At the confluence of Ahrensfeld Creek and Rush Creek, Winona State University geology professor Dylan Blumentritt talked about how “legacy sediment” from historic tillage practices affects the muddiness of local trout streams today.
by CHRIS ROGERS
The first stop on a tour of the Ahrensfeld Creek watershed last weekend wasn’t even in the watershed. It was quarry a few miles away where a key feature affecting local water quality could be clearly seen in the cliff-like wall of the quarry: joints and fissures in the bedrock and a big hole where slightly acidic rainwater had dissolved a tunnel through the limestone bedrock.
“That’s a karst feature,” Winona State University geology professor Dylan Blumentritt said, pointing to the hole and using the catch-all term for a range of underground phenomena in Southeast Minnesota, including sinkholes, springs, seeps, and disappearing streams. The maze of underground passageways makes it hard for scientists to predict how groundwater will flow. Sometimes, karst features allow groundwater to hop from one valley, underneath a bluff, and into the next valley over, Blumentritt said. Shortly before it meets Rush Creek, the water in Ahrensfeld Creek disappears into an underground passageway and the creek bed partly dries up. Karst features like that are frequently changing; Winona County Water Planner Sheila Harmes said that Ahrenseld Creek only became a disappearing stream after the 2007 flood. But despite the complexity, one thing is constant. “What happens in this upland area affects what happens downstream,” Blumentritt stated.
In a sort of water quality field trip, local farmer Erik Harris, University of Minnesota Extension Educator Jake Overgaard, Blumentritt, and Harmes hosted a tour of the Ahrensfeld Creek and Rush Creek watersheds last weekend, from the intermittently flowing waterway southeast of Lewiston where Ahrensfeld Creek begins to the confluence of Rush Creek and the Root River in Rushford. A tour bus half full with local landowners, students, and Minnesota Green Corps members cruised past cornstalks dusted with snow, empty soybean fields striped with grass waterways, an erosion-carved gulley leading from an open feedlot toward the creek, one big patch of prairie, the bright green of newly sprouted cover crops, and a man hauling hay bales with his young son inside the tractor cab, sitting on his lap.
The tour was Harris’ idea. He is growing alfalfa while he transitions his farm to organic agriculture, and in part, the idea occurred to him after watching snowmelt flowing off his land one spring. Most of the fields handled the water just fine, but in one section, all of that water was constricted into a small space where it scoured away soil. “I was trying to figure out how to slow it down and minimize the gouges,” he said. Harris was curious, too, about where the water went when it left his fields and how his land was connected to the rest of the watershed — the bigger picture.
Up on the ridge near Harris’ land, Overgaard talked about nitrate pollution, the value of alfalfa acreage, and his work to offer local farmers nitrogen management trials. “We have a lot of alfalfa because we have a lot of cattle in Winona County, which is great. We should look at our alfalfa fields with gratitude,” Overgaard said, describing how perennial hay crops slow down runoff and allow water to soak into the soil. In nitrogen management trials, the extension office and participating farmers test out lower applications of fertilizer to certain plots, then compare the yield from those plots against others. The goal is to reduce nitrate pollution in streams and wells, he explained. “People used to say you need one pound of nitrogen for every bushel of corn you were going to produce. That’s not really true these days,” Overgaard stated, citing trials that produced two bushels of corn per pound of nitrogen in fields with a corn-on-corn rotation. It does depend on the weather, however, Overgaard said. In 2015 and 2016, ideal weather allowed test plots to produce high yields with very little nitrogen; that has not been the case as often this year, he stated. Second applications are one way for farmers to hedge their bets without over-applying, Overgaard added.
Down in the valley, the tour stopped at a piece of Arlene Nelson’s land, where the local Trout Unlimited chapter completed a stream restoration project to improve habitat for the water-quality-sensitive fish. Blumentritt said that when ridge fields were first plowed in the area generations ago, there was a lot of erosion that washed sediment off the ridge and deposited it thickly on the valley floor. Now, many streams on the valley floor cut through this thick “legacy sediment” creating steep stream banks that constrict water during floods, increasing erosion and making the streams more muddy, he explained. Muddy streams are worse for trout. So the Trout Unlimited restoration project used earthmoving equipment to push back the steep banks and make them more gradual. That gives flood water more space to expand without gouging the banks and allows creekside vegetation to better filter water entering the stream, the tour hosts explained.
Marlene Schuler lives on land beside Rush Creek and she grew up nearby, but she had never seen the headwaters of the Ahrensfeld Creek or the confluence where it meets the Rush before attending the tour. “It’s interesting to see the whole picture,” she said. “If your water supply is down here, it’s good to see the practices all through it. You’re just a piece of it,” she added.
Down at the confluence of Rush Creek and the Root River, a fisherman in waders was clambering out of the river to reach his tackle box on the bank. The topic on the tip of several tour attendees’ tongues was nitrate pollution, both in water that flows to the dead zone in the Gulf of Mexico and in local drinking water. Why do people have to keep drilling deeper and deeper wells, one woman asked. Blumentritt both validated her concern and cautioned attendees about drawing conclusions. “It makes sense to look at where the excess [nitrogen] is going,” he said. “There used to be perfectly good groundwater right under the ground,” the professor added. However, he continued, “We don’t understand 100 percent what’s going on … In this area, the water system is extremely complicated. So to point fingers, we have to be really sure.”