Benefits of Products 
The benefits of the products will be a reduction in the uncertainty associated with setting SAV 
based nutrient criteria and TMDLs for our nation’s receiving waters. A compendium of 
requirements of important SAV species will provide a convenient reference and a sound basis for 
setting protective limits in coastal receiving waters. Development of a classification scheme will 
aid in setting nutrient criteria in receiving waters where large historical databases are not 
available. An improved understanding of the factors affecting nutrient-SAV loss relationships 
will provide water quality managers with better tools to manage nutrient input to our nations 
waters while protecting these important habitats. 
Project Title 3, Food Web and Community Composition Changes in Response to Nutrient 
Loading in Freshwater and Marine Coastal Systems (Estuaries and Coastal Wetlands) 
Project Coordination and Resources (14 FTEs: AED-3.0, GED-5.0, MED-3.0, WED-3.0) 
Objectives 
The primary objective of food web research is to identify nutrient loading thresholds that cause 
shifts in primary producers and other key components of the food web. A secondary objective is 
to assess the use of food web structure and processes to improve our ability to classify systems 
and to predict changes in response to nutrients that affect hypoxia and SAV. Research will 
require identification of measurement endpoints that are sensitive to nutrient loading and reliably 
forecast adverse effects to assessment endpoints. 
Scientific Approach 
As with the DO and SAV assessment endpoints for nutrient research, we are concerned that 
increased concentrations or changes in ratios or timing of nutrient inputs can adversely affect 
populations of ecologically and commercially important organisms. For food webs, nutrient 
loading-response relationships are not as well understood as for DO and SAV; however, food 
webs may reveal subtle, low threshold responses to nutrient loading that are more sensitive than 
DO or SAV endpoints (Livingston 2000). Changes in patterns of energy flow alter habitats and 
support systems required by important organisms. Variations in nutrient ratios, ccmcentrations, 
or timing of inputs can alter the competitive advantages of primary producers causing the demise 
of species on which important consumers depend. Research investigating the relationships 
between nutrient loading and food webs will focus on identifying thresholds of nutrient loading 
where pathways of energy flow from primary producers to consumers are altered and populations 
of commercially and ecologically organisms are adversely affected. NHEERL research will 
focus on the effects of nutrients on primary producers and subsequent interactions with pelagic 
and benthic communities. Process-oriented research, such as analysis of food web structure via 
stable isotopes will provide basic data for development of nutrient load-response relationships, 
and will provide insight into biological factors controlling primary production and energy flow in 
coastal systems. This research will focus on three critical food web shifts: 1) changes from 
benthic to pelagic basis of production (i.e., SAV or periphyton to phytoplankton), 2) shifts in 
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