Acidification of Aquatic Habitats

Compared with the bloods of animals, the waters of most natural aquatic habitats, such as the oceans, are not buffered in a way that would significantly impede a rise in H⁺ concentration caused by addition of acidic materials. Acid rain has been a recognized problem in bodies of freshwater—streams, ponds, and lakes—for many decades. It is often caused by sulfur and nitrogen oxides liberated into the atmosphere by the combustion of fossil fuels. The oxides react with water to form acids, such as sulfuric acid.

Rising atmospheric CO₂ acidifies oceans, leading to chemical reactions that can dissolve calcium carbonate skeletons

Acidification caused by atmospheric CO₂ is a more recently identified challenge. The CO₂ concentration of Earth’s atmosphere has risen from about 300 parts per million (ppm) to about 400 ppm in the past century because of the burning of wood, coal, and petroleum. Because of the principles we have discussed, the CO₂ concentration in the waters of the ocean has increased (see Chapter 22), and this has made the oceans more acidic by about 0.1 pH unit by driving the reaction shown in Equation 24.5 to the right. Animals are not always able to regulate processes that are affected by the environmental acidification. For example, the acidification tends to erode certain types of animal skeletons that are composed of calcium carbonate (e.g., skeletons of reef corals) or to interfere with production of such skeletons. It can also interfere with sensory and developmental processes. Box Extension 24.6 provides references for further reading.

References

Frommel, A. Y., R. Maneja, D. Lowe, A. M. Malzahn, A. J. Geffen, A. Folkvord, U. Piatkowski, T. B. H. Reusch, and C. Clemmesen. 2012. Severe tissue damage in Atlantic cod larvae under increasing ocean acidification. Nature Climate Change 2: 42–46.

Hoegh-Guldberg, O., P. J. Mumby, A. J. Hooten, R. S. Steneck, P. Greenfield, E. Gomez, C. D. Harvell, P. F. Sale, A. J. Edwards, K. Caldeira, N. Knowlton, C. M. Eakin, R. Iglesias-Prieto, N. Muthiga, R. H. Bradbury, A. Dubi, and M. E, Hatziolos. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318: 1737–1742.

Munday, P. L., D. L. Dixson, J. M. Donelson, G. P. Jones, M. S. Pratchett, G. V. Devitsina, and K. B. Døving. 2009. Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proc. Natl. Acad. Sci. U.S.A. 106: 1848–1852.