Results for 2010-2012 indicated that 12* percent of the Bay was attaining water quality standards for water clarity/underwater bay grasses within 91 tidal water segments containing the shallow water habitat designated use.
Date created: Nov 06 2013 / Download
This map demonstrates the attainment status of those Chesapeake Bay Program monitoring segments that have SAV and/or water clarity standards for the Shallow Water Bay Grasses designated use during the 2010-2012 assessment period.
Clear water is critical to underwater life. Bay grasses need sunlight to grow, and fish need sunlight to see. But what factors cause water clarity to fluctuate? Adam Davis from the Chesapeake Research Consortium explains, and uses a secchi disc to measure water clarity in Spa Creek.
Produced by Matt Rath
Music: “A Moment of Jazz” by Ancelin
This indicator measures progress towards the achievement of water quality standards for water clarity/underwater bay grasses for each 3-year assessment period beginning in 1985. The indicator is fully consistent with how Delaware, the District of Columbia, Maryland, and Virginia currently list their portion of the Bay’s tidal waters, and provides a means for illustrating improvements through time.
* Based on best available data, not including water clarity assessment results from Maryland. The percentage may change after water clarity assessment data for 2010-2012 assessment period become available from Maryland and are incorporated into the calculations. At that time the 2010-2012 status will be revised, if necessary.
Water clarity assessments are only conducted on a biennial basis since the 2006-2008 listing cycle. Furthermore, water clarity assessments are only conducted for a given set of segments throughout the Bay, which rotate every three years. When water clarity assessments are not available for any segment, the attainment of the shallow water bay grasses designated use is assessed using the measured underwater bay grass acres meeting the segment-specific restoration acre goals only. When water clarity assessment data are available the shallow-water bay grasses designated use is considered in attainment if:
Assessment of either measure, or a combination of both, serves as the basis for determining attainment or impairment of the shallow-water bay grasses designated use.
Nutrients, along with sediments, are the primary causes of impairments to the Chesapeake Bay and its tidal tributaries. To meet the objectives of the Clean Water Act, the EPA’s implementing regulations specify that states must adopt criteria that contain sufficient parameters to protect existing and designated uses. In 2003, EPA Region III developed Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity, and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. This was developed in order to achieve and maintain water quality conditions necessary to protect the aquatic living resources of the Chesapeake Bay and its tidal tributaries from the effects of nutrient and sediment pollution. Within the publication, five designated uses were identified and described, that when adequately protected, will ensure the protection of the living resources therein.
The methodology used for the calculation of the indicator considers the achievement or non-achievement of water quality standards for water clarity/underwater bay grasses within 91 tidal water segments containing the shallow water habitat designated use. This indicator uses a surface area-weighted approach, which factors in the relative size of each segment, ensuring we report the best available measure of how much of Bay tidal waters were achieving water quality standards in the applicable designated use areas.
The University of Maryland Center for Environmental Science reports a different water clarity indicator which tracks mid-channel data in all tidal waters and not in relation to Chesapeake Bay water quality standards. The results of that indicator are available at http://ian.umces.edu/ecocheck/report-cards/chesapeake-bay/2012/indicators/water_clarity/ and are updated annually in the Bay Report Card.
Chesapeake Bay Program