September 30, 2015

Two-Stage Ditch Could Reduce Farm Runoff on Eastern Shore

Nancy Averett

Nancy Averett

Freelance Journalist


John Swaine III, Talbot County, Md.

John Swaine III, Talbot County, Md.

John Swaine III stands with his back to a field of soybeans, his sunburnt arms crossed, a dusty John Deere cap tucked over his strawberry blond hair. Near his feet is a ditch that runs adjacent to the winding country lane, Bellevue Road, that bisects his Talbot County, Maryland, farm.

The ditch is meant to collect rainwater that flows off of the fields and the road. For years, Swaine felt helpless when he saw the muddy brown water accumulating in the channel during a storm, knowing it contained soil from his fields that was enriched with commercial fertilizers. “It bothered me to see that water with sediment in it flowing right into the creek,” he says. “Still does.”

The problem is especially bad when the ditch overflows. The water crosses the road, runs through a field on the other side and eventually into Tar Creek. From there it enters the Tred Avon River, which empties into the Choptank River, which discharges into Chesapeake Bay. Unlike his grandfather, who bought the farm in 1921. Swaine uses cover crops and minimal tilling to keep soil out of nearby waterways.  “But,” he says, “it’s still a problem.”

Two-stage ditch before rain.

Two-stage ditch before rain.

Two-stage ditch after rain.

Two-stage ditch after rain.

So when the 58-year-old heard about an innovative ditch design that has been shown to reduce the amount of soil and fertilizers getting into nearby streams, he decided to give it a try. In April, a bulldozer carved a 4-foot shelf of land in between the field and the original 18-inch wide channel—which Swaine believes was probably dug by slaves more than 150 years ago—creating what’s called a “two-stage ditch.” The shelf is slightly higher than the lip of the ditch but lower than the field. As rainwater runs off the field, it collects on the shelf before emptying into the channel. Native plants on the shelf trap the sediment in the water and soil microbes living on it consume some of the fertilizer, or nutrients, before it enters the ditch.

“The idea is that it mimics nature. It mimics a natural flood plain,” says Jennifer Tank, biology professor at Notre Dame University, who has studied the water-quality benefits of the two-stage ditch. “If you have intact flood plains, you really don’t see big losses of soil and nutrients.”

Those nutrients, nitrogen and phosphate, can cause an overgrowth of algae in streams and rivers that hurts water quality and can be toxic to humans. In August 2014, an algal bloom in Lake Erie forced the city of Toledo to ban tap water use for half a million people. Such blooms, which are occurring with increasing frequency in the Bay, create dead zones by consuming all the available oxygen, leaving little for fish and aquatic animals.

Even without fertilizers in it, soil runoff in rivers and streams causes problems, especially for wildlife. “It just mucks everything up,” Tank says. “Endangered (freshwater) mussels can’t live in it. Fish have a really hard time with it. Macro invertebrates, or bugs, don’t like it. It really reduces the biodiversity of a system.”

Jennifer Tank / Photo by Matt Cashore/University of Notre Dame

Jennifer Tank / Photo by Matt Cashore/University of Notre Dame

A Win for Farmers and the Bay

Nutrient pollution doesn’t just come from farms. Fertilizers that drain off suburban lawns and sewage overflow from wastewater treatment plants are two examples of urban nutrient pollution. Roads are also a problem. In rural counties, like Talbot, they hold small amounts of fertilizer and manure (along with other pollutants such as salt and oil) that can easily wash into roadside ditches during rainstorms and end up in nearby creeks and rivers.

In order to comply with the federal Clean Water Act, the state of Maryland is requiring counties to reduce both their agricultural and urban nutrient pollution loads. Talbot County, for instance, must lower its urban nitrogen pollution from 191,300 to 126,792 pounds by 2025. But reducing urban runoff can be expensive. Upgrading the county’s wastewater treatment plant to stop sewage overflows, for instance, would cost about $40 million. So the county teamed up with the Chesapeake Bay Foundation (CBF) and The Nature Conservancy (TNC) to look for more cost-effective solutions.

The two-stage ditch quickly came to the fore, says Amy Jacobs, watershed restoration director for TNC. “Since the county has 370 miles of agricultural roadside ditches, the installation of two-stage ditches could address both agricultural and road pollution at the same time.” She adds: “It’s an approach that’s science-based, has real water-quality benefits and has a very small footprint in terms of taking any agricultural land out of production.”

Keeping as much land in production as possible is important to farmers. “I told Amy, you do whatever you want, just don’t take half my field,” Swaine says with a chuckle, recalling his conservation with Jacobs before his two-stage was built. In his case, there was already a 10-foot buffer strip of fescue—another conservation practice that can help with agricultural runoff—between his field and the roadside ditch.

But other farmers in the county, who grow crops right up to the edge of their ditches, might not be as willing to install a two-stage knowing they would lose some productive land.  Still it’s a better option than what Talbot County officials first proposed: requiring farmers to give up 50 feet of land alongside the ditches to use as buffer strips.

Not only did Jacobs come up with a solution that would save more land for farming, she also tried to make it as efficient and effective as possible by using topographic data to analyze water flow and land use across the county’s landscape. She identified and ranked 150 “hotspots,” where if two-stage ditches were installed, nutrient pollution in the county would decrease by about 8,000 pounds a year. The price tag for those projects would be $3 million. So far the county has allocated $100,000 from its budget and received an additional $508,000 in grant money.

“The two-stage is not very expensive to design and install,” says Alan Girard, eastern shore director of the CBF. “And in cases where there is productive land that needs to be taken out of production, there’s cost-share money from the state that will pay the farmer an annual rental rate for the land and for the cost and maintenance of the ditch.”

averett-2-stage-ditch-TNCScientific Study Says Two-Stage Works

The two-stage may be a new tool in Maryland, but it’s not so novel in the Midwest. The first one was built in Ohio in 2002, and Indiana leads the way with 52 in 21 counties. TNC’s Indiana office has been involved with many of those projects, including a demonstration two-stage ditch that was built in 2007 along a half-mile stretch of the Shatto agriculture ditch in Kosciusko County, Indiana, that has been continuously monitored for water quality by Tank and her graduate students.

The Shatto drains into the Tippecanoe River, which flows into the Wabash River, which empties out into the Mississippi and finally drains into the Gulf of Mexico. Like the Bay, the Gulf has suffered large, devastating algal blooms. Recent ones have measured more than 5,000 square miles.

TNC officials hope that if enough two-stage ditches are built in the Midwest, algal blooms in the Gulf will shrink in size. Tank’s data suggest they may be right. She has studied nine Midwestern sites with half-mile long two-stage ditch projects and determined that the design can remove nitrogen from runoff, improve water clarity, and reduce phosphorous export. Her results, which were published in the July 2015 issue of the Journal of the American Water Resources Association, were not uniform. Some sites did a better job at reducing phosphorous export while others were better at keeping sediment out of the water. The variation, Tank says, is due to the fact that each site had somewhat different environmental conditions. Some of the projects had gravelly bottoms, for instance, while others were sandy. In addition, each was designed slightly differently in terms of the width and height of the shelf.

“What we realized about the practice is that it has potential benefits for all these different things— nitrogen removal, phosphorous removal, sediment, but it’s not a one size fits all,” Tank says. “Each system has their own unique character and that’s probably the way flood plains are in the real world.”

Some of the best results were found along the Shatto, where the two-stage was designed by scientists to best mimic nature (some of the other two-stage ditches in the study were designed to stabilize the banks of the ditch to prevent erosion, a common problem with agricultural ditches; the farmers who had them installed were less concerned with water-quality benefits). At the Shatto site, Tank found the two-stage increased nitrate removal by 63 percent, decreased phosphorus export by 27 percent and improved water clarity (by keeping sediment out of the ditch) by 72 percent during rainstorms.

The two-stage ditches in Talbot County will have a fundamental difference from those in Indiana. Because the ditches run parallel to the road, there is room for a shelf only on one side. There isn’t any scientific literature showing that a one-sided two-stage ditch is effective in keeping soil and nutrients out of local waterways. “Having it just on one side is something we’re definitely trying out,” Jacobs says. “But if you think of it from a purely engineering standpoint, we’re widening the area that the water has to move through and it’s coming into contact with vegetation that can perform wetlands functions so it’s definitely going to have some benefits.”

Swaine, as with many farmers, has taken a wait-and-see attitude toward his two-stage. Like most farmers in the area, he is well aware of the concerns regulators and scientists have with nutrient pollution from agriculture. He also knows that conservation practices put into place today will not bear fruit immediately. “It’s going to take a long time for us to do so stuff on the surface of the ground that will impact the watershed,” he says.

Still he’s hopeful that if farmers adopt proactive practices like the two-stage, they will help stave off nutrient pollution legislation that could make it too expensive to farm their land. Swaine loves what he does and he’d like to keep the farm in his family. Even though so far neither of his two daughters has expressed interest in farming, he hates the idea of his land—which like much in Talbot County could probably fetch a high price from housing developers due to its proximity to the Bay—being turned into a suburb.

“That’s not happening,” he says with a firm shake of his head, looking out across his fields at the little blue house where he, his kids, and his father all grew up.

Images of John Swaine and ditches by Nancy Averett, 2015. Image of Jennifer Tank by Matt Cashore/Notre Dame University. Diagram by The Nature Conservancy.

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This work by Nancy Averett and the Johns Hopkins Center for a Livable Future is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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