Airborne nitrogen shifts aquatic nutrient limitation in pristine lakes

Scientist Jim Elser (Arizona State University) is sampling Green Lake 5, located at the Niwot Ridge Long-term Ecological Research (LTER) site in the Front Range of the Colorado Rocky Mountains. Like other lakes in the Front Range, this lake receives elevated inputs of atmospheric N deposition due to transport of polluted air from urbanized areas and from high intensity agricultural operations. Photo: James Elser/ASUThe impact of airborne nitrogen released from the burning of fossil fuels and wide-spread use of fertilisers in agriculture is much greater that previously recognised and even extends to remote alpine lakes, according to a study published Nov. 6 in the journal Science.

Examining nitrogen deposition in alpine and subalpine 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 centres.

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 is poor food – basically 'junk food' for animal plankton, which in turn are food for fish."

"Such a shift could potentially affect biodiversity," he adds. "However, we don't really know, because, unlike in terrestrial systems, the impacts of nitrogen deposition on aquatic systems have not been widely studied."

Elser's collaborators include researchers Tom Andersen and Dag Hessen from the University of Oslo; Jill Baron of the United States Geological Survey and Natural Resource Ecology Laboratory at Colorado State University; Ann-Kristin Bergström and Mats Jansson with Umeå University, Sweden; and Koren Nydick of the Mountain Studies Institute in Colorado, in addition to members of his own group in ASU's College of Liberal Arts and Sciences, Marcia Kyle and Laura Steger.

Hessen, a well-known limnologist, and Elser have had a long-standing collaborative relationship, looking not only at nitrogen deposition, as in this study, but also zooplankton nutrition and a broad range of stoichiometric studies. Elser met Bergström at a conference at Umeå University and discovered that she had performed similar experiments in Sweden.

"By combining these studies we were able to achieve a more global picture of how nitrogen was impacting a broad range of lakes and come to firmer conclusions about effects of deposition," Elser notes.

Elser and Hessen hope to expand on these findings and have a pending grant proposal with the Norwegian government. In addition, Elser says he hopes to perform similar studies in China "where atmospheric nitrogen pollution is extremely high," but, as yet, unstudied.

Queensland coal export terminal shut down

Photo: Abraham Powell, GreenpeaceOn the eve of the Pacific Islands Forum in Cairns, Greenpeace activists have shut down Abbot Point coal export terminal in Queensland to demand Kevin Rudd stops risking the future of Pacific Islands by undermining real action on climate change and expanding Australia's coal industry.

The action was launched from aboard the Greenpeace vessel the Esperanza, which is currently stationed just metres from the coal export terminal.

"Abbot Point epitomises the hypocrisy of the Rudd Government's climate policy," said Fijian Greenpeace campaigner Lagi Toribau. "As Pacific Island leaders call for the 40-45percent emission cuts needed to save their homes, Kevin Rudd is presiding over a massive coal industry expansion while masquerading as a climate hero. He needs to back Pacific calls for concrete action, not try to bully their leaders into submission."

Kevin Rudd has made highly conditional promises to reduce domestic carbon emissions by 5 to 25percent by 2020, yet this export coal expansion would cancel out even the most ambitious target six times over. For the 5percent reduction, this rises to fifteen times the target.

Financed by more than $328 million of public money in 2009/10, the doubling in size of the coal terminal at Abbott Point alone will result in an extra 67.5 million tonnes of carbon pollution per year. This is equivalent to the annual carbon footprint of 2.4 million Australians.

Abbot Point is only a small part of Australia's largest coal export expansion in decades, which will see total capacity more than double from 332 to 730 million tonnes per year.

"It doesn't matter where this coal is burned, carbon pollution has no borders," said Papua New Guinea activist Sam Moko at Abbot Point. "Climate change is already having a devastating impact on our homes and we need genuine support from our Australian neighbours. Unless emissions are drastically and rapidly reduced, low lying atolls such as Tuvalu will soon be uninhabitable."

Moreover, as a new Greenpeace briefing demonstrates, far from being a boon to Australia, coal is becoming an economic and environmental millstone around our necks. Public support for continued expansion is also in short supply, with a July poll commissioned by Greenpeace showing that 76percent of Australians support a cap or reduction of coal exports.

By reinforcing Australia's position as the world's largest coal dealer, Kevin Rudd continues to shun not only his neighbours, but also common sense. Supporting Pacific leaders at the Pacific Island Forum would be a major step in the right direction.

Rodent size linked to human population and climate change

You probably hadn't noticed - but the head shape and overall size of rodents has been changing over the past century. A University of Illinois at Chicago ecologist has tied these changes to human population density and climate change.

The finding is reported by Oliver Pergams, UIC research assistant professor of biological sciences, in the July 31 issue of PLoS One.

Pergams said that such size-and-shape changes in mammals, occurring around the world in less than a century, are quite substantial.

He had done earlier studies on a century's worth of anatomic changes between two geographically isolated rodents - Channel Island deer mice from coastal California and white-footed mice northwest of Chicago - and noted fast change among both.

"I suspected they weren't unique examples," he said. "I wondered whether these changes were occurring elsewhere, whether they were global in nature, and what some of the causes may be."

Pergams examined specimen rodents from museums around the world, including the big collections held at Chicago's Field Museum and the Smithsonian in Washington.

Altogether, he recorded more than 17,000 body and skull measurements from 1,300 specimens from 22 locations in Africa, the Americas and Asia. The animals were collected from 1892 to 2001, and Pergams compared those from before 1950 to those collected after.

He also compared specimens gathered from sparsely populated islands to those from the mainland, where human populations were denser.

Pergams found both increases and decreases in the 15 anatomic traits he measured, with changes as great as 50 percent over 80 years. Ten of the 15 traits were associated with changes in human population density, current temperature, or trends in temperature and precipitation.

"Rapid change, contrary to previous opinion, really seems to be happening quite frequently in a number of locations around the world," Pergams said. "There seem to be significant correlations with 'people-caused' parameters, such as population density and anthropologically-caused climate change."

While Pergams' study was by no means comprehensive, it was the first attempt of its kind to examine data on mammals from many global locations to find links between morphological change and variables such as population density and changing climate.

"Species can adapt quickly to rapid environmental changes - quicker than many people have thought, especially for mammals," said Pergams. "Those mammals that can adapt quickly have a much higher chance to survive big environmental changes caused by humans. Understanding which species and populations have the greatest ability to change has a crucial impact on being able to conserve biodiversity."