Lake Michigan researcher part of discussion about phosphorus impacts on Wisconsin's freshwater systems
Two hundred fifty people will be putting their heads together at a conference in Madison to discuss a pressing freshwater challenge: how to reduce runoff, especially from agricultural fields, that carries phosphorus.
While phosphorus is commonly used to fertilize crops, the nutrient continues to run off, especially during storms. That results in the growth of algae—some of it toxic—in lakes and streams, which drives down water quality and threatens aquatic life.
The conference is hosted by the Center for Water Policy at UW-Milwaukee’s School of Freshwater Sciences. It is convening tribal, state and government representatives, as well as water utilities, farmers and researchers.
READ: Milwaukee River Basin's Water Quality Decline: "It's Hard To Sugarcoat"
Harvey Bootsma of UWM’s School of Freshwater Sciences will be among them.
He points to two small tanks in his School of Freshwater Sciences lab. The bottom of one is thick with quagga mussels, an invasive species that entered the Great Lakes system around 1990.
“These were just taken out of the harbor this morning. We took them out with a couple buckets of water. And we filled both tanks with the same water,” Bootsma says.
In just over an hour, the water in the “quagga-musseled” tank is nearly crystal clear, while the other,” is very murky and cloudy and that shows you how effective the mussels are at clearing the particulate material out of the water,” Bootsma says.
And that’s not a good thing. Quagga mussels have thrown off the lake’s food web.
When Bootsma joined UWM’s freshwater sciences team in 1999, mussels weren’t on his research radar. His focus was algae. “Algae that grows on the lake bottom. There was this real problem in Lake Michigan. It was just growing too fast, and there weren’t fish or other organisms that feed on that algae,” he says.
This wasn’t the first algae problem Lake Michigan has faced. Bootsma says back in the 60s and 70s, “Those were the heydays of eutrophication: too much phosphorus going into the lakes, causing too much algae to grow,” Bootsma explains.
In 1972, concerned about the entire freshwater basin, Canada and the U.S. took action—crafting the Great Lakes Water Quality Agreement. Bootsma says it did a good job establishing phosphorus limits for each lake and setting policies in motion, including, “Improvement of sewage treatment plants, some changes in agricultural practices and restrictions of phosphorus in laundry detergents,” Bootsma says.
Boostma says algae abundance and phosphorus concentrations dropped in Lake Michigan, “which is why when the algae came back in the late 1990s and early 2000s, we were puzzled."
Bootsma looked for answers through experiments in his lab, “And we did a lot of diving in the lake, collecting the algae, measuring how much there was, measuring how fast it was growing, measuring conditions in the lake temperature, light, phosphorus—both dissolved in the water but also how much phosphorus there was in the algae itself,” he says.
That research led Bootsma to the quagga mussels we met earlier in the story.
“These mussels are great filter feeders, filtering the plankton out of the water column and at the same time they’re sucking phosphorus out and pumping it down into the bottom of the lake where the mussels live,” Bootsma says.
Actually, the mussels cover much of the lake, including rocky reefs where algae have taken hold. That’s where Bootsma carried out more research on the Michigan side of the lake. He and his team spent a summer scraping mussels from an area about the size of a large kitchen he says.
“A small area in the Sleeping Bear Dunes National Lakeshore area. Our hypothesis is that there should be less algae when there aren’t mussels there and the phosphorus content of that algae should be lower because we believe that the algae was getting a lot of its phosphorus from the mussels,” Bootsma says.
To his surprise, the algae are only slightly less abundant. “Even though the phosphorus content of the algae really went down, and we’re still trying to find that out. If the phosphorus content is so much lower in that algae, why does it still seem to be growing fairly quickly?” Bootsm says.
Another puzzle, Bootsma says mussels have not recolonized that section of reef.
“The only way a rock can be recolonized is if veligers, that’s mussel larvae, the very small larvae settle on those rocks and start to grow as small mussels and eventually become big mussels,” Bootsma says.
The scientist suspects a different invasive—a small fish called the round goby—is gobbling up the larvae before they have a chance to mature.
“Ironically, it looks like one invasive species is helping to controls another one,” Bootsma says. “That’s what we’re following up on.”
Bootsma along with other researchers, elected officials and farmers will looks at ways to control the impacts of phosphorus at the conference in Madison this Tuesday.
Bootsma says the discussion will be immensely complex and important.
"These phosphorus issues in Lake Michigan, which are quite unique and distinct from what's going on inland. But the fact is that both of those are affected by what we're doing on the land in agriculture and our cities, so how do we achieve a balance there," Bootsma says.
If you’re intrigued by Tuesday’s phosphorus conference in Madison, you can sign up to listen to the conversation that will be available after the event.