Monday, December 19, 2011
Nitrogen from Humans Pollutes Remote Lakes for More Than a Century
The distinctive signal of human-caused nitrogen going back more than 100 years appears in 25 lakes in temperate (green circles), alpine (blue) and arctic (red) areas of the Northern Hemisphere. Data from two lakes are shown in comparison to a similar signal revealed in the Greenland Ice Sheet (yellow). (Credit: University of Washington)
Nitrogen derived from human activities has polluted lakes throughout the Northern Hemisphere for more than a century and the fingerprint of these changes is evident even in remote lakes located thousands of miles from the nearest city, industrial area or farm.
The findings, published in the journal Science Dec. 16, are based on historical changes in the chemical composition of bottom deposits in 36 lakes using an approach similar to aquatic archeology. More than three quarters of the lakes, ranging from the U.S. Rocky Mountains to northern Europe, showed a distinctive signal of nitrogen released from human activities before the start of the 20th century, said Gordon Holtgrieve, a postdoctoral researcher at University of Washington School of Aquatic and Fishery Sciences and lead author of the report. The UW and a dozen other research institutions contributed to the research.
"When it comes to nitrogen associated with humans, most studies have focused on local and regional effects of pollution and have missed the planetary scale changes," Holtgrieve said. "Our study is the first large-scale synthesis to demonstrate that biologically-active nitrogen associated with human society is being transported in the atmosphere to the most remote ecosystems on the planet."
Burning fossil fuel and using agricultural fertilizers are two key ways humans increase the amount of nitrogen entering the atmosphere. Once in the atmosphere, this nitrogen is distributed by atmospheric currents before being deposited back on Earth in rain and snow, often thousands of miles from the source.