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Dr. Bill Showers, 919/515-7143 or [email protected]
Sara Frisch, News Services, 919/515-3470 or [email protected]
July 7, 1999
El Nino, La Nina Harming Water Quality Along N.C. Coast
FOR IMMEDIATE RELEASE
In the last decade, swelling human and animal populations have helped load Eastern North Carolina ecosystems with nitrogen, phosphate and other nutrients that can be harmful to air, water and land resources. Now, scientists at North Carolina State University say Mother Nature, and the violent weather patterns she controls, could be at the root of the state's water quality problems.
Marine researchers at NC State say historical data on weather patterns and environmental responses suggest that nutrient loading, algae blooms and fish kills are closely tied to El Nino and La Nina events on the state's Coastal Plain. The intense, inter-annual weather events bring increased amounts of rainfall and high discharge of river water into estuaries in that region.
The team also has identified farming and livestock operations in the middle part of the Neuse River Basin as major sources of nitrogen in estuarine systems miles away on the North Carolina coast. Data analysis shows that nutrient loading is heaviest in the Neuse River's central basin, and that non-point sources are responsible for the majority of nutrients. Non-point nutrient sources can be agriculture, forest, and residential land, while point sources include municipal sewage treatment plants and industrial sites.
"We know that El Nino and La Nina control rainfall in North Carolina, Florida and in Louisiana, along the Gulf Coast and the southeastern coast," says lead researcher Dr. William Showers, associate professor of marine, earth and atmospheric sciences at NC State. "But this is the first time it's ever been correlated with water quality events."
Showers, doctoral student Jon Karr and their team presented their findings at the American Geophysical Union spring meeting earlier this month. Karr's paper, "Nitrogen Isotope Tracing of Eutrophication Sources on a Watershed Scale: Neuse River Basin, North Carolina" was nominated for the best student paper honor at the conference.
The chain of events affecting water quality, Showers says, begins with El Nino Southern Oscillation (ENSO) activity. Shifting winds in the Pacific Ocean cause North Carolina's weather to be controlled by storms coming from the Gulf, instead of from the north. The result is warm, wet winters during El Nino events, and cool, wet springs during the following La Nina events. A major El Nino event in 1972 marked a slight change in the cycle, and since then there have been fewer and less intense La Nina events ñ possibly a sign of global warming, Showers says.
Showers and Karr compared years of ENSO activity to river discharge figures in Eastern North Carolina and found that both El Nino and La Nina events were correlated with high levels of river discharge. The river discharge levels, in turn, were highly correlated to high nutrient fluxes to the estuaries, and to fish kill events in the Neuse River Basin. During heavy rains, rivers push more water into the estuaries, and that water contains more non-point source nitrates ñ compounds that stimulate algae blooms, which can be harmful to fish.
"During periods of high ENSO activity, there are more algal blooms and fish kills," Showers says. "There's lots of river discharge. There's lots of nutrients moving into the estuaries. During periods of low ENSO activity, like the mid-ë90s, there are a low number of fish kills."
He also points to Hurricane Fran as a trigger of more intense nutrient loading on the Coastal Plain. The violent 1996 storm, which cut a path of downed trees across North Carolina into the Piedmont region, occurred outside the ENSO cycle. Showers says there's never been anything like Hurricane Fran in the past 40 years. Following the storm, river discharge measured at Kinston more than doubled, nitrate flux increased, and the number of fish kills remained high.
"Fran put a tremendous amount of nutrients into the estuary and was associated with a lot of fish kills," he says. "It not only flushed all the groundwater out, but it also washed tremendous amounts of debris from the river basin ñ downed trees, leaves and litter ñ into the river."
Another component of Showers' research is identifying the sources and movements of nutrients in groundwater, surface water and rainfall using stable isotope technology. Water samples contain nitrogen compounds of different isotopes, or atomic weights. Previous research has shown that animal wastes, isotopically distinct from other nitrogen sources, constitute the heavier isotope of nitrogen (15N.)
Isotopic tracing of nutrient inputs for the entire Neuse River Basin shows that non-point sources are the most important nutrient-loading sources in the watershed, Showers says. He found low nutrient flux levels in the upper Neuse ñ a predominantly urban area. The middle part of the watershed, sampled at Smithfield, Goldsboro and Kinston, showed the highest concentrations of nutrients. And the nutrient flux dropped down again in the lower basin.
"The point sources are responsible for only about 13 percent of nutrient flux in the basin," Showers says. "The urban sources are about 5 percent. So, most of our nutrients are coming from what we call non-point sources: agricultural lands."
Geographically, that points to the middle and lower parts of the river basin, where populations of swine, turkey and broiler farms have grown tremendously in the last decade.
"When you apply fertilizer or animal waste to cultivated fields, the plants uptake only about 40 to 60 percent of that nitrogen," Showers says. "You then have pools of nitrogen building up underneath the cultivated fields." In the groundwater under animal waste application fields, he has found very high levels of the heavier nitrogen isotope.
Groundwater comprises most of the surface water in Eastern North Carolina, where sandy and loamy soils allow water and sediment to flow easily. In the central and lower parts of the Neuse River Basin, heavy rainfall brought on by ENSO activity picks up nitrogen under the ground and flows into the rivers, and on to the coastal waters. The end result, Showers says, is more nutrient loading in the estuaries, and the risk of harmful algae blooms and fish kills.
Environmentalists and state regulators have been vexed by the cycles of fish kills in Eastern North Carolina. Water quality problems were worsening in the late ë80s to early ë90s, and then in the mid-ë90s, the situation improved, Showers says.
"So we thought we were doing the right thing. And then, Fran hit, and we had a lot of water quality problems. The number of fish kills rose in ë97 and ë98. So does that mean we're doing the wrong thing? We've enacted stricter regulations, we've had more water quality monitoring."
Showers says increased ENSO activity, along with increased agriculture, is driving changes in North Carolina's coastal waters. The correlation of nutrient flux and water quality to ENSO events can explain the five-year to 10-year cycles of algae blooms and fish kills, he says.
In the coming years, meteorologists predict more violent, but less frequent, ENSO-related storms. Showers says that by using these weather patterns to predict rainfall and river discharge, we can adjust land use policies to take better care of our rivers and sounds in the future.
A good plan, Showers says, would include reducing nutrient loading and strengthening barriers ñ wetlands and riparian buffers ñ to be more effective during high-discharge periods. He says farmers and landowners may need to change how they apply animal waste and fertilizer to land as we continue to develop sustainable agricultural practices.
The research team used existing data on fish kills and nutrient flux from the N.C. Department of Environment and Natural Resources, and river discharge data from the U.S. Geological Survey.
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NOTE TO EDITORS: The abstract from Dr. William Showers and Jon Karr's American Geophysical Union meeting presentation follows.
"Nitrogen Isotope Tracing of Eutrophication Sources on a Watershed Scale: Neuse River Basin, North Carolina"
Authors: Jon Karr, Gayle Plaia, Bernard Genna, Dr. Reese Barrick, Dr. William J. Showers; NC State University. Presented at American Geophysical Union, Spring 1999 meeting Published in Eos, Transactions of the American Geophysical Union, Vol. 80, No. 17
ABSTRACT: Increased nitrogen flux to coastal and estuarine ecosystems through atmospheric and groundwater/surface water transport stimulates exogenous or new production that alters the composition of the primary producer phytoplankton communities, and may be linked to the expansion of harmful algae blooms (HABs) and fish kills. We have used the stable isotopes of nitrogen to distinguish between different eutrophication sources and sinks. Animal wastes concentrate the heavier isotope of nitrogen (15N) in liquid wastes (lagoons) and elevated levels of 15N are found in groundwater under animal waste application fields. Nitrogen that is volatilized to the atmosphere from animal waste lagoons concentrates the lighter isotope of nitrogen (14N). These sources are isotopically distinct from chemical fertilizers used in row crop agriculture, and from municipal sewage treatment plant point sources. 15N isotopic tracing of nutrient inputs on a basin-wide scale indicates that non-point s! ources are the most important eutrophication source in these watersheds, and that the nature of non-point sources has changed over the past decade. Over the past 10 years there has been a dramatic increase in the human population as well as in the number of intensive livestock operations (poultry & swine.) Isotope data combined with GIS population data indicate that the isotopic change is associated with intensive livestock operations in the central portion of the basin. Nitrogen inputs to the estuaries are controlled by the links between surface and groundwater. It has been suggested that the sporadic occurrences of fish kills in North Carolina estuaries are linked with heavy spring rains and high river discharge. The long-term control of the connection between the groundwater nutrient pools and surface waters that drain into the estuaries is not well understood. Time domain analysis indicates that interannual weather, precipitation and climate variability on river basin scal! es in eastern North Carolina is linked to the ENSO state. We postulate that long-term links to inter-annual climate variability are key to understanding the coupling between groundwater nutrient pools, nutrient loading into eastern North Carolina estuaries, and fish kills and HABs.
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