Fossil water

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Fossil water is water in deep rock bodies that has  not had any contact with the earth's atmosphere or surface waters since prehistory - sometimes significantly longer . There is no uniform stipulation for an exact minimum age; it is not uncommon for an early Holocene age, i.e. 10,000 to 12,000 years, to be given as a guide value (see →  Fossil ). The term fossil water is predominantly (paläometeorische) for correspondingly old meteoric waters, that is, before at least several millennia seeped rainwater used. The aquifers of these deep groundwaters (English also known as old groundwater or paleowater ) lie in the range of at least a few hundred meters below the level of the surface water or are otherwise more or less completely isolated from the inflow and outflow to the earth's surface . But also deeply submerged, synsedimentary (that is, from the period of sedimentation of the rock body containing them) pore waters of primeval surface waters, so-called connate waters , are referred to as fossil water .

The age of fossil water can be determined with relative precision radiometrically or with the help of other isotope studies , and the amount or the mere presence of certain substances dissolved in the water allows conclusions to be drawn about its origin (meteoric vs. konnat) as well as the regional or global environmental conditions at the time of his last participation in the water cycle or at the time of its infiltration into the aquifer.

Fossil water is considered to be “particularly pure”, which means that it is virtually free of anthropogenic pollution. On the other hand, many fossil waters, including those that have emerged from meteoric water, are heavily enriched with minerals due to their long dwell time in the subsurface and can only be used to a limited extent as drinking water or for irrigation.

Occurrence

Examples of different groundwater systems ( unsaturated (vadose) zone and soil water zone ; saturated (phreatic) zone ; groundwater non-conductor ). Example (a) shows an untensioned (phreatic) aquifer, not hydraulically isolated from the surface, in a region with a humid climate . Example (b) is a similar groundwater system, but in a region with a semi-arid to arid climate . Example (c) shows a strained aquifer that is largely hydraulically isolated from the surface. Predominantly or exclusively fossil water occurs in the aquifers in example (b) or in the areas relatively close to the source in example (c), provided that it is assumed for (c) that the spatial distance between the new groundwater formation area and the source outlet or extraction point and therefore the temporal distance The distance between the infiltration of the groundwater into the aquifer and its re-emergence at the source or its extraction via the artificially created well is sufficiently large (many 100 km or several 1000 years).

General

An exact distinction between meteoric and fossil or deep groundwater "is often not possible". In the area of ​​the North German lowlands , groundwater with a high salinity that occurs at a depth of at least 250 to 300 meters below the level of surface water is considered to be fossil or deep groundwater. According to an evaluation of the data from water samples from around 6500 groundwater extraction points worldwide in the top 1000 meters of the earth's crust , aquifers at a depth of at least 250 meters contain on average ( median ) more than 50% water, which has been there at least since the Pleistocene - Holocene turn before 12,000 Years ago. In aquifers at a depth of at least 400 meters, the average is even more than 75%. On this basis, it is conservatively estimated that a significant proportion (42 to 85%) of the groundwater resources in the top 1000 meters of the earth's crust is fossilized water. The aquifers in which fossil water has a share of more than 50% also include those from which fresh water is obtained for industrial agriculture .

Examples

Deep aquifers in arid areas, especially in the Sahara and on the Arabian Peninsula and in particular the Nubian sandstone aquifer in the eastern Sahara, are prime examples of the occurrence of fossil water . These aquifers are often isolated from the water cycle less for geological (i.e. hydraulically) and more for climatic reasons, as the amounts of precipitation in these regions are so low that groundwater recharge does not take place at all or only to a very limited extent and thus almost all of the water in these aquifers is drained the rainier times before the onset of the Holocene. For example, the water of the Nubian sandstone aquifer has been found to have a maximum age of 1 million years and more based on its content of the "cosmogenic" radioactive isotopes chlorine-36 (in the form of chloride ions) and krypton-81 . The deep groundwaters in the semi-arid to arid north of China, on the other hand, are all no older than approx. 45,000 years, and at least the deep aquifer in the northern part of the North China Plain is only partially hydraulically isolated from the surface at the edges of the plain and receives seepage water from the Alluvial fans of the great rivers emerging from the Taihang Mountains . Similar maximum age as for northern China are using the radiocarbon (m 82-152 under for not too deep GOK ) Groundwater in the West Canning Basin in the north of Western Australia has been determined.

Although the deeper groundwater in the Kalahari Basin is referred to as "semi-fossil" due to "its sedimentological and tectonic position and the predominantly low hydraulic gradients ", there are at least north of the Okavango Delta in the so-called Lower Kalahari Aquifer (LKA; depth range of the extraction points 130– 250 m), using the chlorine-36 method, predominantly groundwater ages well over 100,000 years have been determined.

The previously oldest known groundwater comes from relatively high-yielding "fissure water pockets" m- 2900 on the sole of the Kidd Creek Mine in the Superior Province of the Canadian Shield were drilled. Corresponding samples were isotopically dated to an average age of 1.7 billion years ( Paleoproterozoic ) based on their content of radiogenic (i.e., from the decay of uranium and thorium ) noble gas .

Use as a resource and overuse problems

Intensive agriculture in the middle of the desert, made possible by pivot irrigation with fossil groundwater from the Nubian sandstone aquifer (Egypt, not far from the Sudanese border). The satellite image shows the state from 2001, the cultivation area has increased significantly since then.

In regions with low rainfall and hardly any surface water, provided its dissolved matter content is sufficiently low, fossil water is often the main source of drinking water for the population and / or for irrigation of fields. The problem here is the recent low level of new groundwater formation in these regions, which leads to the fact that the groundwater supplies extracted with modern technology via deep boreholes are visibly depleted under the pressure of a growing population with a correspondingly growing demand for water and food. So were modeling under the most realistic climatic and socio-economic parameters that could be completely exhausted in the Arabian Peninsula, all usable groundwater supplies within 60 to 90 years and in North Africa within 200 to 350 years.

In northern China, the groundwater levels at the extraction points in the deep, fossil-fueled aquifers decreased at a rate of up to 4 m / year by 2012. In the densely populated North China Plain, excessive groundwater abstraction from the deep aquifer in the last decades of the 20th century led locally to considerable land subsidence (due to a decrease in pore pressure and the resulting compaction of the aquifer rock) and to salinisation of the groundwater (e.g. due to the seeping in of overlying brackish groundwater).

Natural (geogenic) and potential anthropogenic contamination

Apart from a generally too high solution load , the use of fossil groundwater can be restricted by geogenic radioactive pollution. Groundwater from the Cambodian - Ordovician Disi sandstone aquifer in the south of Jordan , for example , which is otherwise of drinking water quality, has up to 20 times more radium -226 and radium-228 activity than is classified as harmless according to international drinking water standards. In order to be able to use it as drinking water in the desert country, it would have to be treated with relatively high technical effort. The radium comes from the decay of uranium and thorium in the heavy minerals of the aquifer sandstone . The fact that it is present in the water to a comparatively high degree despite a rather unfavorable chemical environment (relatively high pH value , high oxygen saturation) is explained by the fact that the aquifer sandstone has a very low content of clay mineral particles, on the surface of which the radium could be adsorbed again.

Contrary to the widespread view that aquifers with fossil water are essentially shielded from anthropogenic pollution, increased levels of tritium could be detected at around half of the sampling points investigated worldwide in waters with more than 50% fossil fuel . The natural proportion of tritium in the earth's atmosphere is extremely low. Since the first tests of certain nuclear weapons in the 1950s, however, the proportion has been artificially increased, and with it the tritium proportion in meteoric waters. An increased proportion of tritium in deep groundwater, the formation of which should actually have taken place well before the 1950s, would therefore be an indication that these are not completely cut off from the water cycle. This means that anthropogenic pollutants released on the surface could penetrate these aquifers within several decades. However, the frequency of increased tritium in groundwater that is at most 50% fossilized is just as high as that in groundwater that is more than 50% fossilized. Therefore, it seems more likely that many of the sampled extraction points of water that is more than 50% fossil, not only extract water from the deep aquifers, which are actually largely isolated from the water cycle, but that they also "tap" shallower aquifers, and that within the Withdrawal points, groundwater of different ages from aquifers of different depths has been mixed.

Individual evidence

  1. ↑ a b c d Scott Jasechko, Debra Perrone, Kevin M. Befus, M. Bayani Cardenas, Grant Ferguson, Tom Gleeson, Elco Luijendijk, Jeffrey J. McDonnell, Richard G. Taylor, Yoshihide Wada, James W. Kirchner: Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience. Vol. 10, 2017, pp. 425–429, doi: 10.1038 / ngeo2943 (alternative full text access : GIWS 600 kB); see also Lucian Haas: New dirt in old water - fossil groundwater contains impurities ( Memento from April 27, 2017 in the Internet Archive ). Recording of a contribution in the program “ Forschung aktuell” including an interview with Scott Jasechko, Deutschlandfunk, April 25, 2017.
  2. ^ Jean E. Moran, Menso de Jong, Ate Visser, Michael J. Singleton, Bradley K. Esser: California GAMA Special Study: Identifying Paleowater in California Drinking Water Wells. Lawrence Livermore National Laboratory / California State University, East Bay, 2015 ( PDF 1 MB), p. 3.
  3. ^ A b Marc FP Bierkens, Yoshihide Wada: Non-renewable groundwater use and groundwater depletion: a review. Environmental Research Letters. Vol. 14, No. 6, 2019, Item No. 063002, doi: 10.1088 / 1748-9326 / ab1a5f (Open Access).
  4. ^ Andreas Thurner: Hydrogeology. Springer, 1967, ISBN 978-3-7091-7595-8 , p. 4.
  5. ↑ a b c Bernward Hölting. Hydrogeology. Introduction to General and Applied Hydrogeology. 5th edition. Enke, Stuttgart 1996, ISBN 3-8274-1246-3 , p. 18.
  6. ↑ a b c d Claus Kohfahl, Gudrun Massmann, Asaf Pekdeger: Fossils and new groundwater as part of the total water. P. 90–97 in: José L. Lozán, Hartmut Graßl, Peter Hupfer, Ludwig Karbe, Christian-Dietrich Schönwiese (eds.): Warning signal climate: Enough water for everyone? 3rd edition, 2011 ( PDF ).
  7. ↑ a b Fossil water. Spectrum online encyclopedia of geosciences, accessed September 15, 2019.
  8. ^ Herbert Karrenberg: Hydrogeology of non-karstifiable solid rock. Springer, 1981, ISBN 978-3-7091-7038-0 , p. 63.
  9. ↑ A. Suckow, PK Aggarwal, L. Araguas-Araguas (eds.): Isotope Methods For Dating Old Groundwater. International Atomic Energy Agency, Vienna 2013 ( PDF 18 MB).
  10. ↑ Pierre D. Glynn, L. Niel Plummer: Geochemistry and the understanding of ground-water systems. Hydrogeology Journal. Vol. 13, No. 1, 2005, pp. 263-287 doi: 10.1007 / s10040-004-0429-y (alternative full text access : ResearchGate ).
  11. ↑ a b Abdou Abouelmagd, Mohamed Sultan, Neil C. Sturchio, Farouk Soliman, Mohamed Rashed, Mohamed Ahmed, Alan E. Kehew, Adam Milewski, Kyle Chouinard: Paleoclimate record in the Nubian Sandstone Aquifer, Sinai Peninsula, Egypt. Quaternary Research. Vol. 81, No. 1, 2014, pp. 158–167, doi: 10.1016 / j.yqres.2013.10.017 (alternative full text access : University of Georgia 1.5 MB).
  12. ↑ Scott Jasechko, Debra Perrone, Kevin M. Befus, M. Bayani Cardenas, Grant Ferguson, Tom Gleeson, Elco Luijendijk, Jeffrey J. McDonnell, Richard G. Taylor, Yoshihide Wada, James W. Kirchner: Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience. Vol. 10, 2017, Supplementary Information 1 , Fig. S3.
  13. ↑ NC Sturchio, X. Du, R. Purtschert and 15 other authors: One million year old groundwater in the Sahara revealed by krypton ‐ 81 and chlorine ‐ 36. Geophysical Research Letters. Vol. 31, No. 5, 2004, Item No. L05503, doi: 10.1029 / 2003GL019234 (Open Access).
  14. ^ Mahmoud I Sherif, Mohamed Sultan, Neil C. Sturchio: Chlorine isotopes as tracers of solute origin and age of groundwaters from the Eastern Desert of Egypt. Earth and Planetary Science Letters. Vol. 510, 2019, pp. 37-44, doi: 10.1016 / j.epsl.2018.12.035 (Open Access).
  15. ^ A b c Matthew J. Currell, Dongmei Han, Zongyu Chen, Ian Cartwright: Sustainability of groundwater usage in northern China: dependence on palaeowaters and effects on water quality, quantity and ecosystem health. Hydrological Processes. Vol. 26, No. 26, 2012, pp. 4050–4066, doi: 10.1002 / hyp.9208 (alternative full-text access : Chinese Academy of Sciences 450 kB), pp. 4052 ff.
  16. ↑ a b Stephen Foster, Hector Garduno, Richard Evans, Doug Olson, Yuan Tian, ​​Weizhen Zhang, Zaisheng Han: Quaternary Aquifer of the North China Plain - assessing and achieving groundwater resource sustainability. Hydrogeology Journal. Vol. 12, No. 1, 2003, pp. 81-93, doi: 10.1007 / s10040-003-0300-6 (alternative full text access : University of Washington 1.5 MB), pp. 87 f.
  17. ↑ Karina Meredith: Radiocarbon age dating groundwaters of the West Canning Basin, Western Australia. ANSTO Institute for Environmental Research, Menai (NSW) 2009 ( PDF 2.2 MB), p. 19 f.
  18. ↑ Roland Bäumle, Thomas Himmelsbach, Ursula Noell: Hydrogeology and geochemistry of a tectonically controlled, deep-seated and semi-fossil aquifer in the Zambezi Region (Namibia). Hydrogeology Journal. Vol. 27, No. 3, 2019, pp. 885-914, doi: 10.1007 / s10040-018-1896-x (alternative full text access : ResearchGate ).
  19. ↑ Oliver Warr, Barbara Sherwood Lollar, Jonathan Fellowes, Chelsea N. Sutcliffe, Jill M. McDermott, Greg Holland, Jennifer C. Mabry, Christopher J. Ballentine: Tracing ancient hydrogeological fracture network age and compartmentalization using noble gases. Geochimica et Cosmochimica Acta. Vol. 222, 2018, pp. 340–362, doi: 10.1016 / j.gca.2017.10.022 (alternative full text access : Earth Sciences, University of Toronto ).
  20. ↑ Annamaria Mazzoni, Essam Heggy, Giovanni Scabbia: Forecasting water budget deficits and groundwater depletion in the main fossil aquifer systems in North Africa and the Arabian Peninsula. Global Environmental Change. Vol. 53, 2018, pp. 157-173, doi: 10.1016 / j.gloenvcha.2018.09.009 .
  21. ↑ Avner Vengosh, Daniella Hirschfeld, David Vinson, Gary Dwyer, Hadas Raanan, Omar Rimawi, Abdallah Al-Zoubi, Emad Akkawi, Amer Marie, Gustavo Haquin, Shikma Zaarur, Jiwchar Ganor: High naturally occurring radioactivity in fossil groundwater from the Middle East . Environmental Science and Technology. Vol. 43, No. 6, 2009, pp. 1769-1775, doi: 10.1021 / es802969r (alternative full text access : ResearchGate ).