Eighty-eight percent of the Maumee River’s phosphorus and 89 percent of its nitrogen comes from nonpoint sources such as agricultural runoff, according to a new Ohio Environmental Protection Agency report issued Monday night.
In the Sandusky River watershed, the impact from that sector was even greater, with an estimated 93 percent of its phosphorus and 94 percent of its nitrogen derived from nonpoint sources. In the Portage River watershed, 87 percent of its phosphorus and 89 percent of its nitrogen comes from nonpoint sources.
Phosphorus is the nutrient most closely associated with algal bloom sizes, while nitrogen often influences toxicity.
In the study, the second of its kind, the state agency attempts to identify the major sources and annual amounts of phosphorus, nitrogen, and other nutrients flowing from Ohio’s watersheds into Lake Erie and the Ohio River.
Called the Nutrient Mass Balance Study for Ohio’s Major Rivers, the authors said their research was consistent with past studies that show as little as 7 percent of the total phosphorus likely comes from point sources such as sewage-treatment plants.
Part of the reason is this: Seventy-nine percent of the Maumee River watershed’s land is in agricultural production.
In the Sandusky River watershed, 80 percent of the land is in agricultural production. In the Portage River watershed, that figure is 81 percent.
The figures are rough estimates based on years of trending data.
Runoff figures in spring and early summer — when most of the fertilizers are applied — often are dictated by not only volumes of rainfall between March 1 and July 31, but also the severity, timing, and duration of thunderstorms, according to multiple presentations over the years by Laura Johnson, director of Heidelberg University’s National Center for Water Quality Research. That center is the Great Lakes region’s oldest, continuing one for collecting runoff data.
Ohio EPA Director Craig Butler and Karl Gebhardt, Ohio Lake Erie Commission executive director and Ohio EPA deputy director for water resources, told The Blade last week the report had no major surprises and wouldn’t radically change the administration’s latest strategy for addressing runoff, which involves a yet-to-be-introduced bill into the Ohio General Assembly that would give the Ohio Department of Agriculture power to order nutrient management plans for sites within watersheds considered to be distressed.
The report amplifies the long-held belief that manure and commercial farm fertilizers are the primary sources of algae.
Fertilizers that escape lawns, gardens, golf courses, and other types of land also contribute to some degree, but experts have pointed out their combined acreage and environmental footprint is nowhere near that of northwest Ohio’s agriculture.
The study also shows little change in phosphorus loading, despite more than $6 billion spent statewide — including more than $3 billion in the Lake Erie watershed — since 2011 on voluntary incentives that encourage more efficient farming practices.
“While it is too early to detect statistically sound trends, the results of this study show no clear decrease in loading yet, especially in nonpoint source dominated watersheds like the Maumee where the loading in 2017 was the highest of the years reported,” the report states.
The study covers the Maumee, Portage, Sandusky, Vermilion, Cuyahoga, Great Miami, Scioto, and Muskingum watersheds, and includes some direct tributaries to Lake Erie.
Point sources such as municipal and industrial wastewater systems were studied, as were home septic systems, the agency said.
Among the biggest improvements on that front was a 34 percent reduction in phosphorus discharges from industrial and municipal sources in the Sandusky River and Muskingum River watersheds between 2013 and 2017, the report said.
The Ohio EPA said it is required by state law to update the study every two years.
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