Fish lying on the banks of the Neuse River, belly up. Seems a straightforward sign that, in this water, something is wrong. But figuring out how to fix it is nowhere near simple.

Monitoring of the Neuse does show periodic fish kills, especially during mid to late summer, though their frequency varies with rainfall, salinity of the water, temperature, water circulation. Hans Paerl and Rick Leuttich, Carolina marine scientists, are concerned about fish kills, especially since they may be a sign of declining water quality. But both point out that fish kills are a normal part of the river’s life, that they happened long before people littered its banks. Even if we follow science’s suggestions for cleaning up the water, some fish will die.

And the exact number of fish affected is very hard to pin down, Paerl says. The numbers vary with who reports the kill and when, where the fish are found, and how they are dispersed. “We think that there are more fish dying now,” he says, “but that’s a soft conclusion. Because in the past, we didn’t monitor fish kills to the extent that we do now.”

Paerl, professor of marine sciences, attributes the kills mostly to low oxygen levels in the parts of the Neuse that are important habitats for fish. Pointing out a chart that combines his oxygen sampling with fish-kill data from the N.C. Department of Environment and Natural Resources, Paerl explains that many of the fish kills from 1994 to 1997 happened precisely at the times when there was little or no oxygen in these habitats.

The oxygen deficit is caused mainly by algae buildup. If there’s an excess of the green stuff, especially algae that microorganisms can’t eat, such as blue-green algae, it dies and sinks to the river bottom, where it’s decomposed by tiny bacteria. That decomposition can use up the oxygen fish need to survive.

“Fishermen can tell you when the water is low in oxygen,” Paerl says. “They can smell it–it smells like sulfide, a rotten-egg smell. They call it `bad water.’” Scientists call it “hypoxia” (oxygen levels below 5 milligrams per liter of water) or “anoxia” (almost no oxygen at all). Hypoxic water can severely stress fish, making them more susceptible to parasites, disease, and infections. Anoxic water can kill them in a couple of hours.

To find the culprit in the fish kills, Paerl says, we have to find what causes the algae to grow. In the Neuse, carpets of excess algae–algal blooms–are nourished mainly by nitrogen.

Nitrogen has also been thought to contribute to the growth of Pfiesteria piscicida, the single-celled “fish-eating” organism that’s gotten so much press. To study that possibility, Paerl and Jay Pinckney, assistant research professor, took water samples from the Neuse and isolated them in “mesocosms”–70-liter tanks of water. Then they added different mixes of nutrients to simulate the conditions in the Neuse. They found that excess nitrogen did not result in an immediate increase in pfiesteria counts. Over time, there was a slight increase in pfiesteria, which means that the increased phytoplankton caused by nitrogen enrichment may be a nutrient source for pfiesteria.

Paerl has studied nitrogen loading, or how new nitrogen ends up in rivers, for more than 15 years. Over the past 20 years, nitrogen loading in the Neuse has increased–estimates range from 30 to 50 percent. Point sources (human and industrial wastewater pumped directly into the river) make up only one-third of this loading, Paerl says. As much as 75 percent of it comes from non-point sources, which include runoff from fertilized farmland and lawns as well as atmospheric emissions from animal waste, car exhaust, and industry.

“That makes for a strong argument for controlling non-point-source loading,” Paerl says. “Politically, it’s not the most popular course, because you have to take a hard look at agriculture, energy use, cars, and industrial and urban growth. But we’ve pretty much legislated sewage-treatment plants to the point where we'll gain only small amounts of nutrient reduction from further regulation.”

Runoff from such sources is only part of the problem. Surprisingly, about one-third of the total nitrogen going into the Neuse, according to Paerl’s estimates, comes from the atmosphere. That figure might seem high. But, Paerl says, “The numbers we're finding in North Carolina are pretty much the norm, if you compare them to data from other East Coast estuaries. The number’s large because we’re downwind of a lot of sources of atmospheric nitrogen–agricultural, industrial, and fossil fuel emissions.”

Nitrogen gets into the air from, say, the exhaust from your car. The gases in exhaust, called “NOX” (nitrogen oxides), can dissolve in water or become attached to particles in pollen or dust. Either way, they’ll come back down in rain or in dry precipitation, called “dryfall.” The ammonia gas emitted from animal waste gets into the water much the same way. After this gas comes back down in rain or dryfall, the nitrogen it contains is available to algae in the water.

“Depending on wind direction and speed, the nitrogen can come down in the next backyard, or it can come down hundreds of miles downwind,” Paerl says. This process is called atmospheric deposition.

North Carolina has passed a law requiring a 30 percent reduction in nitrogen put into the river by humans. That goal is only the beginning, says Leuttich, associate professor of marine sciences. “The idea of reducing nutrient input by 30 percent is an easy one,” he says. “Implementing it is difficult. And it's hard to even tell if you're achieving that goal.”

Also, no one is sure what long-term effect that reduction will have on water quality. We can’t wait, though, until we have the perfect solution, Luettich says. By trying to achieve a 30-percent reduction, “we’re conducting a grand experiment” he says. “So we want to make sure that we’re monitoring how the system is responding so we can take advantage of this experiment.”

That’s one reason why Luettich, Paerl, and others from North Carolina universities, corporations, and organizations started the Neuse River Estuary Modeling and Monitoring project (MODMON). The team collects data about the chemical and physical characteristics of the water and bottom sediment in the estuary, between New Bern and the mouth of the Neuse. For instance, team members go out weekly to 17 locations in the middle of the river to measure oxygen and nutrient levels, salinity, temperature, and algal density and growth. The data are regularly posted to the MODMON web site <www.marine.unc.edu/modmon>, so anyone can follow the health of the river.

Carolina researchers use the data to find patterns. Some MODMON data will also be fed into an ambitious long-term modeling project that involves scientists from the Environmental Protection Agency, Carolina, N.C. State, and the state's division of water quality.

While MODMON is only a year and a half old, the extensive monitoring is beginning to show some patterns. The data confirms the idea that the health of fish and other animals in the estuary is closely related to oxygen levels. “This makes perfect sense,” Luettich says. “Fish don't hang out where there's low oxygen.” The same holds true for crabs, worms, and other invertebrates that live near or in the bottom sediment.

MODMON data also show that circulation patterns of the water quickly respond to strong winds or other weather. Measurements indicate that when there is hypoxic water near a bank, as little as six hours later, that water can “slosh” to the other side of the bank. This fact strengthens a hypothesis about how fish kills may happen. Saltier water that’s low in oxygen tends to settle to the bottom of the estuary, while fresher, higher-oxygen water stays on top. Scientists have speculated that when this situation occurs, and a strong wind comes along, the wind can slosh the low-oxygen water up from the bottom, against the bank.

“If there’s fish hanging out by the bank, they can get trapped by that low-oxygen water,” Luettich says. Fish will swim away from this hypoxic water if they can. But if a large wave of bad water sloshes in quickly, then fish may not know which way to swim, and the lack of oxygen can overwhelm them.

The variability of circulation also makes it hard to determine the exact cause of fish kills, Luettich says. By the time scientists get to a kill site to make measurements, the low-oxygen water may be long gone.

These pieces of information help, Luet-tich says, but they’re just pieces. “It takes a long-term commitment to develop a model of a system like the Neuse, which has so much year-to-year variability, just because of weather.” And once we begin to reduce nutrient loading, we may not see immediate effects. Nitrogen already in the river recirculates many times before it leaves the system. “The bottom sediments are a big bag of stored nutrients,” Luettich says.

In the meantime, researchers will keep tracking the patterns of health and sickness in the river. It looks like the story of the Neuse will be a long one.

The Many Faces of Pfiesteria

Pfiesteria, the one-celled organism that has been linked to open sores on fish and to fish kills in North Carolina’s waters, has a complex life cycle–24 different forms. But it seems to have as many lives in the newspapers as it does in the water. William Roper, dean of the School of Public Health and chair of a scientific panel that studied health risks of exposure to fish-kill waters, says that pfiesteria has been called everything from a “terrible plague” to a “harmless organism.”

On that range of opinions, the task force ended up taking a view somewhere in the middle. In its final report, submitted in June 1998, the task force concluded that it appears that pfiesteria has had some human health effects. But they found that, in the general population, there was no evidence of widespread, chronic adverse health effects, Roper says. But he stresses that it’s an issue that needs further study. “I believe that pfiesteria has caused problems. It’s just that we don't have clear evidence of it.”

A series of follow-up studies will look for that evidence. David Savitz, chair of epidemiology, and Christine Moe, assistant-professor of epidemiology, are leading these studies of human health problems from exposure to fish-kill water.

“Many of the previous studies were done under tremendous pressure to find an answer quickly,” Savitz says. As a result, the studies were small, including only a handful of subjects–about 20 or so. “The numbers were really inadequate to address the question,” Savitz says. For the new study, researchers are recruiting 100 to 150 North Carolinians, mostly fishermen, and equal numbers in Virginia and Maryland.

Also, Moe and Savitz’s team will have time to approach the study more systematically. Previous studies often relied on subjects already experiencing health problems. “People came forward saying, `I’ve been exposed, and I’m sick,’” and they became the study subjects, Savitz says. This time, researchers will measure the baseline health of fishermen and others who work in North Carolina’s estuaries, which are prone to fish kills. Changes in the health of the workers will be monitored as fish kills occur.

The extra time will also allow researchers to refine methods, develop questions, and conduct pilot tests. “All of these things make a substantial difference,” Savitz says.

Even if the researchers find that fish-kill waters have adverse health effects, it will be hard to tell whether or not they’re caused specifically by pfiesteria, Savitz says. “It’s very hard to isolate pfiesteria from other organisms that may be related to fish kills.” The researchers will, however, determine if any health effects are occurring in places where pfiesteria counts are high, using data from the state’s periodic monitoring of the organism.

“Even if this study doesn’t answer all the questions, we’ll know a lot more than we know now,” Savitz says.