Study: Algae fixes may trigger more lake pollution

Published 10:44 am Friday, October 11, 2013

ST. PAUL, Minn. — A new University of Minnesota study says cutting phosphorus in lakes reduces algae blooms and improves water quality but can lead to an unintended consequence: too much nitrogen in lakes.

According to the study published online Thursday in the journal Science, reducing phosphorus also can result in less of the microbial processes that eliminate another unwanted nutrient: nitrogen.

As a result, nitrogen can accumulate in large lakes and lead to nitrogen pollution downstream, the study found.

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Phosphorus, a nutrient that promotes algae blooms, is washed into Minnesota lakes with leaves and lawn fertilizer. Nitrogen sources include wastewater treatment plants, farming, lawn fertilizer and pet waste. Nitrogen can contaminate drinking water sources and has led to a large low-oxygen “dead zone” in the Gulf of Mexico where nutrient levels are too high to sustain most aquatic life.

Rather than relaxing efforts to reduce phosphorus, the researchers said efforts to reduce nitrogen in lakes should be stepped up even more, Minnesota Public Radio News ( ) reported.

“We need to pay attention to the way that nutrients interact in ecosystems and maintain our focus on reducing phosphorus and nitrogen pollution,” the study’s lead author, Jacques Finlay, an associate professor in the College of Biological Sciences, said in a news release. “If we do that, we’ll be taking steps toward improving water quality locally as well as downstream.”

The researchers looked at a dozen large freshwater lakes around the world.

Additional research is needed before drawing conclusions about how phosphorus and nitrogen interact in smaller lakes, Finlay said.