Hydrography of the Russian River Estuary - Sonoma County Water ...

Given that the expansion of hypoxia into the inner estuary is excluded from this mass
budget, it is interesting to review Figure 3.41 to see where DO is being lost. While the
near-bottom waters have the lowest DO, these levels are already low at the time of
closure and near-bottom changes in DO are small and occur prior to 15 September.
However, at mid-depth, DO decreases are larger and this mid-depth loss of DO occurs
across a layer that continues to thicken. Presumably this is due to decreasing light
exposure at these elevations as the water level rises and as the days become shorter in
the fall. It thus appears that this mid-depth and near-bottom hypoxia will not be mitigated
by surface oxygenation nor by biochemical processes until the water column
stratification is reduced and vertical mixing can replenish DO at these depths. Thus, the
question of stability addressed in Section 3.4 becomes paramount to the understanding
of the extent, severity and persistence of hypoxia and anoxia in the estuary.
Figure 3.42. Time-series of dissolved oxygen mass from mouth to Sheephouse Creek.
3.5.3 – Sources of error in budgets
Calculation of salt and DO budgets include several sources of error, which are
described here to provide perspective on the error in the estimates of total mass. The
following factors are addressed:
• Section uniformity
• Elevation estimates
• Pycnocline tilt
• Bathymetry resolution
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