116 3rd St SE
Cedar Rapids, Iowa 52401
This could be another banner year for pond scum, state water quality experts say.
“My sense is we are going to be seeing some big blooms of blue-green algae this summer,” said Iowa State University limnologist John Downing, a nationally recognized expert on the sometimes toxic blooms that can impair swimming, boating and fishing.
Nutrients in the water and summer heat fuel algae blooms, according to Downing, who has been studying nutrient levels and algae blooms in more than 130 Iowa lakes for the past 13 years.
High volumes of fertilizer washed off farm fields during record spring rains could set the stage for more frequent and intense blue green algae blooms later this summer, according to both Downing and Mary Skopec, a research geologist with the Iowa Geological and Water Survey.
Iowa, Downing said, “has some of the most nutrient rich waters in the world,” and it's getting richer.
By nutrients, Downing means primarily phosphorus, which “leaks” into surface water from commercial fertilizer, manure and sewage.
“We are in uncharted territory, going from drought to flood in a couple of months,” said Jason McCurdy, who coordinates the Department of Natural Resources' state park beach monitoring program, which began testing for microcystin, the algae-produced toxin most common in Iowa, in 2008.
The DNR tests for microcystins at 38 state park beaches. When toxin levels reach 20 micrograms per liter, the DNR posts signs advising beach users to stay out of the water.
Lake Macbride in Johnson County experienced an uncommonly early blue green algae bloom in the first week of June, McCurdy said.
Samples taken from a cove near the beach tested above the threshold while samples collected at the beach did not, he said.
McCurdy said the DNR issued two elevated microcystin advisories on Friday – one for Crandall's Beach on Big Spirit Lake in Dickinson County and one for the beach at Viking Lake in Montgomery County.
Signs will be posted at those beaches advising that swimming is not recommended, he said.
The latest sample at the beach at Macbride State Park was well below the threshold at 0.95 micrograms of microsystin per liter, he said.
Last year nine separate alerts of elevated microcystin levels were posted at state park beaches, according to Stuart Schmitz, an environmental toxicologist with the Iowa Department of Public Health.
Lakes with phosphorus concentrations above 50 parts per billion are likely to have decreased water clarity, low oxygen and frequent algal blooms dominated by blue-green algae, the Geological and Water Survey said in its 2013 annual report.
According to test data compiled by Downing and colleagues, the average phosphorus concentration in Iowa lakes for 2012 was 117 ppb, more than double the threshold level.
Ninety of the 130 lakes sampled had average phosphorus concentrations above the 50 ppb threshold level, and 33 lakes had concentrations above 150 ppb, more than three times the threshold level, the annual report said.
Those 33 hypereutrophic lakes experience continuous blue-green algae blooms in the summer, low oxygen concentrations near the bottom of the lake and very low water clarity, according to the report.
The Iowa Department of Public Health began tracking human exposure to toxic algae blooms in the summer of 2008, the same year the DNR began testing for microcystins.
So far the department has identified 24 doctor-reported cases in which people suffered adverse health effects – typically skin irritation or gastrointestinal upsets, Schmitz said. Such cases are likely under-reported, since many people with symptoms do not seek medical treatment, he said.
Schmitz said the department's data come only from DNR monitoring of beaches at state parks so most of the state's water is not monitored for algae-produced toxins.
Livestock, wildlife and pets -- which are less particular than people about the water they consume and expose themselves to -- are much more likely than people to suffer the ill effects of algae toxins, said Steve Ensley, a toxicologist with the Veterinary Diagnostic Laboratory at ISU.
“Though we don't have real good numbers because it is hard to diagnose – you need a necropsy and water samples – we definitely see animals die from it each year,” he said.
Fish and other aquatic animals are not generally susceptible to algae toxins, but they can suffer from other side effects of high nutrient concentrations such as low oxygen levels and ammonia toxicity, according to Downing.
Most people don't need advisory signs to keep them out of algae-infested waters, Downing said.
“It stinks for one thing, and looks unappealing for another” he said.
Still, blooms inhibit recreational use of waters, a key component of one of the state's most valuable resources, he said.