Small ponds could make a big difference to the Le Sueur River and downstream waters.
Holding back water in small areas of farm fields for 5 to 10 days after rain would make a big difference to the river, according to Patrick Belmont, an assistant professor at Utah State University who has studied the Le Sueur watershed for several years.
Holding that water would reduce the peak flows in the river system, helping prevent erosion that is degrading the water and the life within it.
“That 5 to 10 days is the Goldilocks time where you reduce sediment and also phosphorus and nitrogen,” he told 50-some citizens and landowners at a meeting in Pemberton in southern Minnesota this summer. The meeting was held by the Le Sueur River Watershed Network, whose members started meeting in 2012 and developed seven recommendations for a healthier watershed.
“This place is not going to turn back into tall grasses and prairie,” Belmont said. “But we can use a small portion of the land — 4 to 5 acres per field – for 5 to 10 days to reduce sediment.”
That reduction could be 50% to 75% of the sediment load hurting the Le Sueur, the Minnesota River, and waters further downstream.
“A small fraction of the landscape could get us there,” Belmont said.
The idea met with some concern from farmers and landowners about taking land out of production. One producer likened the idea to the duck ponds that dotted area fields in his grandparents’ farming days. But who pays for setting aside those acres? he asked.
Belmont responded, “It’s your land — what incentive do you want to pay for that?” He encouraged landowners to be proactive, decide on incentives they need to set aside land, and seek support for them.
Some landowners offered the idea of creating wetland banks, selling credits to developers and others who need to replace wetlands destroyed for road construction and other purposes.
Big landscape, big problems
The Le Sueur watershed spans 1,111 square miles in five counties in southern Minnesota. Farming dominates the landscape, and for good reason. This is some of the most productive ag land in the world.
However, the river sends a disproportionate amount of sediment downstream every year. That sediment — soil and other particles in the water — muddies the water, destroying habitat for fish and other aquatic life to breathe, find food, and reproduce.
Flooding, tree snags, collapsing streambanks and bluffs — they’re all symptoms of an ailing watershed. So are the river’s high levels of nutrients, high levels of bacteria, and poor habitat for fish and wildlife. Numbers of mussels, fish and bugs — in both diversity and abundance — are much lower in the Le Sueur than for similar river systems.
“If you don’t have many bugs, then you don’t have many for fish to eat,” Belmont said.
Researching the river
Belmont’s recommendation for holding back water followed his presentation on research results. He studied at the University of Minnesota with the National Center for Earth Dynamics after receiving his Ph.D. in Earth and Environmental Sciences from the Lehigh University in Pennsylvania. He continues studying the Le Sueur River, seeing his job as providing information so people can decide how to best invest money in healing the river.
“By and large we’re all on the same page. We don’t want to see an excessively muddy river. We don’t want to see fields eroded,” he said.
While it’s easy to point at erosion as the cause of the river’s problems, it’s more difficult to pinpoint the reasons for the erosion.
“The answer isn’t obvious, but through a lot of science we’ve pulled together a compelling story,” Belmont said.
He and his team of researchers use several tools to study the geologically sensitive landscape of the Le Sueur drainage area:
- Monitoring gauges throughout the river system to record flows and other data
- High-resolution topography maps • LiDAR (Light Detection and Ranging, a way to survey areas of land by airborne laser mapping)
- Field surveys
- 70 years of aerial photos
- Streambank measurements
- Sediment finger-printing (chemical markers detect where sediment originated such as from a field or bluff)
Flowing through a watershed primed for erosion, the Le Sueur River is one of the fastest down-cutting rivers in the world, meaning it’s still seeking a stable path through land that dips in elevation. It’s also “thoroughly plumbed” with artificial drainage.
The upsides of drainage:
- Crop productivity is way higher
- More rain infiltrates the soil so runoff is lower
The downsides of drainage:
- It’s concentrating the flow of water in sensitive areas
- It’s increasing the amount and velocity of water delivered to the river
- It’s increasing flows in the river system that erode streambanks and bluffs
Compounding the problem — but not causing it — are increased rainfall and more intensive storms.
“Drainage makes sure that rain gets to the river faster,” Belmont said.
He was part of a team that developed a sediment “budget” for the Le Sueur, showing where sediment comes from, how much remains or is deposited in the system, and how much leaves or goes downstream. In places where the river drops sharply in slope — called knickpoints — the vast majority is coming from bluffs, banks, and ravines. In the flatter areas, the majority comes from farm fields.
No matter where the sediment comes from, the solution is the same: Hold back the water.
Belmont summed up the situation in five points:
- The watershed is geographically primed to erode.
- This is some of the most productive ag land in the world.
- Ag drainage and rainfall have increased.
- Driven by increased flows from drainage, sediment is eroding from bluffs, banks and ravines.
- The river is special and its water quality can benefit health, biology, recreation, industry and land values. The key is holding back water and reducing the peak river flows.