by Nikolai FILATOV, Dr. Sc. (Geogr.), Institute for Northern Water Studies, Karelian Research Center, RAS, and Dmitry POZDNYAKOV, Dr. Sc. (Phys. & Math.), Nansen International Center for Remote Study Methods and the Environment, St. Petersburg The last decade has been marked by visible global climatic changes and their effect on water systems, and, happily, an easing of man's pressure on them. As things are today, the health of large lakes around the world has shown an improvement from what was a relatively short while ago. The ecosystems of Ladoga and Onega have been deteriorating for some time now, especially since the 1970s. A threat looms over the life and health of millions in St. Petersburg and Leningrad Region, and in the nearby Republic of Karelia. Lake Ladoga, for one, is not only the principal source of water for domestic and industrial needs, but also a major influence on the biosphere of a territory that spreads over Russia's northwestern fringes and Finland, the Neva River, and, to an extent, the Gulf of Finland and the Baltic Sea. EUTROPHY THREATENS LAKES The "phosphorus burden" on Ladoga has been growing since the early 1960s, turning the previously oligotrophic(*) lake into a mesotrophic(*) one in the mid-1980s, and threatening to make it eutrophic(**) by the end of the 1980s. Similar processes were developing in two of the North American Great Lakes, Erie and Ontario (the remaining three having been spared). They have changed significantly the principal functional relationships in these lakes, wrested the elements of their ecosystems out of balance that had been building up for millennia. True enough, experts tended to believe that Ladoga can escape the fate of the two American lakes because of its cold water, lying as it is in relatively high latitudes, and the rock type of its basin. Their hopes have not been fulfilled, however. Despite the phosphorus burden stabilization at 6,100 tons a year by the early 1990s, and even its decrease in mo ... Читать далее