Acidity levels in the Bay could harm clam and oyster production.

Research published last month in the journal Nature Communications showed that acidification is already apparent in the bay. The team that measured acidity across the bay, led by the University of Delaware marine science professor Wei-Jun Cai, found a zone of increasing acidity at depths of about 30 to 50 feet across the Chesapeake. While surface waters hover around the pH norm of 8.2, the deeper waters registered almost one point lower — nearly 10 times more acidic.

The Chesapeake Bay can absorb carbon dioxide from the atmosphere. In turn, that increases the acidity of the water, making it harder for oysters and clams to grow shells and stay alive.

The global effects of carbon dioxide emissions add to the problem of dead zones of low or no oxygen. The zones are created when nitrogen and phosphorus runoff from farms, lawns and sewage fertilize large algae blooms. Microbes strip oxygen from the water to decompose the blooms when they die, and release more carbon dioxide in the process.

The problem is worsened when organic matter is decomposed in water that is already stripped of oxygen — the bacteria use up other compounds in the water that produce an acidic chemical, hydrogen sulfide. Hydrogen sulfide is what makes the muck around the bay smell like rotten eggs.

The bay, and other waterways struggling to reduce nutrient loads, are especially vulnerable as the pH of waters around the globe decline.

Atmospheric and oceanic carbon dioxide (CO2) concentrations have been rising during the past century due to anthropogenic CO2 emissions (combustion of fossil fuels). The oceans have absorbed nearly half of the anthropogenically-produced CO2 during the past century1, causing changes in marine carbonate chemistry and reduction in oceanic pH, also called ocean acidification (OA). Average open ocean pH is about 8.2 and current models predicting the degree of ocean acidification will reduce pH by 0.3 to 0.5 by the year 2100 and possibly by 0.8 to 1.4 by 2300, depending on the CO2 emission scenario.

Researchers are calling for more resources to be allocated for measuring and understanding acidification similar to the way state and federal agencies have tried to limit pollution to protect crabs, oysters, marshes and underwater grasses.

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Wayne Creed

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