Pacific Northwest Estuaries Were Born of Fire and Ice (First in a series)

The Pacific Northwest coastal zone is punctuated by many distinct, small estuaries. They fringe a strip of land bordering nearly a thousand miles of the eastern Pacific Ocean and Puget Sound. This expansive coastline is the focal point of ocean currents that drive one of the globe’s four great upwelling zones that sustain oceanic food webs. It is the terminus of several large rivers – the Fraser River in British Columbia, the Columbia River between Oregon and Washington, the Klamath River in California – that carry the runoff of the Pacific Northwest temperate rainforest and can extend the signature of the estuaries far out to sea. These estuaries and their watersheds produce salmon – five species of them – and oysters, crabs, flounders and other commercially important fish besides. The estuaries inside of Puget Sound – the Fraser, Hood Canal, and South Puget Sound – tend to be larger than the estuaries found on the outer Washington coast. The Columbia River estuary extends from Bonneville Dam 146 miles downstream to Astoria and includes 236 square miles of estuarine habitats (Hayslip et al., 2007).
South of the Columbia River the estuaries become smaller. Oregon has 17 principal estuaries. The largest is Coos Bay with 13,300 tidally-influenced acres. Oregon also has 16 minor estuaries of 50 acres or less. Minor estuaries form at the mouths of coastal creeks and small rivers and provide important habitat, especially for anadromous fish (Oregon Estuary Plan Book, 1987).
The Pacific Northwest’s estuaries were born of the movements of tectonic plates millions of years ago. Those movements altered coastlines, pushed up mountains, and have been reshaping the northwest coast of North America ever since, in part by lifting layers of sandstone and mudstone, weathering them, and redistributing their sediments along the beaches. Many Oregon beaches are demarked by basaltic headlands – the eroded remnants of flood basalt that originated hundreds of miles inland and flowed westward to the sea.
The estuaries began to assume their present forms during the last glacial epoch. About 15,000 to 25,000 years ago, the level of the sea off of the Oregon coast was about a hundred meters lower than it is now. Dry land extended far to the west of the present coastline. As the continental glaciers melted, rising coastal waters reflooded the rivers’ mouths and Oregon’s signature drowned-river-mouth estuaries began to take shape. During this same time geologic forces caused sections of the coast to rise rapidly. Mature rivers meandered across a broad coastal plain when the uplift began. Today those rivers meander through deeply-incised canyons that they carved through the mountain as the mountains rose.
In Washington the glaciers advanced out of Canada, south and west, as far as Olympia. They filled Puget Sound with an estimated 2,383 cubic miles of ice. The weight of the ice pressed portions of the Sound deep into the crust. As the glaciers retreated, the melting ice formed a huge freshwater lake in Puget Sound where glacial till mixed with marine sediments. The retreating glaciers carved deep channels through the sediments. All this activity resulted in the fjords, the layer-cake bluffs and the mixed-sediment beaches that characterize Puget Sound today (Washington Department of Ecology, 2008).
As the sea level rose, the wind and waves pushed the exposed sands of Oregon’s beaches into great ranges of dunes. These dunes supplied sand to build the point bars and sandspits that define many of Oregon’s smaller, bar-built or blind estuaries, which exist precariously for as long as the sandy features that formed them remain stable.
Today things look quiet compared to when fiery rivers of lava left their eroded remnants as foundations for lighthouses. But the clash of ocean and rivers continues to mold Pacific Northwest estuaries. Winter storms reshape beaches, cliffs, and rivers. The northwest coast is vulnerable to the destructive force of tsunamis triggered by earthquakes at the plate boundary a few hundred miles west of Oregon, or by great quakes originating far across the Pacific. A small tsunami rolled down the coast following the Alaska Earthquake in 1964, causing death and destruction as far south as Crescent City, California. The destructive power of great earthquakes and tsunamis reshapes the coastline at 300 to 500 year intervals. The most recent great tsunami occurred about 300 years ago when, in what was probably a typical tectonic event for the region, a large section of the coast suddenly subsided to establish a new equilibrium between land and sea. It left its signature in the oral histories of Native Americans and in layers of estuarine mud and sand exposed in the tidal channels of the South Slough National Estuarine Research Reserve at Coos Bay.
Winds and ocean currents drive the Pacific Northwest’s climate. The Sub-Arctic Current flows eastward across the northern Pacific Ocean and encounters North America on a broad front along British Columbia and Washington. The current diverges. The northern portion turns left and becomes the Alaska Current, while the southerly waters turn right to form the California Current.
As the California Current mixes with fresh water discharged from the Columbia River and numerous small coastal streams, it gives rise to a complex nearshore marine environment. During spring and summer, northwest winds trigger ocean upwelling. Upwelling brings cold, deep, nutrient-rich water to the nearshore surface, where sunlight stimulates rapid growth of phytoplankton. Twice each day the tides carry these highly-enriched waters into the estuaries, where they account for spring and summer plankton blooms. Pacific Northwest estuaries are highly marine in comparison with estuaries of other regions. Although flushing rates tend to be rapid, especially during winter monsoons when runoff from the steep, coastal rivers is high, the tidal prism of a typical northwest estuary may be comprised of nearly 40 percent salt water. Upwelling is affected by variations in ocean climate, such as the El Nino/Southern Oscillation and the Pacific Decadal Oscillation (Rumrill, 2006.)
Pacific Northwest estuaries share many of the problems that face coastal managers in other regions – invasions of exotic plants and animals, loss of habitat, degraded water quality and the impacts of development among them. New issues are complicating those concerns, among them: proposals to develop wind or waves for energy, or to extract methane from buried coal, or to import liquefied natural gas. Using marine reserves to protect important ocean resources remains controversial in Oregon. Managing shoreline development remains a critical issue in Puget Sound. Beyond these concerns managers are asking: how will Pacific Northwest estuaries fare as the regional climate changes?
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Sources:
Bottom, Dan, Becky Kreag, Frank Ratti, Cyndi Roye and Rick Starr. 1987. Oregon Estuary Plan Book. Oregon Department of Land Conservation and Development, 800 Oregon Avenue NE, Portland, Oregon 97201
Emmett, Robert, Roberto Llanso, Jan Newton, Ron Thom, Michelle Hornberger, Cheryl Morgan, Colin Levings, Andrea Copping, and Paul Fishman. 2000. Geographic Signatures of North American West Coast Estuaries. Estuaries Vol. 23, No. 6, p. 765-792.
Hayslip, G., L. Edmond, V. Partridge, W. Nelson, H. Lee, F. Cole, J. Lamberson , and L. Caton. 2007. Ecological Condition of the Columbia River Estuary. EPA 910-R-07-004. U.S. Environmental Protection Agency, Office of Environmental Assessment, Region 10, Seattle, Washington. December 2007.
Hickey, Barbara M, and Neil S. Banas. 2003. Oceanography of the U.S. Pacific Northwest Coastal Ocean and Estuaries with Application to Coastal Ecology. Estuaries Vol. 26, No. 4B, p. 1010–1031 August 2003.
Puget Sound Shorelands webpage. http://www.ecy.wa.gov/programs/sea/pugetsound/tour/geology.html. Washington Department of Ecology Shorelands Program (accessed September 23, 2008).
Rumrill, Steven S. 2006. Site Profile of the South Slough National Estuarine Research Reserve. Oregon Department of State Lands. Charleston, Oregon 97420.