Two hundred and fifty people will gather at a conference in Madison to discuss a pressing freshwater challenge: how to reduce runoff, especially from agricultural fields, that carries phosphorus.
Although phosphorus is commonly used to fertilize crops, the nutrient continues to run off, especially during storms. This causes the growth of algae, some of it toxic, in lakes and streams, which reduces water quality and threatens aquatic life.
The conference is organized by the UW-Milwaukee School of Freshwater Sciences Center for Water Policy. It is convening tribal, state and government representatives, as well as water companies, farmers and researchers.
READ: Declining Milwaukee River Basin water quality: ‘It’s hard to sugar coat’
Harvey Bootsma of UWM’s School of Freshwater Sciences will be among them.
Inside Harvey Bootsma’s lab, the tank on the left containing quagga mussels illustrates their ability to filter nutrients from their environment.
He points to two small tanks in the laboratory of the School of Freshwater Sciences. 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 of buckets of water. And we filled both tanks with the same water,” says Bootsma.
Extended conversation with Harvey Bootsma of UWM’s School of Freshwater Sciences.
In just over an hour, the water in the “quagga mussel” tank is almost crystal clear, while the other “is very murky and cloudy, and that shows you how effective the mussels are in the time to remove particulate material from the water,” Bootsma says.
And that’s not good. Quagga mussels have dropped out of the lake’s food web.
When Bootsma joined UWM’s freshwater science team in 1999, mussels weren’t on his research radar. Their focus was algae. “Algae that grow at the bottom of the lake. There was this real problem in Lake Michigan. It was just growing too fast, and there were no fish or other organisms that would feed on this algae,” he says.
This was not the first algae problem Lake Michigan has faced. In the 1960s and 1970s, Bootsma says, “Those were the heyday of eutrophication: too much phosphorus going into the lakes and causing too much algae to grow,” Bootsma says.
In 1972, concerned about the entire freshwater basin, Canada and the United States took steps to develop the Great Lakes Water Quality Agreement. Bootsma says he did a good job setting phosphorus limits for each lake and putting policies in place, such as “Improving wastewater treatment plants, some changes in farming practices, and restrictions on phosphorus in detergents for the clothes,” says Bootsma.
Boostma says that algae abundance and phosphorus concentrations dropped in Lake Michigan, “so when the algae came back in the late 1990s and early 2000s, we were baffled.”
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 the conditions of the temperature of the lake, the light, the phosphorus … both dissolved in the water, but also the amount of phosphorus that was in the algae itself,” he says.
This research led Bootsma to the quagga mussels we met earlier in the story.
“These mussels are excellent filters, they filter plankton out of the water column and at the same time they suck up phosphorus and pump it to the bottom of the lake where the mussels live,” says Bootsma.
In fact, the mussels cover much of the lake, including the rocky reefs where the algae have taken over. That’s where Bootsma conducted more research on the Michigan side of the lake. He and his team spent a summer scraping mussels from an area the size of a large kitchen, he says.
“A small area in the shoreline area of Sleeping Bear Dunes National Lake. Our hypothesis is that there should be less algae when there are no mussels and the phosphorus content of these algae should be lower because we think the algae got a lot of their phosphorus from the mussels,” says Bootsma.
To his surprise, seaweed is only slightly less abundant. “Even though the phosphorus content of the algae actually went down, and we’re still trying to figure that out. If the phosphorus content is so much lower in these algae, why does it still seem to be growing quite quickly?” Bootsm says.
Another puzzle, Bootsma says, is that mussels have not recolonized this section of reef.
“The only way a rock can be recolonized is if the veligers, which is the mussel larvae, the very small larvae settle on those rocks and start growing as small mussels and eventually they turn into big mussels,” says Bootsma.
The scientist suspects that a different invasive, a small fish called the round goby, is gobbling up the larvae before they have a chance to mature.
“Ironically, one invasive species appears to be helping to control another,” says Bootsma. “That’s what we’re following.”
Bootsma, along with other researchers, elected officials and farmers, will study ways to control the impacts of phosphorus at the conference in Madison on Tuesday.
Bootsma says the discussion will be immensely complex and important.
“These phosphorus issues in Lake Michigan, which are quite unique and different from what happens inland. But the fact is, they’re both affected by what we’re doing on the land in agriculture and in our cities, so how we get it. there’s a balance,” 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.