The Columbia River Estuary provides juvenile and adult salmon critical habitat to allow sufficient time to gradually adjust body chemistry to the demands of a new environment. During this period, which can range from several weeks to several months, salmon use aquatic vegetation and channel structure to hide from predators and take advantage of abundant food supplies created by the interface between river and ocean waters (Groot and Margolis 1991).
Estuaries also allow juveniles an opportunity to achieve the critical growth necessary to survive in the ocean (Wissmar and Simenstad 1988; Neilson and Geen 1986). Juveniles spend days or weeks gradually acclimatizing themselves to increasing concentrations of salts. Adults use estuary areas to readjust body chemistry to a freshwater environment (Simenstad et al. 1982). Migration timing and size of juvenile salmon entering the estuary are key factors affecting stock life histories, maturation and ultimate survival (Reimers 1973; Schluchter and Lichatowich 1977; Groot and Margolis 1991).
Unfortunately, as is the case with tributaries and the mainstem, the Columbia River estuary habitat diversity has been significantly diminished and degraded. Human induced impacts in the last 150 years have substantially affected essential habitat. Reductions in sustained peak flows, and river sediment transport, as well as dredging, filling, diking and channelization of the estuary have had major regional and localized impacts on habitat (Sherwood et al. 1990). For example, target flows for the lower Columbia River and estuary recommended in the NMFS 1995 Biological Opinion for the FCRPS are only one third of average historical peak flow. Bottom and Jones (1990) hypothesized that fish production could be limited by the detrimental shifts in dynamic physical processes that control prey availability and create an advantage for predators. Dodge (1989) and Welcomme et al. (1989) demonstrated the close relationship between lower river and estuarine floodplains and fish production and diversity for river basins worldwide.
Changes to littoral ecology in the Columbia River basin have been significant. Sherwood et al. (1990) estimated that 20,000 acres of tidal swamps, 10,000 acres of tidal marshes, and 3,000 acres of tidal flats had been lost from 1870 to 1970. Sherwood et al. (1990) also estimated that an 82% loss of emergent estuary plant production and a 15% loss of benthic macro algae production has contributed to a 52,000-metric-ton loss of local carbon input into the estuary. Concurrent impoundment of basin organic sediments behind mainstem dams has produced large blooms of phytoplankton in the reservoirs (Sherwood et al. 1990). As these populations are washed into the estuary, they increase microdetrital accumulations. The result is a shift in food webs to the benefit of exotic species, such as American shad, and benthic detrital feeders to the disadvantage of anadromous salmon (Bottom and Jones 1990).
Implementation of available restoration measures such as moratoriums on floodplain development, and restriction of dredging will protect the remaining estuary for juvenile and adult anadromous fishes of the Columbia River Basin. Increasing flood events by controlled flooding will restore lost Columbia River lower river and estuarine areas resulting in increased fish diversity and production (Dodge 1989; Reiger et al. 1989; Lichatowich et al. 1995).
- Protect the remaining wetlands and intertidal areas in the estuary upon which anadromous fish are particularly dependent.
- Undertake an immediate assessment of remaining and potential estuary habitat.
- Protect existing estuary habitat complexity.
- Evaluate and condition additional proposals for hydroelectric and water withdrawals developments, navigation projects, and shoreline developments on the basis of their impact on estuarine ecology.
- Identify and implement opportunities to reclaim former wetland areas by breaching existing dikes and levees.
- Reestablish sustained peaking flows that drive critical river and estuarine processes.
Physical, chemical, and biological attributes of the estuary complexity and diversity will be protected and restored, thus preserving necessary functions and values of critical anadromous fish habitat. This will result in increased fish production and diversity.
Because of its authority to regulate dams and dredge and fill activities, the Corps of Engineers and other federal and local agencies with water management and land development jurisdiction must be actively involved in implementing these measures along with the states of Oregon and Washington and the Columbia River treaty tribes. The designation of the Columbia Estuary into the National Estuary Program (NEP) provides a framework for working with a federal, state, tribal, local, public interest, and industry management structure and strategy for restoring the Columbia Estuary. Coordination with the Columbia NEP is crucial for estuary protection and restoration.