvement in analytical facilities gave this subject a dissolved solid content, SGD has considerable impact on boost and, from the mid-1990s onwards, drew the the quality and the ecosystem of the receiving waters, as attention of scientists. It was then that the floodgate of rightly recognized by Johannes (1980). related publications opened. Modern equipment capable of Generally speaking, marine and oceanography texts or quickly and reliably measuring tracers, especially 222Rn even textbooks of any field do not include a section on and 226Ra (e.g. RAD7), as well as isotopes of seawater SGD (see for example Chester 2003). However, very dissolved gases such as CH4, and the development of a recently a few books have dealt with this subject, though new generation of seepage meters, all motivated research- mostly in a peripheral way. These include Zektser et al. ers to concentrate again on this subject. Up until a few (2007); Judd and Hovland (2007); Davis and Elderfield years ago, quantitative estimation of SGD was difficult/ (2004); Taniguchi et al. (2003), and very marginally impossible to achieve and the consequences of SGD on Vacher and Quinn (1997). With the exception of the first two, the rest are edited books comprised of a variety of articles by different authors. Considering that the book by Received: 4 October 2007 / Accepted: 15 November 2007 Judd and Hovland (2007) only briefly touches the topic, Published online: 4 January 2008 Zektser et al. (2007) is left as the only book entirely * Springer-Verlag 2007 dedicated to this matter. In the world of journals, articles related to SGD have appeared commonly in Limnology and Oceanography, G. A. Kazemi ()) Biogeochemistry, Continental Shelf Research, Estuarine, FSahcauhlrtoyoodfUEnairvthersSictyienocfeTse,chnology, Coastal and Shelf Science, Earth and Planetary Sciences Shahrood, Iran and to a lesser extent in Geophysical Research Letters, e-mail: Water Resources Research, Journal of Hydrology, etc. Tel.: +98-273-3336007 Also, the December 2004 special issue of Ground Water Fax: +98-273-3334419 was allocated to SGD, though there have only been a Present Address: couple of other short articles recently published in that G. A. Kazemi journal (Taniguchi et al. 2005, 2007). In contrast, there are DGirvadisuioante oSfcEhoarotlhoafnSdcPielnancee,tary System Science, no articles in Hydrogeology Journal that specifically Hokkaido University, document work on SGD and its characteristics, although N10 W8, Kita-ku, Sapporo, 060-0810, Japan there are a few reports that document submarine springs. - The equivalent of SGD in the hydrogeological literature is Akawwi (2006), for example, which quantifies SGD into perhaps what has been termed “marine hydrogeology”. An the Dead Sea, Jordan, was supervised by Martin Sauter essay in the Future of Hydrogeology theme issue (Fisher and Elias Salameh, two well-known hydrogeologists. 2005) has narrowly touched this field though not Professional organizations and scientific bodies inspecifically mentioning SGD. Another essay in the same volved with SGD research projects include Intergovernissue is partially related to this subject (Post 2005). These mental Oceanographic Commission (IOC), Scientific are just not enough, though some hydrogeologists pub- Committee on Oceanic Research (SCOR), Land-Ocean lished high-value SGD papers in Nature recently (e.g. Interactions in the Coastal Zone (LOICZ) and InternaMichael et al. 2005). However, one may argue that tional Association of Physical Sciences of Oceans hydrogeologists have written on this subject, but have (IAPSO). Again, here, one could easily see that these not used the term SGD specifically (e.g. Benduhn and bodies, in general, have an ocean-marine root with Renard 2004). The response to that would be that SGD is minimal connection with land hydrology or hydrogeology. a well-established term now, and hydrogeologists should As a milestone, the International Atomic Energy Associrecognize and adapt to it. To further support the point, ation (IAEA) and UNESCO initiated a 5-year plan in 2000 another example is provided here. A recent comprehen- to study the importance of SGDs and the methodologies sive article (Burnett et al. 2006) reviews the topic of SGD used to study SGDs in the management of the coastal at length and in detail and summarizes the findings of zone. This comprehensive research project was carried out various research projects across the globe. Coauthors of by: the Isotope Hydrology Section of IAEA in Vienna, this article, 22 in number, are from a variety of disciplines, Austria; the Marine Environmental Laboratory in Monaco; mainly from oceanography and marine departments (nine the Intergovernmental Oceanographic Commission (IOC), coauthors), with only two coauthors from geological and the International Hydrological Program (IHP), along departments. This mixture, which is a good representation with nine laboratories in eight countries (Burnett et al. of the involvement of professionals with different back- 2006). A couple of commissions by the International grounds with SGD studies, shows that hydrogeologists are Association of Hydrogeologists (IAH), e.g. commissions not particularly well represented in this field of ground- on groundwater-dependent ecosystem and aquifer dynamwater science. Another review article (Gallardo and Marui ics and coastal zone management, relate to SGD, but have 2006), which demonstrates the participation of hydro- not yet focused on this subject. geologists, has been published in Geo-Marine Letters. The author of this editor’s message, a hydrogeologist SGD comprises three words, two of which (groundwater and a member of IAH, is currently a guest researcher at and discharge) are the main domains of hydrogeologists. Hokkaido University, Japan to initiate a research program Therefore, while appreciating the undertaken research in order to quantify the SGD into the Caspian Sea in Asia work, no doubt is left that the participation of hydro- from its southern Iranian margins. Concentration and 13C geologists in SGD studies has been less than what it isotope content of methane in the Caspian Sea waters is should have been. Having said that, it should be added the main approach that will be adopted. A substantial that there are at least two reasons why hydrogeologists are component of this large project is the continuous generally absent from this field: collaboration with the Japanese scientists who are front runners in this field. This research project will try to 1. Hydrogeological research projects are commonly driv- estimate the quantity of SGD into the Caspian Sea using en by practical problems (indeed, Hydrogeology Jour- available technology and expertise at the University of nal used to be called Applied Hydrogeology). In coastal Hokkaido, which is one of only a handful of institutions in areas, a typical issue is freshwater salinization due to the world with the capacity to measure 13C content of seawater intrusion and, in this respect, hydrogeologists methane in water samples. Water samples from the often treat offshore aquifers as a source of salt rather Caspian Sea and adjoining aquifers will be analyzed for than a sink of freshwater. this purpose. As yet, there has been no published work, 2. Measurement of SGD requires seaborne equipment that whether national or international, on this region. Iranian oceanographers and marine scientists are more familiar shorelines of the Caspian Sea are 750 km in length, just with. This obstacle, however, is gradually vanishing over 10% of the total shoreline. However, higher because of the ease of operation of sophisticated hydraulic gradients, as well as higher rainfall in the modern equipment. southern Caspian Sea area, result in a proportionally greater share of the SGD for this region. Based on an estimate by Zektser et al. (2007), about 30% of Caspian Similar to articles and books, a handful of PhD theses Sea SGD is from the Iranian side. have dealt with this subject. These include: Akawwi 2006; The intention of this editor’s message is to alert fellow Loveless 2006; Prieto 2005; Michael 2005; Schwartz hydrogeologists to the need for further participation in 2002; Corbett 1999; Young 1996; Robinson 1996 and such studies. Hydrogeologists can improve SGD studies Millham 1993. Again, these dissertations have been by quantitative analysis of groundwater flow dynamics in mainly carried out at departments other than Geology or coastal aquifers. This complements the current, mainly Earth Sciences, though hydrogeologists supervised some. tracers-orientated studies adopted by marine scientists and oceanographers, which focus on the SGD at surface, i.e. after entering surface waters. The involvement of hydrogeologists can lead to a more complete picture of subsurface flow conditions and the effect of this flow field on coastal processes. One very good recent example is the work by Thompson et al. (2007) , which shows how isotopic tracers alone may be misleading. In addition, hydrogeologists need to be aware of SGD because the unawareness of SGD and fresh groundwater in the offshore realm can lead to misunderstanding of the hydrogeology of coastal aquifers. For example, the salinization of a coastal well field is (in general) instantly attributed to seawater encroachment. However, if relatively fresh groundwater is present below the seafloor, this explanation is incorrect and a different cause is to be held responsible for the salinization process. Therefore, even if hydrogeologists are not directly involved in quantification of SGD itself, they need to be more aware of it than is presently the case. Based on the above explanation, there is a need to include SGD in the curriculum of groundwater hydrology and hydrogeology subjects of the Geology and Earth Science departments of universities. Topics like definition and description of SGD, sampling and measurement techniques, the impact of SGD on the receiving waters and the coastal processes, factors controlling SGD quantity, the impact of seawater level fluctuations on the quantity of SGD, SGD as a water resources management issue and case studies worldwide should be taught as part of this subject. Seawater intrusion, the other side of the SGD coin, has been a core subject of hydrogeologygroundwater textbooks. SGD, however, has not found its rightful place in these types of texts and there is a justified need to include a thorough discussion in newly published books, as well as in subsequent editions of the present hydrogeology textbooks. Acknowledgements One should not write an editorial message about SGD that does not mention the name of William Burnett from the Oceanography Department of the Florida State University, USA. Prof. Burnett has written extensively on this subject for the past 12 years and has been the driving force behind these kinds of research projects. He has participated in almost all of the SGD case studies worldwide and continues to do so. Makoto Taniguchi from Research Institute for Humanity and Nature (RIHN), Japan, has also been a key researcher in this field and has invented the Taniguchitype seepage meter. Prof. Taniguchi is the most active and highly published member of IAH in the field of SGD. I should also acknowledge with thanks the Matsumae International Foundation (MIF), Tokyo, Japan, for the award of the MIF fellowship. Further, special thanks go to Prof. U. Tsunogai from the Graduate School of Science, Hokkaido University for his hospitality and for providing access to the analytical facilities at his geochemistry laboratory. Lastly, this message has benefited from the comments and editing of Sue Duncan, Maria-Theresia Schafmeister, Philippe Renard, Charles Harvey and especially Vincent Post and I am grateful to all. Akawwi E (2006) Locating zones and quantifying the submarine groundwater discharge into the eastern shores of the Dead Sea Thompson C , Smith L , Maji R ( 2007 ) Hydrogeological modeling of submarine groundwater discharge on the continental shelf of Louisiana . J Geophys Res 112 , C03014 . DOI 10.1029/ 2006JC003557 Vacher L, Quinn T ( 1997 ) Geology and hydrogeology of carbonate islands , vol 54 ( Developments in sedimentology) . Elsevier , Amsterdam Young JE ( 1996 ) Tracing groundwater flow into the northeastern Gulf of Mexico using naturally occurring Radon-222 . PhD Thesis , Florida State University, USA Younger PL ( 1996 ) Submarine groundwater discharge . Nature 382 : 121 -122 Zektser IS , Ivanov VA , Meskheteli AV ( 1973 ) The problem of direct groundwater discharge to the Seas . J Hydrol 20 : 1 -36 Zektser IS , Everett LG , Dzhamalov RG ( 2007 ) Submarine groundwater . CRC, Boca Raton , FL


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Gholam A. Kazemi. Editor’s Message: Submarine groundwater discharge studies and the absence of hydrogeologists, Hydrogeology Journal, 2008, 201-204, DOI: 10.1007/s10040-007-0251-4