Zurich, Victoria, Erie, Caspian Sea - Rising Cyanobacterial Threat In World's Largest Lakes
The warming waters of one of central Europe's most popular holiday destinations, Switzerland's Lake Zurich, have created an ideal environment for a population explosion of algae including Planktothrix rubescens, a toxic cyanobacterium. It has the potential to harm humans, animals and the tourism that pumps up the economies of lake districts.
Although harmful algal blooms have been documented for more than a century, recently the number and frequency of cases have drastically increased.
According to research published in leading scientific journals, Lake Zurich is by no means alone. Cyanobacteria now threaten the ecological well-being of some of the world's largest water bodies, including Lake Victoria in Africa, Lake Erie in the United States and Canada, Lake Taihu in China, the Baltic Sea in northern Europe, and the Caspian Sea in west Asia. They've also been found in Lake Kokotel in eastern Siberia, which is next to Lake Baikal, the world's largest, deepest and most ancient freshwater lake. Baikal contains 20 percent of the world's total unfrozen freshwater reserve.
"During the 1940s through the 1950s, all of the lakes in western Europe were affected by raw sewage," Posch said. "Then in the 1970s, we started to treat wastewater. Problem solved." Or, he added, so we thought. His measurements have shown that since 1990, despite the drastic decrease in phosphorus, the whole lake biomass of P. rubescens has been rising. One reason is that P. rubescens doesn't need a lot of phosphorus. It thrives on nitrogen. "Nitrogen concentrations haven't dwindled much," Posch added. "The chemical mix of the lake now favors P. rubescens."