Planet Earth/5h. Earth’s Endangered Lakes and the Limits of Freshwater Sources
Earth’s Endangered Freshwater edit
The lakes of Earth are slowly disappearing, including the largest natural lake in Utah, the Great Salt Lake. Lakes provide a regional base level for the flow of freshwater, that captures meteoric water. Meteoric water is water derived from precipitation in the form of rain and snow. This includes water from lakes, rivers, and ice-melts, which all originate from precipitation indirectly. Meteoric water is in demand, particularly in the dry desert latitudes between 30° to 40° latitudes, where water scarcity is a major issue. Some of the largest and fastest growing cities in the United States are located in these southwestern deserts including Phoenix, Las Vegas, Los Angeles, Denver, and Salt Lake City. These cities and the agricultural regions around them are dependent on a fresh supply of water.
The urban growth of the American Southwest has led to many projects to divert freshwater toward cities and prevent water from reaching either the ocean or saline lakes where the water can no longer be used for drinking or agriculture without costly desalination processes. One of the most drastic examples of this capture of freshwater was the development of the aqueduct system that feeds into the urban center of Los Angeles. For the last hundred years, the city of Los Angeles has diverted large amounts of water from the water drainages of the Colorado River Basin, the Owens Valley, and Feather River Basin. The story of the dry lake beds of Owens Valley is a story of how water was diverted across the Mojave Desert in man-made canal systems to transport freshwater to the city, but subsequently resulted in the draining of Owens Lake. Owens Lake was completely drained by the 1940s, other naturally occurring lakes have also shrunk in the last fifty years from water usage in Southern California including Mono Lake, the Salton Sea, and in Nevada Walker Lake, which has been at record low levels. Utah has seen the lake levels of the Great Salt Lake drop to 35% of previous lake levels more than a century ago, when John Fremont mapped the geography of the Great Salt Lake in the 1840s. At that time Lake Utah nearly connected with the Great Salt Lake along the Jordan River, and the lake contained six islands. Today the Great Salt Lake is a sliver of its former expanse, with a dramatic drop in lake levels since the early 1980s, when levels were higher, due to higher runoff.
The Great Salt Lake is fed from three major rivers, the Bear River to the north, the Weber River from the east, and the Jordan River from the south. The Great Salt Lake occupies a low basin, known as the Great Basin which extends across much of western Utah to the Nevada border. This large basin was once entirely filled with a massive lake called Lake Bonneville about 25,000 years ago, which extended into Cache Valley, draining into the Snake River valley toward the north in Idaho. Today, the lake lacks any external drainage, and the water is subjected to evaporation in the dry climate. This dry lake bed has left behind massive deposits of salts, which form salt flats that extend for miles on the flat topography of the Great Basin, which is only broken by graben mountain ranges that poke above the barren landscape. Few plants can tolerate the salt, and the ground lacks vegetation. Wind storms from the west carry salts and other dust particles in suspension, which results in respiratory health issues for people living on the salt flats and dried up shorelines of the Great Salt Lake. The major reason for the declining lake levels is due to the construction of dams and diversion of water away from the lake. This includes Deer Creek Reservoir above Provo, Jordanelle Reservoir near Park City, and Pineview Reservoir near Ogden, which capture freshwater for use in municipal drinking water and agriculture for the Salt Lake City metropolitan area.
The plight of the Great Salt Lake is not in isolation, many other saline lakes on Earth are also shrinking due to increased demands on freshwater. Some of the most dramatic examples of saline lakes disappearing on Earth can be found with the Aral Sea which lays across the Kazakhstan and Uzbekistan border in Asia. The Aral Sea used to be the fourth largest lake on Earth, covering 26,300 square miles (about the size of West Virginia), but in 2009 the lake shrunk to only 2,600 square miles, a 10% of its previous size. This reduction was due to the diversion of freshwater through canals and dams, toward regions with agricultural crops between the border of the two countries. Lake Urmia in Iran, has also seen a dramatic decline in lake levels since the year 2000, with water diverted for crops, resulting in a dry lake bed forming in the northern part of the country. As human populations grow, freshwater becomes a valuable, but limited resource.
The Chemistry of Freshwater edit
Freshwater contains fewer dissolved salts than ocean water, but does contain some dissolved molecules. Rain tends to be acidic, with a pH between 6 to 7 caused by the dissolution of carbon dioxide in the atmosphere which forms carbonic acid. Streams tend to buffer this somewhat with pH between 6 to 8, but in general freshwater tends to be more acidic than ocean water, which has a pH higher than 8. This low pH results in the ability of freshwater to dissolve calcium carbonate to form bicarbonates and calcium ions. Calcium carbonate is abundant in rocks, particularly limestones. The ability of freshwater to dissolve calcium carbonate into ions of bicarbonate and calcium results in what is called hard water and soft water. Hard water contains more ions of bicarbonate and calcium, as well as magnesium, which results in white crusty rings of calcium carbonate in pipes, faucets and bath tubs. It also makes it difficult to wash soap off. Soft water contains less ions of bicarbonate and calcium, and more easily rinses soaps off your skin. Often houses are equipped with a water softener, which removes some of these ions, to make water easier to use when cleaning and in the shower. Often freshwater will become hard when it passes through a region with thick limestones and other calcium carbonate-rich rocks. As a result of its lower pH, freshwater dissolves calcium carbonate in limestones resulting in something called karstification. Karstification is the process of water dissolving rock to produce an irregular surface on rocks, and if allowed to continue for many years, eventually form caverns and caves underground.
Ground Water edit
Much of the world’s supply of freshwater is found underground, where water occupies the spaces between the grains in rocks. Porosity is the amount of space within a rock. A rock, such as limestone which has undergone karstification is said to have high porosity because there are many spaces within the rock for water to occupy. Permeability is how well-connected spaces are within rocks. If a rock has high permeability, water is able to easily flow between spaces within the rock. An aquifer is a rock layer that has both high porosity and high permeability, allowing water to easily flow and occupy the space within the rock layer. Water wells are often dug down to an aquifer to extract this source of freshwater from below ground. The water table is the dynamic level that water can be found in the subsurface, and fluctuates greatly depending on the season, and local precipitation of the area. Aquifers are filled during times of recharge, where rain or snow melt trickles down into these layers below ground, or where water flows above these areas along the course of a river or below a lake. Discharge occurs when these aquifers contribute water to a flowing stream or river, often in cracks where the aquifer is exposed above a canyon or river cut, producing a spring. A spring is any flow of groundwater emerging from the ground surface due to discharge.
This hidden source of underground freshwater is an important resource to understand, as drainage of freshwater from these regions often goes unnoticed until the water table drops and wells go dry. This underground source of freshwater can become contaminated, making it unsafe to drink. Freshwater can become concentrated with sulfates and chlorides, particularly in arid regions, where sulfur-rich hydrogen sulfide accumulates with buried organic carbon and salts, like sodium chloride and potash, resulting in toxic or noxious bitter water. Underground disposal of waste water (from oil and gas extraction or uranium mining) can also contaminate ground water that can make it into the rivers and lakes through an aquifer. Cleanup of contaminated underground water is extremely difficult and very costly.
Water Quality edit
Water quality is an important issue, and one that most people take for granted, until they do not have a source of clean drinking water. LeeAnne Walters was of those people, raising twin toddlers and a teenage son, she assumed that the water her family drank in their Michigan home was safe in 2014. Water from a faucet in the United States is often taken for granted to be healthy to drink, and often assumed that it undergoes testing to assure that it is safe, but Michigan was facing harsh economic conditions in early 2014, as the city of Flint was looking to save money, and had switched water sources from Lake Huron to the Flint River. The Flint River which runs through the city would save the city a large amount of money, since they no longer had to pay for the source of lake water from Lake Huron. The local Flint River contains freshwater that has a lower level of pH and is softer (containing less calcium carbonate) than water sourced from Lake Huron, but also contains more chloride (from sodium chloride put on icy winter streets) and bacteria. The switch was made, but testing of drinking water was not carried out to see if the switch was safe for citizens to drink. For months, the water from faucets in Flint, Michigan, was observed to be discolored. The elevated chloride reacted to the old lead pipes that carry drinking water to various neighborhoods in the city. Citizen’s began to complain of the water tasting bad. They complained to public officials with the fear that the water was no longer safe to drink. The city officials argued that that testing was being carried out, and it was safe to drink, but LeeAnne Walters who lived in the neighborhood was not convinced. As a medical technician, she was trained in science, and began collecting samples of water from her neighborhood. She sent off these samples for testing to Marc Edwards at Virginia Tech, who specializes in water quality, particularly how water can become contaminated from lead pipes. Testing of the water samples collected by Walters showed extremely high levels of lead within the drinking water. Chloride is a corrosive element that oxidizes with metals, such as lead, and typically is removed from drinking water to prevent corrosion when passed through lead pipes. The excessive lead from the dissolution of these old pipes by the chloride in the drinking water was slowly poisoning thousands of people in Michigan. Lead (Pb) in water is taken up by the body in different organs, resulting in gastrointestinal, neuromuscular, and neurological symptoms. It also causes growth and developmental issues in children, such as severe learning disabilities. The publication of LeeAnne Walters and Marc Edwards study on contamination of water in Michigan inspired another scientist named Mona Hanna-Attisha to follow up with a study based on electronic medical records of blood samples collected from children living in Flint, Michigan. She published her scientific results demonstrating high levels of lead in the bodies of children living in Michigan, in the journal American Journal of Public Health in 2015. The fallout of the study revealed a conspiracy by elected officials to save tax payer money by diverting water from one source to another, and then covering up the results of this change on water quality reports. The discovery would not likely have been made, if LeeAnne Walters had not undertaken the initial study by gathering water samples to be tested and sending those samples to be tested by an outside lab. Science is something that anybody can do and should do, it is a valid way to test and retest any hypothesis, and in the case of the Flint Water Crisis, such retesting of the water resulted in saving people’s lives in Michigan. In 2018, LeeAnne Walters was awarded the Goldman Environmental Prize, and has been campaigning for safe drinking water ever since.
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h. Earth’s Endangered Lakes and the Limits of Freshwater Sources. |