Saving Earth's Rivers: The Preservation of Ecosystem Health Must Become an Explicit Goal of Water Development and Management

By Richter, Brian; Postel, Sandra | Issues in Science and Technology, Spring 2004 | Go to article overview

Saving Earth's Rivers: The Preservation of Ecosystem Health Must Become an Explicit Goal of Water Development and Management


Richter, Brian, Postel, Sandra, Issues in Science and Technology


The odds do not look good for the future of the planet's rivers. As populations and economies grow against a finite supply of water, many previously untapped rivers are being targeted for new dams and diversions, and already-developed rivers are coming under increased pressure. A number of major rivers, including the Colorado, the Indus, and the Yellow, are already so overtapped that they dry up before reaching the sea. Meanwhile, India is proposing to link all 37 of its major rivers in a massive water supply scheme, Spain plans to build 120 dams in the Ebro River basin, and China intends to transfer water from the Yangtze River north to the overstressed Yellow River basin. In the United States, a project has been proposed in Colorado in which a pipeline would capture Colorado River water at the state's western boundary and move it eastward across the Continental Divide to the growing metropolitan areas of the Colorado Front Range.

These proposed projects will almost certainly add to the ledger of ecological damage already wrought on the planet's rivers. Dams and diversions now alter the timing and volume of river flows on a wide geographic scale. According to Carmen Revenga and colleagues at the World Resources Institute, dams, diversions, or other infrastructure have fragmented 60 percent of the 227 largest rivers. Most of the rivers of Europe, Japan, the United States, and other industrialized regions are now controlled more by humans than by nature. Rather than flowing to the rhythms of the hydrologic cycle, they are turned on and off like elaborate plumbing works.

During recent decades, scientists have amassed considerable evidence that a river's natural flow regime--its variable pattern of high and low flows throughout the year as well as across many years--exerts great influence on river health. Each aspect of a river's flow pattern performs valuable work for the system as a whole (see table). For example, flood flows cue fish to spawn and trigger certain insects to begin a new phase of their life cycle; very low flows may be critical to the recruitment of riverside or riparian vegetation. When humans alter these natural patterns to supply growing cities and farms with water, generate electricity, facilitate river-based navigation, and protect expanding settlements from floods, the vitality and productivity of river ecosystems can become seriously degraded.

Societies have reaped substantial economic rewards from these modifications to rivers. However, because inadequate attention has been paid to the ecological side effects of this development, society has lost a great deal as well. In their natural state, healthy rivers perform myriad ecosystem services, such as purifying water, moderating floods and droughts, and maintaining habitat for fisheries, birds, and wildlife. They connect the continental interiors with the coasts, bringing sediment to deltas and coastal beaches, delivering nutrients to fish habitats, and maintaining salinity balances that sustain productive estuaries. From source to sea and from channel to floodplain, river ecosystems gather, store, and move snowmelt and rainwater in synchrony with nature's cycles. The diversity and abundance of life in running waters reflect millions of years of evolution and adaptation to these natural rhythms.

In little more than a century, human societies have so altered rivers that they are no longer adequately performing many of their evolutionary roles or delivering many of the ecological services on which human economies have come to depend. Just as each river has a unique flow signature, each will have a different response to human disruptions of its flow regime. But in nearly every case the result will be a loss of ecological integrity and a decline in river health. In addition to harming the ecosystems themselves, these transformations also destroy many of the valuable goods and services on which people and economies rely. …

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