Citizen Scientists Study the St. Croix

Water testing volunteers provide essential data to guide river clean-up.




4 minute read

In a well-practiced routine, Roberta Harper drops a secchi disc overboard to measure how far it can be seen below the surface while her husband Jim measures air and surface water temperature. Then they use a five-foot PVC tube to pull a water sample from several feet down (using the same method you use when you put your thumb over the top of a straw to pull liquid from a glass). That sample is then dumped into a bucket and a battery of tests are performed on it, including filtering out the algae, which will be analyzed in a Metropolitan Council laboratory.

The St. Croix River reflected a shimmering blue sky when Jim and Roberta Harper’s boat pulled away from Sunnyside Marina just before 9 a.m. one morning in early August. Roberta steered into the main channel, where Jim dropped the anchor and the couple started a battery of tests to help better understand the health of the St. Croix’s water.

The pair spent the rest of the day on the boat, only testing the last of seven sites late in the afternoon, 20 miles downstream. Even with the help of two guests on the boat that day, they didn’t get back to the dock until 6 p.m.

The Harpers have been doing this for several years, going out once a month during open water season. Between these outings, they also do more limited tests at two sites. And they do this all as volunteers.

Committed to the St. Croix

The monitoring work is the perfect retirement job for two retired scientists. The Harpers both had long careers at 3M in Maplewood, MN. Roberta was a chemist and Jim a chemical engineer.

“I always loved to go field testing,” Jim said. He added that the river is much more pleasant than what he experienced studying pavement markings in the 100-degree heat of Las Vegas.

The Harpers aren’t alone in their dedication to the water quality monitoring. Several other volunteers regularly take samples along Lake St. Croix – although the Harpers are alone in doing a monthly trip to all seven locations to measure dissolved oxygen in the water.

“Their work provides scientific data essential to improving the St. Croix’s water quality,” said Deb Ryun, executive director of the St. Croix River Association. “The monitoring will help ensure future generations have a chance to enjoy the river as we have.”

The dissolved oxygen measurements the Harpers provide have changed the way scientists understand how water moves through Lake St. Croix, with significant implications for efforts to reduce harmful algae in the river.

Half-lake, half-river

Like any plant, algae “inhale” carbon dioxide and “exhale” oxygen. Water with elevated levels of oxygen indicates abundant algae. (On the Harper’s August outing, the oxygen in the water at the site near Prescott was the highest they had recorded since they started measuring it in 2007.)

These measurements are leading researchers like Sue Magdalene, who works at the St. Croix Watershed Research Station, to think of the lower St. Croix as a warm, oxygen-rich river on top and a cold, low-oxygen lake on the bottom. A decade ago, it was thought to act entirely like a river.

“Lake St. Croix is not just a wide spot in the river… It flows like a river, but it stratifies like a lake into four cold pools. The combination is much like a warm river sliding over four isolated lake bottoms,” Magdalene explained. The four pools are separated by narrow channels where the Willow River, Valley Creek, and Kinnickinnic River join the river.

The fact that water settles on the bottom of each pool during the summer could mean a lot for efforts to reduce nutrients like phosphorus, which can cause increased algae in the water.

“When a lake stratifies with a cold hypoxic (low oxygen) bottom layer, the conditions are ripe for phosphorus release from lakebed sediments, called internal loading,” Magdalene told me. “We’re still working on the extent of internal loading, but it’s more than previously estimated.”

Measuring oxygen means slowly dropping a probe from the boat, stopping every meter to record data. A little humor makes this tedious task go faster. When it’s Jim’s turn to lower the probe, his favorite joke is to shout out, “Cinco de meter!” when the probe reaches five meters.

‘Measuring stick’

The answers the Harpers are helping provide are essential to knowing what’s happening with the St. Croix’s water, and what needs to be done to improve it, says Kent Johnson of the Metropolitan Council, which leads the volunteer monitoring program.

“This is an important, ongoing measuring stick,” Johnson said. “The volunteer program has been phenomenal, basically we wouldn’t have had any any data between Stillwater and Prescott if not their for efforts.”

The monitoring program and the analysis of the data recently received a boost from a Legacy Amendment grant provided by the Minnesota Pollution Control Agency and the St. Croix River Association.

Johnson explained that data from this program and other sources led to Lake St. Croix being declared “impaired” in 2008. It’s also what will reveal the success of efforts to clean up the river.

“The monitoring program is the measurement tool, it lets us know how we’re doing, and hopefully will tell us when the St. Croix can be removed from the impaired waters list,” Johnson said.

Good data, good management

The research, policies and conservation efforts being done throughout the river’s watershed to improve its water quality ultimately start with the data provided by people like the Harpers.

“After 30-plus years at 3M, I learned that bad data is worse than no data at all,” Jim said. “If we can collect good data, we’re happy.”

As the Harpers were taking measurements in the narrow channel below the Hudson swing bridge, they pointed out a gentleman swimming next to his boat with two kids who were probably his grandchildren. It was Harry Martin, one of the other monitoring volunteers.

Martin knows better than most people what’s in the water, and the sight of him and his grandkids swimming in the river without hesitation was a welcome sight.

After writing down the oxygen reading, the citizen scientists heaved the anchor aboard and headed downstream to the next site.