State water quality standards consist of numeric criteria that measure a critical parameter and a designated use that applies that criteria. The Bay Program is developing a set of criteria and designated uses to apply in different parts of the Bay and its tidal tributaries.

Designated Uses:

Migratory Spawning & Nursery: designed to protect egg, larval and early juvenile states of shad, striped bass and other anadromous and semi-anadromous fish species. The areas extend from the upper extent of tidal waters to the lower reach of existing spawning and nursery habitats, and from the water surface to the bottom or to the pycnocline where it exists.

Applicable Bay Water Quality Criteria: Dissolved oxygen and chlorophyll a?Migratory spawning/nursery criteria apply Feb. 15 to June 10.

Shallow Water: Designed to protect largemouth bass, speckled sea trout, blue crabs, underwater grass beds and other species that live in shallow areas. The area includes tidal waters to a 2-meter depth, measured from low tide.

Applicable Bay Water Quality Criteria:.Dissolved oxygen, chlorophyll a and water clarity.

Open Water: Designed to protect species such as striped bass, bay anchovy and menhaden living in surface waters throughout the Bay. The area includes tidal waters extending vertically from a 2-meter depth into the water column to the bottom, or to the pycnocline in areas where it exists.

Applicable Bay Water Quality Criteria:"Dissolved oxygen and chlorophyll a.

Deep Water: Designed to protect blue crab, oyster, hardshell clams, spot, croaker and other species that live in deep areas below the pycnocline where oxygen is often in short supply during the summer. The areas include tidal waters below the depth of the pycnocline or, in the absence of a measured pycnocline, below a certain depth that would vary in different parts of the Bay based on geographic conditions.

Applicable Bay Water Quality Criteria: Dissolved oxygen. Deep water criteria apply May through September; open water criteria apply October through April.

Deep Channel: Designed as a refuge for such species as sturgeon, striped bass and blue crabs, which overwinter in deep channel habitats. It covers very deep water located principally in the channels at the lower reaches of major tidal rivers and along the spine of the upper and middle mainstem Bay.

Applicable Bay Water Quality Criteria: Dissolved oxygen. Deep channel criteria apply May through September; open water criteria apply October through April.

 

Criteria

Dissolved Oxygen

Migratory Spawning & Nursery Areas: 6 milligrams per liter averaged over 7 days with a 5 mg/l 1-day minimum mid-May to mid-June.

Shallow Open Water Areas: 5 mg/l as a 30-day average, with a 7-day average of 4 mg/l & a 1-day minimum of 3.5 mg/l

Deep Water Uses: ‚ mg/l as a 30-day average, with a 1-day minimum of 1.7 mg/l. October through April, the shallow open water use criteria applies.

Deep Channel Uses: 1 mg/l May through September, with an absolute minimum of 0.2 mg/l in areas where natural factors, such as stratification and circulation, create deep holes that trap pockets of water that exceed the 1-day minimum. October through April, shallow/open water use criteria would apply

Chlorophyll a

Chlorophyll is the pigment that allows plants (including algae) to convert sunlight into organic compounds. Chlorophyll a is the predominant chlorophyll in algae. Excessive amounts of chlorophyll indicate the presence of harmful blooms. Too little chlorophyll a means there is not enough “fish food” to fuel the food web.

The draft criteria identify different seasonal chlorophyll a concentrations for different shallow water and open water areas of the Bay (and areas with varying degrees of salinity) which represent high-quality algae communities that supply adequate food without causing blooms.

Water clarity

Water clarity criteria are based on the minimum amount of light needed by underwater grasses to survive. In low salinity water, at least 9 percent of the light striking the surface must reach the plant. In high salinity water, at least 15 percent of the light hitting the surface must reach the plant.