The EPA is proposing that measurable limits be established for algae concentrations in the Bay and portions of its tidal tributaries to provide an added layer of protection for the Chesapeake, and reduce the risk of harmful algal blooms.

In September, the EPA Chesapeake Bay Program Office released draft water quality criteria for chlorophyll a—a measure of the amount of algae in the water—which, if adopted by the states, would join water clarity and dissolved oxygen as the key measures that indicate whether areas of the Chesapeake are healthy or “impaired.”

The criteria are open for public comment until Oct. 13. Developed in consultation with representatives from all of the states in the Bay watershed, the criteria are expected to eventually be adopted as legally enforceable water quality standards by jurisdictions bordering tidal waters.

The EPA in 2003 developed Bay-specific dissolved oxygen and water clarity criteria which, when they were adopted by the states, became the driving force for nutrient and sediment reductions throughout the 64,000-square-mile Bay watershed.

At that time, EPA officials developed a “narrative” criteria for chlorophyll a, which said algae concentrations “should not exceed levels that result in ecologically undesirable consequences,” but did not establish what those levels were.

The new criteria, which were developed by a team of scientists from both around the Bay and the nation, draw on decades of water quality monitoring and research to set measurable thresholds for chlorophyll a.

Algae contribute to multiple problems in the Bay. They create blooms that prevent sunlight from reaching underwater grass beds. When algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen. Certain species, in large amounts, can be toxic.

The goal of the proposed criteria is to reduce chlorophyll a levels in the mainstem of the Chesapeake to about the levels that existed in the 1960s, when the Bay was considered relatively healthy compared with today.

In low-salinity areas of the Bay and its tributaries, the proposed criteria also establish limits aimed at reducing the likelihood of harmful algae blooms. The criteria also set chlorophyll a thresholds for shallow water areas to protect water clarity.

The nutrient reductions already under way to address dissolved oxygen and water clarity issues are expected to reduce algae concentrations in most of the Bay and its tidal tributaries to acceptable levels, according to Rich Batiuk, associate director for science with the EPA’s Bay Program Office. “Adoption of the proposed chlorophyll a criteria as state water quality standards is not expected to cause a huge new burden on people responsible for reducing pollutant loads,” he said. “But it is going to tighten up our definition of restored Bay water quality to make sure we are protecting more local tidal water habitats.”

The new criteria will serve as a backup for local areas where the Baywide nutrient reductions may not be enough to resolve local water quality issues. For instance, it may be possible that nutrient reductions that resolve downstream dissolved oxygen problems may not be enough to eliminate harmful algae blooms in some areas farther upstream.

The proposed criteria are included in a draft addendum to the Bay criteria established in 2003. Besides addressing chlorophyll a, the document makes clarifications about how monitoring information will be interpreted, and decisions made, as well as how sections of the Bay are to be added to or removed from the impaired waters list.

The goal, Batiuk said, is to have “a standard operating protocol” so anyone looking at the same information would reach the same decision about whether a section of water is impaired or not. “It adds a transparency that we think is important,” he said. “These standards are driving hundreds of millions of dollars, to billions of dollars of decisions, both close to the waters and a state or two away.”

The documents are available on the internet at www.chesapeakebay.net/baycriteriaaddendum.htm.