concentrations was done as a step-function (Table 12.1). In these model simulations, water column 
DIN was used in nutrient uptake kinetics for the seagrass plant, but does not include indirect nutrient 
effects such as epiphyte, macroalgal or phytoplankton blooms. Additionally, simulations were 
conducted for parameters at a series of depths ranging from 0 m relative to mean lower low water 
(MLLW) down to a maximum depth of 5 m below MLLW in Zone 1 and 0 to 2.5 m below MLLW in 
Zone 2. The expanded depth range in Zone 1 was used because of lower light attenuation in this 
region. Additionally, this range encompasses the known depth distribution of Z. marina in Yaquina 
Estuary and allows for the expansion of the seagrass into deeper waters. 
12.4 Results 
As described above, the individual model simulation runs differed by depth, irradiance 
attenuation and DIN (Table 12.1), and temperature and salinity (Appendix Figure E.2). Temperature 
and salinity were also different between Zones 1 and 2, with a greater range in each variable occurring 
in Zone 2 as a result of seasonal heating and cooling. The model incorporated functions that increased 
photosynthesis and metabolism with temperature. The larger range in water temperature in Zone 2 
affected seagrass physiology, while the relatively stable water temperatures in Zone 1 had a minimal 
impact (Appendix Figure E.2). Salinity had no influence on seagrass biomass or production in Zone 1 
but affected production in Zone 2 during winter months. 
Model results indicated that the median values would maintain the existing distribution of 
seagrass within Yaquina Estuary (Figure 12.1). Current maps indicate that seagrass covers 
approximately 0.97 km' 2 in Zone 1 and 0.013 km' 2 in Zone 2. In Zone 1 (lower estuary), seagrass 
would be protected to a depth of about 2 m below MLLW. The median values are representative of 
present conditions. In Zone 2 (upper estuary), the median criteria would protect seagrass to a depth of 
about 0.5 m below MLLW. Model simulations indicated that criteria based on the 25 th percentile were 
the most protective (Table 12.2), permitting seagrass survival to depth of 3 m below MLLW in Zone 1 
and 1 m below MLLW in Zone 2 (Figure 12.2). In contrast, model simulations using criteria generated 
from the 75 th percentile were the least protective of seagrass (Table 12.2). The 75 th percentile was 
protective of seagrass to about 2 m below MLLW in Zone 1 but, only maintained seagrass at a depth of 
0 m MLLW in Zone 2 (Figure 12.3). Model simulations for each case and zone are provided in 
Appendix Figures E.3-E.8. 
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