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ISAB Urges 'Aggressive' Estuary Study Actions

by Barry Espenson
Columbia Basin Bulletin - December 8, 2001

Large-scale manipulations -- such as through dike removal, changes in hydrosystem-controlled flow regimes and altered predation management -- may be necessary to assess the impact human development has had on Columbia River estuarine habitats and their fish and wildlife populations, according to a scientific report released this week.

That "interface between a highly modified freshwater system and the open ocean environment" has been beset by dramatic changes to both the physical habitat and biological communities, according the report, "The Columbia River Estuary and the Columbia River Basin Fish and Wildlife Program." The report was produced by the Independent Scientific Advisory Board at the request of the Northwest Power Planning Council.

The ISAB was asked by the NWPPC to review the impact of estuary conditions on Council efforts to "protect, mitigate and enhance" fish and wildlife affected by development and operation of the hydro system. That Council mission is carried out in large part through the $127 million annual fish and wildlife program. The 10-member ISAB was formed by the NWPPC and National Marine Fisheries Service to provide scientific advice on fish and wildlife issues.

While there is considerable documentation of estuary change, the ISAB said in launching the review that it was unlikely that the panel could quantify the impact of specific changes. Rather it focused on detailing the forces that have altered the estuary and recommending what actions might be taken to identify impacts wrought by a complex set of changes. Those actions must be accompanied by appropriate monitoring and evaluation programs.

"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," wrote the ISAB.

"You can go in and start tinkering, but it's a complex place," the report's lead writer, Dr. Brian Riddell, said of the environment and its many man-caused influences.

Major changes noted in the report result from the "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 overall impact of those changes on fish is unknown, as is the impact of the individual components.

"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," according to the report.

"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 ISAB said in its report that "it is our assessment that theses changes have been detrimental to salmonids and the rebuilding objectives of the program." The significant loss of peripheral wetlands and tidal channels represent the loss of nearly 25 percent of estuarine habitat, according to Riddell.

"It (the Columbia River estuary) is in much better shape than almost any estuary on this coast," Riddell told the Council Wednesday. Still, the habitat losses are significant.

The habitats are important to the early rearing, survival and growth of chum salmon, sub-yearling fall chinook and smaller coho salmon.

"Big fish don't use it very much but they have to go through it," Riddell said of the estuary.

Among the large-scale programs "envisioned" by the ISAB to determine impacts of specific estuary changes is the removal of dikes in the lower river and upper estuary to restore connections between floodplains and the river.

"Clearly such a program would depend on the use and ownership of these old floodplains but there are likely areas that are no longer in use for agriculture and/or the use may benefit from periodic inundation by the river and its sediments," according to the report.

The report also cited the extent of change to seasonal flows resulting from development of the hydrosystem. Those changes from historic flows include an estimated 40 percent increase in winter, largely for power production, and 50-55 percent decrease in the spring/summer, for flood control.

The controlled flows also reduce variability, not allowing peak flood events that can cause damage but also serve to create habitat and refresh the estuary with nutrients, according to Riddell.

The ISAB, in another of its suggested manipulations, says an allocation of water within the annual Basin water budget should be established that simulates peak seasonal discharge, increases the variability of flows during salmonid emigration and restores tidal channel complexity.

"The reduction in peak seasonal discharge under the current hydrosystem is one of the most significant changes in (the) river-estuary system. Short duration pulses of controlled but higher flows would be intended to increase turbidity to reduce predation, increase movement through the estuary, increase sediment transport into the estuary, and connect the river system with restored floodplain habitats," according to the report.

The ISAB also suggests programs for "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."

The report used as an example Rice Island and other islands created with navigation channel dredge material. The islands represent altered habitat, providing havens for large concentrations of avian species, such as Caspian terns, that prey on migrating juvenile salmon.

"However, fewer and larger colonies increases the risk to the (bird) species through catastrophic events, possibly via disease, predators, or an environmental event. Restoring the natural population structure of this species could reduce the risk of loss and improve its productivity, and reduce salmonid losses.

The report's executive summary acknowledged that such programs might be viewed with skepticism.

"To achieve the vision statement of the 2000 Fish and Wildlife program in the estuary province, however, programs of these magnitudes are likely necessary given the magnitude of the estuary and the stated desire to evaluate these actions….

"All of the investment and effort in the Fish and Wildlife Program flow through this unique environment, but interaction of change in the estuary with projects of the Fish and Wildlife Program, and their combined effect, has basically been ignored.

"The ISAB strongly recommends that the Council recognize the potential value of the estuary to the Fish and Wildlife Program and the immediate need to improve our understanding of its ecological processes."

The ISAB said that the types of programs it suggested would be consistent with the vision statement in the Council's newly adopted 2000 Fish and Wildlife Program which says: "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 ISAB labeled the report delivered Wednesday as "preliminary." It said an extensive National Marine Fisheries Service study now under way should provide additional detail that would "add significantly to an informed response to the Council." That NMFS study will be more substantive, Riddell said, than the ISAB review. It will document historical changes in the estuary, develop new conceptual models that include application of new data linking these physical changes to biological diversity in Columbia salmonids, and will evaluate management strategies to improve estuarine conditions for salmonids," according to the ISAB report.

Link information:

Barry Espenson
ISAB Urges 'Aggressive' Estuary Study Actions
Columbia Basin Bulletin, December 8, 2001

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