Looking for changing clues
MONTEVIDEO -- Like an investigator probing for clues, Carrie Jennings tipped over stones, sifted soil through her fingers, and compared what she saw on the landscape with the maps she carried.
She was searching for clues left here when the last glacier retreated 10,000 years ago, but her 1965-dated map also revealed how much has changed in recent years. Her map showed a landscape smattered with wetlands of different sizes and shapes. We saw tilled fields of dark, rich loam.
The changes were witnessed by Mark Dahl, a member of the Chippewa County board of commissioners. His family once farmed the Sparta Township soil that now fell through Jenning's fingers like sand in an hour-glass.
One-half of the land that surrounded us was too wet to farm when he was growing up, Dahl told Jennings. He recalled how he used to escape the summer heat as a youth by jumping into a pool of water just a short walk from his house.
It disappeared in 1976 when a ditch was opened. Gone too are the dairy farms and grass pasture lands that once filled much of the township.
Jennings, a geologist with the Minnesota Geological Survey, led an entourage of nine on a geological tour of the Minnesota River Valley near Montevideo last Saturday. She is trying to find answers to a mystery.
We have made great strides in reducing the sediment that washes into the river from our farm fields and urban landscapes. Yet the Minnesota River is carrying a sediment load to the Mississippi River at a rate that is 10 times-or-greater than what it would naturally be. Lake Pepin, on whose waters Ralph Samuelson invented water skis in 1922, is fast filling with silt as a consequence.
Knowing what happened on this landscape 10,000 years ago, and what is taking place today, are equally important in understanding the mystery that Jennings hopes to solve.
Two men with a passion for conservation, Dick Unger and Del Wehrspann, had bid $450 at a silent auction to benefit the citizens group Clean Up the River Environment when they learned that Jennings had offered to lead a geological tour of the Minnesota River Valley.
Unger is working to restore a river backwater near Wegdahl that early explorers once described as holding the largest bed of wild rice in this part of the state. It was an important feeding stop for migrating waterfowl. It still is, although the wild rice is long gone. In the spring, the backwater swells with water to form a small lake. This year, Unger said the first big wave of waterfowl arrived is such prodigious numbers that he watched the water rise by an inch.
Wehrspann has witnessed similar signs of revival in the Minnesota River, where he spends as much of his spare time as possible fishing and exploring. He has seen improvements in water quality due to conservation land programs and best management practices on the land.
Jennings devoted many hours to researching the geology of the Upper Minnesota River Valley more than a decade ago, and has kept returning ever since. She told those who joined the tour that she is motivated by the passion she finds in people here for the river valley, and by her quest as a scientist to find answers.
Why is it that the Minnesota River delivers only 25 percent of the flow to Lake Pepin, yet is responsible for 85 to 90 percent of the sediment load?
Jennings has found some of the most important clues to the answer in Redwood Lake, which was created by a dam built in 1902. It took only 100 years to fill the lake with 28-feet of sediment, she said.
The layers of sediment can be read like chapters in a history book. Prior to the 1930s, about 80 percent of the sediment was soil washed from farmed fields. The elimination of nearly all of the native prairie and farming practices in the pre-Dust Bowl years were to blame.
Today, we've reduced the contribution of sediment from farm fields to about 20 to 25 percent of the load carried in the river, according to Jennings.
Scientists believe the majority of sediment today is coming from the banks of rivers and streams, but that's where the questions only begin. Is most of the soil sloughing from the bluffs of big, steep banks like those found on Hawk Creek?
Or, is the sediment coming from the low, soft banks of smaller streams and tributaries like Shakopee Creek?
Or, it's just as possible that the biggest share of the sediment loads is actually coming from the much smaller ravines that feed into all of these streams.
The modern drainage systems that make the land so productive for farming are believed to be accelerating the rate that this sediment is being moved, said Jennings.
She said the river valley is very young in geological terms. Much of the sediment now being carried is the material that naturally resulted from the cataclysmic event that created the valley 10,000 years ago. Glacial Lake Agassiz -- a water body far larger than all of today's Great Lakes combined -- suddenly began pouring south. Glacial River Warren needed only a few weeks to carve what we now call the Minnesota River valley.
Ever since that event, the landscape and waterways have been seeking to adjust to the sudden change, to find equilibrium, said Jennings. The natural evolution for landscapes is for drainage systems to become more complex with time.
Myriad waterways eventually develop and carve the land and drain away the wetlands and lakes.
Modern drainage systems might be slowing the process by draining the land yet keeping the land relatively flat, kind of like keeping a puppy's face on an aging dog, said Jennings. Or, we might just be speeding up the aging process that will turn our landscape into something more akin to that found in parts of western North Dakota and Wyoming today, she said.
Dick Unger is hoping to preserve the Minnesota River Valley by restoring the backwater near Wegdahl. Unger said that previous owners had built dikes and installed a pump station so that the area could be farmed. Dahl said he remembered earning summer income as a youth by pulling weeds in the farm fields that replaced the shallow waters that had held wild rice.
Jennings said we are a longs ways from knowing all the answers, but we do know that restoring areas like this matter. She pointed out that holding or slowing the flow of water where we can, adding buffers and finding ways to increase our perennial cover all serve to reduce the flow of sediments and preserve the landscape.
"Every little bit helps,'' she said.