A new wetland treatment system at Grand Lake St. Marys dramatically reduces levels of agricultural runoff that have fueled blue green algae outbreaks, the Ohio Department of Natural Resources said.
The system is a series of wetlands on 40 acres along Prairie Creek, one of seven waterways on the southern side of the lake that have over the years deposited fertilizer-rich runoff from farm fields into lake waters, firing up outbreaks of hazardous cyanobacteria blooms.
The wetlands allow phosphorous and nitrogen to separate from the flows. Weekly testing shows that the system is removing up to 89 percent of the phosphorus and up to 57 percent of the nitrogen, ODNR said.
The constructed wetlands, a cooperative project among ODNR, the Ohio Environmental Protection Agency, the Ohio Department of Agriculture, and The Grand Lake St. Marys Restoration Commission cost$1.9 million. An adjacent 40 acre parcel has been purchased and will also be used as wetland treatment, Mark Bruce, ODNR spokesman, said.
To help boost the removal of the nutrients, water pumped from the creek is treated with alum, which binds to phosphorous, and is then released into the wetlands. The water settles in the wetland where it is naturally filtered prior to entering the open water of the lake.
There are plans for other treatment wetlands along two other creeks that feed into the lake, the Chickasaw and the Coldwater. Funding has been lined up for $2.1 million for an additional treatment train, Bruce said.
“This treatment train addresses one of our main objectives of targeting nutrient loading into the lake,” ODNR Director Jim Zehringer said. “This project continues to build upon our commitment to improve the valuable resource that is Grand Lake St. Marys.”
Beyond that, other projects are helping keep cyanobacteria outbreaks at bay, outbreaks that have at times virtually shut down lake recreation. The state is now on track to dredge 300,000 cubic yards of sediment from the lake bottom this year to create an in-lake wetland of about 80 acres, said Grand Lake St. Marys Restoration Commission manager Milt Miller.
Building that wetland could take two years, he added, and go a little ways toward restoring thousands of acres of original wetlands eliminated over the years by development.
That will help keep the lake clean because wetlands — and the plants in them — function naturally as nature’s kidneys and help remove nutrients. More of those in-lake wetlands will likely be built as the state continues to dredge over a decade of improvement projects, Miller said.
“Our state partners continue to show their commitment to improve the water quality at Grand Lake St. Marys,” Miller said. “We share the same goals, and I’m confident our hard work will produce a cleaner, healthier lake.”