Table 3.1 Comparison of the magnitude of nitrogen sources during wet and dry seasons for 
Yaquina Estuary, Oregon. Benthic flux measurements not available (NA) for wet season. 
Source 
Wet Season 
Nitrogen Input (mol N d' 1 ) 
Dry Season 
Annual Average 
River 
2.7 x 10 3 
2.5 x 10 4 
1.4 x 10 3 
Ocean 
3.0 x 10 4 
3.7-4.7x I0 5 
2.3 x 10 5 
Wastewater 
1.7 x 10 3 
1.5 x 10 3 
1.6 x 10 3 
Benthic Flux 1 
NA 
4.3 x 10 4 
NA 
Atmospheric Deposition 2 
On Estuary 
2.2 x 10 2 
1.2 x 10 2 
1.7 x 10 2 
On Watershed 
1.1 x 10 4 
6.0 x 10 3 
8.5 x 10 3 
Source: 'DeWitt et al. (2004); 
2 NADP (2003) 
3.2.3 Benthic Processes 
Intertidal and subtidal sediments can be sources and sinks for nutrients and organic 
matter, with the direction and magnitude of fluxes determined by infaunal invertebrates, benthic 
primary producers, and microbial communities living on or in the estuarine benthos. (See 
Appendix A for additional details on benthic processes). 
Five studies of benthic nutrient flux have been conducted in Pacific estuaries north of San 
Francisco, however the reported benthic flux data in four of the studies (i.e., Dollar et al. 1991; 
Garber et al. 1992; Thom et al., 1994; Lamed, 2003) may not accurately estimate estuary-scale 
nutrient fluxes in Yaquina Estuary because they do not account for the presence of thalassinid 
burrowing shrimp. The presence of burrowing shrimp can result in the water inside of the 
benthic flux chamber being exchanged with water outside of the chamber via shrimp burrows 
(e.g., Hughes et al., 2000), which violates the requirement that benthic chambers be closed 
microcosms (Forja and Gomez-Parra, 1998). 
To avoid this problem, DeWitt et al. (2004) inserted 1-m deep core barrels into sediments 
at their study sites, and fit benthic chambers to the tops of the core barrels to isolate water, 
sediments, shrimp and burrows inside the chamber from the outside world. DeWitt et al. (2004) 
demonstrated that DIN efflux was strongly affected by both burrowing shrimp species and 
population density (Appendix A). Integrated over the whole estuary, net DIN efflux for 
intertidal habitats in Yaquina Estuary was 4.3 x 10 4 mol N d~' from the benthos to the water 
column (DeWitt et al., 2004). (Additional details on composition of estimated DIN efflux 
provided in Appendix A) 
11- 
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