27
spring
2013
arches
I
t’s a fall day about eight miles from campus, and the atmosphere is
doing what it always does around here at this time of year: looking
gray and feeling damp. Students from geology Professor Jeff Tepper’s
Environmental Geochemistry” class are suited up in Gortex and gum boots,
trying to stay balanced on a borrowed fireworks barge in the middle of Gravelly
Lake. They assemble sections of steel pipe, lower the long tube into the water,
and when it hits the lake floor push it down by hand, like a straw into a choco-
late milkshake, as deep as they can. Then up comes the pipe, and they carefully
extrude a column of mud—a kind of mucky timeline made possible because in
the deep spots of most lakes, new sediment accumulates on top of old with little
disturbance, and clues about a place’s geological and biological history are well
preserved. The deeper you dig, the further into the past you go.
For several years Professor Tepper’s geology students have been doing this
at lakes around Tacoma. They have pieced together some interesting local his-
tory, and their work may soon pay off for the community as the students get
involved in public policy and environmental restoration.
The sediment record in Tacoma-area lakes extends back 13,000 to 14,000 years and contains
unmistakable evidence of several major events, according to Tepper. A thick layer of volcanic
ash settled into the lakes about 7,700 years ago, when Mount Mazama in Oregon blew its lid
and became Crater Lake. Closer to the surface there’s a spike in levels of copper, lead, arsenic,
and zinc in the sediment that dates to around 1900—a souvenir of the defunct ASARCO smelt-
er in Tacoma.
Tepper had students study Gravelly Lake in Lakewood to figure out why its water has higher
silica content than nearby lakes that are in other ways quite similar. The water is loaded with
diatoms—a form of algae that leaves behind microscopic skeletons of silica. Tepper said each
of thousands of species of diatoms has a specific set of environmental conditions in which it
thrives, so the silica remains are good indicators of what lake conditions were like at the time
the diatoms lived.
It had been hypothesized that high silica levels at Gravelly Lake were caused by pollution
from increased residential density and leaking septic systems. But when the students analyzed
the cores, they found that the jump in silica happened around 1840—way too early to be caused
by busted underground plumbing.
That’s where the detective work came in. Digging into local history, students learned that
the Hudson’s Bay Company established Fort Nisqually near Gravelly Lake in 1833. Maps of the
fort from that time indicate its herd of cattle was pastured around the lake, and where there are
cows there is manure. It turns out the diatoms were there all along. With extra nutrients con-
taminating the water, they flourished.
High silica is a natural characteristic of the lake water,” Tepper said. “Only after Europeans
showed up and brought livestock did the system have the ingredients that let the algal blooms
take off.”
It was inevitable that anyone working on lakes in Lakewood would meet Don Russell,
a local retiree and one-time biology teacher who is a volunteer water-quality monitor for the
Pierce Conservation District. Russell, 83, has been concerned about the lakes here since the late
1980
s, when several dogs died from drinking the water in American Lake. He has been pushing
for a cleanup of Waughop Lake for years.