Fossil water

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Fossil water, fossil groundwater, or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vostok. UNESCO defines fossil groundwater as "water that infiltrated usually millennia ago and often under climatic conditions different from the present, and that has been stored underground since that time." [1]

Contents

Determining the time since water infiltrated usually involves analyzing isotopic signatures. Determining "fossil" status—whether or not that particular water has occupied that particular space since the distant past—involves modeling the flow, recharge, and losses of aquifers, which can involve significant uncertainty. Some aquifers are hundreds of meters deep and underlie vast areas of land. Research techniques in the field are developing quickly and the scientific knowledge base is growing. In the cases of many aquifers, research is lacking or disputed as to the age of the water and the behavior of the water inside the aquifer. [2] [3]

Renewability

Large, prolific aquifers (notably the Nubian Sandstone Aquifer System and the Ogallala Aquifer) containing fossil water are of significant socio-economic value. Fossil water is extracted from these aquifers for many human purposes, notably, agriculture, industry, and consumption. In arid regions, some aquifers containing available and usable water receive little to no significant recharge, effectively making groundwater in those aquifers a non-renewable resource. Extraction rates greater than recharge rates result in lowering of the water table and can lead to groundwater depletion. Extraction of non-renewable groundwater resources is referred to as groundwater "mining" because of their finite nature. [4]

General geology

Aquifers are typically composed of semi-porous rock or unconsolidated material whose pore space has been filled with water. In the relatively rare cases of confined aquifers, an impermeable geologic layer (e.g. clay or calcrete) encloses an aquifer, isolating the water within, sometimes for millennia. More commonly, fossil water is found in arid or semi-arid regions where the climate was significantly more humid in recent geologic history. In some semi-arid regions, the majority of precipitation evaporates before it can infiltrate and result in any significant aquifer recharge.

Most fossil groundwater has been estimated to have originally infiltrated within the Holocene and Pleistocene (10,000–40,000 years ago). Some fossil groundwater is associated with the melting of ice in the time since the last glacial maximum. Dating of groundwater relies on measuring concentrations of certain stable isotopes, including 3
H
(tritium) and 18
O
("heavy" oxygen), and comparing values with known concentrations of the geologic past. [1]

Fossil water can potentially dissolve and absorb a number of ions from its host rock. Salinity in groundwater can be higher than seawater. [5] In some cases, some form of treatment is required to make these waters suitable for human use. Saline fossil aquifers can also store significant quantities of oil and [6] natural gas. [7]

Notable bodies of fossil water

Ogallala Aquifer

The Ogallala or High Plains Aquifer sits under 450,000 km2 of 8 states of the United States of America. It is one of the largest freshwater deposits in the world. The aquifer is composed of unconsolidated alluvial deposits. Groundwater in this aquifer has been dated to have been deposited in the humid time following the last glacial maximum. [8] In much of the aquifer's area, an impermeable layer of calcrete prevents precipitation from infiltrating. In other regions of the aquifer, some relatively small rates of recharge have been measured. [9]

The aquifer supplies water for the many people who live above it and for widespread agricultural uses. In many areas, the water table has dropped drastically due to heavy extraction. Depletion rates are not stabilizing; in fact, they have been increasing in recent decades. [10]

Transport of pipe segments for the Great Manmade River in Libya: a network of pipes that supplies water from the Nubian Sandstone Aquifer System. ManMadeRiverLibya-7A.jpg
Transport of pipe segments for the Great Manmade River in Libya: a network of pipes that supplies water from the Nubian Sandstone Aquifer System.

Nubian Sandstone Aquifer System

The Nubian Sandstone Aquifer System is located in northeastern Africa, under the nations of Sudan, Libya, Egypt, and Chad, covering about 2,000,000 km2. It is largely composed of many hydraulically interconnected sandstone aquifers. Some parts of the system are considered to be confined, if somewhat leaky, due to impermeable layers such as marine shales. The water was deposited between 4,000 and 20,000 years ago, varying by specific locality. [11]

The water in the Nubian Sandstone Aquifer System is of high importance to the people living above it, and has been for millennia. In modern times, as demand increases, avoiding rapid depletion and international conflict will depend on careful cross-boundary monitoring and planning. Libya and Egypt are currently planning development projects to withdraw significant amounts of the aquifer's fossil water for use.

Other fossil aquifers have been identified throughout Northern Africa as well.

Kalahari Desert aquifers

The Kalahari Desert is in central southern Africa (Botswana, Namibia, and South Africa). Geology of the area includes significant karst formations. Most of the precipitation in the region evaporates before it can contribute to significant recharge of the aquifers below. Whether or not the region's aquifers receive any significant recharge has long been the subject of debate and research. [12] In the northern region of the Kalahari, a deep aquifer in Cave sandstone was found to have isotopic signatures that suggested it had been confined with little to no leakage for long periods of time. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Aquifer</span> Underground layer of water-bearing permeable rock

An aquifer is an underground layer of water-bearing material, consisting of permeable or fractured rock, or of unconsolidated materials. Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could lead to the formation of a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.

<span class="mw-page-title-main">Ogallala Aquifer</span> Water table aquifer beneath the Great Plains in the United States

The Ogallala Aquifer is a shallow water table aquifer surrounded by sand, silt, clay, and gravel located beneath the Great Plains in the United States. As one of the world's largest aquifers, it underlies an area of approximately 174,000 sq mi (450,000 km2) in portions of eight states. It was named in 1898 by geologist N. H. Darton from its type locality near the town of Ogallala, Nebraska. The aquifer is part of the High Plains Aquifer System, and resides in the Ogallala Formation, which is the principal geologic unit underlying 80% of the High Plains.

<span class="mw-page-title-main">Water table</span> Top of a saturated aquifer, or where the water pressure head is equal to the atmospheric pressure

The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the locality. It can also be simply explained as the depth below which the ground is saturated.

<span class="mw-page-title-main">Groundwater</span> Water located beneath the ground surface

Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from the surface; it may discharge from the surface naturally at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

<span class="mw-page-title-main">Kansas Geological Survey</span>

The Kansas Geological Survey (KGS) is a research and service division of the University of Kansas, charged by statute with studying and providing information on the geologic resources of Kansas. The KGS has no regulatory authority and does not take positions on natural resource issues.

<span class="mw-page-title-main">Edwards Aquifer</span> Source of drinking water in Texas

The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer's region. Additionally, the Edwards Aquifer feeds the Comal and San Marcos Springs, provides springflow for recreational and downstream uses in the Nueces, San Antonio, Guadalupe, and San Marcos river basins, and is home to several unique and endangered species.

<span class="mw-page-title-main">Guarani Aquifer</span>

The Guarani Aquifer, located beneath the surface of Argentina, Brazil, Paraguay, and Uruguay, is the second largest known aquifer system in the world and is an important source of fresh water. Named after the Guarani people, it covers 1,200,000 square kilometres (460,000 sq mi), with a volume of about 40,000 cubic kilometres (9,600 cu mi), a thickness of between 50 metres (160 ft) and 800 metres (2,600 ft) and a maximum depth of about 1,800 metres (5,900 ft). It is estimated to contain about 37,000 cubic kilometres (8,900 cu mi) of water, with a total recharge rate of about 166 km3/year from precipitation. It is said that this vast underground reservoir could supply fresh drinking water to the world for 200 years. However, at closer inspection, if the world population were to stay at an equilibrium of about 6.96 billion, not even taking into account that babies need less water than grown adults, this figure reaches 1600 years, allowing about 9 liters per day per person. Due to an expected shortage of fresh water on a global scale, which environmentalists suggest will become critical in under 20 years, this important natural resource is rapidly becoming politicised, and its control becomes ever more controversial.

<span class="mw-page-title-main">Nubian Sandstone Aquifer System</span> Fossil water aquifer system in northeastern Africa

The Nubian Sandstone Aquifer System (NSAS) is the world's largest known fossil water aquifer system. It is located underground in the Eastern end of the Sahara desert and spans the political boundaries of four countries in north-eastern Africa. NSAS covers a land area spanning just over two million km2, including north-western Sudan, north-eastern Chad, south-eastern Libya, and most of Egypt. Containing an estimated 150,000 km3 of groundwater, the significance of the NSAS as a potential water resource for future development programs in these countries is large. The Great Man-Made River (GMMR) project in Libya makes use of the system, extracting substantial amounts of water from this aquifer, removing an estimated 2.4 km3 of fresh water for consumption and agriculture per year.

<span class="mw-page-title-main">Groundwater recharge</span> Groundwater that recharges an aquifer

Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally and through anthropogenic processes, where rainwater and/or reclaimed water is routed to the subsurface.

<span class="mw-page-title-main">Overdrafting</span> Unsustainable extraction of groundwater

Overdrafting is the process of extracting groundwater beyond the equilibrium yield of an aquifer. Groundwater is one of the largest sources of fresh water and is found underground. The primary cause of groundwater depletion is the excessive pumping of groundwater up from underground aquifers. Insufficient recharge can lead to depletion, reducing the usefulness of the aquifer for humans. Depletion can also have impacts on the environment around the aquifer, such as soil compression and land subsidence, local climatic change, soil chemistry changes, and other deterioration of the local environment.

The Nubian Sandstone is a variety of sedimentary rock deposited on the Precambrian basement in the eastern Sahara, north-east Africa and Arabian Peninsula. It consists of continental sandstone with thin beds of marine limestones, and marls. The Nubian Sandstone was deposited between the Lower Paleozoic and Upper Cretaceous, with marine beds dating from the Carboniferous to Lower Cretaceous.

<span class="mw-page-title-main">Groundwater-dependent ecosystems</span>

Groundwater-Dependent Ecosystems are ecosystems that rely upon groundwater for their continued existence. Groundwater is water that has seeped down beneath Earth's surface and has come to reside within the pore spaces in soil and fractures in rock, this process can create water tables and aquifers, which are large storehouses for groundwater. An ecosystem is a community of living organisms interacting with the nonliving aspects of their environment. With a few exceptions, the interaction between various ecosystems and their respective groundwater is a vital yet poorly understood relationship, and their management is not nearly as advanced as in-stream ecosystems.

<span class="mw-page-title-main">Lens (hydrology)</span> Layer of fresh groundwater

In hydrology, a lens, also called freshwater lens or Ghyben-Herzberg lens, is a convex-shaped layer of fresh groundwater that floats above the denser saltwater and is usually found on small coral or limestone islands and atolls. This aquifer of fresh water is recharged through precipitation that infiltrates the top layer of soil and percolates downward until it reaches the saturated zone. The recharge rate of the lens can be summarized by the following equation:

<span class="mw-page-title-main">Ogallala Formation</span> Geologic formation in the western United States

The Ogallala Formation is a Miocene to early Pliocene geologic formation in the central High Plains of the western United States and the location of the Ogallala Aquifer. In Nebraska and South Dakota it is also classified as the Ogallala Group. Notably, it records the North American Land Mammal Ages (NALMAs) Hemphillian, Clarendonian, and Barstovian. It also includes an excellent record of grass seeds and other plant seeds, which can be used for biostratigraphic dating within the formation. The Ogallala Formation outcrops of Lake Meredith National Recreation Area preserve fish fossils. Similar specimens from the same unit are found at Alibates Flint Quarries National Monument in Texas.

The Central Valley in California subsides when groundwater is pumped faster than underground aquifers can be recharged. The Central Valley has been sinking (subsiding) at differing rates since the 1920s and is estimated to have sunk up to 28 feet. During drought years, the valley is prone to accelerated subsidence due to groundwater extraction. California periodically experiences droughts of varying lengths and severity.

Groundwater in Nigeria is widely used for domestic, agricultural, and industrial supplies. The Joint Monitoring Programme for Water Supply and Sanitation estimate that in 2018 60% of the total population were dependent on groundwater point sources for their main drinking water source: 73% in rural areas and 45% in urban areas. The cities of Calabar and Port Harcourt are totally dependent on groundwater for their water supply.

<span class="mw-page-title-main">Fresh water</span> Naturally occurring water with low amounts of dissolved salts

Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include non-salty mineral-rich waters such as chalybeate springs. Fresh water may encompass frozen and meltwater in ice sheets, ice caps, glaciers, snowfields and icebergs, natural precipitations such as rainfall, snowfall, hail/sleet and graupel, and surface runoffs that form inland bodies of water such as wetlands, ponds, lakes, rivers, streams, as well as groundwater contained in aquifers, subterranean rivers and lakes. Fresh water is the water resource that is of the most and immediate use to humans.

<span class="mw-page-title-main">Coastal hydrogeology</span> Branch of hydrogeology

Coastal Hydrogeology is a branch of Hydrogeology that focuses on the movement and the chemical properties of groundwater in coastal areas. Coastal Hydrogeology studies the interaction between fresh groundwater and seawater, including seawater intrusion, sea level induced groundwater level fluctuation, submarine groundwater discharge, human activities and groundwater management in coastal areas.

The Equus Beds Aquifer is a distinct part the High Plains Aquifer System and is a principal municipal aquifer in south-central Kansas, underlying Hutchinson, McPherson, Newton, and Wichita.

References

  1. 1 2 "Non-renewable groundwater resources: a guidebook on socially-sustainable management for water-policy makers; 2006". unesco.org. Retrieved 2015-12-16.
  2. "Deep Water: Researchers find more below than previously thought". News. Retrieved 2023-05-09.
  3. McIntosh, Jennifer C.; Ferguson, Grant (2021-03-16). "Deep Meteoric Water Circulation in Earth's Crust". Geophysical Research Letters. 48 (5). Bibcode:2021GeoRL..4890461M. doi:10.1029/2020GL090461. ISSN   0094-8276.
  4. "Glossary of Hydrologic Terms". nws.noaa.gov. Retrieved 2015-12-16.
  5. "Groundwater Information Sheet: Salinity". CA State Water Resources Control Board. http://www.waterboards.ca.gov/gama/docs/coc_salinity.pdf
  6. Wilmoth, Adam (2015-11-29). "Reading the Rock". The Oklahoman. Retrieved 2015-12-21 via m.newsok.com/article/5463442.
  7. "The Basics of Underground Natural Gas Storage - U.S. Energy Information Administration". eia.gov. Retrieved 2015-12-16.
  8. McKinney, Michael L.; Schoch, Robert; Yonavjak, Logan (2012-07-01). Environmental Science . Jones & Bartlett Publishers. ISBN   9781449628338.
  9. "Groundwater depletion in the United States (1900–2008)". pubs.er.usgs.gov. doi:10.3133/sir20135079 . Retrieved 2015-12-16.
  10. "USGS High Plains Aquifer WLMS: Generalized geology and hydrogeology". ne.water.usgs.gov. Retrieved 2015-12-16.
  11. Thorweihe, Ulf (1998). "Groundwater Resources of the Nubian Aquifer System". Sahara and Sahel Observatory .
  12. de Vries, J. J.; Selaolo, E. T.; Beekman, H. E. (2000-11-30). "Groundwater recharge in the Kalahari, with reference to paleo-hydrologic conditions". Journal of Hydrology. 238 (1–2): 110–123. Bibcode:2000JHyd..238..110D. doi:10.1016/S0022-1694(00)00325-5.
  13. Mazor, E.; Verhagen, B.Th.; Sellschop, J.P.F.; Jones, M.T.; Robins, N.E.; Hutton, L.; Jennings, C.M.H. (1977). "Northern Kalahari groundwaters: Hydrologic, istopic and chemical studies at Orapa, Botswana". Journal of Hydrology. 34 (3–4): 203–234. Bibcode:1977JHyd...34..203M. doi:10.1016/0022-1694(77)90132-9.