Scientists say runoff regs don’t factor in phosphorus already in lake

New findings indicate that state and federal regulators hoping to improve water quality in Lake  Champlain will need to adjust their policies to address warming temperatures that trigger toxic  blue-green algae blooms, according to a research team based at The University of Vermont. 

Current water-quality standards focus on levels of phosphorus that run off from farms and other  property into rivers that flow into Lake Champlain, but they don’t account for existing phosphorus  that has settled into the sediment from previous years, the researchers report in a recent article in Earth’s Future, a prominent publication focused on sustainability. That “legacy” phosphorus lies  in wait for warm weather, which creates the ideal oxygen-choked environment for the growth of  cyanobacteria, commonly called blue-green algae.  

A multidisciplinary team working with the Vermont Established Program to Stimulate  Competitive Research, or VT EPSCoR, used a unique modeling method to predict more than 100  potential scenarios of the changing climate – specifically temperature and precipitation – and the  consequences for phosphorus-fueled algae that plagues the shallow Missisquoi Bay in Lake  Champlain’s northeastern corner. Their computations incorporated current standards set by the U.S. Environmental Protection Agency in 2015 to reduce the total maximum daily load, or TMDL, of  phosphorus running into Missisquoi Bay by 64.3 percent, leaving the water cleaner. 

“These indicators do not address, completely, the direct effects of climate change on the  warming of the water in the fresh bays and the lakes,” said Asim Zia, a UVM professor of public  policy and computer science and the lead author of the recent article, part of a larger study applying these advanced modeling tools to assess the various ways that climate change has consequences  for water quality in Lake Champlain. 

“Despite these aggressive policy targets, the legacy phosphorus that is already in the lake, in  the bay, would offset that reduction and we will continue to see these blooms.”

While the EPA’s standard is helpful, it’s only one piece of the cyanobacteria solution, Zia said.  The regulations involve measuring both “external” phosphorus at the runoff point and “internal”  phosphorus that settles in the lake. The UVM team recommends two additional criteria — the  amount of cyanobacteria growth itself and the number of days that those blooms surpass a certain  threshold. A day or two of bursting blooms aren’t serious, Zia suggests, but 10 or more days have  crucial consequences for public health and recreation around the lake.  

Policymakers can use satellite imagery, drone technology, reports from citizen and scientist  observers, or sensors to record algae levels, Zia said. Looking to reduce those levels, scientists are  studying aeration technology to increase oxygen in the bottom layers of Lake Carmi in Vermont  to mitigate the conditions that cause blooms, an effort led by fellow researcher, Dr. Andrew Schroth,  a University of Vermont bio-geochemist. 

An updated policy would have benefits far beyond Vermont, Zia said – for any waterway where the TMDL standard applies: parts of the Great Lakes; estuaries of the Gulf Coast and Everglades  of Florida; and some areas of the Chesapeake Bay. 

The EPA’s current strategy to improve water quality by 2035 – with nutrient levels down to  0.025 micrograms per liter in Missisquoi Bay – should be reconsidered given these new findings,  according to the researchers. Zia said “It’s about setting the right expectations for people and the  public.”