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chapter 8\/ 
Refinements to the Chesapeake 
Bay Dissolved Oxygen Criteria 
Assessment Procedures 
BACKGROUND 
In 2003, the EPA published detailed criteria for dissolved oxygen tailored to 
different habitats within the Chesapeake Bay and its tidal tributaries (U.S. EPA 
2003a) (Table IV-1). Oxygen is critical to most forms of life in the Bay; it must be 
available in adequate concentrations to support overall ecosystem health. Minimum 
concentrations of oxygen must be present to support the wide range of species 
requiring protection as well as their various life stages. 
Dissolved oxygen criteria were established for Chesapeake Bay that varied in space 
and time to provide levels of protection for different key species and communities. 
The criteria were also designed around several lengths of time to reflect the varying 
oxygen tolerances for different life stages (e.g., larval, juvenile, adult) and effects 
(e.g., mortality, growth, behavior). Thus, the dissolved oxygen criteria include 
multiple components. Each component includes a target of dissolved oxygen 
concentration, the duration of time over which the concentration is averaged, the 
space (designated-use area) where the criterion applies, and a time (season, month) 
when the criterion applies. 
The dissolved oxygen criteria include 30-day, 7-day, and 1-day means along with an 
instantaneous minimum. Each of these criteria components applies to a specific 
season, such as the migratory spawning nursery period or the summer months (June 
through September) or all-year round. Each also relates to one of four tidal-water 
designated uses, according to the species and biological communities to be protected 
(U.S. EPA 2003a, 2003c). The EPA published, and the states adopted into their water 
quality standards regulations, dissolved oxygen criteria protective of migratory and 
spawning, open-water, deep-water, and deep-channel designated-use habitats (U.S. 
EPA 2003a) (Table IV-1). 
chapter iv 
Refinements to the Chesapeake Bay Dissolved Oxygen Criteria Assessment Procedures 
