EPA seeks source of element in waterways

Scientists are trying to determine the cause of rising phosphorus levels in streams, rivers, lakes, wetlands and coastal waters across the country.

The U.S. Environmental Protection Agency hosted a webcast on Thursday to discuss the issue. Data from the EPA's National Lakes Assessment and the National Rivers and Streams Surveys indicate increasing amounts of phosphorus in bodies of water, especially in areas that had previously shown almost no phosphorus.

Results of the streams survey ending in 2004 show a median phosphorus level of 26 micrograms per liter. Five years later the median was 48 microgram per liter. Another survey that ended in 2014 showed phosphorus at 56 micrograms per liter. Similarly, phosphorus levels in lakes moved from 20 micrograms in 2007 to 37 micrograms in 2012. The latest edition of the National Lakes Assessment will be taken later this year.

"We're seeing a lot of changes, particularly at the low end of the phosphorus gradient," said Dr. John Stoddard, research scientist at the EPA's Office of Research and Development in Corvallis, Oregon. "This set off a lot of alarm bells and made us realize we have to go back and do a better job of trying to figure out what is driving this, particularly because of the change that is happening at the lower end of the concentration gradient."

Stoddard went on to say that while bodies of water with the least phosphorus content in 2007 showed large increases five years later, the data also show almost no increase in phosphorus content for bodies of water with higher levels. About 25 percent of lakes had very slight phosphorus levels in 2007. By 2012 only 7 percent have low phosphorus levels.

The presence of more phosphorus in the water is cited as a cause for the growth of toxic blue-green algae in places such as Grand Lake. The waters of Grand Lake have been under a recreational no-contact order since July 30, 2015, due to the presence of the algae.

Stoddard said he can't explain the reason why this change is happening. The largest contributors are believed to be runoff from agriculture, stormwater and/or wastewater. But since the amount of nitrogen is not significantly increasing along with the phosphorus levels, more investigation is needed. Also, the condition is noticed in areas with little to no agricultural, storm or wastewater runoff issues.

Possible reasons for the phosphorus changes, Stoddard said, could be acid rain, migratory birds, the death of the peripheral parts of trees or woody plants or atmospheric dust.

Continued tracking of the conditions of the nation's waters is needed to answer these questions.

The National Aquatic Resource Surveys are conducted every five years on a rotating basis among streams and rivers, lakes, wetlands and coastal waters. The next lakes survey is set for this year while the streams and rivers survey will be completed again in 2019.