Acid rain has a disproportionate impact on coastal waters

September 07, 2007

The release of sulfur and nitrogen into the atmosphere by power plants and agricultural activities plays a minor role in making the ocean more acidic on a global scale, but the impact is greatly amplified in the shallower waters of the coastal ocean, according to 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. 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; a printed version will be issued later this month.

"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."

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 em9/7/2007issions 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.

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.
-end-


Woods Hole Oceanographic Institution

Related Ocean Acidification Articles from Brightsurf:

For red abalone, resisting ocean acidification starts with mom
Red abalone mothers from California's North Coast give their offspring an energy boost when they're born that helps them better withstand ocean acidification compared to their captive, farmed counterparts, according to a study from the Bodega Marine Laboratory at the University of California, Davis.

Ocean warming and acidification effects on calcareous phytoplankton communities
A new study led by researchers from the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB) warns that the negative effects of rapid ocean warming on planktonic communities will be exacerbated by ocean acidification.

Sentinels of ocean acidification impacts survived Earth's last mass extinction
Two groups of tiny, delicate marine organisms, sea butterflies and sea angels, were found to be surprisingly resilient--having survived dramatic global climate change and Earth's most recent mass extinction event 66 million years ago, according to research published this week in the Proceedings of the National Academy of Sciences.

Great Barrier Reef 'glue' at risk from ocean acidification
Scientists have suspected that increasing ocean acidity would weaken and thin the structures underpinning tropical reefs.

Ocean acidification causing coral 'osteoporosis' on iconic reefs
Scientists have long suspected that ocean acidification is affecting corals' ability to build their skeletons, but it has been challenging to isolate its effect from that of simultaneous warming ocean temperatures, which also influence coral growth.

Arctic Ocean acidification worse than previously expected
Arctic Ocean acidification worse than previously expected.

Protecting bays from ocean acidification
As oceans absorb more man-made carbon dioxide from the air, a process of ocean acidification occurs that can have a negative impact on marine life.

Ocean acidification prediction now possible years in advance
CU Boulder researchers have developed a method that could enable scientists to accurately forecast ocean acidity up to five years in advance.

Ocean acidification impacts oysters' memory of environmental stress
Researchers from the University of Washington School of Aquatic and Fishery Sciences have discovered that ocean acidification impacts the ability of some oysters to pass down 'memories' of environmental trauma to their offspring.

Coral 'helper' stays robust under ocean acidification
A type of algae crucial to the survival of coral reefs may be able to resist the impacts of ocean acidification caused by climate change.

Read More: Ocean Acidification News and Ocean Acidification Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.