9. Water Clarity {kj) and Turbidity as Water Quality Response Measures 
9.1 Seasonal and Zonal Patterns in Water Clarity and Turbidity 
A turbidity maximum occurs about 15 km from the mouth of the Yaquina Estuary (Figure 9.1). 
The water is relatively clear throughout the year in the lower estuary due to the input of ocean water, 
which is evident in the low turbidities and light attenuations near the mouth (0-5 km; Figures 9.1 and 
9.2). Turbidity tends to decrease upriver of the turbidity maximum (Figure 9.1). There is a significant 
increase in light attenuation with distance from the mouth of the estuary during both the wet and dry 
seasons (Figure 9.2). In situ light attenuation measured at fixed stations up estuary from the turbidity 
maximum at 16 and 19 km from the mouth was generally greater than for fixed sites at 4 and 9 km 
from the mouth (Figure 9.3). This difference is not as clearly seen in the turbidity data set (Figure 9.1). 
There was not a significant difference in dry and wet season total suspended solids (TSS) with 
median values of 7.8 and 8.9 mg f 1 , respectively (Zones 1 and 2 combined; Mann Whitney Rank Sum, 
p> 0.05). TSS levels in Zone 2 (Median =11.7 mg F, n = 119) were significantly higher than those in 
Zone 1 (Median = 6.5 mg f 1 , n = 158; Mann Whitney Rank Sum, p<0.001). Light attenuation is 
positively correlated with turbidity (r = 0.70, n = 1400), but not with chlorophyll a. 
Figure 9.1. Spatial variation in turbidity during wet and dry seasons (1998-2006). 
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