1.4 Oregon Estuarine Water Quality Criteria 
Water quality criteria standards are developed to protect beneficial uses. The State of 
Oregon presently has numeric water quality criteria for chlorophyll a and dissolved oxygen for 
estuarine waters (Table 1.2). The dissolved oxygen (DO) criterion for estuarine waters is 
primarily based on the freshwater literature and on salmon and trout requirements (ODEQ, 
1995). This DO criterion is relatively high compared to DO criterion for other estuaries, such as 
the Chesapeake Bay (U.S. EPA, 2003). In addition to the criteria in Table 1.2, the state wide 
narrative criteria states that: 
“where a less stringent natural condition of a water of the State exceeds the numeric 
criteria ”... “the natural condition supersedes the numeric criteria and becomes the 
standard for that water body. ” 
In the narrative criteria, the natural condition refers to non-anthropogenic conditions. A review 
of the DO criterion (ODEQ, 1995) found that the 6.5 mg T 1 may be difficult to achieve in Oregon 
estuaries during the summer due to natural background conditions. If it is not achievable due to 
natural background conditions, then the background conditions become the criteria. 
Table 1.2 Selected water quality criteria for Oregon estuaries. 
Parameter 
Estuarine Criterion 
Water Quality Limited Determination 
Chlorophyll a 
15 Mg r 1 
Average based on minimum of 3 samples collected 
over any 3 consecutive months at a minimum of one 
representative location exceeds criterion 1 
Dissolved Oxygen 
6.5 mg l 1 
Greater than 10% of samples exceed the criterion and 
a minimum of at least 2 exceedances of the criterion 
for the time period of interest. A minimum of 5 
representative data points per site collected on 
separate days per applicable time period. Daily 
means of continuous data represents 1 data point. 2 
Note: Criterion applies to river and estuaries; ^Estuarine waters defined as those with 
conductivity > 200 pS cm' 1 for dissolved oxygen criterion. Other dissolved oxygen 
criterion applies to freshwater region. 
1.5 Summary of Yaquina Case Study Approach 
In Chapter 2, we provide a description of the watershed and estuary, including a 
description of landuse in the watershed, and a brief history of anthropogenic activities in the 
estuary and watershed. Chapter 3 presents a summary of the nitrogen inputs to Yaquina Estuary 
with discussion of the seasonality and magnitude of natural and anthropogenic sources. A 
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