Ocean Acidification and the Clean Water Act Section 303(d) Program

Ocean acidification (OA) refers to the decrease in the pH and carbonate saturation states of the Earth's oceans caused by the absorption of anthropogenic carbon dioxide (CO2) from the atmosphere. Like climate change, OA is primarily caused by the increasing CO2 concentrations in the atmosphere from anthropogenic fossil fuel emissions. To date, surface ocean waters have exhibited an average pH decrease of 0.1 units with an estimated additional decrease of 0.3–0.4 units predicted to occur by the turn of the 21st century. The absorption of anthropogenic carbon dioxide has resulted in the most drastic shift in ocean chemistry in roughly 800,000 years. These changes in ocean chemistry could negatively impact marine ecosystems, especially those with coral reefs and shellfish (e.g., clams, oysters, crabs) because these species rely on carbonate availability to produce and maintain their calcareous skeletons and shells.Ocean acidification awareness is in its infancy, but attention to this issue is increasing in both the public and private sectors. On November 15, 2010, the US Environmental Protection Agency (US EPA) issued a Memorandum to provide information to assist the Regions and States in preparing and reviewing Integrated Reports related to OA impacts under Sections 303(d), 305(b), and 314 of the CWA as part of a settlement agreement with the Center for Biological Diversity. One of the conditions of the agreement was that EPA would sign a Federal Register (FR) notice requesting comment on how to address OA under the CWA 303(d) program. In addition, EPA agreed to issue a Memorandum by November 15, 2010, describing how EPA will proceed with regard to the interplay between OA and the 303(d) program in light of the responses to the FR notice. This paper summarizes these actions, and presents additional information on assessment methods related to OA that could be useful to States as they move forward to address this important issue.