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SCDHS Contact: Lori Benincasa, 516/853-3009




Groundwater Flow, Different Kinds of Nitrogen Seen as Key Players

UPTON, NY -- A precarious balance between two kinds of nitrogen may be the long-sought trigger for the devastating brown tides that have plagued Long Island's bays and decimated its shellfish harvest since 1985.

And the finger on the trigger may be year-to-year variations in groundwater flow that carries nitrogen from land slowly to the bays variations that are influenced by the force of regional climate change.

That new idea is being published in the peer-reviewed journal Global Change Biology by scientists from the U.S. Department of Energy's Brookhaven National Laboratory (BNL) and the Suffolk County Department of Health Services (SCDHS). The scientists presented their results at the New York Sea Grant's Brown Tide Symposium today in Westhampton Beach.

Brown tide takes its name from the color of the water when an algae called Aureococcus anophagefferens "blooms," or reproduces in vast numbers. The cause has been a mystery since the first brown tide clouded the waters of several major bays along the eastern U.S. coast in 1985, nearly wiping out Long Island's $2 million shellfish industry.

Scientists have blamed many culprits for causing brown tide over the years, including too much or too little nitrogen, or salinity, and trace elements, but no explanation has proven all-encompassing. The authors now believe that it is the balance between two very different forms of nitrogen that is the key to the mystery.

According to their paper, inorganic nitrogen carried to the bays by groundwater in a wet year feeds the growth of algae other than A. anophagefferens. Over the subsequent year, it is converted to organic nitrogen through the decay of plants and algae. If there is relatively little inorganic nitrogen delivered during that second year, the imbalance of nitrogen supply may create ideal conditions for a Brown Tide. The scientists also suggest that population growth and fertilizer use on land may amplify the effect, by increasing the inorganic nitrogen levels in the bays during wet years.

"This is perhaps the simplest scenario that fits in with all that scientists already have learned about brown tide," said Julie LaRoche, the paper's lead author. And, she added, it means that brown tides may even be predictable.

LaRoche and her colleagues say that large year-to-year shifts in rainfall patterns caused equally large changes in the amount of groundwater and therefore inorganic nitrogen that entered the bays in the 1980s and 90s. The result was that the supply of the two forms of nitrogen got out of balance, creating opportunities for the brown tide algae to bloom.

"The brown tides consistently occurred in relatively dry years when the groundwater flow to the bays was low and the organic nitrogen levels were quite high," said Doug Wallace of BNL. "Low groundwater flow to the Bay means low inorganic nitrogen input. It also means higher salinity, which is another factor associated with brown tides."

"Many people have long suspected that specific forms of nitrogen caused brown tide," said Robert Nuzzi of SCDHS. "Others considered climatological factors to be important. Finally, we have a plausible hypothesis which ties both factors together."

It was 11 years of data collected by Nuzzi's staff that led the scientists to formulate their ideas. Every week since the first brown tide 12 years ago, the team has tested water in Flanders Bay, the Peconic Bay and Gardiners Bay for the presence of A. anophagefferens, and recorded the temperature, salinity, and other factors. Those data were combined with the U.S. Geological Survey's information on groundwater levels in local wells, information that relates to the flow of groundwater to the bays.

"Without Suffolk County's remarkable effort and the Geological Survey's data, it just wouldn't have been possible to figure this out," said Wallace. He added that Suffolk County and BNL have gone even further in their brown tide research, entering a $100,000 cooperative venture to place monitoring buoys in the Peconic Bay that will collect continuous information on brown tide conditions.

Groundwater is estimated to carry much more nitrogen to the bays than any other external source, but its slow flow rate about a foot per day means that it may take decades to reach the open water.
So, the scientists speculate, higher nitrogen input to groundwater from activity on land during the boom years of the 1950s, 60s and early 70s may have started to affect the Peconic Bay strongly during the 1980s. And the unusual weather patterns of the 1980s may have compounded the effect.

"It's as if the Bay's algae population was being fertilized through the groundwater in wet years. And in others, the fertilizer just wasn't there, and the vegetation that died as a result decomposed to provide organic nitrogen to feed a brown tide," said LaRoche. But she also urged caution until further studies are performed. "Obviously we think we're on the right track, but there are certainly things we don't understand," she said.

The researchers think their ideas may apply to similar coastal areas throughout the world, where "nuisance" algae, some with toxic effects, have become much more prevalent over the past 20 years.

The paper's authors are BNL's LaRoche, Wallace, and Kevin Wyman and Paul Falkowski, and SCDHS's Nuzzi and Robert Waters.

Brookhaven National Laboratory carries out basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. BNL is operated by Associated Universities, Inc., a nonprofit research management organization, under contract with the U.S. Department of Energy.

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