Puget Sound's Case of Acid Reflux Disease Will Get Worse

The New York Times seems delighted to dispel any remaining myths about the untouched natural beauty of Washington state. Just this week readers have learned that there's three times the amount of plutonium waste at Hanford as "thought," and that the Puget Sound's pH level is declining in part due to ocean acidification and the water is growing more corrosive. (Thanks. We'll be expecting a make-up "36 Hours in Seattle," soon.)

The Seattle Times goes straight to the pH-decline bottom line: the impact on the Puget Sound shellfish industry.

The Taylor Shellfish hatchery on Hood Canal's Dabob Bay had its first good year in several in 2009, but company spokesman Bill Dewey said he suspects that's merely because the winds cooperated, preventing acidified seawater from entering the relatively stable bay.

The company recently installed sophisticated pH monitors at its hatchery to determine when it's best to draw water off the surface, from way down deep—or not at all.

In an earlier story, from January this year, the Seattle Times looked at the cause-and-effects of ocean acidification in general. The world's oceans act as a carbon dioxide sink, claiming excess CO2 from the atmosphere, but CO2 dissolved in water creates a weak acid solution. It turns out that shellfish larvae, for one, are very sensitive to changes in pH.

The new study on the Puget Sound's ocean-acidification intake represents the work of researchers with NOAA, the University of Washington, and the state's Department of Ecology. (It's published in the latest issue of Estuarine, Coastal and Shelf Science.) The researchers make it clear that the Sound is struggling mightily with the human activity around it--the toxic pollution and "nutrient-rich" flows that are channeled into it, both killing off life and promoting algae blooms that...also kill off life.

However, the influence of carbon dioxide is not trivial, and it is only going to increase for the foreseeable future. Currently, the researchers estimate, ocean acidification is responsible for 24 to 49 percent of the pH decrease they measured in the deep waters of the Hood Canal sub-basin (compared to estimates of pre-industrial values.

Since 1850, atmospheric CO2 has risen from 280 parts per million to 387 ppm--it would be higher but during that same time, the oceans have absorbed about 30 percent of CO2 emissions. The resulting "ocean acidification" refers not just to the decrease in pH of 0.1 in surface waters, a 30 percent increase in acidity, but also the "concentration of carbonate ion, and the saturation states of biominerals aragonite and calcite," per the study's authors.

That last is why the waters are termed "corrosive"--when carbonate biomineral saturation falls below the saturation point, shells and coral give up those biominerals.

Again, ocean-wide, we've managed a drop of 0.1 in pH since about 1850 (from 8.2 to 8.1), and the results have been remarkable. In Puget Sound main basin, cruises found pHs of 7.73 in deep water in winter, and 7.77 in summer. Hood Canal gave results of 7.56 (winter) and 7.39 (summer).

A Seaglider (UW Applied Physics photo)

But "[b]y the end of this century, ocean pH is expected to decline another 0.3-0.4 pH," note the study authors. "These acidified, oxygen-depleted waters have the potential for entering Puget Sound via the Juan de Fuca submarine canyon in the summer and fall months," in seasonal upwellings. At this point, ocean acidification could account for 49 to 82 percent of the Sound pH decrease in waters below 40 meters.

To track this, NOAA and the University of Washington's Applied Physics Laboratory are launching a water-chemistry monitoring buoy 15 miles of the coast out by La Push, reports the Seattlepi.com, and a remote-control mini-sub called a Seaglider to roam the Sound, taking measurements of its own.