Increased Atmospheric Nitrogen In North Atlantic Ocean Basin May Be Stimulating Algal Blooms

The report is authored by Hans Paerl, North Carolina Sea Grant research scientist, and Kenan professor of marine and environmental sciences at the University of North Carolina at Chapel Hill Institute of Marine Sciences. Paerl co-wrote the report with David Whitall, a University of North Carolina at Chapel Hill graduate student.

In the study, scientists found that atmospheric nitrogen accounted for 46 to 57 percent of the total externally supplied or new nitrogen deposited in the nitrogen-sensitive North Atlantic Ocean Basin. The increase can be attributed to the growing agricultural, urban and industrial emissions of nitrogen oxides, ammonia and possibly organic nitrogen.

"The study is significant because it is reconfirms that atmospheric nitrogen has been found to be a regional and global source of pollution," said Paerl. "We also found a strong spatial linkage between water in areas with high amounts of atmospheric nitrogen and in places where there has been documented increases in harmful algae blooms. This is critical as we are only beginning to understand the importance of links between human-induced pollution of coastal oceans and harmful algal bloom expansion."

Paerl was one of the first environmental scientists to identify atmospheric nitrogen as a possible pollutant issue in the marine environment, publishing early research results in the journal Nature (Vol. 316:747-749) in 1985.

When algae blooms decompose on an ocean or river bottom, they use up oxygen in the water. If waters become anoxic - having no dissolved oxygen - then the fish and shellfish can die. Certain toxic or inedible bloom species can alter food webs on which all commercial and sportfishing species rely.

In North Carolina, researchers found that increased atmospheric nitrogen in coastal waters reflects changing land use and human activities. One of the most prominent land-use changes since the late 1970s has been the rapidly growing swine and poultry industry in the Mid-Atlantic coastal plain, said Paerl. This has been accompanied by production of animal wastes and an increase in atmospheric nitrogen from storage and land application. Nitrogen volatilizes as ammonia from hog waste, lagoons and crop sprays. These ammonia emissions travel downwind and are ultimately deposited in nitrogen-sensitive waters.

"Ammonia is the most preferred source of nitrogen for many algae species, including harmful forms," said Paerl. "We are closely examining the linkage between enhanced ammonia deposition and the potential for harmful algae bloom expansion."

In Western European coastal regions that are downwind of agricultural, industrial and urban emissions, the increase in atmospheric nitrogen also was found to contribute to algae blooms in the Baltic Sea and North Sea.

Sea Grant researchers also found that a significant amount of the new nitrogen is being directly deposited on ocean surfaces, bypassing estuarine processes that filter runoff. "This makes the nitrogen a more direct source for coastal algae, including harmful algae blooms," said Paerl.

Expanding urbanization and agricultural and industrial activities associated with coastal population growth will make atmospheric deposition an ever-important source of new nitrogen, stimulating eutrophication - the process of nutrient-enhancement that triggers algae growth -- in coastal waters, said Paerl.

Sea Grant is a network of 29 university-based programs involving more than 300 institutions nationwide in research, education and the transfer of technology regarding coastal, marine and Great Lake issues. Sea Grant is supported by the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) in partnership with the states and private industry.