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Nebraska Sand Hills Extensive tracts of sand dunes are common throughout the central Great Plains and Rocky Mountains. The greatest among these is the Nebraska Sand Hills, which cover nearly 20,000 square miles (52,000km2) in north-central Nebraska and southernmost South Dakota.
Pac-Man farming and the disappearing Ogallala aquifer At first glance, this 2000 Landsat 7 image of Garden City in Kansas looks like an overly ambitious game of Pac-Man. But these rigid, circular patterns are actually crop fields, with tan circles representing harvested crops, and the red circles denoting healthy, irrigated crops. Central pivot irrigation created the Pac-Man motif of Garden City’s agriculture, and has transformed the local economy into America’s breadbasket powerhouse.
Underneath the Dry Valleys may not be so dry
A recent study led by a researcher from the University of Tennessee revealed that there are interconnected aquifers beneath the glaciers and permafrost. The briny liquid is about 300m under the surface and around twice the salinity of sea water and of course, is well below freezing (though it stays a liquid due to the salinity and pressure).
To map this groundwater, the team used a new instrument called SkyTEM which can generate images of subsurface environments. It does this by measuring the electrical resistivity beneath the frozen ground, and as liquids, especially salty liquids, are more conductive than ice, soil or rock it is possible to differentiate what lies beneath the surface.
If Blood Falls (see previous post:http://on.fb.me/1FJVyeK) is representative of the groundwater discovered in this study, then it is likely that a rather diverse and large living ecosystem is existing below the Dry Valleys! This is particularly important for understanding the ways in which life might survive on Mars, as the Dry Valleys have conditions remarkably similar to those of Mars.
It is well known that sub-glacial water exists throughout the icy continent, but this is the first time subsurface water has been discovered in areas that are not covered by ice.
-MJA
Image credit: VALMAP
Further reading: http://bit.ly/1I206NM
Reference: Mikucki, J. A., Auken, E., Tulaczyk, S., Virginia, R. A., Schamper, C., Sørensen, K. I., ... & Foley, N. (2015). Deep groundwater and potential subsurface habitats beneath an Antarctic dry valley. Nature Communications, 6.[_
_](https://www.facebook.com/TheEarthStory/photos/a.352867368107647/870438003017245/?type=1&theater#)
Fossil Water in Africa
Is water a renewable or nonrenewable resource? Like many questions in science, the answer is “it depends”. Surface water, in ideal conditions, is replenished through rainfall and the hydrologic cycle (although like we’ve seen in recent droughts—such as the one in California—this not always the case). Groundwater can be replenished this way too, however, some aquifers contain fossil water—very old water that is definitely a finite resource.
Although it's a bit of a misnomer since it isn't quite a fossil, he term “fossil water” refers to groundwater that is no longer being replenished, originally got there by processes that are no longer active, and may have been untapped for thousands of years. Most commonly, fossil water was deposited in wetter climates that no longer exist. Although it is a bit of a misnomer since it’s not a fossil, the name works as comparable to nonrenewable fossil fuels as fossil water resources are also nonrenewable—since the water is no long being replenished, when it’s gone, it’s gone.
The world’s largest fossil water aquifer is, ironically, sitting below the world’s largest desert. The Nubian Sandstone Aquifer System lies underneath the Sahara, specifically Egypt, Libya, Sudan, and Chad. Studies show that portions of this water may be as old as a million years, although on average the water is between 20,000-50,000 years old.
Four thirsty desert countries all grappling after the same water could potentially cause political conflict, but these countries have done fairly well at sharing their resource. A collaboration to research and regulate the aquifer was established in the 90’s and remains one of only four official agreements in the world regarding international (ground) waters.
-CM
Photo credit (an oasis in Libya): Sfivathttp://bit.ly/1HQOlIj
For a map of the Nubian Sandstone Aquifer System:http://bit.ly/1yVRKjZ
For more information: http://bit.ly/1y4CA0s
To read more about another fossil water aquifer, the Ogallala aquifer: http://on.fb.me/1NTLNe9
What is the deal with the Ogallala aquifer?
Located in the center of the United States is a region known as the high plains. It is comprised of portions of eight states and has a rough area of 450,000 km2. World renowned for its agricultural production, the region often touts the nickname the United States’ “breadbasket.” It contains about 5% of the country’s area, yet produces 30% of the nation’s agriculture and 40% of its beef. Looking at this landscape one hundred years ago, it would never be guessed that this region could not only produce that amount of food, but sustain that level of production for years.
The High Plains climate is one of low humidity, low to moderate precipitation, frequent winds and a high rate of evaporation. In other words, it was not suitable for intensive agriculture. Two droughts in the 1900s, spurred technological advancements in well drilling and groundwater pumping. From the 1950s to the 1970s groundwater withdrawal increased from 5 km3/year to 23km3/year. Depletion of one of the world’s largest aquifers had begun. (A km3 may be hard to visualize. It is the amount of water that covers 1 square kilometer of surface, 1 kilometer deep. It is an extremely large amount of water!)
An aquifer is not an underground river or an underground cave full of water. It is saturated sediment particles. A good analogy is a sponge. A wet sponge does not look like it is holding much water but once it is squeezed, its potential is revealed. The same is largely true for soils. They do not look like much but they can transmit and store a large amount of water. The Ogallala is not the technical name for this aquifer, whose real name is the High Plains aquifer. The Ogallala is one of the formations that make up the High Plains aquifer. The other two formations, the Brule and the Arikaree, are not as hydraulically conductive or large, which is why some refer to the aquifer as the Ogallala.
Water levels in this region have dropped precipitously over the past sixty years. Some places in Texas and Kansas have had water tables declines of fifty meters. If the amount of water entering the aquifer as recharge (rain, re-infiltrated irrigation water) is equal to the amount of water leaving the aquifer (irrigation, domestic use) water levels will stay constant. A water table drop of fifty meters indicates that recharge is minimal and groundwater withdrawals are exhausting the groundwater reserves.
The problem with managing the High Plains aquifer is that generalizations are tough to make. The aquifer is huge. It extends from Southern South Dakota to northern Texas. The eastern portion of the aquifer can receive over 50 cm more rain per year than areas in the west. On top of that, temperatures vary moving north to south, with temperature variations of 10-15°C common. Areas in the southwest region of the aquifer receive little rain and the rain that does fall is evaporated before it can enter the soil. Compare this to the northern portion of the aquifer, where water can infiltrate before it is evaporated and it is easy to see that climate has a huge effect on recharge rates. This may be part of the reason where the largest water table drops have been seen in Kansas and Nebraska.
Groundwater in arid regions is a vital resource. In some places it is the only source of drinking water for people. Agriculture uses an estimated 95% of the water that is withdrawn from the High Plains aquifer. It makes sense to curb and restrict the amount of water that can be withdrawn. Yet, so much of our food is produced in the region and thousands of livelihoods depend on the Ogallala. It is a complex situation that will be interesting to watch as groundwater levels continue to drop.
KKS
Reading about aquifer:
Photo courtesy of Texas A&M University
OMAHA!
This photo shows some outcrops of the Dakota formation…which happens to underlie the area around Omaha, Nebraska.
The Dakota formation is a sandstone. It is cretaceous in age, formed when sea levels were much higher and a shallow ocean covered much of the interior of the North American continent. The sandstones were deposited in environments near the shoreline of this seaway as the water levels rose and fell.
The sand grains were delivered from rivers that were eroding both the Rocky Mountains in the west and higher ground in the east. Those rivers carried sand and mud to the continent’s interior, where it was deposited, buried, and gradually cemented into sandstones.
Today this formation underlies much of the Great Plains. It runs from Nebraska in the south to Minnesota in the north, with a thickness of about 100 meters.
In Nebraska, there are a variety of sediments on top of it, including the thick Pierre clay, deposited when the Cretaceous seaway became deeper, and the younger sediments deposited during the recent glacial periods.
Sandstones have quite a bit of pore space; open gaps between the sediment grains which can fill with water. The Dakota Sandstone, although deeply buried in places, hosts a variety of aquifers that have been tapped for irrigation in places. The waters are supplied in the areas near Omaha and near the Rocky Mountain front, where the unit outcrops at the surface.
-JBB
Image credit: Kansas Geological Survey http://www.kgs.ku.edu/Publications/Bulletins/ED10/04_occur.html
An Oasis in the Desert.
In south-western Peru, in amongst the desert landscape, you can find the village of Haucachina. Development took place around a lagoon located in the area and serves a modest population of around a hundred permanent residents.
For drinking water, the inhabitants installed private, groundwater wells. Unfortunately, this water extraction caused the level of water in the oasis to drop dramatically. As a result, water has to be pumped in from the city of Ica, 8 kilometres away, to preserve this area of natural beauty.
Oases form when underground rivers or aquifers break the surface forming a body of water. However, prior to this knowledge, some interesting folklore was often attributed to these formations. In this case, local legend has it that the lagoon was created when a young hunter disturbed a bathing princess. The princess fled, leaving the pool of water behind her!
-Jean
Image by: Ingo Mehling
Groundwater depletion in the United States
In 2002, the United States and Germany teamed up to launch a satellite known as GRACE, the Gravity Recovery and Climate Experiment. That satellite's goal was to monitor the earth’s gravity field in unprecedented detail, giving insights into the Earth’s shallow levels. You might not think about variations in the Earth’s gravity, but as described by Isaac Newton, every object exerts gravity on every other object. It can’t see the gravity change from me heading home every night, but changes in the gravity field from earthquakes, melting or expanding of glaciers, and so on can all be measured by GRACE with high precision.
GRACE is so precise that it is able to measure the gravity change associated with a removal or addition of 1.5 centimeters of water. That gives it enormous abilities to measure changes in water storage within the ground.
Groundwater is a major resource globally. In areas where there isn’t sufficient rainfall to support agriculture, or in dry years, pumping groundwater often fills in for a lack of precipitation. On top of that, for many areas, it's the main source of drinkable water due to pollution of surface supplies.
Groundwater can take decades to centuries to adjust to climatic conditions and refill or drawdown, so areas of heavy use are using up a limited resource that, if depleted, will not be replenished in our lifetime. The GRACE satellite is able to use changes in gravity to monitor the levels of drawdown or replenishment in great detail.
This map shows groundwater drawdowns and increases over the first 10 years of the GRACE mission. Deep red is a drawdown of 3 centimeters per year, dark blue is an increase of 3 centimeters per year. Over the time period, areas such as Texas and Alabama have seen total decreases in ground water of 20 to 30 centimeters.
The dark blue areas are interesting – they suggest that the repeated floods in the Missouri River basin might indeed be a unique event; they’re pushing groundwater recharge in those areas at a level sufficient to increase storage over the last decade.
The reddish areas are of course the concern; many of them are centered in agricultural areas or highly populated areas, such as California or in the Great Plains and they suggest that throughout the area, groundwater supplies are continuing to be depleted.
This depletion will continue to put strain on the people who live and work in these areas. Groundwater isn’t coming back any time soon, and not only does depletion increase the risk of running out, every centimeter of drawdown makes it more expensive to pump out the next centimeter since the water moves farther from the surface.
-JBB
Image credit: Science Magazine available for teaching: http://www.sciencemag.org/content/340/6138/1300.full (subscription required for full paper)
Greetings from the R/V Tangaroa, offshore the South Island of New Zealand. At the moment we are deploying a Controlled-Source Electromagnetic instrument offshore the Canterbury Plains, which will allow us to measure sub-seafloor resistivity. Once the data are integrated with new multi-channel seismic reflection data that we plan to acquire next week, we will be able to characterize the distribution and geometry of one of the shallowest offshore freshwater aquifers in the world. We are 12 days out on a 24 day research cruise. In the following weeks we plan to ground-truth our geophysical data by acquiring seafloor pore-water and water column samples where the groundwater is seeping into the sea to determine its origin and age.
You can follow our cruise on: www.facebook.com/marinegeologyseafloorsurveying/ The cruise is supported by a European Research Council grant (MARCAN) and NIWA.
Silver Springs, where 550 million gallons of water flow out of the ground daily from the Floridian Aquifer.
Silver Springs State Park, FL
Mantle degassing in the Rockies.
As you bathe in Colorado's hot springs, your legs may be being tickled by bubbles containing mantle gas, seeping through the whole thickness of the continent to the surface. Their presence far from plate boundaries, where most of the interaction between mantle and surface occurs, has been a surprise to tectonicists.
These mantle gases are found mixed with groundwater, and their rise through the crust is linked to basement penetrating faults, providing a direct connection for mantle and crustal fluids to mix. The fluids then emerge as hot springs or travertine marble terraces, generally linked with the same extensional tectonics that produced the faults. Mantle contributions were found to increase with seismic activity, and lower again afterwards. The team has named them xenowhiffs, foreign gases in groundwater, after the mantle xenoliths brought up in volcanic eruptions.
The results came from measuring the ratios of helium and carbon dioxide across 25 hot springs and a variety of travertine deposits throughout the Rockies. Helium has two main isotopes, called He3 (light) and He4 (heavy). The heavy isotope is created by radioactive decay of metals like uranium, that are mostly concentrated in the crust. The lighter one is a relic of the Earth's formation. Most of the crust's light helium has been lost to space during post Archaean crustal reworking, so the only He3 left on Earth is believed to lie in deep mantle reservoirs. A high proportion of He3 relative to He4 if held to indicate mantle contributions, whether found in lavas, volcanic gases or groundwater. These results were then compared with seismic tomographic maps of earthquake wave speeds under the western USA to compare mantle gases with magma reservoirs. Low wave speeds tend to indicate the presence of magma.
Over a quarter of the helium in the groundwater, and a whopping three quarters of the CO2 was found to come from a mantle source, transported by fluids that had moved though more than 50Km of continental crust. Due to the complex tectonic history, ascribing exact sources for these gases is hard. Some may come from the recent extension related magmatism in the basin and range province, some may be due to the subduction of the Farallon plate and the Laramide Orogeny, which hydrated the mantle, lowering its melting point, resulting in magma that is visible on seismic tomograms. This mountain building event also heated and thinned the continental keel. Another possible contribution may be the consequences of part of the subducting Farallon slab breaking off and sinking into the deeper mantle as its minerals pass through the eclogite pressure transition and metamorphose to denser forms.
The pervasive presence of mantle gases in groundwater throughout the western USA has several implications. Carbon sequestration plans may not mitigate atmospheric CO2 as efficiently as we hope, because if mantle gases can pass through the whole thickness of the continent via faults and seepage, and the whole west is seismically active, then no formation may be truly safe from leakage events if used to store man made CO2. The ratios suggest that the mantle gases are taking less than three million years to pass through the crust. The relative contributions of fault and seepage based transport will have to be estimated, though with careful assessment procedures sequestration should work, since gases have been injected into reservoirs with favourable geometry without signs of significant leakage. It must also be emphasised that the amount of CO2 degassing from the mantle is minute relative to anthropogenic emissions, so like volcanoes, this process cannot be blamed for climate change.
A second problem is related to contamination of water resources, since these mantle gases bring dissolved metals such as arsenic and uranium with them, that then end up in the groundwater. Some of the springs had higher levels of arsenic than permitted for human or agricultural use. As the easily mined aquifers of the west, the Oglala in particular, become depleted, people are going to be seeking water elsewhere, and the risk that this metal rich water will be used is high. This will either require costly separation of the metals, or accepting the type of serious health problems that plague Bangladesh, ever since NGO's dug wells into an arsenic bearing aquifer back in the 70's and 80's.
Tectonically, these results imply that the entire mantle beneath the western USA is degassing heterogeneously. Similar results have been found near the San Andreas fault and other places in California and Nevada. By contrast, springs above the thick craton of the Canadian Shield show no similar geochemical connection between mantle and surface. This type of research offers vital clues to the nature of the complex interactions between asthenosphere, mantle and crust, in a tectonically complex area of extension, accreted terranes and recent orogenies.
Loz
Image credit for Pinkerton Hot Spring: E.R. Pape, via state geothermal data project.
http://www.geosociety.org/gsatoday/archive/15/12/pdf/i1052-5173-15-12-4.pdf
Original paper, paywall access: http://gsabulletin.gsapubs.org/content/121/7-8/1034.abstract
Earth Science Week 2015: Water, water everywhere but not a drop to drink?
Water is a valuable resource and, with the predicted global warming, it’s due to become a key bargaining chip in world trade. Even in countries with minimal rainfall, vast reserves of water may exist within the ground, held within porous rocks known as aquifers. While these rocks are being constantly recharged, these processes happen on a geological time scale and therefore it is fairly easy for humans to extract water at a rate that far exceeds the natural supply.
A good example of this were the mysterious Garamantes who lived in the Sahara desert between 1CE and 500CE. The civilisation is thought to have been highly advanced, with irrigation systems that turned the surrounding sand from inhospitable desert to a lush and fertile paradise. By exploiting the natural aquifers beneath their feet the Garamantes were able to grow wheat and barley in an area otherwise blanketed in sand. However, the aquifers eventually dried up and this is thought to be the key driver of the Garamantes’ swift and sudden demise.
Even today, many cities around the globe depend on the water held in aquifers to provide for the millions of people who live there. In London the dependence on aquifer sourced water has led to Thames Water developing the North London Artificial Recharge Scheme. In times of heavy rainfall, engineers recharge aquifers via 31 carefully placed boreholes. This means in times of drought the aquifer can be used to supply an extra 180 million litres of water a day, roughly enough to support the needs of 1.2 million people.
However, aquifers do not always contain water suitable for human consumption. This was learned the hard way in the 1970s when UNICEF started drilling tube wells (just as the name suggests, a tube drilled to around 200m depth with a pump attached to extract water from the ground) in Bangladesh in response to the lack of clean drinking water. Surface water was often contaminated by bacteria leading to outbreaks of Cholera and other water borne diseases. To combat this, a huge campaign was run and vast numbers of wells were drilled, to the point that in 1997 UNICEF announced that it had already surpassed its goal for the year 2000 by supplying over 80% of the Bangladeshi people with a means of accessing clean water.
Unfortunately, this was when disaster struck. Up to half of all the tube wells were drilled into aquifers containing life threatening concentrations of arsenic. In the areas worst affected, people began to develop skin lesions as well as skin and internal cancers. The World Health Organisation (WHO) declared an emergency and medical teams were dispatched to try and isolate the cause of the arsenic poisoning. It didn’t take long before scientists realised the arsenic was within the groundwater itself and had been leached from the underlying rock units. While geology was not the only factor at play, a better understanding of the underlying strata may have raised concerns before the project even begun. In many parts of the world water is regularly tested for arsenic and in some American states concentrations can be as high as those seen in Bangladesh.
So how does this story fit into the topic of Earth Science Week? Well many geologists spend their days trying to understand the underlying rock units so that safe and reliable water can be fed into people’s homes. The more people that are interested in geoscience the better our understanding of the Earth, and the resources it holds, will be. As the demand for oil/minerals/water increases so does the demand for people who understand the complex and diverse nature of the subsurface and are keen to expand on the limited knowledge we already have.
Image Credit: USGS sourced from http://ti.me/1LzbZJ8 References: http://bit.ly/1L5A3X4 http://bit.ly/1OrzlY7 http://bit.ly/1hxoIEv Further Reading: http://bit.ly/1qt9bCv
Groundwater depletion worldwide
Groundwater is an important resource worldwide. Unlike surface water, groundwater supplies are typically clear of pollutants like biological waste and groundwater can represent a stable water supply during drought years.
Groundwater supplies are therefore used worldwide as resources for people and for agriculture. In the United States, removal of groundwater from the aquifers in the Central Plains and California is already a major issue as pumping is gradually depleting these aquifers, removing a resource that will take hundreds of years to replenish. This result is well established in the United States – we can even monitor how much the land surface shifts in response (http://tmblr.co/Zyv2Js1W8T6Bu), but what about the rest of the world?
Where there is clean groundwater, it will likely be used as a resource and not every country has the resources available to monitor how rapidly their aquifers are being depleted. Thankfully, there is a way to monitor groundwater resources worldwide: gravity.
When water is pumped out of the ground, mass is removed and the total gravity in a location is slightly changed. In 2002, NASA launched a pair of twin satellites called the Gravity Recovery and Climate Experiment (GRACE) program – the satellites precisely measure the distance between each other as they orbit the planet and that distance can be converted to a measurement of the Earth’s gravity field. Using this data, a group led by researchers from UC Irvine was able to compile a 10-year record of groundwater depletion worldwide. What they found is troubling, to say the least.
We’ve commented on the threatened High Plains aquifer in the United States before (http://tmblr.co/Zyv2Js1mqMTRu) but that aquifer looks stable compared to the rapid depletions elsewhere in the world. Out of the world’s 37 largest aquifers, more than 1/3 is being rapidly depleted, with water levels decreasing by several centimeters per year on average and with little to no active replenishment. Considering that over 60 million people depend on it and it is being rapidly drawn down, the Arabian Aquifer that covers much of the Arabian Peninsula was listed as the most threatened aquifer system in the world. Other stressed aquifers include the Indus Basin in India and Pakistan and several found in North Africa.
As levels decrease, the water in aquifers tends to get saltier and it gets more expensive to pump that water to the surface. Eventually, the water can get so salty that neither people nor agriculture can to use it. What happens when an aquifer that millions of people rely on suddenly is unable to support those people? In many of these areas there is no other readily available source of clean drinking water, so what do the people do? Are governments prepared to supply other sources of drinking water or will people become refugees?
These are questions we don’t have to answer yet, but they’re questions that the world might have to answer within our lifetimes if these resources continue to be depleted at these rates.
-JBB
Image credit: UC Irvine http://bit.ly/1SlrZnS
Read more: http://onlinelibrary.wiley.com/doi/10.1002/2015WR017351/full http://onlinelibrary.wiley.com/doi/10.1002/2015WR017349/full
Pac-Man farming and the disappearing Ogallala aquifer
At first glance, this 2000 Landsat 7 image of Garden City in Kansas looks like an overly ambitious game of Pac-Man. But these rigid, circular patterns are actually crop fields, with tan circles representing harvested crops, and the red circles denoting healthy, irrigated crops. Central pivot irrigation created the Pac-Man motif of Garden City’s agriculture, and has transformed the local economy into America’s breadbasket powerhouse.
Garden City is in the middle of the High Plains, a region in the Midwest known for its dry summers and winters with less than 45 cm of rain a year. When central pivot irrigation was first developed, it shifted Garden City from its dependence on sporadic rainfall to groundwater from the Ogallala aquifer. Farming in the High Plains now relies fully on the Ogallala aquifer, one of the world’s largest groundwater sources that spans from Wyoming to Texas.
You’ve likely seen the equipment for central pivot irrigation before — a water pump that is extended down to an underground aquifer in the center of a crop field is connected to a wheeled pivot hooked up with sprinklers. The pivot slowly rotates around the field, spraying and irrigating the crops with fresh groundwater, creating the circular Pac-Man motif that is now synonymous with groundwater-dependent farming.
Despite once having enough water to cover all fifty American states by half a meter, the Ogallala aquifer is slowly running dry. Annually, about one-fifth of the crops in the United States are grown using fresh groundwater from the Ogallala aquifer, a volume of water equivalent to that of 18 Colorado Rivers. The semi-arid climate of the High Plains doesn’t supply sufficient rainfall to naturally recharge the aquifer, and in some counties, the water table has decreased by as much as half a meter in one year. Researchers estimate that agricultural production using water from the Ogallala aquifer will begin to decline after 2040, but if farmers could lower groundwater usage by just 20 percent, the decline will only begin after 2070.
But here is the real question — can the aquifer be sustained forever? Researchers estimate that it would take 6000 years for the aquifer to be naturally recharged. But for that to happen, farmers would immediately need to reduce their groundwater usage by 80 percent, which would dramatically lower crop production. That possibility is as realistic as beating the world record in a perfect game of Pac-Man — the Ogallala aquifer is an indispensable component of a $20-billion industry that exports crops and crop products to many parts of the world.
So the original question remains — how much more can the Ogallala aquifer be preserved as a finite resource? Many farmers are already preparing for that day of reckoning by growing crops don’t need irrigation and require less water. Other farmers are developing new methods that don’t depend on groundwater: instead of completely plowing fields after harvest, new crops are planted in the residual stems, which helps to lower soil erosion and moisture loss from the soil. Federal programs also offer incentives to farmers who help conserve grasslands — 25 million acres of which have been converted to crop fields since 1982 — that can be used to graze cattle and buffalo. But at the same time, subsidies for irrigation-dependent crops, such as corn, soybeans, and cotton, are higher than that for grassland conservation, with national and worldwide demand for irrigation-dependent crops remaining as high as ever.
So for many farmers, the choice to continue irrigating their crop fields with Ogallala groundwater is a straightforward one. However, the federal government and agricultural industry will eventually have to come to terms with the future of farming in the High Plains — farming using a water source that will not depend on the seemingly infinite Ogallala aquifer.
-DC
Photo credit: http://1.usa.gov/1G0qGFt More reading: http://1.usa.gov/1MtEF94 http://on.doi.gov/1Jszwjp
More on center pivot irrigation: http://bit.ly/1T1VSec http://bit.ly/1FCuutm More on the Ogallala aquifer: http://bit.ly/1Qxwedl http://wapo.st/1dk7QiD http://bit.ly/1Iq68dh
If you feel like trying against the world Pac-Man record: http://bit.ly/1eTY0VH
"aquifers such as the Oglala that have sustained an artificially high population and level of human activity throughout the West" -- I must be really stupid, but what is the Oglala aquifer? I know about the Ogallala aquifer, but that's in the midwest, not the west. Are there big aquifers west of the Rockies that are sustaining western populations? I thought the problem was that we've been depending on snowpacks in the Sierras and the Rockies, and thy've dried up.
Not sure how long ago the post was this article refers to, but there’s a translation issue that’s being confusing here. The most accurate name I know of for the aquifer that runs from Texas to the Dakotas is the “High Plains” aquifer. However, it is also known as the Ogallala aquifer, as you note.To my knowledge, the Ogallala aquifer is named after Ogallala, a town in Nebraska. That town carries the name Ogallala after the Oglala, one of the original seven tribes of the Lakota people, part of the Sioux nation in North America. Therefore, basically the spelling depends on whether the nickname of the aquifer is being taken from the town or it is being taken directly from the Sioux nation name.This appears to be the 2nd “indigenous term spelling” issue I’ve had to interpret for The Earth Story this week and I’m hoping I got it somewhat accurate.
Fossil Water in Africa
Is water a renewable or nonrenewable resource? Like many questions in science, the answer is “it depends”. Surface water, in ideal conditions, is replenished through rainfall and the hydrologic cycle (although like we’ve seen in recent droughts—such as the one in California—this not always the case). Groundwater can be replenished this way too, however, some aquifers contain fossil water—very old water that is definitely a finite resource.
The term “fossil water” refers to groundwater that is no longer being replenished, originally got there by processes that are no longer active, and may have been untapped for thousands of years. Most commonly, fossil water was deposited in wetter climates that no longer exist. Fossil water resources are nonrenewable—since the water is no long being replenished, when it’s gone, it’s gone.
The world’s largest fossil water aquifer is, ironically, sitting below the world’s largest desert. The Nubian Sandstone Aquifer System lies underneath the Sahara, specifically Egypt, Libya, Sudan, and Chad. Studies show that portions of this water may be as old as a million years, although on average the water is between 20,000-50,000 years old.
Four thirsty desert countries all grappling after the same water could potentially cause political conflict, but these countries have done fairly well at sharing their resource. A collaboration to research and regulate the aquifer was established in the 90’s and remains one of only four official agreements in the world regarding international (ground) waters.
-CM
Photo credit (an oasis in Libya): Sfivat http://bit.ly/1HQOlIj
For a map of the Nubian Sandstone Aquifer System: http://bit.ly/1yVRKjZ
For more information: http://bit.ly/1y4CA0s
http://bit.ly/1Fh1e0C
http://bit.ly/1FBMUxc
To read more about another fossil water aquifer, the Ogallala aquifer: http://on.fb.me/1NTLNe9
What is the deal with the Ogallala aquifer?
Located in the center of the United States is a region known as the high plains. It is comprised of portions of eight states and has a rough area of 450,000 km2. World renowned for its agricultural production, the region often touts the nickname the United States’ “breadbasket.” It contains about 5% of the country’s area, yet produces 30% of the nation’s agriculture and 40% of its beef. Looking at this landscape one hundred years ago, it would never be guessed that this region could not only produce that amount of food, but sustain that level of production for years.
The High Plains climate is one of low humidity, low to moderate precipitation, frequent winds and a high rate of evaporation. In other words, it was not suitable for intensive agriculture. Two droughts in the 1900s, spurred technological advancements in well drilling and groundwater pumping. From the 1950s to the 1970s groundwater withdrawal increased from 5 km3/year to 23km3/year. Depletion of one of the world’s largest aquifers had begun. (A km3 may be hard to visualize. It is the amount of water that covers 1 square kilometer of surface, 1 kilometer deep. It is an extremely large amount of water!)
An aquifer is not an underground river or an underground cave full of water. It is saturated sediment particles. A good analogy is a sponge. A wet sponge does not look like it is holding much water but once it is squeezed, its potential is revealed. The same is largely true for soils. They do not look like much but they can transmit and store a large amount of water. The Ogallala is not the technical name for this aquifer, whose real name is the High Plains aquifer. The Ogallala is one of the formations that make up the High Plains aquifer. The other two formations, the Brule and the Arikaree, are not as hydraulically conductive or large, which is why some refer to the aquifer as the Ogallala.
Water levels in this region have dropped precipitously over the past sixty years. Some places in Texas and Kansas have had water tables declines of fifty meters. If the amount of water entering the aquifer as recharge (rain, re-infiltrated irrigation water) is equal to the amount of water leaving the aquifer (irrigation, domestic use) water levels will stay constant. A water table drop of fifty meters indicates that recharge is minimal and groundwater withdrawals are exhausting the groundwater reserves.
The problem with managing the High Plains aquifer is that generalizations are tough to make. The aquifer is huge. It extends from Southern South Dakota to northern Texas. The eastern portion of the aquifer can receive over 50 cm more rain per year than areas in the west. On top of that, temperatures vary moving north to south, with temperature variations of 10-15°C common. Areas in the southwest region of the aquifer receive little rain and the rain that does fall is evaporated before it can enter the soil. Compare this to the northern portion of the aquifer, where water can infiltrate before it is evaporated and it is easy to see that climate has a huge effect on recharge rates. This may be part of the reason where the largest water table drops have been seen in Kansas and Nebraska.
Groundwater in arid regions is a vital resource. In some places it is the only source of drinking water for people. Agriculture uses an estimated 95% of the water that is withdrawn from the High Plains aquifer. It makes sense to curb and restrict the amount of water that can be withdrawn. Yet, so much of our food is produced in the region and thousands of livelihoods depend on the Ogallala. It is a complex situation that will be interesting to watch as groundwater levels continue to drop.
KKS
Reading about aquifer:
http://on.doi.gov/19MiFIc
http://on.doi.gov/1y3rgCh
http://bit.ly/1DrDJ4B
Photo courtesy of Texas A&M University
