certainly include dominant SAV species as well as many of the parameters listed in Clean 
Coastal Waters (NRC 2000). Development of a classification scheme for the SAV endpoint will 
be a common effort across all Divisions. Our plan is to use knowledge of species-specific 
requirements and link existing models or develop models that include the effects of light, 
nutrients, and sediment geochemistry on seagrass physiology. We also will link these with 
models of water column chlorophyll a-light absorption/attenuation and nutrient-phytoplankton 
biomass relationships to provide a basis for setting nutrient criteria for coastal receiving waters 
where protection or restoration of SAV is needed. 
4. Develop a common approach across Divisions. Select methods, parameters and measurement 
endpoints for SAV response to excess nutrients so that data and models are interchangeable 
across Divisions and regions. Each Division will provide measures of the key parameters (the 
final list of these parameters will be developed and standardized); however. Division-specific 
research plans may focus on specific parameters or measurements as part of individual research 
projects (e.g., epi-periphyton community metrics, sediment sulfide production/toxicity). This 
phase of the plan development will include interaction with seagrass and SAV specialists in other 
governmental and academic institutions where possible. 
5. The final step of this SAV critical path is a verification that tests the model’s prediction and 
our classification scheme against the actual endpoint response. Once tested and verified, the 
proposed classification scheme and models will provide the scientific basis for development of 
nutrient criteria or TMDLs based on nutrient load-SAV response for different classes of 
receiving waters. 
Modeling Plan 
Our modeling approach for the seagrass endpoint is embodied in a three-tiered scheme that 
couples model development, field monitoring, and direct experiments to test specific hypotheses 
(Figure 6). We plan to use both holistic and mechanistic approaches that integrate the scientific 
literature and conceptualize how seagrasses are affected by stressors by using numoical and 
empirical models that quantify the production and distribution of seagrass. Characterization of a 
suite of parameters (e.g., light, sediment biogeochemistry, nutrients, and exposure during part of 
the tidal cycle) and their inclusion in models and classification schemes will allow EPA to 
determine which stressors are most important controlling factors in a particular region. Stressors 
which will impact SAV vary between regions as a result of variations in climate, industry, 
agriculture, and other land use practices. Consequently, it is critical to include a wide variety of 
parameters that influence all SAV (seagrass and freshwater aquatics), regardless of region. The 
appropriate scientific approach will likewise be an approach combining model development, 
field monitoring, and direct experimentation to test specific hypotheses generated by the models. 
Built into this SAV modeling plan is a set decision point used to determine if the conceptual 
model, the numerical or empirical model, or the field test of the model has been successful. This 
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