Scientists have discovered that the water chemistry in the Hood Canal and the Puget Sound main basin is becoming more "acidified," or corrosive, as the ocean absorbs more carbon dioxide from the atmosphere. These changes could have considerable impacts on the region's shellfish industry over the next several decades.
The study, co-sponsored by NOAA, the University of Washington Applied Physics Laboratory and School of Oceanography (UW), the Washington State Department of Ecology and the U.S. Environmental Protection Agency, was conducted in the winter and summer of 2008 to determine the combined effects of ocean acidification and other natural and human-contributed processes on Puget Sound waters. Annual survey support is typically provided by UW's Puget Sound Regional Synthesis Model Program (PRISM), while EPA provided the ocean survey vessel Bold for the summer survey.
"We observed unusually low pH values in the deep waters of southern Hood Canal," said Richard Feely, Ph.D., director of the Ocean Acidification Program at NOAA's Pacific Marine Environmental Laboratory. "Our calculations suggest that ocean acidification can account for a significant part of the pH decrease in this region."
"This is the first time that the combined impacts of ocean acidification and other natural and human-induced processes have been studied in a large estuary like Puget Sound," says Jan Newton, Ph.D., University of Washington co-author on the study and chief scientist for the winter cruise. "We are concerned that ocean acidification may be contributing to the recent loss of oyster larvae reported by oyster hatcheries in the Pacific Northwest including within Puget Sound."
The research team estimated that ocean acidification accounts for 24-49 percent of the pH decrease in the deep waters of the Hood Canal sub-basin of Puget Sound relative to estimated pre-industrial (before 1850) values. The remaining change in pH between when seawater enters the Sound and when it reaches this deep basin results from the decomposition of organic matter.
Over time, the relative impact of ocean acidification could increase significantly, accounting for 49-82 percent of the pH decrease in Puget Sound subsurface waters (depths greater than 40 meters) for a doubling of atmospheric carbon dioxide, according to the study.
To better understand the effects of ocean acidification on shellfish within Puget Sound, the Puget Sound Partnership, with funds from EPA, has partnered with the Puget Sound Restoration Fund to support UW, NOAA, Pacific Shellfish Institute, Washington Department of Ecology, Taylor Shellfish and Baywater, Inc., to conduct collaborative studies investigating whether or not corrosive seawater is affecting shellfish populations.
The work monitors both water conditions and shellfish larvae, providing high-resolution oceanographic data along with measurements on ocean acidification and larval settlement from two locations where shellfish are growing, Dabob Bay and Totten Inlet.
As part of this study, UW moved one of the existing Oceanic Remote Chemical-optical Analyzer (ORCA) marine monitoring buoys from Hood Canal to Dabob Bay and added surface water carbon dioxide measurements with a NOAA sensor to the existing suite of measurements.
"We simply need more data near the shellfish growing sites in order to evaluate causal relationships," said Allan Devol, Ph.D., UW, an oceanographer and the designer of the ORCA buoy.
The findings are scheduled to appear in the August issue of Estuarine, Coastal, and Shelf Science.
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