EVERY MONTH, BIOLOGISTS IN BOATS CRUISE along the rivers and mainstem of Chesapeake Bay, stopping at certain predetermined sites to collect water samples and take them back to a laboratory to measure nitrogen, phosphorus, and other nutrients. Later, researchers plug this boat-gathered data into the computer models they use to study excess levels of nutrients in the Bay.

But those monthly readings leave large data gaps in our view of the estuary — gaps that limit our ability to understand the causes of poor water quality and how to improve it. Why are those gaps a problem? Imagine trying to appreciate a symphony by listening to every tenth note.

Some solutions may be coming to help fill the gaps. This summer, prototypes of new high-tech nutrient sensors will start probing the waters at three field testing sites, including one in the Chesapeake.

The tests mark the culmination of a four-year effort to upgrade scientists' ability to monitor and understand nutrient pollution. A key player is the Alliance for Coastal Technologies. This federally funded program is based at the Chesapeake Biological Laboratory (CBL), part of the University of Maryland Center for Environmental Science.

The alliance is a consortium of research labs, resource managers, and private companies that work together to develop and apply new tools to study and monitor aquatic environments — whether in streams and rivers, estuaries, or oceans. Among other things, the alliance conducts independent evaluations of equipment, like the new nutrient sensors.

In a series of laboratory tests and field trials at the three sites, alliance scientists will assess how well the sensors perform over a wide range of water conditions and nutrient levels. CBL is one of the field sites where the prototypes will run through their paces for three months off the lab's 750-foot research pier.

The sensors that meet the tough test criteria could be a boon to scientists and natural resource managers in the many locations that struggle with nutrient pollution. When dissolved in water, nitrogen and phosphorus form chemicals such as nitrate and phosphate. Plants need these nutrients to thrive. But excessive nutrient levels fuel algae overgrowth or blooms, which lead to large and persistent oxygen-starved "dead zones" in the Chesapeake.

A better way to track the nutrients is part of the solution. And that's why the Challenging Nutrients Coalition, made up of federal agencies and the alliance, launched a technological I-dare-you called the Nutrient Sensor Challenge. The coalition thinks the key first step to reining in nutrient pollution is creating a new generation of affordable, compact, easy-to-use sensors that can detect and measure nitrogen and phosphorus in a variety of environments. If this new hardware meets a critical price point — less than $5,000 — the number of nutrient sensors in operation could rise exponentially.

More sensors mean more data, both to feed the computer models scientists use to study nutrient pollution and to inform management decisions. Better and cheaper nutrient sensors could also be a boon to wastewater treatment plants, aquaculture operations, and hydroponic farms.

That is, if the new sensors can pass muster in tough laboratory and field tests. The project's tester-in-chief is Mario Tamburri, a marine biologist and expert on aquatic instruments who directs the Alliance for Coastal Technologies. The Nutrient Sensor Challenge is unlike anything the alliance has done before, and Tamburri is excited. "We are transforming the way nutrients are monitored," he says.

The Nutrient Sensor Challenge grew out of an effort at the White House to identify important national problems that could be solved with technology challenges. To spur new solutions to worthy problems of broad public interest, technology challenges offer an incentive — typically a cash prize.

The White House's Office of Science and Technology Policy (OSTP) asked for advice from its staff experts and others in federal agencies. "They said that nutrient management and pollution is a huge problem, and we are just not solving it," says Bruce Rodan, OSTP's assistant director for environmental health.

Another ACT site is off a research pier at the mouth of the Patuxent River (above, top), where ACT scientists previously tested sensors for water acidity. The sensors that pass muster might become new products, similar to the solar powered nitrate sensor (above) for measuring nitrates in farm soils. Photographs, Alliance For Coastal Technologies (above, top) and Decagon Devices (above)

But what was the solution? To find out, the coalition held another meeting at the White House with experts on nutrient management. They said that progress in solving the nutrient problem would require better tools to measure nutrients and more data — collected more often, in many more locations.

In most nutrient monitoring, someone collects water samples and carts them back to a lab for analysis. This sharply limits the frequency and coverage of the sampling, creating blind spots. "You miss things like the true range — the true highs, the true lows," Tamburri says. "It doesn't tell you the total amount of the nutrients present because you don't have enough samples to get a good estimate."

To fix that, scientists could try putting out more of the automated nutrient sensors currently on the market. But these devices can be difficult to operate and are expensive, costing $15,000 to $25,000. The coalition decided to sponsor a grand challenge to develop more affordable and easy-to-use nutrient sensors.

That's when the Alliance for Coastal Technologies got involved. It was tapped for its expertise in testing aquatic sensors and its connections to equipment manufacturers and academic labs. The alliance could help to figure out the key capabilities that the sensors needed to have to advance nutrient monitoring. How sensitive and precise would they need to be? What nutrients should they measure? And how cheap would they need to be to help clean up America's nutrient pollution problem?

Through a series of surveys, studies, workshops, webinars, and numerous phone calls and conversations, alliance and coalition experts discovered that a diverse range of professions could benefit from new sensors. Researchers and natural resource managers wanted them, but so did citizen scientists, environmental nonprofits, wastewater-treatment-facility engineers, and even hydroponic-greenhouse operators and farmers, who could use them to fine-tune the amounts of fertilizer they applied.

The sensors should be able to measure either nitrogen or phosphorus, or both, in a variety of settings — freshwater, estuary, and ocean.

They should keep good data flowing under a range of temperatures and depths, and be accurate and precise enough to meet high scientific standards.

They had to perform well in water clouded with sediment or organic matter.

They had to take measurements at least every hour, but every minute if needed.

Users wanted the ability to deploy the sensors in a variety of ways — handheld devices, on floating buoys, at the edge of the water, and from boats.

The sensors needed to keep working on their own for at least three months — a tall order. That meant special design features to combat biofouling, in which devices get overgrown with bacterial films, algae, seaweed, sponges, barnacles, and even shellfish. Biofouling causes sensors to either fail altogether or spit out bad data.

And one more really important thing: the sensors needed to be affordable. Careful analysis showed that if the sensors cost less than $5,000 they would proliferate, potentially changing what we know about nutrient pollution and how we know it.

The Challenging Nutrients Coalition was asking for a lot. In return, the companies that entered the challenge would gain an early foothold in a lucrative new market for nutrient sensors. An alliance market study determined that companies could sell 24,000 to 30,000 sensors in the United States alone in the first five years, with total sales of $120 to $150 million. The alliance was also providing free lab and field testing of the sensor prototypes.

Out of 29 companies or teams that initially expressed potential interest in the Nutrient Sensor Challenge in early 2015, five made it to the final testing phase in 2016. Some of the devices are lap-sized miniature chemistry labs; other instruments scan water samples with ultraviolet light to capture the spectral fingerprint of the nutrients. The entrants included companies from England, Ireland, Italy, Canada, and one firm in the United States.

To start the testing, the alliance will stage laboratory trials at Chesapeake Biological Laboratory to subject the sensors to the wide range of temperatures, salinities, sediment and organic material levels, and nutrients levels they are likely to encounter in actual use. That would test for accuracy, precision, and range.

Biologists on boats measure nutrients in the Bay once or twice a month, but this leaves gaps in the record that real-time automated sensors can fill and help to improve understanding and management of nutrient pollution. Photograph, courtesy of the Chesapeake Bay Program

Then the devices go to three alliance partner field sites, representing a range of typical freshwater, estuarine, and ocean environments.

The University of Michigan will test the sensors in the freshwater conditions of the Maumee River, which contains relatively high levels of sediment and nutrients because of agricultural activity in that watershed.

The Hawaii Institute of Marine Biology will test the sensors on a shallow reef in Oahu's Kaneohe Bay, where the ocean waters are relatively low in nutrients.

The sensors will also be dunked off the research pier at CBL, where the brackish waters contain moderate levels of nutrients but where biofouling is extremely high. Three months in this environment will show just how well the instruments' anti-biofouling features work.

At the end of 2016 or early in 2017, independent judges will award prizes identifying what might be the next generation of nutrient sensors.

Jeremy Testa is eager for the data that would flow from real-time sensors. The CBL researcher uses computer models to study nutrients in the Chesapeake Bay. Are there data gaps he would like to fill? "Always, everywhere," he says. For example, automated sensors could better characterize the sharp spikes in phosphorus in waterways when rainstorms wash that nutrient off the land surface.

Testa and other Chesapeake nutrient modelers rely heavily on monthly boat sampling, but they rarely have data to bridge the gaps. "Having continuous nutrient sensors would be transformative for us," he says, "not just for modeling, but also for doing experiments and understanding natural variability."

New products from the Nutrient Sensor Challenge could start appearing in 2017. And more data could soon make a difference for a lot of scientists and managers working to reduce the impacts of nutrient pollution on the health of Chesapeake Bay. "All kinds of things are going to fundamentally change," says Tamburri, "because we will have the tools to understand them."