Corvallis, Or. : School of Oceanography, Oregon State University
Abstract
The Port of Astoria has proposed to fill a 32.4 hectare inter- and
subtidal area at the mouth of Youngs Bay, Columbia River, Oregon. The
possible effects of this fill on the biota and sedimentation patterns
of this area were studied from 31 August 1975 to 29 February 1976. Part
I, the biological studies, analyzed the quantity of benthic life at the
fill site in comparison to that in the lower 28 miles of the Columbia
River estuary. The sediment textures of benthos samples were analyzed
to determine sediment-fauna relations; salinity-temperature measurements
were made at selected sites. Fish life at the fill site was also sampled
to determine species composition and the relation of fish stomach contents
to benthic life. Studies on sedimentation patterns (based on
dredging records, photographs, and sediment samples taken in Slip 2 of
the port docks) aimed at identifying undesirable sediment deposits
which might occur because of the fill.
The dominant benthic taxa at most stations were amphipods and polychaetes,
although oligochaetes were abundant at some muddy stations.
Amphipod densities in the lower river varied from about 200/m2 in deep
areas to between 5,000 and 50,000/m2 in shallow, fine sediment areas
such as Youngs Bay and extensive shoaling areas. These areas of high
density, which include the fill site, were dominated by the tube-building
amphipod Corophium. Twenty-five species of fish have been captured in
this and previous work in Youngs Bay. Food habit studies have shown
Corophium to be eaten in large quantities by many of these species.
Using density estimates and river bathymetry as guides, it was very
roughly estimated that 0.8 percent of the amphipod standing crop in
the study area (CRM 0-28) occurred at the fill site, which represents
0.09 percent of this area.
Net sediment transport seems to be from the Columbia River into
Youngs Bay, but transport out of Youngs Bay does occur and may contribute
greatly to sediment deposition in Slips 1 and 2. Sediment samples
from Slip 2 were mud, but this changed abruptly to coarse sand at the
slip mouth. This shows that slip sediments arise from suspended fine
mud and not from coarser-grained bed-load sediments. There is little
that can be done to prevent such deposition. The proposed extension
would probably not affect this problem, but might alter the flow of
water around the port. More extensive investigations of circulation
and suspended sediment content should be made
