Farmers and residents near Willmar are finding out that city stormwater runoff affects lake water quality a lot more than farm practices do.
A six-year project, led by University of Minnesota scientists, is looking at contaminants in Lake Wakanda that come from intensively tiled farm fields and city stormwater runoff. The stormwater runoff originates from a 1,700-acre residential section of Willmar; the field drainage water flows from about 300 acres of cropland, most of it owned by Gorans Brothers.
Thus far, with slightly below- and near-normal annual rainfall, the data are consistent. Since August 2007:
• Of eight pollutants monitored in drainage (nitrate-nitrogen, ammonium nitrogen, soluble phosphorus, particulate phosphorus and total phosphorus, sediment, fecal coliform, and E. coli), all but nitrate-nitrogen were lower from farm fields compared to stormwater runoff.
• Total phosphorus losses were much higher in stormwater runoff than farm fields over the entire study. From 2007 to 2008, P losses were 11 times greater from stormwater.
• Most of the P from stormwater was associated with sediment.
• Most of the P from farm fields was in soluble form (dissolved in drainage water).
• There was twice as much nitrate in the drainage from fertilized farm fields compared to stormwater.
• An unfertilized control field had 65% more nitrate in drainage, due to release from native-soil organic matter, than stormwater.
• Stormwater had about 20 times more ammonium than farm fields.
• Fecal coliform and E. coli levels were higher in stormwater compared to farm fields in 2008 and 2009.
• Pathogens were slightly higher for the fertilizer field compared to the manure-fertilizer and control fields in 2009.
• The amount of sediment in stormwater appears to be decreasing over time, depending on rainfall. Initially, it was hundreds of times greater in stormwater than in farm fields. In 2009, sediment loss in stormwater was just eight times greater than in farm fields. Sediment causes water turbidly and acts as a carrier for other pollutants.
“We were surprised that there was more sediment from Willmar and the stormwater ditch than in fields,” says U-M soil scientist John Moncrief. “This is likely due to erosion from construction sites or other nonvegetated areas.” He adds that they also were surprised by the high levels of ammonium/ammonia nitrogen from Willmar stormwater.
The research team responsible for the study is comprised of Moncrief; Ed Dorsey, U-M Department of Soil, Water and Climate, St. Paul; and Curt Reese, West Central Research and Outreach Center, Morris. Moncrief leads the effort. Dorsey, the team’s tech guru, designed and built the intricate, automated water sampling system that measures 100% of the storm and drainage water flowing from the city and fields. Reese faithfully visits weekly, in mosquito-slapping humidity and thigh-high snow, to retrieve water samples from automated samplers at five sites — one on the southern edge of Willmar; two in fertilized fields; one in the control, unfertilized field; and one at the lake.
With the project situated on a working farm, the scientists incorporated current cropping and management practices into its design. The Goranses work with a corn-corn-soybeans rotation and fertilize with turkey manure and commercial fertilizer. To evaluate the impact of different fertilizers on soil structure and drainage, Moncrief and team established three soil fertility strategies on three fields with isolated drainage — commercial fertilizer, turkey litter and an unfertilized control.
The manure is applied once in the rotation after soybeans. Nitrogen at 110 pounds per acre for first-year corn was applied. The amount was based on estimating crop-available N from turkey manure by chemical analysis of ammonium and total manure N. The same rate of anhydrous ammonia was applied on the fertilizer field. The control field has not had fertilizer or manure applied since the fall of 2005.
For second-year corn, a variable rate of anhydrous ammonia based on a soil nitrate test (average rate of 122 pounds N per acre) was applied in the fall. Nothing is applied for soybeans.
“The goal is to capture most of the N associated with the turkey litter by the first-year corn and residual N by second-year corn,” Moncrief says. “The phosphorus and other nutrients in with the 2007 turkey litter application are being used over the entire three-year rotation.”
The Goranses use different tillage depending on the crop. Following soybeans, they incorporate turkey manure with aggressive chisel plowing (parabolic shanks following disks to chop stalks). After first-year corn, they moldboard plow in the fall and rely on that to evenly distribute turkey manure and fertilizer to depth. And after second-year corn, they fall chisel plow. In the spring, they prepare all seedbeds with field cultivation. They plant corn with a 24-row planter on 22-inch rows.
After the first two years into the project, the average corn yield was 204 bushels per acre; yield was 196 bushels and 212 bushels per acre in 2008 and 2009, respectively.
“This demonstrates that soil fertility levels are high enough to support 200-bushel yields. For the cropping system to be viable, it first has to be profitable,” Moncrief says. Yields from the manure-fertilizer fields averaged 4% more (9 bushels) than fertilizer-only fields. The control field was 29% (56 bushels) and 49% (103 bushels) lower than the amended fields in 2008 and 2009, respectively.
Last year, the researchers noted, too, that supplemental N didn’t boost yield on small replicated test strips. Yield was 6% higher for corn grain in manure and fertilizer fields compared to fertilizer-only fields (4% higher over the two years).
The control field yields dropped from an average of 140 bushels in 2008 to 109 bushels per acre in 2009.
Due to phosphorus entering Lake Wakanda, algae levels have been increasing. Water-quality tests show the pH level is almost one full unit higher than the drainage from fields and stormwater. There are times when the lake pH is 9.3 as a result of the photosynthetic activity of the algae.
Researchers also note that the average ammonium/ammonia levels in the stormwater are much higher than the fields and slightly higher than the lake. These two factors — algae and ammonium/ammonia — result in toxic levels of ammonia, the likely cause of occasional fish kills, Moncrief adds.
With two years remaining in the project, Gorans and the scientists plan to make a few changes in protocol and the drainage system and monitor them accordingly. Gorans will apply manure to all fields — one 150-acre field with surface inlets in depressions and another with surface intakes. Without surface tile inlets, runoff and associated contaminants are prevented from entering the tile system, Moncrief says.
Gorans also will install a woodchip bioreactor along the edge of a field. Researchers will compare its cost-effectiveness at nitrate reduction to a wetland located next to another field.
“This project has resulted in a positive dialogue between all stakeholders with an interest in good lake water quality,” Moncrief says, “and it has been an eye-opener for some.”
Adds Reese, “We’re not looking to point fingers. We’re looking to see what happens so we all can make meaningful, responsible management decisions.”