The Northwest Power Planning Council (Council) requested the Independent Scientific Advisory Board (ISAB) to undertake a review of the impacts of estuarine conditions on the Council’s mission to "protect, mitigate and enhance" fish and wildlife in the Columbia River as affected by development and operation of the hydroelectric system. The ISAB agreed to undertake the review but cautioned that it was unlikely that it could quantify the impact of changes in the estuary relative to specific program or management actions taken in the upper river. The ISAB could, however, provide a historical perspective and qualitative assessment of impacts, identify potentially useful collaborations, and provide recommendations concerning future efforts needed to more quantitatively address this issue (letter to Council, Jan. 26, 2000).
While conducting this review the ISAB became aware that there was extensive overlap between a study by the National Marine Fisheries Service (NMFS) and this ISAB assignment. The ISAB expects the NMFS study will add significantly to an informed response to the Council. Consequently, this report has been prepared as a preliminary reply, with additional detail possible following publication of the NMFS study.Before human influence, the Columbia River estuary was a high-energy environment dominated by physical forces, with extensive sand-beds and highly variable river flows. Several authors have suggested that the biological processes in this environment may have been unique on the Pacific coast. The estuary of today, however, has been extensively modified in terms of physical and biological processes. The development and operation of the hydroelectric system have contributed significantly to these changes. Direct effects have been through changes in seasonal flow rates, reduced sediment discharge, and resultant changes in the estuary’s energy balance.
There is extensive documentation about changes in the estuary over the past century. The major changes resulting from development of peripheral wetlands and their isolation from the estuary, development and deepening of the Federal Navigation Channel, and regulation of upper Columbia River flows for hydrosystem needs and flood control. The effects of these changes do not function discretely. The estuary is a complex interaction of physical features (predominated by the energy balance between river flow and tidal forces), resultant changes in circulation, salinity intrusion, sediment processes, and ultimately the biological consequences of these changes. Superimposed on this dynamic environment have been changes in water quality, introduction of exotic species, and the enormous investment in hatchery production of salmonids to mitigate for related losses due to the hydrosystem.
The question of the potential biological impacts associated with these changes is more complicated than detecting the physical impacts. Changes in the biological processes varied from a fundamental alteration in the basis of the food web to the exclusion of subyearling chinook and chum salmon from a large portion of the tidal marshes. The effects of these specific changes, however, are difficult to partition from the effects of numerous other impacts in the Basin. Furthermore, our ability to assess impacts of estuarine conditions on the Fish and Wildlife Program has been limited by a lack of appropriate and available data. Information necessary to meet the 1994 Program objectives was simply not acquired for the estuary. Similar obstacles were expressed to the ISAB by the NMFS study team who noted that the data are insufficient to even determine the extent of modern estuarine use by salmonids.
While the ISAB recognizes the limitations of data to directly assess impacts of changes in the estuary on the Fish and Wildlife Program, after our review it is our assessment that these changes have been detrimental to salmonids and the rebuilding objectives of the Program. We base this advice principally on three major issues:
- The significant loss of peripheral wetlands and tidal channels; these habitats are important to the early rearing, survival and growth of chum salmon, sub-yearling chinook, and smaller coho salmon in other west coast estuaries.
- The extent of change to seasonal flows following development of the hydrosystem. The affects of these changes are closely associated with the impact of the development of the navigation channel. In combination these developments have resulted in changes to estuarine circulation, deposition of sediments, and biological processes.
- The need for precautionary advice given the current state of most salmonid populations in the Basin, the magnitude of change in the estuary, and the lack of investigations upon which to base alternative advice.
As the 2000 Fish and Wildlife Program is developed, the ISAB recommends an aggressive experimental program targeted to reduce the likelihood of prolonged uncertainty about the impact of estuarine conditions. Such a program should incorporate monitoring of the physical environment (such as currently begun via the CORIE program, Oregon Graduate Institute) combined with evaluation of large-scale manipulations of estuarine habitats. The intent of these manipulations would be to study changes presumed to have had negative impacts and to conduct these at a scale that can be measured within the natural environment. These types of programs would be consistent with the vision statement in the 2000 Fish and Wildlife Program: "Wherever feasible, this program will be accomplished by protecting and restoring the natural ecological functions, habitats, and biological diversity of the Columbia River Basin."
The types of large-scale programs that are envisioned include: a) removal of dykes in the lower river and upper estuary to restore connections between peripheral floodplains and the river or fluvial zone of the estuary; b) actively managing sources of salmonid predation in the estuary through restoration of natural habitats, removal of habitats artificially created due to channel construction and/or maintenance, or controlling predator populations; c) establish an allocation of water within the annual water budget for the Basin, that would simulate peak seasonal discharge, increase the variability of flows during periods of salmonid emigration, and restore tidal channel complexity in the estuary (aided by removing pile dykes where feasible).