When I was 19 or 20, in college and thrilled with the exploration of my new home in the Pacific Northwest, I regularly ventured to Washington’s Olympic Peninsula and Olympic National Park. The park and surroundings are famous for immense trees, glacially capped peaks, and wild coast. The mountains themselves sit smack in the middle of the peninsula, and rivers reach out from them in all directions like a many-armed sea star.
One of the northern rivers is the Elwha. It’s not huge, and while I was in college, exploring that area, it wasn’t much of a river at all. It was mostly lakes. Two dams blocked the Elwha, creating reservoirs that filled the river’s deep canyons. They’d originally produced some middling amount of electricity and, as advocates liked to claim, “provided flood control”. But mostly they just sat there, as the salmon that used to run the river slowly disappeared. And those weren’t just any salmon. The Chinooks of the Elwha were some of the biggest ever recorded. When the dams inundated their spawning beds, the fish were left with less and less habitat and their young without the seasonal floods which aid their migration to the sea. It didn’t take long before the Chinooks of the Elwha were only slightly more tangible than a memory.
A century after construction, public opinion finally turned on the dams, and eventually, the decision was made to remove them. By 2012, the first dam was demolished and in the summer of 2014, the final chunk of concrete from the Glines Canyon Dam was removed. For the first time in over a century the Elwha flowed free.
There was celebration by those who love free-flowing rivers, some grumblings by those belonging to the old school, and everyone had questions about what would happen next. Some worried it was too late for the Elwha’s salmon, others questioned whether flooding and sedimentation would put the seaside communities at risk, or negatively effect the shore of the Strait of Juan de Fuca.
It took only months to silence the doubters. First bull trout were observed in the newly flowing river, and later that summer the first Chinooks spawned on a stretch of river they’d been unable to access in 100 years. On the coast, the sediments rebuilt a wide beach that had eroded over the past century, providing shore protection from the yearly winter storms.
In my last post, I talked about connections within an ecosystem. This is another example, though perhaps a more obvious one: When the salmon returned to the Elwha, they brought with them hundreds of pounds of marine nutrients. When those salmon spawn and die, they become fertilizer for the river system. Aquatic life flourishes in the new nutrients and with it a cascade rolls through the food chain. One of the species to benefit most directly is a charismatic little bird called the American Dipper.
The American Dipper is an endearing gray bird. An songbird, with the unique ability to submerge itself in fast flowing water, where it forages for aquatic insects along the river bottom. Their feathers are impermeable, and the water sloughs off, well, like water from a dipper’s back.
The relationship between dam removal, salmon, and Dippers was recently illuminated in a new paper in the journal Biological Conservation. A group of researchers from across the country documented the return of marine nutrients to the Elwha drainage. Before, during, and after dam removal the researchers captured American Dippers down the length of the river, and took blood and feather samples from the birds. They analyzed the samples for the presence of stable nitrogen and carbon, both of which originate in the oceans. For comparison they also sampled aquatic invertebrates (an important Dipper food), and the salmon themselves.
Prior to dam removal the only birds to have these nutrients were those downstream from the dam. But almost as soon as the river was set free, the fish moved upstream, and carried those valuable ocean materials with them. The nutrients quickly made their way through the entire river system. From their analyses the authors concluded that in addition to aquatic inverts, the dippers were also eating the eggs of spawning salmon which allowed the nitrogen and carbon to move up the food chain more quickly.
Though the technical aspects of their research are interesting, the real story here lies in how quickly it all happened. Within a year, salmon, steelhead, and other migratory fish were colonizing an area that had been inaccessible for more than a century. And the impacts of that quickly raced up the food chain, benefitting the whole Elwha drainage. As additional time passes, and fish stocks rebuild boosting the volume of nutrients in the formerly dammed river, those effects will become more pronounced, benefitting not just the dippers and inverts, but also the riverside vegetation, scavenging birds, and apex predators. If this study is anything to go on, it won’t be long.
This is a hopeful story. Rivers are resilient, and as old, out-dated dams are decommissioned and removed, life will return far more quickly that we previously could have imagined. Let us hope that the Elwha is only a start.
The paper this article is drawn from:
Tonra, Chistopher M. et al. 2015. The rapid return of marine-derived nutrients to a freshwater food web following dam removal. Biological Conservation 192:130-134.