Average annual deposition during 1980-2002 was 0.6 kg N ha ' 1 y ' 1 (NADP, 2003). Atmospheric 
deposition of nitrogen is a minor component of nutrient input to Yaquina Estuary with direct 
deposition on the estuary only representing 0.05% of the nitrogen input to the estuary. 
Atmospheric deposition on the watershed is a small source ( 8 %) compared to the watershed 
input associated with nitrogen-fixing red alder trees in the watershed (Brown and Ozretich, in 
review). Annual input of nitrogen from WWTF effluent is estimated to be 0.4% of the total 
nitrogen input to the estuary. A NOAA study of estuarine susceptibility to nutrients (Quinn et 
al., 1991) estimated point source loading to Yaquina Estuary as about an order of magnitude 
higher than our estimates. 
3.2.1 Watershed 
There is approximately an order of magnitude difference in the 30-year average daily 
riverine nitrogen input to Yaquina Estuary between the wet and dry seasons. In addition, there 
are considerable interannual differences in riverine nitrogen input, with wet season riverine 
nitrogen input varying from 6.5 x 10 4 mol N d ' 1 to 5.2 x 10 5 mol N d 1 , and dry season riverine 
nitrogen input ranging from 1.1 x 10 4 mol N d _1 to 6.3 x 10 4 mol N d ' 1 (Brown and Ozretich, in 
review). During the wet season, riverine input is the largest source of DIN to the estuary, 
contributing approximately 78% of the input, while 91% of the annual riverine nitrogen input is 
delivered during the wet season. Our estimates of riverine nitrogen loading (Table 3.1) are 
similar to Quinn et al. (1991) whose estimate of non-point loadings are 7% higher than our 
estimate of annual riverine loading. Sigleo and Frick (2007) estimated that the annual riverine 
nitrate (NO 3 ) input to Yaquina varied from 2.4 x 10 5 mol N d ' 1 to 5.2 x 10 4 mol N d ' 1 during a 
drought year. 
Oregon Coast Range streams have high NO 3 concentrations relative to other forested 
watersheds in the PNW (Compton et al., 2003; Wigington et al., 1998). Wigington et al. (1998) 
hypothesized that forest vegetation, in particular the presence of red alder, is the primary factor 
determining stream N0 3 levels in the Oregon Coast Range. Red alder is a native tree species in 
the PNW that colonizes areas disturbed by fires, logging and landslides. Red alder have 
symbiotic N 2 fixing bacteria that can fix 50-200 kg N ha ' 1 y ' 1 in pure stands (Binkley et al., 
1994). Compton et al. (2003) found a significant relationship between alder cover and stream 
NO 3 concentration in the Salmon River watershed, which is about 45 km north of Yaquina 
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