Scientific Approach 
Research on SAV survival and production has generally focused on a few "key” parameters (e.g., 
light, nutrients), and much is known about the basic light requirements of SAV. Nutrients 
primarily affect SAV through their effects on water quality and the associated effects on light 
availability caused by increasing algal biomass (pelagic and epiphytic). Light availability is 
generally considered to be the major factor related to SAV survival (e.g., Kenworthy and Haunert 
1991, Tomasko and Lapointe 1991, Fourqurean and Zieman 1991, Dennison et al. 1993, 
Stevenson et al. 1993, Dunton 1994) and depth of distribution (Dennison 1987, Dawes and 
Tomasko 1988, Duarte 1991). However, recent work is beginning to suggest that a more holistic 
approach may help delineate additional fectors and improve our understanding of the relationship 
between nutrients and SAV loss (Koch 2001, Kaldy et al. 2002). In addition to understanding the 
requirements of SAV, we must also understand the interactions of nutrients and the physical, 
chemical, and biological factors that control accumulation of phytoplankton biomass in our 
receiving waters. This is similar to research needed to understand the relationship between 
nutrients and hypoxia (project 1); however, there are some differences in the factors associated 
with accumulation of biomass versus the increase in production associated with hypoxia. 
The approach will be consistent with the general critical path stated above. Essentially, the main 
components for this research are: 
1. Data gathering, literature review, and compilation of scientific literature (including existing 
information on SAV models for coastal systems) will focus on SAV-nutrient relationships. 
Where existing nutrient-SAV community data are available, this will include the compilation and 
statistical analysis of data. Over the last 30 years, a large body of literature has been published 
with regard to seagrass and other SAV. These publications should provide strong guidelines for 
directing EPA research. As part of this step, we plan to develop a report on the basic 
requirements (e.g., light, salinity, sediment characteristics) of three rooted aquatic seagrasses 
(Thalassia, Halodule, and Zoster a) which together represent a large fraction of the SAV found in 
estuarine/marine systems along the coast of the U.S. Our research on SAV loss-nutrient load 
relationships will not be limited to these three seagrasses and will include freshwater and 
brackish rooted SAV as well. 
2. Develop conceptual models of how SAV communities and nutrients interact with various 
environmental parameters to result in decreased survival or production in this important habitat. 
These models may be regionally specific because of the inherent differences; however, we will 
seek to make them as broadly applicable as possible. Our current conceptual model of how 
nutrients are involved in SAV loss suggests that increased nutrients leading to increased algal 
biomass accumulation is the basis for this pathway. The most likely factors affecting algal 
biomass accumulation are flushing rates, grazing rates, turbidity, climatic conditions, and water 
depth. We realize that excess nutrients also can cause nitrate toxicity, and increase sediment 
sulfide concentrations and/or toxicity. 
3. Propose a classification scheme for coastal receiving waters that groups these waters 
according to their sensitivity to SAV loss in response to excess nutrients. Evaluate and modify 
existing models in order to develop nutrient-SAV loss responses. Classification parameters will 
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