Ag drainage leads to environmental concerns
WORTHINGTON — For years, conservationists in Minnesota have been concerned about agricultural drainage of Minnesota’s farm lands. Miles upon miles of underground tile have been installed through private lands as a way to remove excess water and improve crop yields.
What benefits the farmers, though, has come at a cost to the environment, some say.
“We’re running into more flooding problems because of drain tile,” said Nobles County Soil and Water Conservation District Manager Ed Lenz. “We’re draining agricultural land quicker than it normally would in a natural environment, which results in a much quicker and larger bounce, where the stream comes up quicker for a shorter duration.”
Multiplied by added tile lines and sped up by big rain events, water cuts into stream banks and stream beds, making for wider, deeper channels and eroded soil that ultimately ends up in lakes and rivers.
Last March, the Science Museum of Minnesota and several major universities published a three-year independent study concluding that agricultural drainage is responsible for increased river flows and stream bank erosion, and is a leading cause of excess sediment in lakes and rivers.
The study compared changes in water flow for 21 southern Minnesota rivers between 1940 and 2009 and concluded changes in flow were “strongly correlated” with changes in land use. Artificial drainage was also identified as a major driver of increased river flow.
Lenz sees firsthand the problems created as more tile lines are added to the landscape. At the same time, he understands why farmers are apt to install drainage systems.
“Tiling is important to our local economy and the farming industry,” he said. “There’s no reason to say that we need to end it, but there are certain practices we could use with the tile that could be beneficial to both the ag industry and the local environment.”
Those practices include installation of terraces, sediment basins or conservation drainage structures that slow water movement. Woodchip bioreactors, which work to remove excess nutrients from water outletting from drainage tile before it enters another water body, are another option.
In Nobles County, Lenz said only a small percentage of farmers implement conservation practices to address water storage.
“We will do roughly 40 practices a year,” he said. “Two years ago, our drainage practices hit 600 — that could be to repair a section of tile or to install pattern tile on a quarter-section.”
As more farmers implement pattern tiling or repair existing tile lines, concerns about downstream impacts of drainage aren’t just localized. A statewide drainage work group is now reviewing Minnesota’s drainage laws, from drainage management to flood control and water quality.
“One of the reasons for controlled subsurface drainage is … to hold back some of the water in the soil profile so that water can be used by the crop rather than drain off downstream,” explained Al Kean, chief engineer for Minnesota’s Board of Water and Soil Resources and a member of the work group. “One of the key environmental concerns about tile drainage is transport of soil nitrates. Putting tile in the ground increases the transport of nitrate from the soil profile into downstream waters.”
Dan Livdahl, Okabena-Ocheda Watershed District Administrator, said it has become more apparent that nitrogen transported by agricultural practices is a pollution problem. Excess nitrogen escaping farm fields and getting into lakes, rivers and ultimately into the Mississippi River is blamed for the growing dead zone in the Gulf of Mexico.
Closer to home, Livdahl said higher levels of nutrients like nitrogen and phosphorus are fueling more algal blooms. Lake Okabena in Worthington last year had some of the earliest and latest algal blooms recorded, with blue-green hues visible in the lake for much of the summer.
The presence of algae is not only a visual problem — the odors emitted from decaying algae can be likened to rotten eggs. It could also impact aquatic life.
“More recent information says nitrate … in particular, is probably harmful to aquatic insects, zooplankton and plankton,” Livdahl said. Those species are at the bottom of the food chain and can affect all life in the aquatic system.
Recently, Soil and Water Conservation Districts, watershed districts and other organizations have helped fund projects in southwest Minnesota to reduce the amount of nutrients leaving farmers’ fields through tile and ending up in drainage ditches, streams and lakes.
The SWCDs in Cottonwood and Jackson counties teamed up to earn a $250,000 Clean Water Partnership grant in 2010 to install nine woodchip bioreactors on tile lines feeding into Fish Lake.
Brian Nyborg, Jackson SWCD Manager, said the bioreactors aren’t “cutting-edge” in Minnesota, but are a relatively new option in this part of the state.
The nine bioreactors were placed on all but four of the tile lines that feed into the 300-acre Fish Lake to remove phosphorus and nitrogen from water in the tile lines before it enters the lake. The bioreactors “take hardly any land out of production,” Nyborg said, making them a viable option for farmers.
Bioreactors use woodchips to soak up the phosphorus and nitrogen carried through tile lines.
“If the tile is four feet deep, you’d have three feet of woodchips and one foot of soil on top of the woodchips,” Nyborg explained.
Estimates are the bioreactors kept more than 3,800 pounds of nitrogen and 77 pounds of phosphorus out of Fish Lake in one year, though there’s no monitoring data to show improved lake health. The Clean Water Partnership grant didn’t include funds for lake monitoring.
“(Last) summer, there were some complaints that the water quality hadn’t improved,” Nyborg said. “It will take time. You still have that sediment and phosphorus in the lake (prior to installing the bioreactors).”
The woodchip bioreactors cost from $4,000 to $8,000 each for the Fish Lake project.
Nyborg said he’d like to do more bioreactor projects with willing landowners, and Livdahl wants to get a woodchip bioreactor project started in Nobles County.
“If they’re built and managed well, they’ll remove nitrogen from that tile water before it’s discharged,” Livdahl said. “They also remove dissolved phosphorus … the nutrient that causes the most problem with algae blooms.
“If you’ve got pollution coming out of your tile and you can treat that relatively cheap, why wouldn’t you?” he asked.
Controlled drainage structures, which allow farmers to hold back water — as well as nutrients — in the field for the times they are needed for the crop, are another option. SWCDs and watershed districts have worked with willing landowners on these projects in the past, and government funding is available.
Yet, Lenz said, few farmers install the controlled drainage structures here because of the cost. Instead, he deals primarily with terrace and sediment basin requests, along with streambank erosion projects.
Charlie Loosbrock, co-owner of Loo Con Inc., of Wilmont, said farmers are using conservation tillage and terraces to hold water and nutrients on the soil so it’s available to the crops. He contends that paved roads and buildings — any impervious surface — causes more runoff than agricultural land.
“Those are what are contributing, in my estimation, to these increased flows in rivers,” Loosbrock said. “It is not the farmland.”
Kean acknowledges that while sediment and nutrients are carried in runoff from those impervious surfaces, the majority comes from agricultural land.
“Larger urban areas, they’ve been doing stormwater ponds, trying to reduce peak flows and settle out sediment and other pollutants for a number of years,” he said. “There’s a lot more agricultural land than urban land.”