Coastal Waters very Sensitive to Acid Rain

Coastal Waters very Sensitive to Acid Rain



2007 September -   The release of sulfur 
and nitrogen into the atmosphere by power plants and agriculture plays a 
small role in making the ocean more acidic on a global scale, but the 
impact is amplified in shallow coastal waters, finds new research by 
atmospheric and marine chemists. 
Ocean "acidification" occurs when chemical compounds such as carbon 
dioxide, sulfur, or nitrogen mix with seawater, a process which lowers the 
pH and reduces the storage of carbon. 
"Acid rain isn't just a problem of the land; it's also affecting the 
ocean," said Scott Doney, lead author of the study and a senior scientist 
in the Department of Marine Chemistry and Geochemistry at the Woods Hole 
Oceanographic Institution, WHOI. "That effect is most pronounced near the 
coasts, which are already some of the most heavily affected and vulnerable 
parts of the ocean due to pollution, over-fishing, and climate change." 
The most heavily affected areas tend to be downwind of coal-fired power 
plants and predominantly on the eastern edges of North America, Europe, 
and south and east of Asia, Doney and his team found. 
Ocean acidification hampers the ability of marine organisms such as sea 
urchins, corals, and certain types of plankton to harness calcium 
carbonate for making hard outer shells or "exoskeletons." These organisms 
provide essential food and habitat to other species, so their demise could 
affect entire ocean ecosystems. 
The findings were published this week in the online early edition of the 
"Proceedings of the National Academy of Sciences." 
In addition to acidification, excess nitrogen inputs from the atmosphere 
promote increased growth of phytoplankton and other marine plants. This, 
in turn, may cause more frequent harmful algal blooms and the creation of 
oxygen-depleted dead zones in some parts of the ocean. 
"Most studies have traditionally focused only on fossil fuel emissions and 
the role of carbon dioxide in ocean acidification, which is certainly the 
dominant issue," Doney said. "But no one has really addressed the role of 
acid rain and nitrogen." 
The research team compiled and analyzed many publicly available data sets 
on fossil fuel emissions, agricultural, and other atmospheric emissions. 
They built theoretical and computational models of the ocean and 
atmosphere to simulate where the nitrogen and sulfur emissions were likely 
to have the most impact. They also compared their model results with field 
observations made by other scientists in the coastal waters around the 
United States. 
Farming, livestock husbandry, and the combustion of fossil fuels cause 
excess sulfur dioxide, ammonia, and nitrogen oxides to be released to the 
atmosphere, where they are transformed into nitric acid and sulfuric acid. 
Though much of that acid is deposited on land, some of it can be carried 
in the air all the way to the coastal ocean. 
When nitrogen and sulfur compounds from the atmosphere are mixed into 
coastal waters, the researchers found, the change in water chemistry was 
as much as 10 to 50 percent of the total changes caused by acidification 
from carbon dioxide. 
This rain of chemicals changes the chemistry of seawater, with the 
increase in acidic compounds lowering the pH of the water while reducing 
the capacity of the upper ocean to store carbon. 
A 100 to 150 percent increase in ocean acidity has been predicted by the 
end of this century in previous studies by Doney and others. 
Doney collaborated on this research with Natalie Mahowald, Jean-Francois 
Lamarque, and Phil Rasch of the National Center for Atmospheric Research, 
Richard Feely of the Pacific Marine Environmental Laboratory, Fred 
Mackenzie of the University of Hawaii, and Ivan Lima of the WHOI Marine 
Chemistry and Geochemistry Department. 
Funding for this research was provided by the National Science Foundation, 
the National Aeronautics and Space Administration, and the National 
Oceanic and Atmospheric Administration. 

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