Posted on March 6, 2023
Spreading silt excavated from the Toledo shipping channel on area crop fields looks like a viable concept, initial results from a research project show.
But Angelica Vazquez-Ortega, a Bowling Green State University assistant professor in the School of Earth, Environment and Society who is leading the study, said during a webinar this week that she would like to see more years of data before drawing conclusions.
The outcome of her research has important ramifications for northwest Ohio and western Lake Erie because the Toledo shipping channel is the most heavily dredged in the Great Lakes region.
After almost 40 years of controversy, Ohio banned the U.S. Army Corps of Engineers’ practice of redepositing silt dug up from the shipping channel into Lake Erie’s North Maumee Bay.
Most of the silt that must be dredged is believed to come from farms that lose soil from wind and rain erosion. There have been concerns about what’s in the silt, given releases of industrial chemicals into the shipping channel decades ago.
Ms. Vazquez-Ortega said there is little, if any, evidence of chemical-laden silt now. Background levels of chromium, copper, cobalt, and other heavy metals are nearly identical in silt to what’s in natural farm soil, she said. And there were no detections of polychlorinated biphenyls, or PCBs, in sediment dug up from the shipping channel or the farm where it was applied, she said.
“It’s not posing any detrimental effect,” Ms. Vazquez-Ortega said at the event hosted by Ohio Sea Grant and Ohio State University’s Stone Laboratory.
She said her research team has studied how plants grow in the controlled environment of a greenhouse, as well as at an organic farm near the Wood County village of Hoytville.
In each case, silt from the shipping channel was added to existing soil but at different concentrations.
In the greenhouse, there was a slightly higher yield of corn, and greater biomass in root systems for corn and vegetables such as lettuce, tomatoes, and carrots.
But in the open field, the opposite occurred: Yields of corn were lower than they were in soil with no silt.
The differences in the greenhouse and the field were not substantial, but warrant more investigation, Ms. Vazquez-Ortega said.
One theory: At the farm, silt was heavily compacted and, in combination with an usually wet spring, required multiple runs by farm machinery to incorporate the dredged material into the soil.
The farmer “said he had to work the land more” and “make several passes,” Ms. Vazquez-Ortega said.
The dredged material performed as expected as a fertilizer. Soil tests showed the silt was enriching the dirt.
So the lesson might be how and when it is applied, Ms. Vazquez-Ortega said.
The strategy for future years will be spreading the silt over cover crops in the fall, then mixing both the silt and cover crops into the soil the following spring, she said.
“I want to know more by adding more years [to the study],” Ms. Vazquez-Ortega said.
There were no signs that any contaminants in the dredged material were being taken up by plants, she said.
The silt Ms. Vazquez-Ortega used comes from the Great Lakes Dredged Material Center for Innovation — a North Toledo site where some nutrient-rich sediment dredged from the Toledo Harbor shipping channel was deposited in 2016 and 2017. The center was created in 2014 by then-Gov. John Kasich.
Metroparks Toledo transported 30,000 cubic yards of the silt to its Glass City Metropark in the fall of 2021 to help trees grow. Park district spokesman Scott Carpenter said Monday that adding the dredged material “has made a major difference.”
“We are currently working with Ohio EPA to request a permit to bring in additional dredge to continue working to improve soil conditions, primarily to support areas where we are planting trees,” said Tim Schetter, Metroparks Toledo natural resources director.
Joe Cappel, Toledo-Lucas County Port Authority vice president for business development, said Monday that research at the Center for Innovation is ongoing, and that it can take years to fully dewater silt deposited there.
“The excavation and use of this dredged material has created capacity for additional dredge material placement at the Center of Innovation, and we are currently evaluating the facility to make sure it is ready to receive and continue to dewater newly-placed material,” Mr. Cappel said.
He added there continues to be substantial interest from universities and companies that want to use some of the silt.