the wet season there appears to be little utilization of nutrients within the estuary, chlorophyll a levels 
are low, and the dissolved oxygen concentrations are high. Because of the high degree of ocean 
influence on water quality parameters that occur in Zone 1 during the dry season and strong tidal 
flushing, a first priority would be the establishment of criteria for Zone 2. An additional justification 
for this prioritization is the potential difficulties in sustaining the data collection needed to differentiate 
natural from anthropogenic nutrient inputs in Zone 1. We suggest that priority for monitoring for 
compliance with any proposed nutrient criterion in the Yaquina Estuary be for Zone 2 in the dry 
season. This is the most likely region and time period where anthropogenic nutrient effects would be 
expressed. 
EPA (2001) summarized that a “Recognized Unique Excellent Condition” estuary would have 
a watershed that is unimpacted with “very little human development, is distant from the influence of 
local population centers, adjacent land uses are undisturbed, and is outside of major atmospheric 
deposition of nitrogen.” With the exception of “adjacent land uses are undisturbed” the Yaquina 
watershed meets all of these conditions. Additionally, from a nutrient (and land use) standpoint we 
believe that the Yaquina watershed is undisturbed compared to many other systems in the U.S., even 
though extensive silviculture occurs in the watershed. 
Following the recommendations in U.S. EPA (2001), median values are the suggested criteria 
for estuaries in “Recognized Unique Excellent Condition” (Table 13.1). The assessment of seagrass 
light requirements in Chapter 8 and the Seagrass Stress-Response Model demonstration in Chapter 12 
indicate that the median percentiles for the water clarity criterion in both Zones would be protective of 
the existing Z. marina habitat in the Yaquina Estuary. The dry season median light attenuation values 
(Table 13.1) for Yaquina Estuary are comparable to water clarity criteria for the protection of 
Z. marina habitat in other estuaries, including Chesapeake Bay, Long Island Sound, and Peconic Bay. 
Since the existing State of Oregon dissolved oxygen criterion is based on a review of physiological 
requirements of biota and appears to be adequately protective of the designated uses, we would 
recommend that the DO criterion remain at this level. 
The present Oregon chlorophyll a criterion is determined as a 3-month average. If the 3-month 
average chlorophyll a levels within the Yaquina Estuary were to approach the present criterion, 
significant trophic shifts in the estuary would be likely. Thus, the current chlorophyll a criterion may 
not prevent some impacts on designated use. A more conservative criterion would be the adoption of 
the medians for chlorophyll a within both Zones 1 and 2 (Table 13.1). 
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