Study Aims For Reality Check On Nutrient Runoff From Farms

PRINCE GEORGE’S COUNTY, Md. – At a farm in Prince George’s County, MD, Gurpal Toor and his students have been gathering water samples for more than three years. Their goal is to figure out how much nutrient pollution is running off a six-acre field — toward waterways and the Chesapeake Bay.

It’s a question he still can’t answer with precision. There is too much year-to-year variation: changes in temperature, changes in rainfall, changes in what’s planted.

Providing an exact number for the amount of runoff — or advice about how to reduce it — would be “irresponsible” at this point, said Toor, a professor and agricultural extension specialist with the University of Maryland.

“I don’t want to take a couple of years of data and tell everyone, ‘Here is the conclusion,’” he said.

Toor’s uncertainty starkly contrasts with figures used to guide Chesapeake Bay cleanup actions. While Toor struggles to understand what comes off a single field, figures from the state-federal Bay Program tell you with seeming precision the amount of nitrogen — a key nutrient — that comes off all 80,000 farms in the Bay watershed: 116,372,907.49 pounds in 2024.

That the Bay Program can determine what comes off all farmland to the hundredth of a pound seems a bit unlikely to Toor, who is in the fourth year of an effort that he views as something of a reality check.

Toor is closely monitoring 15 small agricultural catchments in Maryland — essentially fields that drain to a specific point — ranging from 6 to 140 acres.

Funded by the Maryland Department of Agriculture and U.S. Department of Agriculture, it may be the largest detailed study ever attempted of how nutrients actually leave Bay-region farms in multiple settings. The goal is to better understand not only how many, but under what circumstances, nutrients are leaving actively managed fields and how that amount might be reduced.

It’s not simply an academic question.

Agriculture is the largest source of nutrient-laden runoff to the Bay and its rivers, where it spurs algae blooms that cloud the water and lead to oxygen-starved “dead zones.” Bay states count on controlling farm runoff as their primary method of reaching their nutrient reduction goals.

Despite billions of dollars of investments in the past two decades, the Bay region is falling short of meeting those targets. Further, a number of recent studies cast doubt on the effectiveness of the region’s pollution-reduction actions.

States, using computer models, write cleanup plans outlining how many best management practices, or BMPs — such as nutrient-absorbing cover crops, stream buffers or manure storage sheds — need to be installed to meet their goals. The Bay Program assigns a nutrient reduction value for each of more than 200 types of agricultural BMPs, but recent studies suggest they are not having as much impact as anticipated.

A recent study by the U.S. Geological Survey in Smith Creek, VA, found that runoff of the nutrients nitrogen and phosphorus increased there despite a four-fold increase in BMPs. The study found similar results in several Maryland and Pennsylvania watersheds.

Extensive monitoring in small agricultural watersheds on Maryland’s Choptank River by the University of Maryland Center for Environmental Science likewise has found relatively small impacts from BMPs on water quality.

And a 2023 report from the Chesapeake scientific community warned that the Bay Program may “systematically overestimate BMP effectiveness.”

The Bay Program isn’t alone: A 2020 nationwide study found that computer models consistently predicted greater pollution reductions than were observed in real-world monitoring.

Toor said that such findings are not surprising. The BMP nutrient reduction effectiveness assumed by the Bay Program is typically based on limited studies — often from outside the watershed. And they are frequently conducted under tightly controlled circumstances rather than on actively managed farmland.

Many factors influence how much nitrogen and phosphorus flee a field: when crops are planted and harvested, the slope of the land, how much rain falls, how hard it falls, whether the fields are ditched or tiled for drainage, and whether manure or chemical fertilizer was applied to the land.

The types of soil and the history of the field are also important. The six-acre Prince George’s field, for instance, still has high phosphorus concentrations from the application of biosolids as fertilizer two decades ago.

“Our systems are complex,” Toor said, “and if we really want to understand those systems and the actual extent we are making a difference, then we need time to get the data.”

Few studies have been done at the field scale — the level at which the land is managed by a farmer.

Bradley Kennedy, one of Toor’s graduate students, conducted a literature review and found only one published field-scale study of nitrogen loss in the Bay watershed.

“We note that this absence is particularly surprising given the emphasis on nutrient management and regulation in the Chesapeake Bay watershed,” Kennedy said in a paper written with Toor.

In some cases that work has been done, Toor noted, but the results were never published, typically meaning they are not available for use by decision-makers and computer modelers.

There is a reason for the lack of such studies: It is hard, tedious work — and costly.

Toor’s project includes five sites with overland flow from fields on Maryland’s Western Shore and five tile drainage and five ditch drainage sites on the Eastern Shore.

The equipment alone at each monitoring site can cost $25,000, Toor said. Each site includes a device that automatically collects water samples as well as solar panels and batteries that operate the equipment.

At overland flow sites, a flume is constructed on a concrete pad to direct water to a point where it is measured and collected. When it starts raining, the equipment begins gathering samples at set intervals — usually at every 1,000 gallons. Each sample flows through a tube to one of 24 one-liter sample bottles.

The process is similar in ditched or tiled sites, except that instead of a flume, a flow-control device is placed in the drainage system to measure flow.

And the labor is extensive. Kelly Hayden, a faculty assistant who is doing most of the field work this year, typically spends two days a week visiting sites to collect samples, racking up 1,000 miles of travel a month.

“If we get a really large rainfall event, my week’s really busy,” Hayden said.

Even if it doesn’t rain, sites must be inspected periodically to check and calibrate equipment.

There’s a “yuck” factor in the job. The devices are kept in sheds that attract insects. Spiders and their webs have to continuously be cleaned from electronics, and the tubes that carry water have to be cleaned as well. “There’s normally worms or something in there,” Hayden noted.

Last year, Toor got a frantic call from a student visiting a monitoring site who found a snake wrapped around the equipment. It eventually left on its own accord. The student decided monitoring wasn’t for her.

Samples have to be collected on brutally hot summer days and in frigid winter temperatures. Prolonged exposure to heat extremes could change the chemistry in the samples.

Back in the lab, the water samples are filtered and analyzed for different forms of nitrogen and phosphorus, as well as other characteristics such as dissolved organic carbon.

Each of those parameters, from each of the bottles collected from each site, costs $5 to $10 to analyze, and sometimes more. But it allows the team to understand the total amount of nutrients that leave a site, as well as at what point during the storm they leave and under what rainfall intensity.

Such attention to detail is critical to get an accurate picture of the factors that influence the nutrient loss, Toor said.

Many monitoring efforts collect a single sample during a storm but, depending on when it is taken, he said, that sample may not accurately represent what’s leaving. Nitrogen concentrations are typically higher at the beginning of a storm, and phosphorus concentrations get higher later.

Further, the intensity of storms influences what’s leaving the land. That’s important because, although the overall precipitation in Maryland is largely the same, it is coming in more severe events.

The amount of time between rain events is also a factor. “There’s a tremendous year-to-year variability in the rainfall characteristics,” Toor said, making it hard to say what is average, or normal, in terms of runoff.

Working with farmers

Dairy farmer Dick Edwards had been applying liquid manure to fertilize fields that would soon be planted with corn when Toor and Hayden arrived to check the monitoring results from a ditch that drains a 140-acre catchment on his farm.

Edwards operates the 1,000-acre farm with his son and grandson, and the manure from the 750 cows gets recycled back onto fields of corn, alfalfa and other crops, most of which will become food for the cows.

He chose to participate in the study because the Caroline Soil Conservation District was looking for volunteers.

“It doesn’t hurt us, and maybe it benefits them,” he said. “We try to learn to do better by letting you guys do things. And it’s keeping us in line with what’s going on with the environment.”

Working closely with farmers like Edwards is a key part of Toor’s project. Someone from his team regularly talks to farmers to learn when they are applying manure or chemical fertilizer, when they are harvesting, whether they are irrigating, and other specifics that may influence runoff.

Toor hopes that eventually he’ll be able to offer management advice that may help them reduce that runoff. But he’s also up front with farmers that the data could be used to shape future regulations — in fact, one goal of the project is to refine the state’s Phosphorus Management Tool that regulates how fields are managed based on their phosphorus concentrations.

Toor was surprised when one farmer said that was fine. “If you’re going to regulate me,” the farmer said, “you better regulate me on the data that you’re collecting from my farm, rather than collecting data from a neighboring farm or another county.”

Toor understands the frustration. Rules or regulations — like assumptions about BMP effectiveness — are often broad and don’t account for the unique circumstances that affect runoff on a particular farm.

A cover crop of rye planted in the fall can be highly effective at absorbing unused nitrogen, for instance, but it may leave the ground so depleted of the nutrient that more has to be applied in the spring, when it may be more vulnerable to being washed off the land.

On the six-acre Prince George’s catchment, for instance, Toor and his team decided where to locate their monitoring equipment after using wildlife cameras placed along the field to observe exactly where stormwater was running off the land and into the stream. That information would also be important in properly placing a stream buffer — but in the Bay Program nutrient crediting system, a buffer gets the same nutrient reduction credit even if it is not in the path of flowing runoff.

Toor views such BMPs as “common sense” things akin to “using an umbrella when it rains.”

But, as recent studies suggest, those BMPs by themselves are not likely to achieve the Bay’s pollution-reduction goals.

Moving the needle, Toor suggests, will likely require more specific advice that better accounts for variables in the conditions and management actions taking place on individual farms rather than broad-brush recommendations.

After collecting five years of baseline data, which will be completed next year, Toor hopes to be able to test such farm-specific recommendations. And he may test new techniques as well, such as drones that can more closely apply nutrients to crops at times they are actually needed.

“We need more science-based, better practices that we can tell farmers actually work and [we need to] get rid of the ones we have that don’t do anything,” Toor said. And, he added, the advice needs to make sense for farmers, too.

“We can sit in fancy conference rooms and come up with things, but the people who are actually going to do it are going to be the farmers. So we really have to talk to them, and we have to have that trust with them. And this needs to be a collaborative effort.”

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