7.2 Percentile Approach for Chlorophyll a 
The chlorophyll a levels in Oregon estuaries, including Yaquina Estuary, are relatively low 
with median values of 2 - 5 pg l" 1 (Table 7.1). These chlorophyll a levels would be in the ‘low’ 
category when used as an indicator of eutrophication (Bricker et al., 1999) and in the ‘good’ category 
using the West Coast criteria for water quality parameters from the National Coastal Condition Report 
(US EPA, 2004a). The Oregon chlorophyll a criterion of 15 pg f 1 is exceeded 4% of the time during 
the dry season in Zones 1 and 2. At Elk City (tidal fresh part of the estuary) the 15 pg f 1 criterion is 
exceeded 28% of the time during the dry season (WED unpublished data; collected during 2002 and 
2003). There was a significant difference in median chlorophyll a between the Yaquina (dry season), 
Classification Study, and NCA datasets for both Zones 1 and 2 (Kruskal-Wallis one way ANOVA on 
ranks, p<0.001; Table 7.1). Dry season chlorophyll a levels in both zones of the Yaquina Estuary are 
significantly higher than those found in the other Oregon estuaries sampled in the NCA and 
Classification datasets (Dunn’s method for pairwise comparison, p<0.05). Although chlorophyll a 
levels in the Yaquina Estuary are significantly higher than for the other Oregon estuaries sampled, they 
are Tow’ compared to many other U.S. estuaries (US EPA, 2004a). 
Table 7.1 Percentiles for chlorophyll a (pg l’ 1 ) calculated using Yaquina (1998-2006), 
Classification (2004-2005), and NCA Oregon estuaries (1999-2000) data sets. NCA and 
Classification values are for dry season only, while Yaquina include dry and wet season 
values. 
Data set 
Percentiles for Chlorophyll a (pg l" 1 ) 
Sample Size 
25 th 
50 th 
75 ,h 
Zone 1 
Yaquina 
Dry 
2.2 
3.3 
5.7 
347 
Wet 
0.6 
u 
1.7 
95 
Classification 
1.0 
2.0 
3.8 
68 
NCA 
1.5 
2.1 
3.8 
36 
NCA excluding Columbia 
1.5 
2.0 
3.2 
33 
Zone 2 
Yaquina 
Dry 
3.8 
5.3 
7.9 
229 
Wet 
0.4 
0.9 
2.5 
46 
Classification 
0.8 
1.6 
2.5 
78 
NCA 
2.0 
3.3 
4.9 
89 
NCA excluding Columbia 
1.4 
1.8 
2.6 
27 
52 
