August 17, 2001
Columbia River trumps Pacific Ocean when conditions are right
About three quarters of the water pouring into the Pacific Ocean from the West Coast comes from the Columbia River.
At its mouth, the Columbia doesn’t just spray out into the Pacific like water from a garden hose. Instead the plume is pushed and pulled north and south by the Earth’s rotation, ocean currents and the Northwest’s very changeable winds.
“During the course of a year some of that fresh water makes its way many miles north, sometimes into the Strait of Juan de Fuca and — incredibly — as far south as San Francisco,” says Barbara Hickey, University of Washington professor of oceanography.
Columbia River water moving into Willapa Bay and Grays Harbor estuaries on the Washington coast in late spring and summer can greatly dilute the nutritious ocean water entering the estuaries and may cause larvae to bypass them entirely. The massive plume of fresh water interacting with salty ocean waters also creates swirling eddies miles wide off the coast that young fish such as salmon seem to favor.
UW oceanographers for the first time have modeled the dynamics of the Columbia River plume off Washington and Oregon and their results have been accepted for publication in the Journal of Geophysical Research. River modeling efforts by scientists at other institutions have involved rivers much smaller, says Hickey, who is co-author with graduate student Irene Garcia Berdeal and Associate Professor Mitsuhiro Kawase of the paper.
Coastal oceanography and a plume of fresh water up to 50 miles wide, 150 miles long and up to 60 feet thick are important to understand if natural resource managers and citizens are to separate natural cycles from human activities that affect such things as endangered salmon, Hickey says. That’s the goal of the groups funding the plume work: the National Oceanic and Atmospheric Administration with its Pacific Northwest Coastal Ecosystem Regional Study, Washington Sea Grant and the National Science Foundation.
The current drought, for example, could give researchers an inkling of what might happen on the coast if climate change were to reduce Columbia River flows year after year. In years with deep snow pack and high runoff, UW scientists have already found that the Columbia River dominates late-spring and early-summer water properties in estuaries north of the river.
Willapa Bay and Grays Harbor are surprisingly different from East Coast estuaries such as Chesapeake Bay, Hickey says. Nutrients in East Coast estuaries come principally from the rivers draining into them. It appears that estuaries here are enriched more by ocean waters. Along Washington’s coast, offshore shelves are narrow compared to those off the East Coast so ocean water crosses more easily into estuaries. When conditions are right, that ocean water is loaded with nutrients and tiny plants and animals — phytoplankton and zooplankton — on which young fish, crabs and oysters feast, and salmon more indirectly depend.
When the Columbia River plume hugs the coastline, however, it’s river water that makes its way into the estuaries. The nutritious ocean waters that may be present are effectively blocked from entering. Columbia River water also causes dramatic changes in salinity and the amount of sediments and dissolved materials suspended in the water of the estuaries.
This time of year the weather off the coast can change every two or three days. Each time the wind changes direction so do the ocean currents and a whole new mix of ocean and river water can make its way along the coast and into the estuaries. Moving rapidly at about 6 miles a day the waters in Willapa Bay, for example, can be affected end to end in just three to four days.
All these changes are taking place at a time when Washington estuaries are perhaps at their most biologically active, which raises questions and makes scientists wonder about the trade-offs when managers regulate river flows. For young salmon, for instance, is it an advantage to have more water from the plume because it is muddier and more difficult for predators to see them? Is it confusing to those same juveniles as they head toward the ocean and suddenly find themselves swimming in fresher water near the mouth of the estuary?
Hickey first began studying coastal oceanography along the Pacific Northwest Coast in 1995 with funding from Washington Sea Grant and the U.S. Environmental Protection Agency. Since then the EPA has typically funded parallel biological work by Jan Newton, a Department of Ecology scientist and UW affiliate faculty member.
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Hickey through August (360) 825-3911; this fall 206-543-4737; or bhickey@u.washington.edu
