Several estuarine classifications have included Yaquina Estuary. Bottom et al. (1979) 
classified Yaquina Estuary as a “Drowned River Valley” and partially mixed estuary. NOAA 
classified Yaquina Estuary as “River Dominated” with “Straits and Terminal Bay.” Quinn et al. 
(1991) classified estuaries along the west coast of the United States based on their susceptibility 
to nutrient pollution. In this study, they classified the Yaquina Estuary as in the high category 
for dissolved concentration potential (DCP) and in the low category for particle retention 
efficiency. They estimated that the nutrient concentration for nitrogen and phosphorous would 
be in the medium class based on DCP and estimates of nutrient loadings. Additionally, Quinn et 
al. (1991) estimated that Yaquina Estuary would require > 20% increase in nutrient loading to 
change the concentration from medium to high class. Burgess et al. (2004) classified estuaries in 
the U.S. based on a statistical cluster analysis of physical and hydrologic factors. They classified 
Yaquina Estuary as a “Medium Area, Low Volume, Shallow and Mixed Salinity” estuary. 
2.5 Conceptual Model for Yaquina Estuary 
Figure 2.7 illustrates some of the major drivers influencing causal (nutrients) and 
response (chlorophyll a, water clarity and dissolved oxygen) variables within the Yaquina 
Estuary, which will be presented in this case study. Nutrient, chlorophyll a , and dissolved 
oxygen conditions in the lower portion of the estuary are strongly influenced by ocean conditions 
due to close coupling between the shelf and the estuary resulting from strong tidal forcing. The 
watershed is primarily forested, and riverine inputs are related to the presence of nitrogen-fixing 
red alder (Alnus rubra) trees in the watershed. Seagrasses occur at shallower depths in the upper 
portions of the estuary than they do in the lower estuary, which we believe is related to increased 
turbidity upriver and the resulting light limitation. Dense macroalgal blooms occur in the lower 
portion of the estuary, but they appear to be fueled by oceanic nitrogen inputs rather than being a 
response to anthropogenic nutrient enrichment. 
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