State of the rivers: Ruinous?

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State of the rivers: Ruinous?
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Photo: Oct. 7, 2010, friedrich glorian
With red sludge still visible, women survey the damage in Hungary. Eight died when a dike burst at a factory that processed ore into alumina, a raw material for aluminum.

Have you seen the photos of aluminum sludge surging through villages in Hungary, heading for the Danube River? With eight people dead, and new cracks appearing in the wall containing a pond-ful of alkaline sludge, we’re left to hope that the toxic crud is defanged by dilution before it does too much damage to the mighty Danube.

Still, the spill got us to thinking about the plight of the world’s rivers. Rivers are our foremost source of freshwater, used for drinking, industry and agriculture. Their wetlands and floodplains clarify water, temper floods, and provide an irreplaceable habitat for countless plants and critters, many of which are the major source of protein for hundreds of millions of people.

But a new study in the journal Nature shows that the globe’s rivers are being lambasted by pollution and invasive species. Heavy burdens of artificial fertilizer have created dead zones at the mouth of hundreds of rivers. Rivers are being over-fished, channeled into barge canals, and drained for irrigation, industry and drinking water.

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Graphic: Barry Carlsen, copyright University of Wisconsin Board of Regents
A new analysis of 23 threats to global water security and biodiversity shows many regions with a high cumulative level of threats.

When the study1 assessed river health in terms of pollution, biological change, watershed disturbance and water resource development, rivers carrying 65 percent of the total amount of water that rivers bring to the ocean “is moderately to severely threatened on a global basis,” says study co-author Peter McIntyre, a professor of zoology and freshwater expert at the University of Wisconsin-Madison.

Dam difficult

Both human water supplies and the natural world are endangered, McIntyre says. “One-quarter of the world’s vertebrate species live in fresh waters, and hundreds of thousands of plants and animals are at risk because they live in places where threats are high.” In total, biodiversity is more threatened in freshwater than it is in saltwater or on land, McIntyre says; ominous declines are being seen in fish, turtles, mussels and plants.

Lest “biodiversity” sound frivolous, estimates suggest that the value of “ecosystem services” like clean air and clean water exceeds the global economic output. The necessity of clean water is obvious, but we are also utterly reliant on plants, above and below water, to convert carbon dioxide into oxygen.

And these ecosystem services are best served by stable ecosystems.

Two sides of one freshwater crisis

Dams have ensured good water security (blue and green regions), but mouse over the image to see that many of the worst threats to biodiversity (red) are in regions with good water supply. Rivers in China, India and the Middle East face severe threats in both categories.

Managing freshwater is a delicate balancing act, and some experts anticipate that tightening supplies will lead to disputes or even water wars later in the century. The U.S. government says if current trends continue, “by 2025, one-third of all humans will face severe and chronic water shortages,” with the first and worst problems appearing in Africa and the Middle East.

Already, the Colorado River in the United States, and the Yellow River in China, are so thoroughly exploited that they scarcely reach the ocean. Low flows and massive pollution plague rivers in China, India, the Middle East and Africa.

Nile denial

Photo: Bionet
The Nile River supplies virtually all water in Egypt (notice how fields cluster along the river?) and major portions in Uganda, Sudan and Ethiopia. The Nile is polluted by sewage and agricultural chemicals, and is failing to supply growing populations along its dry lower stretches with enough water for a good standard of living. With a watershed that includes parts of 11 nations, disputes over the Nile’s water could devolve into war.

Water security vs. environment: Inevitable tension?

Although pollution, invasive species and overfishing play major roles in declining freshwater biodiversity, dams and associated water diversions are a fundamental part of the tension between environment and river development.

Dams are built to store and divert water, supply hydroelectric power and prevent floods. Dams, and the locks that allow ships to traverse them, remain a keystone of river management in Western Europe and the United States, which is home to an estimated 75,000 dams.

While dam construction is largely over in Europe and North America (where some dams are even being removed), the 20th century was epic for dam building, says Bradley Udall, director of the Western Water Assessment at the University of Colorado. Udall notes that the volume of water stored behind dams has risen 350 times since 1900, to 5,000 cubic kilometers.

At the same time, Udall notes, due to such alterations as damming, draining, levees and development, “We have destroyed one-half of wetlands worldwide, which are very important for all kinds of ecological services, including water purification.” (Watch 23,000-plus large dams spread across the world.)

Chinese (river) checkers

Dam building is booming in developing countries, as an answer to floods and shortages of water and electricity. China’s Three Gorges Dam was essentially completed in 2008, after more than 1 million people were moved away from a new lake that is expected to cover 400 square miles. With a planned electrical output equal to more than 20 large nuclear plants (about 10 times greater than Niagara Falls), Three Gorges was also intended to halt disastrous flooding on the Yangtze River.

The series of dams that China is building or planning along the Yangtze and its tributaries will generate even more electricity than Three Gorges.

Yangtze River in When, China

A few long flat boats sit in brown river; steep river bank covered in cascading, cinder block apartments.

The river, shows intense pollution and human habitation in a city of about 9 million.

Dams can raise issues in any location. As Three Gorges proved, they displace riverside villages and cities and drown archeological sites. As is happening at the Glen Canyon dam in the United States, reservoirs can fill with silt, losing storage capacity and causing erosion as downstream areas are deprived of their normal silt supplies.

Dams also divert money that could be used for other purposes.

Granted, dams are a critical source of usable water, but they can also be a scourge of native plants and animals. “There is definitely a tension between human infrastructure and biodiversity conservation,” says Laurence Smith, a professor of geography at the University of California at Los Angeles, and author of a new book on environmental trends2.

China is embarked on the largest water project in history, a 50-year program to move water from the Yangtze toward population centers in the drier north. Designed to move 50 cubic kilometers per year, the project aims to reduce sandstorms and water shortages while bolstering sinking aquifers in North China.

Pristine river meandering through autumn colored trees and a misty sky overhead
Rivers in the North, like Alaska’s Koyukuk, are far less impacted by pollution, diversion and damming.

Failing fish

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Man fishes with a stick, standing on rocks as river trickles past his feet

Courtesy Peter B. McIntyre
A man fishes at Igamba Falls, on the Malagarasi River, Tanzania, site of a proposed hydroelectric dam. Fish are a major source of protein — and dams are a major cause of fish declines.

Altering rivers with dams enacts fundamental changes in ecosystems, says Smith. “A lot of the most biologically diverse riverine environments are seasonally flooded wetlands and flood plains. Biodiversity is not found in a big reservoir behind a dam… It is more the episodic flooding [of natural rivers] that gives this diverse habitat.”

Dams block the migration of important fish species, including the salmon, which is vanishing along the Atlantic and Pacific coasts of the United States, where dams block the upstream spawning journey.

That problem is widespread, says McIntyre. “In the tropics, species like big catfish, and the family known as the tetras, are very intensively fished. You have regions where people depend on these migratory fish, and if you put in a dam to stop the migration — rivers are aquatic highways — you profoundly change the system. There’s a real concern that if fisheries collapse, hundreds of millions of people worldwide who get a majority of their protein from freshwater fish could go hungry.”

In the central United States, massive dams and engineering projects on rivers like the Illinois, Missouri, Mississippi, Tennessee, Wisconsin and Ohio have also been blamed for ecosystem destruction.

For example, locks and dams north of St. Louis on the Mississippi stabilize the water level so large barges can traverse the river. But that stability, combined with extensive levees on the banks, has eliminated vast wetlands that once bordered the river. When the river no longer surges in the spring and subsides in the fall, remaining flat land along the river turns to muck that can no longer support native plants and animals.

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Wide brown river, forest on one side, dam and lock stretch across width of river

Massive engineering projects along the upper Mississippi River have essentially changed the river into a barge canal.

Biodiversity black hole

One reason to foster biodiversity in rivers and watersheds is this: Biological systems with many interacting species tend to be more stable, and people, like other animals, have adapted to a fairly stable environment. “In experiments with bacteria, if you strip away species, you eventually hit a point where the basic properties change,” says zoologist Peter McIntyre. “It can be on a plateau of high function for a while, but there is a threshold, and we can’t predict where it occurs, things start to fall apart.”

The classic analogy, McIntyre says, “is popping rivets on the wing of an airplane; you pop one too many, and boom! down you go. In the global river context, we are rolling the dice, we know we are losing species. The rates of extirpation and extinction are highest in freshwater; and that is where we are seeing the worst human impacts.”

Scientists who are looking more broadly at the health of river ecosystems are hampered by a lack of information. “There are no global data sets” that would support an exact measurement on the biological health of rivers around the world, says Carmen Revenga, a freshwater scientist at the Nature Conservancy.

Still, new evaluations of biodiversity are delineating the difficulties. Revenga says a recent assessment listed 253 endemic species of freshwater fish in the Mediterranean — meaning they are found nowhere else — and 56 percent of them are threatened with extinction. Another survey found severe declines among 40 percent of the 300 species of freshwater turtles, she adds. “Nobody would have guessed it was that bad.”

The inevitable tension between environment and human water use is growing more intense in dry places such as Africa and Australia, with heavy population pressure and intense land usage.

When farms, people or industry get thirsty, “Freshwater biodiversity has not tended to play role in discussions about water security,” Revenga says. “Usually there is a lot of focus on providing water that is secure and safe. Irrigation took precedence at first, and now cities take precedence, but the ecosystem hardly gets included.”

The sad, dry Aral Sea

Flat and dry former seabed with short woody shrubs, ruins of two rusting boats on solid ground

The Aral Sea in Central Asia dried up after the rivers that fed it were diverted to irrigate vast cotton farms.

And that leaves less water for ecological purposes, Revenga adds. “When we calculate the amount of runoff in a basin, we assume we can tap all the water that’s available” for human uses. “The conservation and environmental community has not interacted with the water supply community, and the environment is almost forgotten.”

Mono Lake in California, whose water was diverted to Los Angeles in the 1940s, is one example showing that cities and farms have come first in American water management. According to the Mono Lake Committee:

“Unfortunately, most of those dams and aqueducts were constructed with little and often no thought to the environmental or local economic consequences of these projects. The classic example is that of LA and the Owens Valley where a thriving agricultural area was returned to sage brush and Owens Lake was reduced to dust.”

In recent decades, California has been pressured to allot some water to environmental purposes, part of a gradual rebalancing of water use in the dry, densely populated American Southwest.

We’ll explore evidence of progress in water management in the next Why Files, but note that cities like New York rely on watershed protection to ensure a clean, adequate water supply. “It’s a very good strategy to protect upland forest, and reduce siltation and runoff into streams, but a lot of projects don’t look at biodiversity in the river,” Revenga says. Watershed protection is rare, and in any case the ecological benefits are secondary to the need to provide clean water to cities, she adds.

Climate change

As more people look to rivers to supply more water, there’s one final factor to consider: the climate. Brad Udall of the University of Colorado, an expert on the waters of the West, told us that climate change is not just about temperature. “You could make a compelling argument that it’s about changes to water cycles; changes in the quantity, quality and timing, almost all of which are detrimental” to freshwater supplies.

In general, Udall says, studies of ancient climate show that “wet areas get wetter and dry areas get drier.” In the Colorado River basin, where climate change has been intensely studied, “we can expect a 10 percent to 20 percent reduction in runoff by 2050.”

Arid canyon filled by blue river with huge dam and bridge with traffic crossing it

Photo: Laslovarga
Hoover Dam and its reservoir Lake Mead are major factors in Western water management, but at what environmental cost?

Because so many rivers in the American West are fed by melting snow, warmer winters already have a major impact, Udall says, with the earlier spring causing earlier runoff in the rivers. Studies project that the floods could happen as much as 60 days earlier in the spring, “and we are already seeing 20-day advances, especially in lower-level snow-dominated systems, like in the Pacific Northwest.”

At the same time, river flow is likely to diminish earlier in the late summer, and the water will also be warmer, Udall says, which poses problems for life. “Many critters in the water are stressed in high temperature, which also carries less dissolved oxygen.”

Dry conditions in late summer also contribute to a longer wildfire season in the West.

Climate change may be even more catastrophic where drinking water comes from rivers sourced in melting glaciers, Udall warns. Large cities like Bogotá and Lima in South America, “could go from having a glacier upstream one day to not having it the next. The United States does not have that problem, but in the Andes, there is potential for very harsh consequences.”

The Ganges: A river or a sewer?

Two men spraying water from hose across cement temple platform, child watching, litter is everywhere

Worshippers leave heaps of offerings alongside the Ganges river in Varanasi. It’s easy enough to hose away the dregs into the river, but that just adds more pollution to the “Mother Ganges.” Says Science Daily, the Ganges “contains untreated sewage, cremated remains, chemicals and disease-causing microbes. … Cows wade in the river. People wash their laundry in it and drink from it. … The Ganges River is a major source of disease.”
If this can happen to a sacred river…

Summary judgment

Rivers collect runoff from their watersheds, and therefore carry messages about conditions from most of the land on our planet. As the authors of the recent Nature study found, trying to assess the health of rivers around the world is not for the data-shy. Differences in economy, history, geography and culture all affect how we view rivers, and how we decide whether to use, alter or preserve them.

Clusters of bright purple flowers along a stream, surrounded by grasses.

Photo: Steve Dewey, Utah State University,
Purple loosestrife is striking, but it invades wetlands near rivers, reducing biodiversity, destroying habitat for native species, and reducing the ability to filter water.

But most “decisions” that affect rivers, like allowing them to be polluted with chemicals, topsoil or fertilizer, or building a dam to store water for the dry season, are made not with rivers in mind, but with another goal, like growing more food or getting people something to drink.

“You don’t miss your water ’til your well runs dry,” pertains to rivers as well as groundwater, says Peter McIntyre, one author of the recent global river survey. “In the industrialized world, we go home at night, turn on the faucet and get beautiful, clear water, it’s safe to drink and bathe; it poses no risk to us and our kids. Mass investments in engineering and infrastructure have granted us this water security.”

As developing countries, where people struggle to find water for faucets, farms and factories, embark on the dam-building that was so crucial to European and American water supplies, saying “don’t do what we did” seems hypocritical at best and repugnant at worst.

And yet experience shows that dams can damage or destroy plants and animals in rivers and their floodplains. We’ll concede that questions about biodiversity, the environment and the long term seldom interest people who are hungry or thirsty. But they may still be worth asking. Will a proposed dam harm an essential fishery? Will it produce benefits over the long term, or will it silt up in a decade because trees have been stripped from its watershed?

There are lessons to be learned from the water-management experience in Europe and North America, and one of the most significant one is to expect a continual tension between human water use and biodiversity. “I am not pretending there is an easy answer,” McIntyre says, “or that I should have the right to dictate to that person whether they build a dam or not.”

Coming Oct. 28: Part II : The Why Files will discuss some river-management ideas for balancing human and environmental needs.

– David Tenenbaum


  1. Global threats to human water security and river biodiversity C. J. Vorosmarty et al, Nature, 30 Sept. 2010.
  2. The World in 2050, Four Forces Shaping Civilization’s Northern Future, Laurence C. Smith, Dutton, 2010.
  3. Red sludge spill in Hungary.
  4. Toxic mud at the Danube
  5. Rivers in Crisis
  6. Freshwater conservation at The Nature Conservancy
  7. National Great Rivers Research and Education Center
  8. Threats to rivers.
  9. World rivers
  10. UN Water.
  11. Western Water Assessment.
  12. Global threats to river biodiversity.
  13. River Network.
  14. The rise of the dam.
  15. Environmental impact of dams.
  16. Undamming rivers.
  17. Improving Mississippi river.
  18. Short film: Aral Sea.
  19. Three Gorges Dam: environmental catastrophe?
  20. PBS: Great Wall Across the Yangtze.