Disappearing Lakes, Shrinking Seas

Disappearing Lakes, Shrinking Seas

Janet Larsen 7-04-05 ( Published on OneWorld Website)West Africa’s Lake Chad has shrunk to a mere 5 percent of its former size. Central Asia’s Aral Sea is shrinking, gradually turning into desert. In Israel, the receding shores of Lake Tiberias—also known as the Sea of Galilee—sometimes allow mere mortals to walk where the water once was. Thousands of lakes in China have disappeared entirely. The diversion of river water in India and Pakistan that allowed for a doubling of irrigated area over the last four decades has depleted many lakes. All told, more than half of the world’s 5 million lakes are endangered.

For more than 4,000 years, farmers have diverted river water for crops in dry areas and dry seasons, reducing the flow into nearby lakes and seas. Over the last half-century world water use has tripled, expanding faster than population. Today irrigation accounts for two thirds of global water use. With the advent of diesel and electrically driven pumps, groundwater extraction in some areas has exceeded recharge from precipitation, also causing water tables and lake levels to fall.

Nestled among deserts, the 5-million-year-old Aral Sea is one of the world’s most ancient lakes. As recently as the early 1960s, it covered some 66,000 square kilometers (25,483 square miles) and held 1,000 cubic kilometers (264 trillion gallons) of water. Two rivers, the Amu Darya and Syr Darya, fed the lake with some 65 cubic kilometers of water each year. Today, however, irrigation of vast fields of cotton has drained the rivers, reducing the annual inflow to only 1.5 cubic kilometers. As a result the Aral has lost four fifths of its volume and split into two sections.

The shoreline of the Aral Sea has receded by up to 250 kilometers, leaving behind a salty desert. The United Nations estimates that every day 200,000 tons of salt and sand containing residual agricultural chemicals and heavy metals from the uncovered seabed are carried by the wind and dumped on farmland within a 300-kilometer radius, destroying pastures and arable land. The pollution of air, land, and water has left a legacy of diseases such as cancer, cholera, and typhus. The once-prolific fishery has been destroyed.

Growing water demands are causing other lakes around the globe to vanish. (See additional examples and data.) Irrigation withdrawals from the waters that feed Africa’s Lake Chad quadrupled between 1983 and 1994. Water consumption, combined with low rainfall levels since the 1960s, has shrunk the lake by 95 percent, from 25,000 square kilometers to 1,350 square kilometers, over the past 35 years.

Overpumping groundwater in China’s Hebei province has lowered the water table, resulting in the loss of 969 of the province’s 1,052 lakes. Madoi County in northwest China's Qinhai province, the first through which the main stream of the Yellow River flows, once had 4,077 lakes. Over the past 20 years, more than half have disappeared.

In 1998, China’s largest river, the Yangtze, experienced devastating flooding, taking the lives of 3,600 people and wreaking more than $30 billion in damages. The floods were largely attributed to the cutting of forests and the loss of more than 13,000 square kilometers of lake area along the Yangtze’s middle and lower reaches. Prior to the flooding, some 800 lakes had disappeared entirely, depriving the basin of needed water storage capacity and flood protection. Following the floods the Chinese government pledged action to restore both forests and lakes.

Tonle Sap in Cambodia, Southeast Asia’s largest freshwater lake, supports one of the world’s largest inland fisheries. Like many lakes it has long provided flood protection, fluctuating in volume according to rainfall and climate. Now, however, eroding deforested and farmed land is silting up the lake and reducing its storage capacity, ultimately increasing the region’s vulnerability to the opposing extremes of flooding and water scarcity. The Hamoun Lakes and nearby wetlands in Iran and Afghanistan’s Sistan Basin are similarly losing their ability to mitigate floods as they are drying from the damming of the Helmand River and years of drought.

Mono Lake, North America’s oldest, dating back some 760,000 years, is an important feeding stop for migrating birds, especially as southern California has lost over 90 percent of its wetlands. Since the first diversions of its tributaries to quench the thirst of growing Los Angeles in 1941, the lake has contracted dramatically, with water level dropping by 11 meters (34 feet) and volume down 40 percent. As a result, its salinity has jumped to three times that of the ocean—far too salty to sustain most fish. The lake likely would have died completely had locals not intervened and defeated Los Angeles in a legal battle over keeping water for the lake.

Mexico’s largest lake, Chapala, is the primary source of water for Guadalajara’s growing population of 5 million. This lake’s long-term decline began in the 1970s, corresponding with increased agricultural development in the Río Lerma watershed. Since then, the lake has lost more than 80 percent of its water. Between 1986 and 2001, Chapala shrank in size from 1,048 to 812 square kilometers. Climbing municipal and industrial water demands now exceed the sustainable supply by 40 percent. The lake’s contraction has come at the expense of several fish species and potentially presages a change in the mild climate that the water supported.

Lakes are not only being drained dry; they also are dying from contamination. Farm wastes, sewage, and nitrogen fallout from fossil fuel burning fertilize lakes, causing excess algal and plant growth that depletes water oxygen levels and kills aquatic animal life. Such eutrophication plagues more than half the lakes in Europe and Asia, 41 percent of those in South America, and 28 percent in North America.

Acid precipitation, largely from fossil fuel burning emissions, is killing thousand of lakes. An estimated 120,000 square kilometers of lakes in Norway are acidified to the point where fish stocks have crashed. Sweden has some 4,000 acidified lakes. In Canada, some 14,000 lakes are severely acidified. The U.S. Environmental Protection Agency estimates that some 70 percent of sensitive lakes in New York’s Adirondack Mountains are at risk of periodic acidification, and that without further reductions in sulfur dioxide emissions the rate of acidification will increase by half or more.

A survey of remote mountain lakes throughout Europe found that even lakes far from human development were acidified by sulfur and nitrogen deposition and that virtually all were contaminated by heavy metals (such as mercury, lead, and cadmium) and fly ash particles. The sediments and fish in these lakes also contained a wide range of persistent organic pollutants.

Rising global temperatures are predicted to increase average lake temperatures by 2–3 degrees Celsius (3.6–5.4 degrees Fahrenheit) over the next 50 years. Unfortunately, as water warms, its natural purification processes can slow down. Climate-related changes in water chemistry and stratification can lead to fish losses, as is already being seen in East Africa’s Lake Tanganyika.

More than 2 billion people live in countries with chronic water stress. Many of the world’s people, especially in developing countries, depend on fish for protein. Lakes are not only reservoirs of fresh water and a source of food, but also important habitats for aquatic organisms and waterfowl. Lakes reduce flood damage, moderate climate, and recharge groundwater supplies. They also offer transportation and recreational opportunities and income from tourism. With all the benefits that we derive from healthy lakes, we cannot afford to let them disappear.
Copyright © 2005 Earth Policy Institute

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