This article was originally published by Inside Science.For more than 35 years, Mark Eck has raised chickens at his farm on Maryland's Eastern Shore, but on a recent muggy August morning, he wasn't focused on his flocks. Instead, he was showing a group of farmers, researchers and state and federal officials an adjustable, dam-like structure he had installed in a ditch that drains water away from his fields and poultry houses.Eck's structure is meant to trap some of the excess nutrients from fertilizers and animal manure leaking from his farm, preventing them from ending up in the Choptank River and, ultimately, the Chesapeake Bay where they can create conditions that harm native species such as oysters and crabs.It is just one of a menagerie of agricultural pollution control methods that the government and environmental groups, among others, have helped farmers implement or install on their properties across the bay's 64,000-square-mile watershed, in an effort to clean up the iconic waterbody over the last three decades.But some scientists have been questioning whether some of the methods -- collectively known as best management practices or BMPs -- actually reduce pollution as much as estimated."They're being put in all over the place, but no one ever checks to see how well they work," said Thomas Fisher, an environmental scientist at the Horn Point Laboratory of the University of Maryland Center for Environmental Science.Fisher and his colleagues are working to change that. They are ending year three of an ambitious five-year, $1.5 million study aimed at figuring out which of the agricultural practices work best at protecting the Choptank, the largest tributary of the Chesapeake Bay on the Eastern Shore.The research is needed. Although parts of the bay may be improving in water quality, "the Choptank is still going downhill," said Fisher. "So why is this happening? Are the BMPs not working?"Going downhill in more ways than oneThe Choptank arises near Dover, Delaware and flows southwest across the flat landscape. Around Cambridge, Maryland, it veers sharply west, eventually draining to the Chesapeake Bay.Fisher's research group has worked in the Choptank basin for nearly 30 years. In the river's estuary -- as in the larger Chesapeake Bay -- they've watched nitrogen and phosphorus fuel algal blooms that turn the water green. When the algal blooms die, bacteria use up oxygen dissolved in the water to decompose their remains, smothering some animals such as fish and crabs.Eroded soil is flushed down the waterbodies, too, where it clouds the water or settles out on oysters, making it difficult for them to survive. And together the algae and sediment can block sunlight from reaching underwater grasses that provide food and shelter for aquatic creatures.For more than three decades, the federal government, several states and various organizations have worked to clean up the Chesapeake Bay. And while farmers have made improvements, agriculture is still the single largest source of nutrient and sediment pollution entering the bay, according to the federal government.And the problem in the Choptank is getting worse. Over the past few decades, stream monitoring stations in the upper part of the river's watershed have tracked increasing levels of nitrogen and phosphorus. A few small areas, however, are showing signs of improvement.Both of the nutrients come from a variety of sources: the atmosphere, sewage treatment plants, septic systems, and fertilized lawns and farm fields. But previous research has shown that agriculture is the major source of nitrogen, phosphorus and sediment in the Choptank and the Chesapeake Bay.Over half of the Choptank's watershed is agricultural. Farmers grow corn, soybeans, wheat and barley, and use many of the crops to feed chickens. The majority of Maryland's hundreds of millions of chickens are raised on farms like Eck's on the Eastern Shore.Farmers use both chicken manure and fertilizers to boost crops yields. The chicken waste is high in phosphorus, which tends to accumulate in the soil and then be washed downstream in rainstorms. Farmers also supplement with other fertilizers, and the excess nitrogen -- in the form of nitrate -- leaches into the groundwater as well as contaminating surface runoff from fields.'Best' practices?That's where practices like Eck's dam-like structure are thought to come in. Known generally as a controlled drainage or water level structure, it works by temporarily backing up water in the ditch and, importantly, in the soil of the surrounding fields, thus raising the local water table. That induces a process known as denitrification, where microbes in the soil convert the nitrate into harmless nitrogen gas. Farmers can use the practice in the winter when fields are fallow and don't need to be drained, and thus reduce the nitrate leaking from their property.And the benefits aren't, perhaps, purely environmental. Keeping the groundwater level high during the winter could mean that some of that soil moisture sticks around for more of the following summer, which could help farmers reduce their irrigation costs.Other agricultural conservation measures include such efforts as encouraging farmers to grow fewer crops along waterways and instead plant trees or other plants to filter out or trap nutrients or sediment. They also cover practices such as minimal tilling or planting winter cover crops that can reduce soil erosion or take up excess nutrients. (There are also BMPs aimed at reducing pollution in sewage or stormwater, which include actions such as upgrading wastewater treatment technologies. The current study only focuses on those applied to farming.)Still, there's an air of braggadocio surrounding the very name of these conservation measures -- best management practices. The term presumes effectiveness. But, said Fisher, "there's a lot of skepticism in the scientific community that many of these BMPs work as advertised."USDA/NRCSThese structures are intended to restrict flow out of fields or drainage ditches todecrease nutrients leaking from farms. Once the water level behind the barrier isgreat enough to surpass the restriction, water is slowly released downstream.Lisa Wainger, an ecological and economic modeler at the University of Maryland Center for Environmental Science's Chesapeake Biological Laboratory in Solomons, Maryland, agrees."Many of the scientists who have thought about this think we don't have enough information about the variability of performance in different kinds of settings," said Wainger, who is also the current chair of the Scientific and Technical Advisory Committee, which provides guidance on scientific issues to the state-federal Chesapeake Bay Program.In 2011, a report from the National Academy of Sciences found that despite "significant investments" in agricultural BMPs, a limited number of peer reviewed studies "rigorously document the water quality improvements from these practices at a watershed scale."The problem is that because of funding and time constraints the practices are typically tested at small scales -- an experimental station on a half-acre plot, for example. Then, managers extrapolate the observed effects of the conservation measures to entire watersheds.But, said Fisher, such extrapolation can be problematic.That's because across the bay watershed, BMPs are implemented or installed in a variety of environmental gradients such as different groundwater conditions, soil types and topography."We have some data," said Wainger, "but not a full suite of replicated studies that look at how things perform across these gradients."Take, for example, the practice of removing land between crops and waterways from production and planting it with trees, shrubs or grasses, creating a buffer that's thought to trap eroded soil and help filter out nutrients. How well that type of practice works is incredibly site-specific, said Ken Staver, a research scientist at the University of Maryland's Wye Research and Education Center. For example, groundwater may flow underneath the buffer in such a way that it doesn't interact with the plants at all, preventing them from sucking up nitrogen.But some practices do scale, he argued. "It's popular to say that the pieces don't add up to the whole," he said. "Cover crops do, assuming farmers meet the technical specs of the practice." Staver has been researching the effectiveness of winter cover crops at controlling soil erosion and removing unused nutrients from the soil's root zone for more than 30 years.Still, scientists have already found that some BMPs don't work as expected at large scales, and, what's worse, instead have contributed to the pollution problem under certain conditions.For example, it was thought that because minimal tilling helps decrease soil erosion, it would help reduce the amount of sediment -- and, thus, phosphorus, which sticks tightly to soil particles -- entering streams. But then Staver showed that in areas like Maryland's Eastern Shore the practice can actually cause more phosphorus to build up in the top layers of the soil, making it easier to wash more of the nutrient into waterways during storms.The Chesapeake Bay Program's science and technical committee that Wainger chairs has called for more testing of publicly funded activities like the installation of BMPs. "We want to avoid supporting an activity for decades with no measurable result," they wrote in a 2015 summary report.Wooing the farmersThe gold standard of BMP testing is to take the evaluation into the real world: install a number of the practices in a watershed and then monitor to see if nitrogen or phosphorus goes down in the stream that's draining the watershed.But before scientists like Fisher can do the experiments they had to get the farmers on board.For example, ditches were originally dug to ferry water off agricultural land as fast as possible, so stopping them up can seem counterintuitive. One farmer once claimed that seeing a drainage control structure like Eck's would have made his dead father turn over in his grave, said Matthew Pluta of the Midshore Riverkeeper Conservancy, which paid for and helped install Eck's structure."We were naïve," said Rebecca Fox, a former doctoral student of Fisher's and now an environmental scientist at Washington College in Chestertown, Maryland. "It took longer than we were expecting to build that trust."Their best asset turned out to be James Lewis, an agent with the Caroline County Agricultural Extension of the University of Maryland since the early 1990s and a farmer himself who's installed a number of BMPs on his property. "Lots of people know and trust him," said Fisher. "Without him, it'd have been a really difficult project to start."Over the last two years, the scientists have managed to convince about 26 farmers -- out of the approximately 40 who live in their study area -- to install around 30 new BMPs including drainage control structures like Eck's, cover crops, and split fertilizer applications, among others. The practices are spread throughout three primary sections of the upper Choptank's basin. A fourth section is also being monitored as a control.Focusing on the science, not advocacy, has been key, said Fox. "We tell the farmers we're not here to save water quality, we're here to test it."But there are important policy and management implications of the research. Without investigating how well the BMPs are working, scientists, farmers and regulators might develop an overly optimistic understanding of how much pollution has been prevented from reaching the bay. Ultimately, that doesn't help cleanup the waterbody, and it could mean wasted money and effort from everyone involved, including the taxpayers whose money helps subsidize some of the practices.The U.S. Department of Agriculture and state agencies currently help farmers pay to implement such pollution control methods, with the government typically funding between 75 and 80 percent of the costs. In 2008, the USDA Natural Resource Conservation Service approved approximately $27 million to help implement the conservation measures across the state on Maryland farms. The state of Maryland provided about $14 million more.The implications are not lost on some of the farmers working with Fisher and his colleagues.At one meeting the researchers held to explain the project, "a farmer stood up and said, 'It's a win-win. If it works, great. If it doesn't, then I won't have people telling me I have to do it,'" said Fisher.Seeing the numbersThere's still about two years to go in the project, so it's still too early to know which practices are working as expected. And the researchers are hoping to pack a few more of the conservation measures into their study sites.That'll be a hard sell -- the third of farmers left have shown little interest in participating. "They're the ones that don't return your calls," Fisher said with a wry smile. When asked what his strategy was to reach them, "persistence," he said dryly. Still others have refused to be involved at all, and the researchers respect their wishes, he added.Already, the researchers have seen some success in getting the farmers to implement more of the conservation measures -- and, in the process, make the connection between the water they see running off their fields with the water that ends up in the Choptank and the Chesapeake Bay.To that end, the scientists give a report to the farmers they work with once a year. It details what the growers are doing well in terms of keeping nutrients and sediment out of the water -- and what they're not."A lot of these farmers are small businessmen, and they love seeing the numbers," Fisher said. "It's been surprising to see how receptive they've been."The knowledge sharing works both ways. The researchers have been steeped in the details of farming on the Eastern Shore, from crop cycles to equipment brands to fertilizer practices. "I never thought I'd learn that much about chicken shit, but here we are," said Fisher.At the end of the project, he and his team hope to be able to recommend, in general, what Maryland, other states involved in the cleanup, and the federal government can do to ensure that what they're paying for works.Still, Fisher's study is just one part of a much larger puzzle. While its results should be fairly transferable to other places in the Delmarva peninsula -- which includes parts of Delaware, Maryland and Virginia -- questions surrounding the effectiveness of BMPs in other parts of the Chesapeake Bay's watershed will remain."How representative are for western Maryland? Or Pennsylvania?" asked Wainger."That's what we need -- very similar studies" in the range of environmental conditions found in the region, she said. That way "we can really understand where our actions are effective so we can do more of the things that are working and less of the things that aren't."