How an upstream ditch limits downstream algae

MENTONE, Ind.– A ditch cuts through the fields of this Indiana landscape.

But it’s no ordinary ditch. This one reduces the nutrients leaving the farm fields that can eventually pollute waterways nearby and far away.

It is called a two-stage ditch because of the two levels of soil, called benches, on either side of the stream that flows through it. The benches act as a buffer, soaking up the fertilizers and other water contaminants draining from the field.

Standard ditches drain phosphorus, nitrogen and excess dirt into rivers and streams, contaminating the water and hurting its inhabitants. The two-stage system prevents them from entering the watershed, said Jennifer Tank, Interim Director of the Notre Dame Environmental Change Initiative.

Farmers are increasingly using this technique and others to reduce their environmental impacts, said Kent Wamsly, the director of The Nature Conservancy’s Upper Wabash project, who oversees a two-stage ditch in the Tippecanoe River watershed in northern Indiana.

“We take the lessons learned in smaller watersheds, and then apply them to larger watersheds,” Wamsly said.

While the Tippecanoe is a small river, the fertilizer running into it can fuel algae growth as far away as the Gulf of Mexico, he said. When the algae dies, the bacteria that eat it also suck up the water’s oxygen, which is harmful to the creatures that live there.

The excess nitrogen and phosphorus from the farm fields are fueling a “dead zone,” an area in the Gulf devoid of oxygen.

The two-stage ditch system helps the Great Lakes, too. The Nature Conservancy is constructing three systems in the Western Lake Erie Basin this year.

Lauren Lindemann, conservation director for The Nature Conservancy’s Western Lake Erie Basin, oversees ditches in Lenawee County, Michigan, Steuben County, Indiana, and Hardin County, Ohio. They have been constructed with support from local, county and state agencies Lindemann said.

Lake Erie has recently struggled with algae growth causing a rapid increase and accumulation of bacteria. Last summer, the bloom spurred a tap water ban in the Toledo area, restricting citizens from drinking the water.

These ditch systems can reduce the size of the bloom, depending on the amount of phosphorus exported.

“It is different per ditch and watershed,” said Lindemann. The impact on Lake Erie is directly correlated to the amount of phosphorus that the ditch retains in the field.

“If we find a way keep phosphorus out of Lake Erie, we will see improvements in just one year,” said Justin Chaffin, a senior researcher and limnologist at the Ohio State University Stone Lab, who researches algal blooms. “Right now we are mostly dependent on weather for keeping the phosphorus out. Projects like these are a huge jump on controlling phosphorus loads.”

While helpful, it’s not enough.

Farmers, scientists and environmentalists agree that the two-stage ditch also needs to be paired with other agricultural practices to be fully effective.

Cover crops, which are planted to retain nutrients that might flow off of bare ground, and filter strips, which are placed between a field and water source, are some ways that farmers help their crops and their watershed.

“We won’t see the end result water quality we want to see without the combination of multiple practices,” said Wamsly.