New Ohio Sea Grant research is helping farmers become part of the solution to reduce Lake Erie’s harmful algal blooms by putting excess sediment to use.
Dredged materials — loose sand, clay, silt, and gravel from the bottom of rivers that drain into the lake — can benefit crops when applied to soil on farm fields, researchers from Bowling Green State University found. The solution could help farmers increase crop yields and while simultaneously improving Lake Erie water quality.
“The idea that I proposed is let’s bring back the soil that was eroded from our very fertile farmland,” said Dr. Angélica Vázquez-Ortega, associate professor of geochemistry at Bowling Green, who led the study. “We’ve had some really great results promoting this potential use of dredged sediments in farm soils.”
Soil and nutrients such as nitrogen and phosphorus run off from agricultural land and enter Lake Erie, with some accumulating in sediments on the lake floor. This abundance of nutrients contributes to the eutrophication process that causes algal blooms, and researchers think dredging may be exacerbating the problem.
Ohio dredges 1.5 million tons of sediment from its Lake Erie ports each year to keep federal navigation channels clear for ships. The majority of the dredging occurs at the Port of Toledo, which has particularly high sedimentation.
In past decades, harbors would dispose of the dredged material by dumping it in the open lake, inadvertently reintroducing nutrients to the water column. In 2020, however, Ohio banned open water disposal of dredged sediments in an effort to improve water quality and reduce annual algal blooms.
“Now, tons and tons of material from the Toledo harbor is no longer going to go back to the lake,” Vázquez-Ortega said. “So we have a logistical problem of what we do with the sediment.”
Ohio agencies are working with the U.S. Army Corps of Engineers to dispose of dredged materials at containment facilities on a man-made island near the mouth of the Maumee River. The containment is expected to last for 20 years, after which there will be no more space to keep storing the sediment, Vázquez-Ortega said.
That’s where farm fields come in. Tasked by the state of Ohio to find beneficial uses for dredged material, Vázquez-Ortega studied the viability of using the excess sediment from the Port of Toledo as a farm soil amendment that can help crops grow.
Researchers conducted both greenhouse and field experiments at the Agricultural Incubator Foundation north of Bowling Green to determine how blends of farm soil and dredged material could benefit crops. In greenhouses, the team used buckets to grow crops with sediment ratios of 0%, 10%, 20%, and 100%. Experiments included row crops such as soybeans and corn as well as specialty crops including tomatoes, lettuce, and carrots.
So far, results from greenhouse crops are overwhelmingly positive. As the amount of dredged sediment in the soil increased, so too did crop yield, biomass — weight of plant material above and below the soil surface — and other measures of crop health. Root systems were more robust and bulk density, an indicator of soil compaction, decreased.
“There’s an improvement in the physical and chemical properties of farm soil when dredged sediments are added, and I think that’s very important to know,” Vázquez-Ortega said. “It seems that dredged sediment is a good farm soil amendment for the region.”
Vázquez-Ortega also worked with a farmer at a field demonstration site to test applying dredged sediments to soil in more realistic conditions. Using the same equipment that farmers use to disperse manure, the farmer applied different quantities of dredge to different fields.
“The logistics are more complex, and it’s more difficult,” Vázquez-Ortega said. “You now have to deal with the weather, and the farmer was very worried how the dredge might affect the quality of the soil.”
While results from the field experiments aren’t final, the team learned important lessons from the practical experience. Additional passes of the manure equipment compacted the soil, and seeds in the sediments may have led to weed growth.
Another concern relevant to dredged materials is the possible presence of contaminants such as heavy metals in the sediment. However, previous research confirmed that the heavy metal concentrations in dredged material from the Toledo harbor had the same or very similar parameters as farm soil.
So far, results from the greenhouse experiments confirmed that there is no preferential bioaccumulation of heavy metals in crops applied with dredged sediment compared to 100% farm soil. Across all soil categories, researchers did find high levels of arsenic — a naturally occurring phenomenon in the region — yet arsenic bioaccumulation actually decreased as dredged sediments were added.
Moving forward, Vázquez-Ortega is continuing this research thanks to a grant from the Harmful Algal Bloom Research Initiative. The new project will use edge-of-field sensors to measure how phosphorus moves through farm fields amended with dredged sediments. The study will occur at the Northwest Agricultural Research Station in Custar, OH.
“I was very happy to find a field there,” Vázquez-Ortega said. “So far we’ve planted a cover crop, dispersed dredge, and then Matthew, acting as a farmer, tilled in everything. It’s going to be automatically instrumented with samplers and solar panels.”
Other goals include ensuring that the dredged material amendments can be economically feasible. The sediments are expensive to transport and spread, and farmers would be more willing to use the amendments if they were subsidized, Vázquez-Ortega said.
“If a farmer needs to pay for the hauling and dispersion, it’s going to be very, very challenging,” she said. “We need to incentivize farmers to use this application like any other best management practice.”
In addition, Vázquez-Ortega is working with the Ohio Environmental Protection Agency and the Lucas Soil and Water Conservation District to conduct outreach and help farmers understand the science.
For more information about this research, contact Dr. Vázquez-Ortega at firstname.lastname@example.org.
Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.