Air pollution is changing our environment and undermining many benefits we rely on from wild lands, threatening water purity, food production, and climate stability, according to a team of scientists writing in the 14th edition of the Ecological Society of America's Issues in Ecology. In "Setting Limits: Using Air Pollution Thresholds to Protect and Restore U.S. Ecosystems," lead author Mark Fenn (USDA Forest Service) and nine colleagues review current pollution evaluation criteria. The authors propose science-based strategies to set new limits and put the brakes on acid rain, algal blooms, and accumulation of toxic mercury in plants and animals.
Power plants, industrial processes, vehicles, farms and stockyards release mercury, sulfur dioxide, and nitrogen compounds into the air. Though several decades of emissions limits and improving technology have resulted in a downward trend in acid rain and mercury contamination in the U.S., up to 65 percent of lakes in sensitive areas exceed critical acid levels, and mercury advisories against fish consumption exist in all fifty states. The authors discuss standard measurements that can be used to monitor ecosystem effects across the country. They review the use of defined "critical loads" of pollutants to design policy and manage ecosystems in the U.S. and Canada.
Organisms and ecosystems tend to tolerate pollutants up to a critical amount of pollutant accumulation, responding slowly up to the critical threshold. Beyond the threshold, scientists observe undesirable, and sometimes rapid, changes. The best limits are set at these thresholds, the authors say. Scientists use standard indicators, such as the calcium to aluminum ratio as a measure of acidity of soil, to identify "critical loads" at which ecosystems start to tip into cascades of bad consequences
"Not all landscapes and watersheds have the same sensitivity to pollutants," said author Charles Driscoll, professor of civil and en
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Ecological Society of America