Polluted groundwater threatens coral reefs

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Coral reefs already stressed by ocean acidification are particularly vulnerable to polluted groundwater, according to a recent study by USGS geologist Nancy Prouty and colleagues.

Rising atmospheric CO2 is causing a gradual decrease in ocean pH, making it more difficult for corals to grow calcium carbonate skeletons and enhancing rates of dissolution and bioerosion—the breakdown of coral by other organisms. The authors show that polluted groundwater discharging onto coral reefs off west Maui, Hawai‘i, further lowers seawater pH and exposes corals to nitrate concentrations 50 times higher than normal. Such land-based pollution could contribute to the collapse of coastal coral reef ecosystems sooner than predicted just on the basis of ocean acidification. The study was published in the American Geophysical Union (AGU) Journal of Geophysical Research: Oceans, featured on AGU’s GeoSpace blog, and reported by the Honolulu Star-Advertiser and the Associated Press.

CT scans and photographs of coral collected from reef near polluted groundwater seeps. One set shows more erosion than the other
Coral collected from reef near polluted groundwater seeps, A, shows more erosion than coral collected away from seeps, B, in these computerized tomography (CT) images and photographs. cm = centimeter. Location map of the island of Maui, Hawaii shows the study area on the western coast.
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