Increasing acidification in coastal waters could compromise the ability of oysters and other marine creatures to form and keep their shells, according to a new study led by UGA researchers.
Their findings were published in the November issue of Nature Geoscience. The researchers determined the combined effects of fertilizer runoff carried by the Mississippi River to the northern Gulf of Mexico and excess atmospheric carbon dioxide from burning fossil fuels result in an unexpected increase in the acidity of Gulf waters.
“Before, scientists only worried about low oxygen in waters along the coast,” said Wei-Jun Cai, a professor of marine sciences in the Franklin College of Arts and Sciences. “Our paper basically says not only do we need to worry about low oxygen, we also need to worry about acidification.”
When plumes of river water rich with nutrients from fertilizer run into coastal waters, phytoplankton thrives. When these algae die, they sink to the sea floor and decompose, releasing carbon dioxide and decreasing the amount of oxygen in the water. The dissolved carbon dioxide forms an acid.
Ocean acidity also increases when excess carbon dioxide released by burning fossil fuels is absorbed from the air at the ocean’s surface. The combination of these two sources of carbon dioxide decreases the ocean’s ability to neutralize acid, increasing acidity beyond what would be expected from the sum of the individual processes.
Cai and his colleagues, including James T. Hollibaugh, Distinguished Research Professor of Marine Sciences, recommend that farmers better manage fertilizer use and that societies limit fossil fuel use.