March 17, 2013 at 11:47 AM
Kelp armageddon at the mouth of the Elwha
There are winners and losers as the Elwha dam removal project underway transforms the Olympic Mountain watershed.
Running 45 miles from its origins in the snow fields of the Olympics, the Elwha reaches the saltwater of the Strait of Juan de Fuca, where a new world is unfolding.
With the Elwha Dam gone as of just about a year ago, and Glines Canyon Dam nearly 2/3 down, silt and sediment, wood, leaves, sticks and other organic material long trapped behind the dams is cutting loose.
Some of it is banked in soft slumping heaps along the river banks, and even the deepest pools in the river have filled in. And some sediment is making it all the way to the near shore at the river mouth.
Where, researchers tracking sediment transport by the river before, during and after dam removal could tell you, a kelp Armageddon is underway. “It’s amazing,” said Helen Berry, Marine Ecologist with the state Department of Natural Resources.
The changes on the seabed are dramatic, from better than 80 to 90 percent coverage by kelp to an environment that is almost completely devoid of kelp. “It’s shocking,” Berry said. “It’s not subtle.”
It’s a similarly big change on the water surface, where great floating rafts of bull kelp have disappeared because the rocky substrate their hold fasts grab onto on the sea floor are smothered over in soft silt.
But it’s a back to the future type of transformation, experts think. Early maps show no kelp at the mouth of the Elwha, notes Jon Warrick of the USGS at Santa Cruz.
Kelp mapping near the Elwha River mouth was conducted in 1911-12 for a U.S. potash survey, of all things, by George B. Rigg. Potash is made from kelp, and useful for fertilizer. As U.S. relations with Germany, a major source of fertilizer worsened in the run up to the outbreak of World War I, the feds were looking for new sources. Potash can also, of course, be used for gunpowder.
Old records sometimes have new relevance for scientists seeking indicators of ecological change.
Warrick points out that a map based on Rigg’s survey in a 1915 book by Frank Cameron and others entitled “Potash from Kelp, published by U.S. Bureau of Soils, reveals two baselines the river is only now beginning to resemble.
Rigg mapped kelp only west of the river mouth, in Freshwater Bay, but none at the river mouth, or east of it. He also described sand reaching from the river mouth to the Strait.
Berry saw floating kelps in her aerial surveys throughout the 1980s-2000s. Yet according to Berry and USGS underwater dive survey crews, kelp did not grow much at all in 2012 — the first year in which sediment unleashed from behind Elwha Dam made it all the way to the river mouth.
The combination of reduced light in the water column and soft muddy sediments building up on what used to be a rocky sea floor has been curtains for the kelp.
Here are some before and after videos from Berry. The first one, taken in 2010, shows lush pastures of kelp on the sea floor. The video was taken by a camera towed under a boat in about 25 feet of water, just to the east of the Elwha River delta.
The before video shows a thick canopy of kelps. The after shows an increase in the fine sediment and almost no vegetation. And what is there is not likely to survive.
Warrick, Berry and others think what we see unfolding at the river mouth is just the beginning of a long term re-set of the river’s ecology.
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