Environmental▼News PERSPECTIVE smoke from forest fires hang over large areas for weeks, such as in the Mato Grosso region in the southeastern Amazon, rain is inhibited. The smoke contains excess condensation nuclei that form water drops that are too small to fall as rain, Nepstad explains. This then increases the likelihood of more fires, he notes. “The tropics play a huge role in
carbon, and we have signals that the feedbacks are significant,” Nepstad says. For instance, estimates reveal that more than 1 billion tons of carbon were emitted from Borneo’s peat forests during the drought-driven fires of 1998, double the 500 million tons of carbon per year targeted to be cut by the international Kyoto Protocol, Nepstad points out.
Climate altering nutrient dynamics in lakes As the warming climate increases evaporation and cuts stream inflow to lakes, resource managers may have to lower point-source nutrient inputs even more to avoid nuisance algal blooms, according to research presented at the Ecological Society of America meeting in August. Climate warming is altering not only the dynamics of the carbon cycle but also the coupling of the cycles of phosphorus, nitrogen, and silica—critical nutrients for algal growth in lakes, says Dave Schindler, an aquatic ecologist at the University of Alberta in Edmonton (Canada). The province of Alberta has already experienced aspects of climate warming: Evaporation has increased by 12% since 1970, and midsummer flows in some rivers have been reduced to about 20% of historic levels, Schindler says. The warming
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“The bottom line is that scientists are finding that most of the feedbacks are positive, especially if the warming becomes substantial. As a consequence, CO2 emissions will have to be ratcheted back even more, if we are to avoid dangerous interference with the climate system,” Field concludes. —JANET PELLEY
and drying trend in western Canada has reduced inputs of silica, nitrogen, and phosphorus to lakes; this trend has led to clearer, more algae-free lakes in undisturbed areas. However, Lake Winnipeg, nestled in a 953,250-km2 watershed spanning from western Alberta to northern Ontario, still receives a big dose of phosphorus and nitrogen from sewage and agricultural runoff that is no longer diluted by inflows, Schindler says. With natural inflows down by 80%, diatoms have been elbowed out by the more noxious blue-green algae, which have spread in a 6000-km2 bloom for the past several summers. “Because there is less silica coming into lake ecosystems and because there is less dilution of point sources to lakes, we may need to cut back phosphorus and nitrogen inputs more than we did years ago to maintain the same water quality,” Schindler says. —J.P.
