The ecology of eelgrass meadows in the Pacific Northwest: A ...

CHAPTER 6
HUMAN IMPACTS-MANAGEMENT CONSIDERATIONS
With the increasing residential,
recreational, and commercial development
of the shorelines of the nation and the
Pacific Northwest, it is inevitable that
pressure on the shallow water resources of
the area have also increased. In
comparison to the high-density development
in southern California, the Gulf of
Mexico, and in the northeastern United
States, that in the Pacific Northwest
could be termed minimal. Yet demands and
impacts have been made, and they are
increasing. Logging has been an important
feature of the economy since the early
19GB1s. In certain areas of heavy
rainfall and where clearcutting of upland
timber has occurred, siltation has also
occurred. Stout (1976) noted the effects
of siltation in Netarts Bay, Oregon,
coincident with historic logging and
burning of timber in the watershed, but
stated this has intensified since the
1940's when clearcutting and roadbuilding
were initiated. Proctor et al. (1980b)
have documented the extensive maintenance
dredging needed to maintain shipping
channels in several areas and the
suspended silts arising from wood chips
and sawdust in Yaquina Bay.
The extensive land cultivation needed £or
agriculture can lead to siltation in
estuarine areas, with an increase in water
turbidity that leads to decreased eelgrass
growth (Thayer et al. 1975a). The role of
solar radiation passing through the water
column, which controls the productivity,
density, depth limit, and even presence of
eelgrass in an area, and thus the presence
and richness of the ecosystem itself were
discussed earlier in this report.
The increasing human use of northern Puget
Sound is having a drastic impact on the
black brantpresence in Padilla Bay and
other local bays (~eiger 1982). state and
Federal agencies continue to receive an
increasing number of applications in the
northern sound area, particularly for
marina development. One observes an
increasing shoreline development of homes
and even condominiums in some areas.
Continued maintenance of shipping lanes
and logging is presumed necessary for the
economic life of the Pacific Northwest.
It is hoped that this report will aid in
the formulation of policy that will
accommodate those activities while
preserving and protecting the water and
habitat qualities of the eelgrass
resources.
Considering the coastal sediment
stabilization function, the nutrient
exports which enhance oceanic procluckion,
and the value of eelgrass to recreational
and commercial fisheries, it is
worthwhile--even imperative--to consider
preserving the resource.
6.1 DREDGING AND FIUW
Of all the possible impacts, dredging
poses the greatest threat to the seagrass
ecosystem (Thayer et al. 1975a; Zieman
1975; Phillips 1978). Not only are the
plants removed, but the entire physical,
biological, and chemical structure of the
ecosystem is changed. The extent of the
area affected by the dredging depends on
the tidal range, current strength, and
sediment texture in the area.
Sediments raised by dredging can bury
plants away from the site. More
importantly, sediments drastically reduce