Carbon dioxide (CO2) released into the oceans as a result of water pollution by nutrients - a major source of this greenhouse gas that gets little public attention - is enhancing the unwanted changes in ocean acidity due to atmospheric increases in CO2.

The changes may already be impacting commercial fish and shellfish populations, according to new data and model predictions published in ACS's journal, Environmental Science and Technology.

William G. Sunda and Wei-Jun Cai point out that atmospheric levels of CO2, the main greenhouse gas, have increased by about 40 percent since the Industrial Revolution due to the burning of fossil fuels and land-use changes.

The oceans absorb about one-third of that CO2, which results in acidification from the formation of carbonic acid. However, pollution of ocean water with nutrient runoff from fertilizer, human and animal waste, and other sources also is adding CO2 via the biological breakdown of organic matter formed during algal blooms, which also depletes oxygen from the water.

Sunda and Cai developed a computer model to project the likely consequences of ocean acidification from this process both currently and with future increases in atmospheric CO2. The model predicted that this process will interact synergistically with the acidification of seawater from rising atmospheric CO2 in seawater at intermediate to higher temperatures.

Together, the two ocean processes are predicted to substantially increase the acidity of ocean waters, enough to potentially impact commercial fisheries in coastal regions receiving nutrient inputs, such as the northern Gulf of Mexico and Baltic Sea. Clams, oysters, scallops and mussels could be the most heavily impacted, the report indicates.