Low DO 
Increased nutrient loading to an estuary/receiving water stimulates primary production (largely, 
though not exclusively, phytoplanktonic) and produces excess carbon biomass that sinks to the 
bottom waters/benthos resulting in respiratory oxygen demand that may exceed oxygen supply. 
For this endpoint, our objective is to define relationships between nutrient load and factors 
affecting DO concentration in sensitive portions of receiving water bodies. As part of this effort, 
NHEERL is developing DO requirements to protect indigenous species in various coastal regions 
(North and South Atlantic, Gulf of Mexico, and Pacific). Criteria have been developed for the 
Atlantic coastline between Cape Cod and Cape Hatteras (EPA 2000). Ultimately, this research 
will provide relationships between nutrient inputs and DO concentrations, which will protect 
indigenous species in various coastal regions. 
SA V Loss 
Increased nutrient loading can result in an accumulation of phytoplankton, epiphytic, and 
macroalgal biomass/carbon that shades SAV or alters sediment geochemistry and results in loss 
of areal coverage. For this endpoint, our objectives are to develop, for the nation's coastal 
receiving waters, sufficient understanding of the relationship between SAV loss and nutrient 
loading to provide a sound scientific basis for establishment of nutrient criteria that would protect 
these important habitats from degradation or loss and aid in restoration efforts. This work will 
directly support or interact with the Habitat Alteration (Section 4) and Diagnostics (Section 8) 
research implemoitation plans. 
Shifts in Food Webs 
Changing nutrient loadings (includes increased loading, changes in loading ratios, and changes in 
the mode/timing of delivery) alter species composition of primary producers. Effects of this shift 
are transmitted through the food web, altering the consumer-food web dynamics (carbon or 
energy flow pathway) in receiving waters. The result is a change in primary producers that does 
not support existing food webs (and hence alters the biological integrity of ecosystems) and does 
not sup|X)rt commercially important fish and shellfish production. The objective of food web 
research is to identify nutrient loading thresholds that qause shifts in primary producers and other 
key components of the food web. In addition, we will assess the use of food web structure and 
processes to improve our ability to classify systems and to predict differences in response to 
nutrients that affect hypoxia and SAV. 
This research will require developing classification schemes for each of these endpoints so that 
aquatic systems can be grouped according to their expected responses to nutrient loading, to aid 
in the process of setting nutrient criteria and TMDLs. NRC (2000) recommends that 
classification frameworks be developed that can be generalized to a broader range of features and 
processes than the current classification schemes, which are focused on individual features (i.e., 
flushing or light). NHEERL’s classification efforts will focus on coastal receiving waters 
(including estuaries, near-coastal waters and the Great Lakes). Our classification efforts will 
focus on understanding and linking the influence of physical, chemical, and biological factors to 
the response to nutrients across the Nation’s coastal receiving waters. 
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