Long-Term Trends of Water Quality and Biotic Metrics in Chesapeake Bay: 1986 to 2008

We analyzed trends in a 23-year period of water quality and biotic data for Chesapeake Bay. Indicators were used to detect trends of improving and worsening environmental health in 15 regions and 70 segments of the bay and to assess the estuarine ecosystem's responses to reduced nutrient loading from point (i.e., sewage treatment facilities) and nonpoint (e.g., agricultural and urban land use) sources. Despite extensive restoration efforts, ecological health-related water quality (chlorophyll-a, dissolved oxygen, Secchi depth) and biotic (phytoplankton and benthic indices) metrics evaluated herein have generally shown little improvement (submerged aquatic vegetation was an exception), and water clarity and chlorophyll-a have considerably worsened since 1986. Nutrient and sediment inputs from higher-than-average annual flows after 1992 combined with those from highly developed Coastal Plain areas and compromised ecosystem resiliency are important factors responsible for worsening chlorophyll-a and Secchi depth trends in mesohaline and polyhaline zones from 1986 to 2008.

Keywords: Biotic, Chesapeake Bay, Eutrophication, Health indices, Water quality