Objectives 
To define nutrient load-DO response relationships for coastal receiving waters that will be used 
by the States and authorized Tribes to aid in the development of nutrient-related WQC and 
TMDLs. 
Scientific Approach 
Low DO in coastal receiving waters is a symptom of eutrophication. Therefore, controlling the 
effects of low DO is not accomplished by directly regulating DO but by regulating nutrients and 
oxygen demanding wastes. 
The ultimate product of this research effort is to provide the scientific basis to develop dissolved 
oxygen based nutrient criteria. The critical path to this product is: 
Step 1: Mine and assess existing information on DO response to excess nutrients for coastal 
receiving waters and minimum oxygen requirements of commercially and ecologically 
important organisms. 
Step 2: Develop conceptual model of how different systems manifest low DO in response to 
excess nutrients. 
Step 3: Propose a classification scheme for coastal receiving waters that groups these waters 
according to their sensitivity to DO depletion in response to excess nutrients. 
Step 4: Develop a common approach across Divisions. Select methods, parameters, and 
measurement endpoints for low DO response to excess nutrients so that data and 
models are interchangeable across Divisions and regions. 
Step 5: Test the proposed classification scheme to provide the scientific basis for development 
of nutrient criteria (or TMDLs) based on nutrient load-DO response relationships for 
different classes of receiving waters. 
Excessive nutrient loading to an estuary/receiving water stimulates primary production (i.e., 
phytoplanktonic, macroalgal). This production, together with allochthonous (labile) organic 
carbon, sinks to the bottom waters/benthos resulting in respiratory oxygen demand (mostly 
through microbial decomposition) that exceeds oxygen supply. This leads to hypoxia or anoxia 
in the bottom waters, which in turn lead to fish avoidance, fish kills, and mortality of sessile 
organisms such as worms and shellfish. Low oxygen also changes the oxidative properties of the 
sediments such that organic matter accumulates rather than being oxidized. Low oxygen can 
decouple nitrification and denitrification (xocesses in the sediments resulting in increased supply 
of nutrients to overlying waters. In addition, the death or debilitation of shellfish and other 
sensitive sessile organisms can cause changes in the structure and function of benthic habitats. 
For example, after hypoxic conditions dissipate, predators return to feed on vulnerable benthic 
organisms before they can rebound from the stressed conditions; this changes the energy balance 
of the system. 
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