Nitrogen Dynamics: In The Field With Scientists Tackling Dual Nutrient Questions

By on October 23, 2015
Silvia Newell holds up a sediment core pulled from the upstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

After the 2014 harmful algal bloom in Lake Erie’s western basin that knocked out Toledo, Ohio’s drinking water supply for several days, there was a rapid scale-up of efforts supporting the study and protection of the lake’s water quality. Some of these included new monitoring initiatives, like a large number of new data buoys deployed around the western basin throughout the year that followed. And the network itself is a good example of increased cooperation between government agencies working around the lake to cover as much water as they can and share the data they collect.

But the Toledo Water Crisis, as it was widely called in news reports, also brought increased public attention to the issue of farm runoff and the bloom-feeding nutrients that flow with it. This led many scientists, as well as politicians, to evaluate the need for new regulations that could keep such a crisis from happening again. In April 2015, Ohio’s General Assembly passed a law to regulate how and when farmers living in the Maumee River watershed can apply fertilizers to their fields. It also establishes new monitoring regimes for phosphorus testing by publicly owned treatment operations.

Since phosphorus has no gas phase that can be “fixed,” unlike carbon (CO2) and nitrogen (N2), the long-held and popular belief is that you can focus on treating it, and the lack of phosphorus will limit algal growth. But Mother Nature is full of surprises, and it turns out that many of the little algae cells out there really like nitrogen.

In fertilizers, nitrogen is commonly added in the form of ammonium and urea. Why is this important?

“There is a theory that these bacteria that are sort of the linchpin of the nitrogen cycle — they’re called nitrifiers — and what they do is they link ammonium, which is something that is often added as fertilizer, to a form that can be removed from the ecosystem,” said Silvia Newell, assistant professor of aquatic biogeochemistry in the Department of Earth and Environmental Sciences at Wright State University. “Ammonium is like the dollar bill. It is the cheapest, easiest currency to use. You never have to worry about anybody breaking it, anybody having change; you know your dollar bill is the easiest thing to pay with. Well, that’s what ammonium is like. It’s so easy to use and to take up.”

Daniel Hoffman (left) and Lee Slone gather sediment cores on the downstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Daniel Hoffman (left) and Lee Slone gather sediment cores on the downstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

She and others talked with the Environmental Monitor about some studies underway at her lab to explore the significance and nature of that chemical relationship during field work along a stretch of the Lower Great Miami River near Dayton, Ohio. These involve several ongoing projects including an investigation into the river’s nutrients and others that touch on water quality issues in Lake Erie and China’s Lake Taihu.

Lower Great Miami River

Luckily for the scientists and our fearless photographer, water flows in the Lower Great Miami were low as they waded out to begin taking sediment cores. This meant that there was little risk of getting knocked over by swift currents. And the weather was good too, as a mild, beaming sun lit up the river and a partially removed dam they worked around.

Of interest to the crew are nitrogen levels and how they are affected by water treatment plants along the river. They specifically want to find if the nutrients are released naturally by sources going into the river or are linked to the treatment plants. If they are not from the plants, then looming new requirements and expensive retrofits proposed for the treatment operations would be a waste.

The study is part of Lee Slone’s master’s thesis work. He was aware of the issue and pitched the study to Newell, who helped him design the experiment.

“What I said was, ‘I want to do this. This is interesting to me. Phosphorus is already being dealt with by the Miami Conservancy District and the Hammerschmidt Lab at WSU,’” said Slone, a master’s student in the Newell Lab and an attorney. “And Silvia said, ‘That’s great, focus on the nitrogen.’”

Lee Slone (left) secures a sediment core on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Lee Slone (left) secures a sediment core on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Getting at those levels, and identifying where along the river they are highest, involves a decent amount of scientific equipment and varying methods. On the field work side, Slone and others collect cores upstream of the dam in a gradient moving toward it and then follow that with water quality measurements taken by a multi-parameter sonde linked to a tablet computer. The sonde gathers data on water temperature, specific conductance, depth, blue-green algae, chlorophyll, dissolved oxygen, turbidity and pH. The scientists collect nutrient samples for nitrogen and phosphorus concentrations, immediately filtering them. They also gather more water samples in 5-gallon water bags. Once the upstream sampling is done, they head to the other side of the dam and do it all over again.

The team uses similar sampling efforts all up and down the Lower Great Miami River, looking specifically around impoundments that cross its wake. After they survey a site, the sediment cores and water samples go back to the lab, where Slone analyzes them.

There are a few expectations for what data from the site we visited will reveal.

“This is urban. Our expectation is that this is going to be a lot of urban runoff,” Slone said, while transferring a sediment core to a large white cooler. “When it rains on your lawn, if you have a dog and it poops, you don’t clean it up, or you fertilize your lawn, that goes into runoff. And here, it’ll go into the street, and the stormwater comes right into the river. Not just this one, but the others that feed this river.”

As for any inputs from combined sewage overflow, the Dayton area doesn’t have a system that joins stormwater and sewage pipes together, so it’s not a concern. And with no treatment plant upstream, the scientists guessed that most of the site’s runoff would come from areas around it.

“When you look at the state as a whole, the majority of nutrients that are being added through runoff are coming from farms,” said Newell. “And wastewater treatment plants are a smaller percentage of that.”

A sediment core taken from the Lower Great Miami River is placed in a cooler. (Credit: Nate Christopher / Fondriest Environmental)

A sediment core taken from the Lower Great Miami River is placed in a cooler. (Credit: Nate Christopher / Fondriest Environmental)

Some of the lab methods that Slone uses to verify or disprove his expectations rely on a mass spectrometer. With that, he analyzes samples from a continuous-flow incubation that simulates what is happening in nature as best as possible. One of the large, 5-gallon jugs of water serves as part of the experiment’s control, marked with a “C,” to which he doesn’t add anything. The other two jugs are marked with “A” or “N,” like their sediment core counterparts, and get treated with ammonium or nitrate.

“In the A, I add heavy ammonium, so NH4+, but the N that’s on the NH4+ is a 15 (isotope) instead of a 14,” said Slone. “And the N, I add nitrate, and the N is 15 instead of 14. So I add heavy nitrate to one tub of water, and I flow that through these two (N) cores. I duplicate cores, and I flow heavy ammonium through these (A) cores, and the controls through these (C cores). And that’s six up (upstream), six down (downstream).”

Slone says that the work is in beginning stages, and there’s still plenty of data to be collected, but the hopes are that the effort will yield something useful to those working to maintain the health of the Lower Great Miami River.

“We’re using very careful analytical methods to quantify rates of nitrogen transformation, and with those numbers, we can go to the Miami Conservancy District, or to the EPA or to the wastewater treatment plants and say, ‘Here’s what we found. Here’s what we think is going on,’” said Slone. “And it’s always a battle between people and nature. Got to feed all the people, got to put fertilizer on all the fields, but at what cost, and where’s the balance?”

Lake Erie

Growing interest into nitrogen’s role in algal blooms has in part spurred another study underway in Newell’s lab. Like the Lower Great Miami River work, it is zeroing in on ammonium but relies on data collection a few hours north of Dayton.

Daniel Hoffman, a doctoral student in the lab, is leading the work. We caught up with him on an exposed sandbar while Newell and Slone gathered sediment cores upstream of the dam.

Daniel Hoffman (left) watches as Lee Slone secures the bottom of a sediment core with electrical tape on the downstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Daniel Hoffman (left) watches as Lee Slone secures the bottom of a sediment core with electrical tape on the downstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

“Specifically what I’m looking at is ammonium. And the reason I’m looking at ammonium is that it is the most reduced form (of nitrogen) in terms of its oxidation state. So what that really means for things that want to grab it is it’s the easiest to grab. It’s the easiest to cross the cell membranes without a whole lot of extra energetic work being put in,” said Hoffman. “And ammonium favors the growth of cyanobacteria, like the toxin-producing Microcystis that is currently blooming in western Lake Erie.”

Part of the reason that researchers elsewhere have not done such a good job measuring ammonium concentrations accurately is that it just gets taken up so quickly, Hoffman says. It is simply in very high demand for biological use. His work so far, as well as studies that Newell has helped on in the past, show just how these concentrations have been missed.

Scientists go out, collect samples and then take them back to the lab for analysis hours later. But after those long periods, Hoffman says, the ambient ammonium concentrations they see aren’t accurate because of the extra time that biological communities within the samples have had to take them up or regenerate them, such as when cells break open or are eaten.

Hoffman is working to alleviate that data gap and learn more about the dynamics of ammonium use through regular trips to Lake Erie, where he gathers samples with help from ship time donated by the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Lab. Scientists from the lab are also sharing data with Hoffman, who will be repaying the favor when his work is finished.

He typically uses a Niskin water sampler to collect discrete samples at varying depths in the lake’s western basin. Samples are gathered about a meter below the surface, just under where blooms typically are, as well as deeper down near the lake bed.

“Kind of tricky, but when you get into the difference of a thermocline, where the temperature difference is, you’ve got a change in nutrient concentrations. And especially where we have these blooms, things are going to be consumed very quickly at the top, though they may not be at the bottom,” said Hoffman. “So we don’t yet know what those differences are, but we’re going to look and see.”

Silvia Newell (right) and Lee Slone collect water samples upstream of an impoundment on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Silvia Newell (right) and Lee Slone collect water samples upstream of an impoundment on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

Hoffman gathers in situ samples for ammonium before making the drive back to Dayton. The water is run through filters that limit the tiny lifeforms within from taking it up.

“We go out and we collect the water and immediately filter it to 0.2 microns, which removes most of the potential bacteria that are going to take it up — it’s a very tiny pore size on that filter – which means that we’re seeing much higher ammonium concentrations, or at least different ones, than the people who were filtering or freezing after an hour or even days,” said Hoffman.

Other ammonium dynamics he’s looking at rely on lab techniques. One is a total nitrification rate experiment in which ammonium is converted in a multi-step process all the way to nitrate. The nitrifiers compete with Microcystis for ammonium, which could determine a threshold the Microcystis have to overcome to bloom. An ammonium oxidation experiment lets him dissect the rate-limiting step of the nitrification process, and he’ll correlate that through a gene’s expression later in the work. He is also studying ammonium uptake and regeneration. Those experiments are complemented, he says, by using 15N, a stable isotope of nitrogen that can be measured using mass spectrometry.

“And that means that we can say, ‘alright, well, if I know that I’m adding this much of the 15 labeled stuff in this form, and it comes out in a different form, there’s a process occurring there, and we know what that process hypothetically is and how fast it goes,’” said Hoffman. “Genetic work is the next step in terms of verifying that, but there are only a handful of processes that are going to contribute to one output from one input. So we can make a pretty good guess just based on that.”

In the future, he would also like to quantify the communities of micro-organisms that take up ammonium to see how many Microcystis there are versus how many are ammonia-oxidizing bacteria and archaea.

“If there are certain species that could potentially outcompete Microcystis for the available ammonium, that could lead to some ideas about how we mediate these really nasty blooms. Because there are tons of other bacteria and archaea in these systems, it’s just that Microcystis are dominant and they happen to be the dominant toxic species as well,” said Hoffman. Figuring out how to shift away from those toxic species and back toward typical phytoplankton dominance would be a great help to all the systems, he adds.

A researcher walks back to the river bank after sampling water quality in the Lower Great Miami River with a multi-parameter sonde. (Credit: Nate Christopher / Fondriest Environmental)

A researcher walks back to the river bank after sampling water quality in the Lower Great Miami River with a multi-parameter sonde. (Credit: Nate Christopher / Fondriest Environmental)

Those and other questions are yet to be answered by Hoffman’s work, which is just beginning. But hopes are that answers to them will one day make splashes in the Lake Erie environmental policy world.

“That’s what we’re hoping. I mean we’d like to be able to get enough information,” said Hoffman. “So we mentioned that nitrogen currently isn’t regulated in Ohio. But as of last year or earlier this year, the EPA has kind of started to say, ‘we should really be looking at a dual nutrient management strategy with both N and P instead of just P. But that’s still in its nascent stage and people are still talking about it.”

Bringing It All Together

There is a growing realization among scientists and policymakers that more attention needs to be given to monitoring and regulating nitrogen making it into U.S. waterways. Recently, that has been given more credence by a bulletin issued by the U.S. Environmental Protection Agency advocating for a dual-nutrient strategy.

“That means that, right now, phosphorus is being monitored and regulated everywhere, and nitrogen is not. So the U.S. EPA is saying, ‘Hey, we should do this.’ So they haven’t made it a law yet, but I really believe that it will be in the next few years,” said Newell, speaking with us after the crew had moved downstream of the dam to begin round two of sampling. “And the trouble with that is that we don’t have much data to base our laws on. We have very few measurements of ammonium in Ohio in rivers. Some people are doing it, but there’s a lot of variability in terms of how the samples are collected, like how people actually collect their samples and run their method.”

For example, some researchers use filters that go down to 0.2 microns whereas others use filters that come in at 0.7 and clear out fewer of the tiny lifeforms that continue to use ammonium. More method variability is also introduced by scientists who freeze samples after collection to halt reactions while others do not.

“There are some flow gauge stations along the river that will actually collect water samples, and they sit there for up to a week before somebody comes and collects them and measures them. And so, that’s obviously kind of a problem for trying to get an accurate measurement,” said Newell. “We want there to be good data for these laws, whatever they are, to be based on. We want to have a good idea of how much nitrogen we have in our rivers and lakes, how much is going in Lake Erie, and what percentage of that nitrogen is ammonium specifically.”

Lee Slone takes a baseline measurement of ammonium before moving on to sampling downstream. (Credit: Nate Christopher / Fondriest Environmental)

Lee Slone takes a baseline measurement of ammonium before moving on to sampling downstream. (Credit: Nate Christopher / Fondriest Environmental)

The ongoing projects may also have implications for another one that Newell has been working on for years with co-investigator Mark McCarthy, a research scientist in Wright State’s Department of Earth and Environmental Sciences. It is focused on hypereutrophic conditions in China’s Lake Taihu, which are choking the water body with bright-green algae just like in parts of Lake Erie.

“It’s very similar to the western basin of Lake Erie in that they’re both shallow, so they’re well mixed,” said Newell. “And they both have big problems with harmful algal blooms, specifically Microcystis. And we are hoping that what we learn from one can be applied to the other and vice versa.”

Of course, the western basin of Lake Erie is a lot different when compared to other parts of the Great Lakes, she says. Lake Superior is a pristine water body by comparison, mostly because of its great depth and the fact that it can’t be mixed as well as Lake Erie.

But there will likely be insights from all the projects going on in Newell’s lab that contribute to improving water quality in lakes and rivers in the Great Lakes basin and elsewhere.

“This project is very local. It’s locally focused and mostly has impacts for the Dayton wastewater treatment plants,” said Newell of the Lower Great Miami River work. “But what’s happening in Taihu and what’s happening in Erie, I think are especially important for water regulations across the nation and in Ohio. We don’t have nitrogen regulations across the board. I think we’re going to. I think it’s very important to understand the Great Lakes. So I think understanding how nitrogen is cycled and moves in the different kinds of lakes and different systems is very important, and there’s been very little work done on it.”

Top image: Silvia Newell holds up a sediment core pulled from the upstream side of a dam on the Lower Great Miami River. (Credit: Nate Christopher / Fondriest Environmental)

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