Our analysis suggests that the 25 th percentile and median criteria are protective of seagrass in both 
Zones 1 and 2 in the Yaquina Estuary (Table 12.2). Simulations using median kd and DIN values 
project that eelgrass maintains its current depth distribution. The present depth distribution of eelgrass 
in Zone 1 (ocean dominated lower bay) is deeper than in Zone 2 (upper bay) due to greater light 
penetration. The 25 quartile simulations show that the seagrass permanent bed in Zone 1 might be 
extended from the present depth of 2 m to 3 m (below MLLW), but the depth limit in the upper bay 
would not change. Adoption of the 25 th percentile criteria would potentially expand seagrass habitat 
by 38% and 41% in Zones 1 and 2, respectively, relative to the median case. The 75 th percentile 
simulations predict a loss of 48% of habitat in Zone 2 relative to the median case. Most of the change 
occurs at the lower margin since the upper margin was fixed at 0.2 m above MLLW. While these 
changes in seagrass habitat are large in Yaquina Estuary, larger changes might be expected in 
shallower bays, while smaller changes might be expected in systems with steep bathymetric gradients. 
Dry season median Rvalues in the Yaquina Estuary (Table 12.1) are comparable to criteria that 
are currently being used in several other systems including Peconic Bay, NY, Long Island Sound, CT 
and Chesapeake Bay (Table 12.3). The criteria from the other systems are based on the requirements 
for restoration of Z. marina; therefore they may be more restrictive than those required for maintaining 
an existing eelgrass bed (EEA Inc., 1999). The Zone 2 median kj values were similar to the criteria 
values for the restoration of seagrass to depths of 1 m below mean low water (MLW) in Chesapeake 
Bay (Table 12.3). The DIN criteria used by other studies are generally lower than the median values 
observed in the Yaquina Estuary (Table 12.1). DIN values from the 25 th percentile in our study were 
comparable to the concentrations for Chesapeake Bay (Table 12.3). The proposed DIN criteria for 
Long Island Sound and Peconic Bay are much lower than observed DIN levels in the Yaquina Estuary, 
illustrating the importance of regional nutrient criteria. As discussed in Section 3.2, nutrient loading to 
Oregon estuaries is highly dynamic and naturally large as a result of coastal upwelling and alder 
dominated forests. 
95 
