Article pubs.acs.org/est An Approach to Developing Numeric Water Quality Criteria for Coastal Waters Using the SeaWiFS Satellite Data Record Blake A. Schaeffer,1,* James D. Hagy,1 Robyn N. Conmy,1 John C. Lehrter,1 and Richard P. Stumpf2 1U.S. EPA National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, 1 Sabine Island Drive, Gulf Breeze, Florida 32561, United States 2NOAA, National Ocean Service, Center for Coastal Monitoring and Assessment, 1305 East-West Highway, N/SCI1, Silver Spring, Maryland 20910, United States *S Supporting Information ABSTRACT: Human activities on land increase nutrient loads to coastal waters, which can increase phytoplankton production and biomass and associated ecological impacts. Numeric nutrient water quality standards are needed to protect coastal waters from eutrophication impacts. The Environmental Protection Agency determined that numeric nutrient criteria were necessary to protect designated uses of Florida’s waters. The objective of this study was to evaluate a reference condition approach for developing numeric water quality criteria for coastal waters, using data from Florida. Florida’s coastal waters have not been monitored comprehensively via field sampling to support numeric criteria development. However, satellite remote sensing had the potential to provide adequate data. Spatial and temporal measures of SeaWiFS OC4 chlorophyll-a (ChlRS-a, mg m−3) were resolved across Florida’s coastal waters between 1997 and 2010 and compared with in situ measure- ments. Statistical distributions of ChlRS-a were evaluated to determine a quantitative reference baseline. A binomial approach was implemented to consider how new data could be assessed against the criteria. The proposed satellite remote sensing approach to derive numeric criteria may be generally applicable to other coastal waters. ■ INTRODUCTION Extensive modification of landscapes associated with increased human population, land development, and agricultural activities contributes to increased delivery of nitrogen and phosphorus to streams, rivers, estuaries, and ultimately to coastal waters.1 Ecological impacts associated with anthropogenic nutrient enrichment are well documented for coastal ecosystems and include increased phytoplankton production and biomass, harmful algal blooms, decreased water clarity, degradation of submerged aquatic vegetation habitats, and hypoxia.2−4 The Clean Water Act (CWA) requires states to identify designated uses of their waters and when necessary develop science-based water quality criteria to ensure protection of the designated uses. In 2009, the U.S. Environmental Protection Agency (EPA) determined that numeric criteria were needed for Florida waters to protect against impairment of designated uses caused by nutrient pollution. Numeric water quality criteria are concentrations or levels of a pollutant that, if achieved, provide an expectation that designated uses will be supported. EPA established a national strategy for development of numeric criteria calling total nitrogen (TN) and total This article not subject to U.S. Copyright. Published 2011 by the American Chemical Society 916 phosphorus (TP) causal variables and chlorophyll-a a nutrient- related response variable. In this work, we evaluate a reference condition approach for numeric criteria development that uses data from satellite remote sensing. We illustrate the approach using data for Florida coastal waters, which are marine waters up to 3 nautical miles (NM) from shore, but excluding waters within semi- enclosed basins, which are defined to be estuaries. These waters tend to be fully open to the Atlantic Ocean or Gulf of Mexico. A reference condition approach involves computing criteria based on water quality present in a water body that can be interpreted as supporting, or not impairing, the designated uses. The reference condition could be based on data collected in the past, when the water body was determined to be minimally impacted by nitrogen or phosphorus pollution (historical reference condition) or from a similar water body that was determined to be minimally impacted by nitrogen or Received: April 25, 2011 Revised: December 7, 2011 Accepted: December 19, 2011 Published: December 19, 2011 dx.doi.org/10.1021/es2014105 | Environ. Sci. Technol. 2012, 46, 916−922