Summary
The potential for rapid, unexpected decline in world ecosystems is discussed, with a focus on characteristics of complex systems. Topics include ecological problems triggered by the Iron Gates dam on the Danube River, damage to the forests of eastern North America, problems affecting coral reefs, convergence of environmental pressures, and the brittleness of monoculture technologies; some key sources are also listed.
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Extract
The Nemesis Effect.
Burdened by a growing number of overlapping stresses, the world's ecosystems may grow increasingly susceptible to rapid, unexpected decline.
In 1972, a dam called the Iron Gates was completed on a stretch of the Danube River between Romania and what is now Serbia. It was built to generate electricity and to prevent the river from visiting some 26,000 square kilometers of its floodplain. It has done those things, but that's not all it has done. The Danube is the greatest of the five major rivers that run into the Black Sea. For millennia, these rivers have washed tons of dead vegetation into this nearly landlocked ocean. As it sinks into the sea's stagnant depths, the debris is decomposed by bacteria that consume all the dissolved "free" oxygen ([O.sub.2]), then continue their work by pulling oxygen out of the sulfate ions (S[O.sub.4]) that are a normal component of seawater. That process releases hydrogen sulfide gas ([H.sub.2]S), which is one of the world's most poisonous naturally occurring substances. one deep breath of it would probably kill you. The sea's depths contain the largest reservoir of hydrogen sulfide in the world, and the dissolved gas forces virtually every living thing in the water to cling to the surface or die. the Black Sea is alive only along its coasts, and in an oxygenated surface layer that is just 200 meters thick at most - less than a tenth of the sea's maximum depth. The Danube contributes 70 percent of the Black Sea's fresh water and about 80 percent of its suspended silicate - essentially, tiny pieces of sand. The silicate is consumed by a group of single-celled algae called diatoms, which use it to encase themselves in glassy coats. The diatoms fuel the sea's food web, but any diatoms that don't get catch eventually die and sink into the dead zone below, along with any unused silicate. Fresh contributions of silicate are therefore necessary for maintaining the diatom population. But when the Iron Gates closed, most of the Danube's silicate began to settle out in the still waters of the vast lake behind the dam. Black Sea silicate concentrations fell by 60 percent. The drop in silicate concentrations coincided with an increase in nitrogen and phosphorus pollution from fertilizer runoff and from the sewage of the 160 million people who live in the Black Sea drainage. Nitrogen and phosphorus are plant nutrients - which is why they're in fertilizer. In water, this nutrient pollution promotes explosive algal blooms. The Black Sea diatoms began blooming, but the lack of silicate limited their numbers and prevented them from consuming all the nutrient. That check created an opportunity for other types of algae, formerly suppressed by t...See the full content of this document
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