|
�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.�
In addition to acidification, excess nitrogen inputs from the
atmosphere promote increased growth of phytoplankton and other marine
plants which, in turn, may cause more frequent harmful algal blooms
and eutrophication (the creation of oxygen-depleted �dead zones�) in
some parts of the ocean.
Doney collaborated on the project 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.
�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.
|
Image 1: Acid Rain Has
a Disproportionate Impact on Coastal Waters |
|
|
|
Maps depict the model-estimated atmospheric
deposition rates of carbon, nitrogen, and sulfur; alkalinity; and
potential alkalinity to the ocean caused by human activity
relative to conditions before the Industrial Age began. (Scott
Doney et al, from Proceedings of the National Academy of Sciences). |
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 (since it
does not remain in the air for long), 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.
The most heavily affected areas tend to be downwind of power plants (particularly
coal-fired plants) and predominantly on the eastern edges of North
America, Europe, and south and east of Asia.
|
Image 2: Acid Rain Has
a Disproportionate Impact on Coastal Waters |
|
 |
|
Perturbation maps of simulated surface water pH,
dissolved inorganic carbon, and total alkalinity trends and air�sea
CO2 flux due to anthropogenic atmospheric nitrogen and
sulfur deposition. (Scott Doney et al, Proceedings of the National
Academy of Sciences) |
Seawater is slightly basic (pH usually between 7.5 and 8.4), but the
ocean surface is already 0.1 pH units lower than it was before the
Industrial Revolution. Previous research by Doney and others has
suggested that the ocean will become another 0.3 to 0.4 pH units lower
by the end of the century, which translates to a 100 to 150 percent
increase in acidity.
Funding for this research was provided by the National Science
Foundation, the National Aeronautics and Space Administration, and the
National Oceanic and Atmospheric Administration.
Woods Hole Oceanographic Institution is a private, independent
organization in Falmouth, Mass., dedicated to marine research,
engineering, and higher education. Established in 1930 on a
recommendation from the National Academy of Sciences, its primary
mission is to understand the oceans and their interaction with the
Earth as a whole, and to communicate a basic understanding of the
ocean's role in the changing global environment.
|
