1. Introduction 
1.1 Purpose of This Case Study 
The Office of Science and Technology (OST), Office of Water, U.S. EPA provides 
guidance to the States and tribes for developing nutrient criteria for estuarine and coastal waters. 
The Office of Research and Development, National Health and Environmental Effects 
Laboratory (NHEERL) has been conducting research to support improvements to the scientific 
basis for estuarine nutrient criteria for over 5 years under the NHEERL Aquatic Stressors 
Research Program. Parallel research efforts have been on going at the Western (WED), Gulf 
(GED) and Atlantic Ecology Divisions (AED). To support the OST criteria effort, NHEERL 
scientists have synthesized the research results of field sampling, trend analyses, and modeling 
approaches to produce nutrient criteria case studies for Yaquina Estuary, OR and Pensacola Bay, 
FL. Each case study describes one or more approaches that may be used for establishing nutrient 
criteria and offers specific recommendations for the particular system. Here we describe a 
recommended approach for developing nutrient criteria values for the Yaquina Estuary. 
1.2 Nutrient Criteria Objective 
The Nutrient Criteria Technical Guidance Manual: Estuarine and Coastal Marine Waters 
(U.S. EPA, 2001) provides a detailed summary description of the nutrient criteria development 
process in Section 1.4 of the manual. This guidance defines two objectives for establishment of 
numeric nutrient criteria: 
To reduce the anthropogenic component of nutrient overenrichment to levels that restore 
beneficial uses (i.e. described as designated uses by the CWA), or to prevent nutrient 
pollution in the first place. 
Quantitative, long term data on the status of eutrophication in most Oregon estuarine systems is 
limited (Bricker et al., 1999). The EPA National Coastal Assessment (U.S. EPA, 2004a) 
sampled Oregon estuaries for a variety of water quality indicators in 1999-2000, and concluded 
that there was little evidence of eutrophication effects in Oregon estuaries. Additional qualitative 
and quantitative assessments of Oregon estuaries by WED generally support the conclusions of 
the NCA report, but also suggest that in limited regions under certain circumstances, water 
quality problems may arise. Thus, the principle objective in developing nutrient criteria for the 
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