Among the many threats to water quality posed by human activities is the burning of fossil fuels, which releases carbon dioxide into the atmosphere. The resulting increase in atmospheric carbon dioxide levels has caused global warming and other aspects of climate change. In addition, about 25% of human-generated carbon dioxide is absorbed by the oceans. In spite of the huge volume of water in the oceans, scientists worry that the absorption of so much carbon dioxide will harm marine ecosystems.
Recent data have shown that such fears are well founded. When carbon dioxide dissolves in seawater, it reacts with water to form carbonic acid, which lowers ocean pH. This process, known as ocean acidification, alters the delicate balance of conditions for life in the oceans. Based on measurements of carbon dioxide levels in air bubbles trapped in ice over thousands of years, scientists calculate that the pH of the oceans is 0.1 pH unit lower now than at any time in the past 420,000 years. Recent studies predict that it will drop another 0.3–0.5 pH unit by the end of this century.
As seawater acidifies, the extra hydrogen ions combine with carbonate ions to form bicarbonate ions, thereby reducing the carbonate ion concentration. Scientists predict that ocean acidification will cause the carbonate ion concentration to decrease by 40% by the year 2100. This is of great concern because carbonate ions are required for calcification, the production of calcium carbonate by many marine organisms, including reef-building corals and animals that build shells. Coral reefs are sensitive ecosystems that act as havens for a great diversity of marine life. The disappearance of coral reef ecosystems would be a tragic loss of biological diversity.
If there is any reason for optimism about the future quality of water resources on our planet, it is that we have made progress in learning about the delicate chemical balances in oceans, lakes, and rivers. Continued progress can come only from the actions of informed individuals, like yourselves, who are concerned about environmental quality. This requires understanding the crucial role that water plays in the suitability of the environment for continued life on Earth.
Urry, Lisa A.. Campbell Biology (p. 53). Pearson Education. Kindle Edition.