I suppose that by now you can see where this discourse on water is leading. It should be obvious that as we take water for our own needs, it is diverted from other uses, such as the support of wildlife. Indeed, some national parks suffer when rivers are diverted or dams are built and disrupt the flow of water. Moreover, if we dam up the water, it has to flood another natural area. Nobody is going to dam up a river in the middle of a thriving city of homes and businesses, although dam projects usually do displace at least a few people. What is at risk? The last few areas where other species can live. At least that is true for land species; we'll get back to the fish and other aquatic creatures shortly.
The effect of dams on the plight of other species is illustrated well by the golden lion tamarin, a coastal monkey of Brazil. It is one of three subspecies of lion tamarins found only in remnant patches of the Atlantic forest region. Its habitat is inviting, and thus was one of the first parts of Brazil to be colonized over four hundred years ago. Given four hundred years of human population growth, the area is now densely inhabited. Moreover, the monkey's lowland habitat was easily cleared for agriculture. Many of the golden lion tamarins were displaced, others sent to zoos, others eaten by the local people.
Great efforts have been made to save the tamarins' genetic heritage in zoos, and to protect the species in the wild. In 1974, a reserve was established, mainly for the protection of this monkey. It was only nineteen square miles (5,000 hectares). But the nearby populace needed water, and part of the "reserve" was flooded by a dam. Today the golden lion tamarin remains on the critically endangered list. It is yet another example of how priorities change when the human population grows.
But it is just one species, some of you may say. Well, actually the golden lion tamarin is only one subspecies, but that is beside the point. What is lost with one type of animal are the others that depend on it. What is lost is an ecosystem. And that one subspecies is an anecdote, symptomatic of what is happening the world over on a daily basis —because the world's growing human population needs water.
Another counterpoint from some eco-optimists: "Well, at least those reservoirs provide a safe refuge for fish and other aquatic creatures." True to an extent, as long as we keep the water clean. But fish that live in reservoirs are different from those that thrived in the river valleys that got flooded by our dam projects. Moreover, what gets created is a large, uncovered expanse of water. This results in a larger surface area for evaporation, and we lose a lot of the water to the atmosphere. And just as with the evaporation of irrigation water, the salt precipitates lead to salinization of the lake bottom. This can be taken care of by the right combination of life-forms, but more often than not humans must intervene — all part of the ecological transition.
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