M6 AM Suspended and Bedded Sediments and Nutrients: Exposure-response Relationships
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 324-326

(BAT-1117-745611) Derivation of Chesapeake Bay Water Clarity and Underwater Bay Grasses Acreage Criteria as the Means for Managing Suspended Sediments.

Batiuk, R¹, ¹ U.S. Environmental Protection Agency, Annapolis, Maryland, USA

ABSTRACT- Underwater bay grass beds in the Chesapeake Bay create rich animal habitats that support the growth of diverse fish and invertebrate populations. In order to restore these critical habitats and food sources, enough light must penetrate the shallow waters to support the survival and growth of diverse, healthy underwater bay grass communities. EPA and its Chesapeake Bay Program partners derived and published Chesapeake Bay water clarity criteria to establish the minimum level of light penetration required to support the survival, growth and restoration of 185,000 acres of underwater bay grasses to shallow water habitats. Using a worldwide literature synthesis, an evaluation of Chesapeake Bay-specific field study findings, as well as model simulation and diagnostic tools, Chesapeake Bay-specific water clarity criteria were derived for low and higher salinity habitats. The water clarity criteria, applied only during the bay grass growing seasons, are presented in terms of the percent ambient light at the water surface extending through the water column and the equivalent Secchi depth by application depth. Application depths from 0.5 to 2 meters, required in order to apply and determine attainment of the water clarity criteria, were established for the more than 70 segments across the mainstem Bay and tidal tributaries. The combined set of water clarity criteria and underwater bay grass restoration acreages were used by the Bay Program partners to establish and allocation caps of nutrient and sediment loads from 40 sub-watersheds making up the 64,000 square mile, six-state watershed. Water quality standards regulations in Maryland, Virginia, Delaware and the District of Columbia now contain these criteria and restoration acreages.

Key words: Chesapeake Bay, Water clarity criteria, Minimum light requirements, Underwater grasses