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Germany: What a Lake Says About Climate Change

When the East German nuclear power plant Rheinsberg was shut down almost 20 years ago, environmentalists expected that fauna and flora in nearby Stechlin lake would survive without further damage.

by Julio Godoy

The power plant in the city 75 km north of Berlin had been functioning since 1966. It took some 300,000 cubic metres of water daily from the lagoon to cool down the facility's installations. The water would then be released back into the lake -- 10 degrees warmer.

Before the plant began to function scientists had declared the waters "the cleanest in Germany," says Peter Casper, biochemist at the Institute Leibniz for Water Ecology in Stechlin.

There was no reason then to doubt their judgement. The lake is surrounded by pristine forests, without any agriculture use. The region is also scarcely populated, guaranteeing that no sewage was channelled into the lake.

Soon after the Rheinsberg nuclear power plant began operating, scientists began to find changes, Casper told IPS. "Algae and other micro-organisms started to grow very rapidly." The fauna started to degenerate.

"This is what we call the divergent development of the food chain," Casper said. "Not all living organisms in the lake reacted at the same speed to changes in the environment. Algae and other micro-organisms grow more rapidly, but also start and end their life cycle more rapidly. This means that fish, which feed on algae, and do not grow at the same new speed, are deprived of their food at a critical point in their growth."

This decoupling of the food chain is carried forward, and alters the biological relationships within the lake's flora and fauna. But, says Casper, "the biochemical structure of the lake never became oversaturated. We believe that this is because the waters were so clean from the very beginning."

When the Rheinsberg nuclear power plant ceased to function in 1988, scientists thought the lake's biodiversity would return to its original form. But it did not -- the changes in the water composition and temperature, as well as in the flora and fauna remain until today.

"Probably the lake is not going to recuperate anyway," says Casper. "The rise of temperatures due to global warming is perpetuating the changes produced by the nuclear power plant."

Analyses carried out by the Institute Leibniz have a particular meaning today due to the continuity and duration of the study. "We consider these changes we found in the lake Stechlin correspond with what is happening on a larger scale in the oceans due to global warming," Rainer Koschel, director of the Institute Leibniz told IPS.

Ocean biologists have found that global warming is modifying the growth periods of algae and other sea plants. According to reports by the Intergovernmental Panel on Climate Change, 80 percent of global warming is absorbed by seawater, leading among other consequences to a rise in water temperatures.

In the North Sea, just offshore on the German and Netherlands side, biologists at the Institute Alfred Wegener for Polar and Ocean Research in Germany have established that the temperature rise, given the late winter and early spring in the northern hemisphere, has led to an earlier blossoming of algae, especially the diatoms, distorting the food chain in the region.

One-fourth of the earth's biomass is formed by diatoms, and it serves as foodstuff for hundreds of fish and other sea species. If it decays too early, the dependent fauna decimates.

Another consequence of rising seawater temperatures is the decelerating blending of water masses. As it is, under normal circumstances warm water tends to float over cold water.

If, additional to this normal distribution of water, the temperature at the ocean's surface rises, the different masses of water blend less than normally with one another, leading to a further concentration of warmer water on the surface and colder water at the depths. A consequence of this is that oxygen in the colder waters shrinks, leading to the death of fauna.

Some fish and other marine organisms can only live under moderate water temperatures. Barbel, a fish common in European rivers, and brown trout, cannot survive in waters warmer than 20 degrees Celsius. Water temperatures of 22 degrees kill their eggs. In 2003 and 2006, river water temperatures in Germany were well over this limit.

Casper says that trout reacts to such water temperature changes by migrating to higher regions, searching for colder waters. But by so doing, the fish invades the habitat of other species, thus disrupting the biological relations and the food chain structure in the new areas.

Biologists at the Institute Leibniz have also found that some exotic algae have developed in the Stechlin Lake. Earlier this year, Casper discovered tropical blue algae, which can only survive in these northern areas due to the high water temperatures.

"But if blue algae expands in lagoons such as the Stechlin lake, it will represent a major bacteriological problem," Casper said.

© 2007 IPS-Inter Press Service

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