3. Description of Sources/Sinks of Nutrients 
3.1 Background 
In most estuaries, the major sources of nitrogen are atmospheric deposition, agricultural 
nitrogen fixation, fertilizer runoff, animal feeding operations runoff, and in heavily populated 
areas point source inputs associated with wastewater treatment facilities (WWTF) (Driscoll et al., 
2003; Howarth et al., 2002; Boyer et al., 2002). For many PNW estuaries (with the exception of 
Puget Sound), there is relatively low population density in the watersheds and low atmospheric 
nitrogen deposition. The watersheds are predominantly forested, resulting in low nitrogen inputs 
associated with fertilizer and agriculture nitrogen fixation. Upwelling provides a major source of 
nutrients to estuaries adjacent to coastal upwelling regions, such as the PNW (e.g., Hickey and 
Banas, 2003 and Brown and Ozretich, in review). Low intensity landuse and coastal upwelling 
result in a significant difference in dominant sources of nutrients to PNW estuaries compared to 
estuaries elsewhere in the U.S. 
In a recent review, Tappin (2002) found that the input of nitrogen to temperate and tropical 
estuaries from the ocean is poorly quantified. It is important to quantify the contribution of 
oceanic input to nutrient loading in order to determine background conditions for estuaries that 
are adjacent to upwelling regions and to distinguish natural variability from anthropogenic 
inputs. We also do not know how susceptible estuaries subjected to large oceanic inputs of 
nutrients (dissolved inorganic nitrogen and phosphorous) are to future changes in anthropogenic 
inputs of nutrients. Addressing issues associated with ocean input of nutrients is critical in the 
process of developing nutrient criteria for estuaries in the PNW region. 
3.2 Nitrogen Loading to Yaquina Estuary 
Brown and Ozretich (in review) compared the sources of nutrients to Yaquina Estuary 
during the wet and dry seasons (Table 3.1). There are large seasonal differences in the sources 
of nitrogen to the estuary. During the wet season, riverine sources dominate, while during the 
dry season oceanic nitrogen inputs associated with coastal upwelling dominate. In the dry 
season, benthic flux of dissolved inorganic nitrogen (DIN= NO 2 + NO 3 +NH 4 ) from the 
sediments into the water column is the second largest source of DIN. Atmospheric deposition of 
inorganic nitrogen along the central Oregon coast is among the lowest in the United States. 
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