Chlorophyll Criteria

Interstate Commission on the Potomac River Basin

Chlorophyll is the green pigment found within the cells of algae and plants. It is common to use chlorophyll as an indicator of phytoplankton biomass in surface waters of large rivers, lakes, estuaries, and oceans.  The partners of the Chesapeake Bay Program established narrative chlorophyll criteria for the entire Chesapeake Bay in 2003.  Virginia and the District of Columbia took the additional step of establishing numeric criteria for specific tidal waters.

In 2011, Virginia Department of Environmental Quality (VADEQ) initiated a review of the scientific basis of their numeric chlorophyll a criteria applied to James River tidal waters.  ICPRB staff, Claire Buchanan, was a member of the study’s Scientific Advisory Panel.  One of her contributions was a report summarizing some of the longer-term data analyses and findings for phytoplankton and chlorophyll that have relevance to Chesapeake Bay as a whole, including the tidal James River.  The report derives, in a logical progression, numeric chlorophyll a thresholds that are protective of Chesapeake Bay’s designated uses. The progression begins with programmatic goals expressed in Chesapeake Bay Program agreements and state water quality standards, and builds on the narrative standards, principal ecological concepts, and empirical evidence.

Click here to download the report, From Programmatic Goals to Criteria for Chlorophyll a

Chlorophyll Criteria

Excerpts from Chesapeake Bay Program Agreements and Virginia Water Quality Standards