Experts refining science of Great Lakes algae forecasts
GIBRALTER ISLAND - In the six years since Lake Erie was hit by what experts thought was the worst possible algal bloom, scientists have made great strides in forecasting the harmful summer blooms.
“We thought 2011 would be what the standard would be (rated a 10 on the severity scale), and 2015, of course, went off the scale as a 10.5. We all know how severe that was,” said Rick Stumpf, lead oceanographer for the National Oceanic and Atmospheric Administration’s Lake Erie bloom forecast.
Stumpf described 2016, which came in at a 3.2 on the scale, as a “dramatic difference” compared to the year prior.
“There was simply a whole lot less discharge and a lot less phosphorus (in 2016),” Stumpf said.
The new forecasting models place far less of an emphasis internal loads — phosphorus already in the lake as sediment from previous years' blooms, which can be later released — and focuses more on phosphorus from land runoff that drains into the lake via the Maumee River after heavy rains.
“It’s the Maumee River that matters,” Stumpf said. “This whole point reinforces the message — if we stop the phosphorus from flowing into the lake, the blooms will end.”
Heidelberg University’s National Center for Water Quality Research has been tracking and studying Maumee River discharge for over four decades.
The researchers measure three different forms of phosphorous: total phosphorus, dissolved reactive phosphorus, and total bioavailable phosphorus, or TBP.
Scientists began measuring the TBP metric only last year.
Developing a new metric that combines dissolved phosphorus, which is entirely available for algae to feed on, with the specific portion of particulate phosphorus that is also available for algae, was done following the worst-ever bloom in 2015.
About 8 percent of particulate phosphorus is bioavailable, according to Laura Johnson, director of the National Center for Water Quality Research.
“The Maumee (River) is like a spigot going into our bucket here, which is Lake Erie,” she said. “We know that the way it works is, during low flow, we have little bit of water coming in fairly clean. When we have high flow and a lot of water coming in, it’s usually fairly dirty.”
The high flows are caused by significant rain events.
“It doesn’t take a whole lot of storm flow to make the lake have a lot of phosphorus,” Johnson said.
This year, from March through May, the amount of rain in the region was only a little above average. In June, there was a total of around 5 inches of rain, which was slightly below average.
That changed in July, when the total amount of rain in the first few weeks was 400 percent above normal for the otherwise typically dry month.
Johnson said there were essentially six significant storm events in the region this year during the loading season, which runs from March 1 to July 31.
“What’s really intriguing is how low we were in March,” she said of the amount of discharge into Lake Erie this year.
Johnson believes that it may have been due to the mild winter the region experienced.
By the end of the loading season, this year's levels were below those measured during the severe blooms of 2011 and 2015, but above those of mild bloom years such as 2012 and 2016.
When data on the levels of discharge throughout the loading season are compared to those of the cumulative phosphorus entering the lake during the same period, the two match up as expected.
“These patterns that we’ve had over the past 10 years or so are just like what we see with flow,” Johnson said. “It really points out that, if it rains, we get runoff, we get phosphorus. If it doesn’t rain, we don’t.”
While that fact is not a surprise to researchers, Johnson said it suggests that concentrations of phosphorus are not varying that much over the recent past.
And those concentrations are still well above “Annex 4” targeted reductions.
“Annex 4” is the section of the binational Great Lakes Water Quality Agreement signed by Ohio, Michigan and Ontario in 2013 dealing with nutrient pollution, specifically phosphorus. The agreement calls for a 40 percent reduction in phosphorus concentrations by 2025.
“We still have progress to be made,” Johnson said.