a third of amphibians, and more than half of freshwater 

 turtles and crocodiles have become either threatened, 

 endangered, or extinct. Freshwater fishes represent a quar- 

 ter of the world's living vertebrate species, and yet more 

 than a third are threatened or endangered. The ecology 

 of freshwater systems may be irreversibly damaged if we 

 humans don't improve the way we treat them. 



The Mekong's name translates from Lao as "mother 

 ot the waters." It's no wonder: the river snakes some 

 3,000 miles from its headwaters on the Tibetan Pla- 

 teau to its outlet through the Mekong River Delta into 

 the South China Sea. It and the uncountable "feeder" 

 rivers and streams in Cambodia, China, Laos, Myanmar, 

 Thailand, and Vietnam make up the 300,000-square-mile 

 Mekong River Basin [see map on preceding page]. 



That mesh of waterways is one of the most productive 

 and diverse ecosystems on Earth, supporting more than 

 6,000 species of vertebrates alone. Its fish fauna, with some 

 2,000 species, of which sixty-two are endemic, exceeds 

 all but those of the Amazon and Congo river basins. The 

 wetlands harbor several threatened and endangered birds 

 and mammals, including the eastern sarus crane, Grus anti- 

 gone sharpii; the Bengal florican, Houbaropsis bengalensis; and 

 the hairy-nosed otter, Lutra snmatrana, which was recently 

 rediscovered after having been feared extinct. Sixty-five 

 million people live there, too, 80 percent of them dependent 

 on the river for their livelihood as farmers and fishers. 



The Mekong River Basin is a microcosm of the Earth's 

 freshwater resources — it includes almost all of the natural 

 forms freshwater takes on Earth: groundwater, lakes, ponds, 

 streams, and wetlands. (Wetlands are defined as shallow, 

 often intermittently wet habitats, such as bogs, floodplains, 

 marshes, and swamps.) Together, freshwater ecosystems 

 c over less than 1 percent of the Earth's surface and hold 

 a mere 0.008 percent of its water, but they support about 



100,000 animal species — an inordinately large number for 

 their size relative to marine and terrestrial habitats. That 

 freshwater fauna includes a third of all known vertebrates 

 and a whopping 40 percent of all known fish species. 



Their rich biodiversity aside, freshwater systems bestow 

 untold — and underappreciated — benefits on people. Indeed, 

 they are the very foundation of our lives and economies. 

 The value of all the services freshwater ecosystems pro- 

 vide worldwide, such as drinking water, irrigation for 

 agriculture, and climate regulation, has been estimated 

 at $70 billion per year — a figure that assumes, rather de- 

 lusionally, that one could purchase the services elsewhere 

 if they became unavailable in nature. 



Dams are a dramatic example of a human activity that 

 degrades freshwater ecosystems. Built to control 

 flooding, store water, and generate electricity, dams 

 have numerous ecologically disastrous side effects. They 

 impede the movement and migration of aquatic species; 

 some kill animals in turbines; and they change the timing 

 and amount of flow downriver, which interferes with the 

 reproductive cycles of fishes, frogs, and water birds that 

 depend on seasonal flooding. 



About a dozen hydroelectric dams in the Mekong River 

 Basin provide the bulk of the region's energy — and another 

 hundred or so are in the planning stages. To date, China 

 has built two dams across the upper mainstream, but 

 there are none across the lower mainstream — in fact, the 

 Mekong is one of the world's few major rivers with so few 

 mainstream dams. That may soon change: local govern- 

 ments view the free-flowing Mekong as an underutilized 

 economic resource. Worldwide, an average of two large 

 dams have gone up each day for the past fifty years, and 

 today there are more than 45,000 dams taller than forty-five 

 feet. Fortunately, increased awareness of the environmen- 

 tal problems they cause has contributed to a slowdown of 



42 



natural history November 2007 



