Acid rain is affecting the coastal ocean on a disproportionate basis. Click on image for full size (190 Kb) Jupiter Images/National Science Foundation

The release of sulfur and nitrogen into the atmosphere by power plants and agricultural activities--commonly referred to as acid rain--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 oceans, according to new research.

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.

The findings were published this week in the online edition of the journal Proceedings of the National Academy of Sciences .

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. It 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.

"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 scientist at the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Mass. "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, overfishing and climate change."

In addition to acidification, excess nitrogen input from the atmosphere likely promotes the overgrowth of phytoplankton and other marine plants that have caused more frequent harmful algal blooms and eutrophication (including the creation of oxygen-depleted dead zones) in the oceans.

"This analysis provides strong evidence that carbon dioxide is the culprit globally, even though locally, contamination by strong acids may be primarily responsible for increasing seawater acidity," said Donald Rice, director of the National Science Foundation (NSF)'s Chemical Oceanography Program, which co-funded the research with NASA and NOAA.

The research team compiled and analyzed many publicly available data sets on fossil fuel emissions, agricultural runoff and other atmospheric emissions. The scientists built theoretical and computational models of the ocean and atmosphere to simulate where nitrogen and sulfur emissions were likely to have the most impact. They also compared their model results with field observations made by other researchers 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 to the coastal ocean.

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.

Seawater is slightly basic (pH 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 suggests that the ocean will become another 0.3 to 0.4 pH units lower by the end of the century, which translates into a 100 to 150 percent increase in acidity.

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 WHOI.

Text above is courtesy of the National Science Foundation

Acid rain is affecting the coastal oceans much more than the rest of the ocean areas. Click on image for full size (190 Kb) Jupiter Images/National Science Foundation

Acid rain plays a small role in making the world's oceans more acidic. But new research has found that acid rain has a much bigger impact on the coastal sections of the ocean. Acid rain is caused by pollution in the atmosphere from power plants, cars, farming, and ranching.

When coastal areas become more acidic, marine animals such as sea urchins, corals, and certain types of planktons have a hard time creating exoskeletons (their hard outer shells). Because these animals are an important food source for other animals in the ocean, if they don't survive the food chain of the entire ocean ecosystem could be affected.

Scott Doney is a scientist on a team that has been looking into the affects of acid rain on the ocean and coastal areas. "Acid rain isn't just a problem of the land; it's also affecting the ocean," said Scott Doney. He added thar the problems from acid rain are the worst near the coasts. Coastal areas are vunerable because they have already been damaged by pollution, overfishing and climate change.

Also, phytoplankton and other ocean plants become overgrown when there is more acid in the oceans. When this happens, there are more areas of the ocean that don't have enough oxygen in them for plants and animals to live.

When doing their study, the research team built models of the ocean and the atmosphere to see where acid rain will probably have the biggest impact. They compared the results of their model with field observations other scientists made in coastal waters around the United States.

Acid rain is affecting the coastal oceans much more than the rest of the ocean areas. Click on image for full size (190 Kb) Jupiter Images/National Science Foundation

Acid rain is what happens when some types of air pollution is washed out of the sky by rain. Power plants, factories, farms, houses, and cars all put pollution into the atmosphere. Sometimes, this pollution mixes with water in the air to form acids; then when it rains or snows, the acid falls onto land or into water on the Earth.

Some scientists have learned that when acid rain falls into the oceans, it damages the coastal areas of the ocean more then the rest of the ocean.

When coastal areas become more acidic, marine animals such as sea urchins, corals, and certain types of planktons have a hard time creating exoskeletons (their hard outer shells). Because these animals are an important food source for other animals in the ocean, if they don't survive the food chain of the entire ocean ecosystem could be affected.