6.2 Percentile Approach for Nitrogen and Phosphorous 
There were significant differences in median DIN and PO4 values 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). The dry season DIN concentrations observed for Yaquina Estuary 
(Zones 1 and 2) were significantly higher than those observed in the NCA data set both with and 
without the Columbia included (Table 6.3, Dunn’s method for pairwise comparison, p<0.05); however, 
there was not a significant difference between dry season DIN levels in the Yaquina Estuary (Zones 1 
and 2) and those observed in the Classification data set (Table 6.3). The PO 4 levels were 
significantly higher in the Yaquina Estuary (Zones 1 and 2) than those observed in the Classification 
and NCA data sets (Table 6.4, Dunn’s method for pairwise comparisons, p<0.05). The higher DIN and 
PO 4 3 levels in Zone 1 in the Yaquina Estuary as compared to the NCA data set is probably an artifact 
of sampling (both time of sampling and differences in the number of samples). In Zone 1, water 
column nutrients are dependent upon ocean conditions at the time of sampling. Inspection of the 
sampling dates during the 1999 NCA field effort, reveals that 82% of the estuaries were sampled 
during a time period of low nutrient conditions in the coastal ocean (determined using flood tide water 
temperature at Yaquina Estuary and a relationship generated between flood tide water temperature and 
NO3 + NO2 , for details see Lee et al., 2006). 
Zone 2 dry season DIN levels in the Yaquina Estuary are comparable to values for streams 
measured in Level III Ecoregion No. 1 - Coast Range (summer median NO3 + NO2 = 12 pM; U.S. 
3- 
EPA, 2000). The PO4 levels in Yaquina Estuary, particularly during the dry season and in Zone 1, 
are higher than Level III Ecoregion No. 1 - Coast Range values for streams (median = 0.28- 0.60 pM; 
3- 
U.S. EPA, 2000), due to the input of PO 4 from oceanic sources. Wet season DIN concentrations in 
Zone 2 of Yaquina Estuary are similar to wet season NO3 observed in Oregon Coast Range streams 
(median NO3 = 56 pM; Wigington et al., 1998) and streams data for Level III Ecoregion No. 1 - Coast 
Range (winter median NO 3 + N0 2 of 37 pM; U.S. EPA, 2000). Higher P0 4 3 levels in Zone 1 
compared to Zone 2 are present in the NCA and classification data sets, demonstrating that oceanic 
3 - 3 - 
input of P0 4 occurs at a regional scale. The DIN and P0 4 levels in Oregon estuaries would be 
considered to be medium levels using criteria from Bricker et al. (2003); however, based on analysis of 
sources (see Section 3.2) we believe that the high DIN and P0 4 3 levels are associated with natural 
48 
