Humans cited in global nitrogen increase

Humans' impact on Earth is more than just depletion of resources and warming of the planet -- we're causing an overabundance of nitrogen, a U.S scientist says. Arizona State University researcher James Elser said a study shows disruption to Earth's nitrogen balance began at the dawn of the industrial era and was further amplified by worldwide production of nitrogen-rich fertilizers. Before that, nitrogen --an essential building block to life on Earth and a major component of its atmosphere -- had cycled around low but balanced levels over millennia, but that balance ended around 1895, Elser said. "Humans have more than doubled the rate of nitrogen inputs into global ecosystems, relative to preindustrial periods, and have changed the amounts of circulating phosphorus (like nitrogen, a key limiting ingredient for crops and other plants) by about 400 percent due to mining to produce fertilizers," Elser said in an ASU release Thursday. One result of the increased nitrogen inputs can be seen in inland lakes, reservoirs and rivers, he said. "Nitrogen deposition to lakes leads to phytoplankton (at the base of food chain) with low content of the important nutrient phosphorus," Elser said. "This is kind of like 'junk food' for animals that eat the phytoplankton. Such effects are likely to ripple upward in the food chain."