Phoenix-The impact of airborne nitrogen released from the burning of fossil fuels and widespread use of fertilizers in agriculture is much greater that previously recognized and even extends to remote alpine lakes, according to a study published Nov. 6 in the journal Science. Examining nitrogen deposition in alpine and sub-alpine lakes in Colorado, Sweden, and Norway, James Elser, a limnologist in the school of life sciences at Arizona State University, and his colleagues found that on average nitrogen levels in lakes were elevated, even those isolated from urban and agricultural centers. The article, “Shifts in lake N:P stoichiometry and nutrient limitation driven by atmospheric nitrogen deposition,” presents experimental data from more than 90 lakes. The researchers’ collaboration also revealed that nitrogen-rich air pollution has already altered the lakes’ fundamental ecology. “This is because plant plankton or phytoplankton, like all plants, need nitrogen and phosphorus for growth,” Elser says. “Inputs from pollution in the atmosphere appear to shift the supplies of nitrogen relative to other elements, like phosphorus.” The increase in the availability of nitrogen means that growing phytoplankton in lakes receiving elevated nitrogen deposition are now limited by how much phosphorus they can acquire. Elser says that this is important because “we know that phosphorus-limited phytoplankton are poor food ?Çô basically ‘junk food’ for animal plankton, which in turn are food for fish.” Elster noted that “Such a shift could potentially affect biodiversity. However, we don’t really know, because, unlike in terrestrial systems, the impacts of nitrogen deposition on aquatic systems have not been widely studied.”
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