|
The Cedar River Watershed provides two-thirds
of Seattle's drinking water.
Soon, the potential will turn to actual: Nearly a
century after the city built a dam that diverts drinking water but
bans salmon from entering the watershed, they will build a fish
ladder for steelhead trout, chinook and coho salmon to return.
The city is guardedly optimistic. Aiding salmon recovery
is one of its goals.
But the transformation that will occur at the Cedar
River watershed has no precedent elsewhere in the region. Exactly
what happens when salmon return to a habitat after a 90-year-long
absence? What happens when that Rip Van Winkle habitat awakens to
a fertile supply of nutrients for bugs, bacteria, algae, fish, plants
and trees? How do salmon colonize new waters? What happens to salmon
diversity? And, city water managers wonder nervously, what happens
to the purity of drinking water that meets or exceeds federal standards
when you add spawned-out salmon carcasses to the mix?
"There�s this real concern about what salmon
might do to water quality. How many salmon can they let up there
before they actually have some kind of material impact on the quality
of the water? And what�s that going to do in terms of what they
have to do in terms of treatment?" said Bob Bilby, former Northwest
Fisheries Science Center watershed processes program manager. "There's
a potential downside they're fairly concerned with."
That's why a small band of NWFSC scientists -- clothed
in waders, slathered with sunscreen and bug dope, outfitted with
clipboards and waterproof GPS monitors -- have fanned through the
Cedar River watershed this summer. They're measuring before and
after water chemistry. They're making predictions of the places
returning salmon might like best. They're running before and after
isotopic analysis to pinpoint how the nutrients salmon deliver are
gobbled up by a nutrient-starved ecosystem.
The scientists fill a dusty Jeep with a clump of waders,
fleece, hiking boots and PVC pipe, like giant Pixi sticks, marked
at intervals with black tape. They negotiate a series of locked
gates and wind along narrow dirt roads that cut through old-growth
and second-growth stands of Douglas fir, Western hemlock, Western
red cedar and Sitka spruce. A polka dot flag dangles from a branch
to mark where they finished up the previous day.
Kiffney predicts Rock Creek, the subject of the morning's
mapping effort, will be the object of coho adoration.
"They like smaller streams. And they love to rear
in this marshy, slow-water habitat," he said. "We're predicting
coho are going to get up there and like what they see."
The sky is gray and ambivalent, neither sighing with
showers nor smiling with sun. Shaggy moss clings to exposed rocks.
Fungi of improbable sizes and colors juts from downed alders. Kiffney
creeps down from road level to stream level, cutting through fox
glove and salmonberry underbrush.
Just as no two faces are alike, no two streams are
the same. Kiffney keeps a keen eye to note and record the specific
characteristics of this stream, stopping at a pool, a puddle of
slow-moving water with a noticeable depression. Lunging under a
downed alder, he flips the marked PVC pole end over end to measure
P1's length and dunks the pole in to measure P1's maximum depth.
Same for R, or riffle, a place where water's flow
has sped, dancing to create a frothy turbulence.
And the same for side channels, which are separated
from the main bar by gravel, masses of tree roots or wood jams,
and which slow the water to nearly stagnant.
No woody debris is complete without a "small," "medium"
or "large" characterization. And there are no mere "rocks." A rock
smaller than a baseball is gravel. Bigger than a baseball yet smaller
than a basketball makes it a cobble. Too big for Michael Jordan
to palm? Call that rock a boulder. Some rocks look pocked with acne.
It's just caddisflies, aquatic insect grazers that are a sign of
a healthy stream.
From previous research, the scientists have a hint
what to expect when salmon negotiate the 17 miles of habitat made
off limits by the Landsburg diversion dam.
Salmon returning in the fall and winter to spawn and
die provide pulses of nitrogen and phosphorus, essential nutrients
for the stream and for the ecosystem. The nutrients are gobbled
up -- used immediately or hoarded for the future -- at every level
of the food web.
"The salmon are the cornerstone of the ecosystem,"
Kiffney said.
Add salmon and, at the base of the food chain, the
community of primary producers like algae increase in number. That
triggers increases in abundance of invertebrates -- the scrapers,
the grazers and herbivores that eat those plants. Insect populations
boom. Predators, primarily salmon, are fueled by that increased
insect productivity, Kiffney said.
Using the specialized fingerprint that marine salmon
carry -- a unique ratio of heavier nitrogen atoms to lighter nitrogen
atoms -- the researchers hope to trace the various places where
salmon nutrients are used by the ecosystem. Water. Insects. Resident
fish. Bushes. Trees. Isotopic analysis can be done at every level
of the food web.
It's not clear how many nutrient deposits the watershed
would need to experience to create the hospitable habitat that would
nurture fat, healthy juvenile salmon.
"That system has been without those nutrients for
90 years," Kiffney said. "So the early fish, they're not going to
have too much trouble once they're up there. Because they're basically
up there to spawn. It's probably those next generations following
that that may have some difficulty, just because of the nature of
how those nutrients have been lost."
The simplest solution would be to tip the scales,
priming the pump by adding spawned-out salmon carcasses. The city
will not allow it on a wide scale but has given the go-ahead for
small experiments that would track water chemistry and other changes
in a few experimental channels.
|
Spawned-out salmon carcasses deliver nutrients that fuel
ecosystem growth - among trees, shrubs, aquatic insects, even
juvenile salmon.
|
"You can make these little experimental
troughs -- basically -- that simulate
a stream. You can add carcasses to
these troughs and see how those carcasses
influence the community, including
juvenile salmon," Kiffney said.
The trough, based on past research,
should become a salmon-eat-salmon
world.
In research of fish behavior along
Washington's southwest coast,
|
Bilby and co-authors found that adding spawned-out adult salmon
carcasses in a stream attracts a flood of juvenile salmon. And they're
not there as innocent bystanders.
"Anywhere from 60 to 90 percent of the material that we recovered
from their stomachs was either carcass flesh or salmon eggs. So,
they were feeding fairly heavily on the carcasses," said Bilby,
lead author of the article published in the "Canadian Journal
of Fisheries and Aquatic Sciences."
And, the bigger the younger salmon are, the better their chances
of surviving when they hit the saltwater stage of their life,
Bilby said.
"The difference is very, very significant. Relatively small increases
in body size translate into large increases in survival in the
ocean."
-- Diedtra Henderson
Cedar River Watershed Map: Copyright 2000 City
of Seattle. All rights reserved. No warranties of any sort, including
accuracy, fitness, or merchantability, accompany this product.
Next: Sniffing Out Salmon Risk From Pesticides
|
