The dog days of summer in Minnesota are hot, calm, and quiet. In August, birds are silent, cicadas buzz, the sun beats down, lakes and rivers are placid, and the water is as warm as it gets.
It’s a fine time to slow down and stay cool with a swim at the local lake, but the warm, dry, and calm weather is also ideal for noxious algae. Several species thrive in late summer, creating toxic chemicals that can kill animals and sicken people. Just when we need water the most, it may be dangerous to the touch.
In early August, Beaver Lake in southern Minnesota was closed to swimming, boating, and fishing after a substance that was first thought to be sewage appeared. It was later identified as a type of harmful algae. Its appearance was surprising and confusing – the lake is known locally for being relatively clean and healthy.
Preventing noxious algae blooms is a priority for the state of Minnesota, but requires better understanding of when, where, and why they occur. Blue-green algae (or Cyanobacteria) can be baffling because they bloom unexpectedly, and can disappear quickly, making the phenomenon hard to catch and study. Its appearance is often dependent on multiple factors.
Boats, buoys and blooms
This summer, research station staff have been tending buoys on five lakes across the state, collecting massive amounts of data, tracking water quality in space and depth and time, seeking to understand complex connections between chemistry, temperature, wind, and toxins.
Along the way, there have been boat ramp mishaps, gas station pizza, sun and rain, wind and calm, blue water and green water.
It’s all to help answer key questions that could help clean up lakes.
“We’re looking at if they bloom, how long they bloom. Why do they produce toxins? How long did the toxins persist at dangerous levels? When we find toxins, what led up to that?” scientist Mark Edlund says.
The data being gathered will give a detailed description of the lake’s temperature, oxygen, and the relative amounts of cyanobacteria in the water, from early summer to fall, from the surface of the water to the bottom. Crunched and clarified and charted, the information will help pinpoint the conditions that cause harmful algae to bloom.
But only if someone remembers to add a safety layer of duct tape to connections between anchor lines and expensive submerged sensors.
A pressing problem
One day in May, scientist Adam Heathcote and lab technician Alaina Fedie launched the station’s research boat into St. James Lake, on the edge of the southern Minnesota town of St. James, just like they have done all summer.
It’s not a big lake, but St. James is clearly well-loved. A large campground on the south shore hosted dozens of camper trailers and R.V.s. The boat launch was spacious. Fishing piers protruded from the north shore.
There was no swimming beach to be seen.
Blue-green algae are natural in Minnesota waters, but human activity can greatly increase their abundance. Like Beaver Lake last week, or Lake of the Woods last summer, where pet dogs died after swimming, more and more of Minnesota’s cherished waters are fouled each year.
The trend has become bad enough that special funds were provided to make the station’s monitoring and analysis possible for three years. The research is supported in part by the emerging issues account of the Minnesota Environment and Natural Resources Trust Fund, as recommended by the Legislative Citizen Commission on Minnesota Resources.
“If they hadn’t done that, we wouldn’t have been able to sample this year, wouldn’t have been able to start until May of 2017,” says senior scientist Mark Edlund.
With the funding in place, this May the team deployed buoys in five lakes, located strategically from the southwest corner of the state to its northern middle. Working with the Minnesota Pollution Control Agency, they picked lakes that represented diverse surrounding landscapes, and were already part of other monitoring or research.
Duct tape and data
The buoys are daisy chains with a concrete block for an anchor and sensors attached every meter up to within sight of the surface. It was only after they sunk the first cinderblock that they realized they forgot the duct tape, the failsafe to prevent a sensor from breaking loose.
“You’re not really doing science if it doesn’t include duct tape,” Alaina says.
“You’re not doing it right, anyway,” Adam adds. They haul the anchor up and add the duct tape.
The sensors record the temperature and oxygen every few minutes, and once a month, the scientists come out to download the data and take other detailed readings about the water quality. In between visits, staff from the Minnesota Pollution Control Agency are taking the same water quality readings.
“The main thing this study is doing that hasn’t been done before is that we are getting out at the beginning of the season, and we are monitoring every two weeks until fall turnover,” says Edlund. “Most previous projects have been the standard three times a year, in June, July, and August.”
The old method was usually enough to determine if harmful algae blooms had been present recently, but not when it bloomed, and what changes had occurred in the lake that led to the bloom.
Putting the puzzle together
The day in the middle of May, they were deploying the buoys and taking initial readings. Bare fields were visible from the lake, which was surrounded by thousands of acres of corn and soybeans that were only now about to sprout. A grain elevator poked above the trees.
The highway into town passed by an ethanol plant – an industry consuming about 40 percent of the corn grown in Minnesota. Ethanol has stabilized the economy of agriculture, but has encouraged vast fields to be planted that increase runoff to Minnesota’s lakes and rivers.
The water in St. James Lake already had a green tint to it.
After motoring to a set of pre-determined GPS coordinates, the pair methodically went about their tasks. Adam lowered a specialized instrument slowly into the water, which automatically recorded multiple measurements as it descended. Alaina took water samples and measured the Secchi depth – how far a white disc could be seen as it was lowered into the water.
All that information will be combined, and weather data like temperature, precipitation, and wind speed will be added. It’s an ocean of information, but statistical analysis will reveal what is causing changes in water quality.
“In the end what we’re going to be looking at is putting the puzzle together,” says Heathcote. “When we find toxins, what led up to that?”
Wind already appears to be an interesting piece of the puzzle. During a calm period, even a shallow southern Minnesota lake like St. James might briefly stratify, with colder water settling to the bottom. But once the lake isn’t being mixed together, plants on the bottom die and decompose, consuming all the available oxygen – and creating ideal conditions to dissolve phosphorus out of the sediment.
Then, a strong wind can create enough wave action to mix the lake water back together. Those bottom waters, full of nutrients, are brought to the top, where more sunlight spurs algae growth.
“We think shallow lakes stratify and destratify frequently,” Edlund says. “Shallow southern prairie lakes do mix frequently, but may stratify for a week or three days, then de-stratify. If you’re not out there sampling, you missed it.”
Heathcote and Edlund first developed the buoy design for the station’s ongoing research on Lake of the Woods on the U.S.-Canada border. That study has shown the difficulty of determining why algae blooms occur – without almost constant monitoring. The remote sensors showed that Lake of the Woods stratified five times in one summer, yet every time the researchers went out there, it was mixed.
Only the buoys could tell them what had happened.
Algae the equalizer
It wasn’t windy the day in May when they went out on St. James and then nearby Madison Lake. A breeze occasionally roughened the water, but it was some of the finest field weather they could remember. The boat bobbed gently, a few birds sang from the banks, numbers were recorded.
Madison Lake is bigger and deeper than St. James, and appeared considerably clearer on that day. Several people were riding jet-skis on it in the late afternoon of the early summer day.
In June they went out in scorching heat. In July it was raining.
In August, the weather was hot and water on both lakes was obscured in green scum, not just ugly but potentially poisonous. The two lakes, which looked very different back in May, looked pretty much the same now.
The scientists took readings and water samples, made notes and observations, and brought it all back to the laboratories in Marine on St. Croix. The big haystack of data will be searched for trends and the tiny needles that could help solve the mystery of blue-green algae.