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ASSESSING WATER CLARITY AS A COMPONENT OF WATER QUALITY IN GULF OF MEXICO ESTUARIES
Citation:
Smith, L M., V D. Engle, AND J K. Summers. ASSESSING WATER CLARITY AS A COMPONENT OF WATER QUALITY IN GULF OF MEXICO ESTUARIES. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 115:291-305, (2006).
Impact/Purpose:
to use water clarity as a water quality indicator for integrated assessments
Description:
The U.S. Environmental Protection Agency Environmental Monitoring and Assessment Program (EMAP) uses water clarity as a water quality indicator for integrated assessments. After the publication of the first National Coastal Condition Report, the national water clarity reference value of 10% of ambient surface light at 1 meter depth was reevaluated and modified to reflect expected differences in regional light conditions. These regional differences range from naturally turbid estuaries like those found in Mississippi and Louisiana areas to clear water estuaries expected to support extensive beds of submerged aquatic vegetation in, for example, Florida and Tampa Bays. For the second National Coastal Condition Report, water clarity was assessed based on regional reference values. Not all states collected light meter data at 1 m; however, all states reported secchi depth. Different regional water clarity reference values and data collection methods necessitated the development of a water clarity index based on light attenuation coefficients (k). This index incorporates regional reference conditions and is interchangeable with secchi depth and percent light transmission calculated from light meter measurements. Evaluation of the water clarity index shows that k values based on transmissivity at 1 m can be estimated from secchi depth measurements and successfully used as a surrogate for transmissivity calculated from light meter data. An approach for assessing water clarity in Gulf of Mexico estuaries using light meter data and secchi depth is presented.