|The Willamette, a large river
associated with 70 percent of the population of Oregon, is
getting cleaner in regard to some persistent toxic pollutants
that are a legacy of past management practices. A 257-mile
portion of the Columbia River between Umatilla, Oregon, and
Skamokawa, Washington, is also showing a similar trend.
These findings are based on research by U.S.
Geological Survey biologists. For 15 years, they have tracked
environmental contaminants in the Pacific Northwest using
ospreys and a variety of fish as environmental indicators.
Ospreys are a good indicator species of aquatic ecosystem
health because they eat almost exclusively large fish caught
within a short distance of nest sites spaced at fairly regular
intervals along large rivers. They often are directly exposed
to pollutants that accumulate in aquatic food chains.
"Some species, like the osprey, can
accommodate human-related changes reasonably well unless they
are consistently exposed to toxic chemicals" said USGS lead
scientist Chuck Henny. "It's gratifying to watch populations
rebound when harmful compounds are managed in an
environmentally responsible manner."
For the Willamette River, contaminant levels
in fish and osprey eggs were sampled in 1993, 2001, and 2006.
Levels of most contaminants declined, reproductive rates of
osprey were above that required to offset natural mortality,
and the osprey population increased dramatically. Declines in
contaminant residues in fish paralleled decreases found in
osprey eggs. During the study, only mercury concentrations
increased in osprey eggs and in a predatory fish called the
pikeminnow, a situation that merits continued monitoring
because of the highly toxic properties of mercury.
For the Columbia River, the scientists
compared population characteristics and contaminant residues
in eggs of ospreys nesting along the river in one set of
years, 1997 and 1998, with the same information from 2004. By
2004, the nesting osprey population had increased,
reproductive rates were higher, and many contaminant
concentrations in eggs were significantly lower than in the
1997 to 1998 samples. Again, mercury was the only contaminant
evaluated that showed a significant increase in 2004. However,
residue concentrations remained below levels known to affect
nesting success of birds.
The contaminants that were analyzed include
industrial pollutants, some banned pesticides and their
byproducts, and many other compounds that are known to harm
living organisms. Over 80 organic chemicals and total mercury
were evaluated, including DDT, a banned pesticide in North
America that causes thinning of egg shells. Also sampled were
polychlorinated biphenyls (PCBs), industrial compounds linked
to harmful health effects in humans.
The work continues. Additional osprey-egg
samples were collected from nests along both rivers in 2007
and 2008 for similar contaminant residue analysis, including
polybrominated diphenyl ethers (PBDEs), a new contaminant
used as a flame-retarding additive to many products. Levels
of PBDEs have increased dramatically in aquatic environments
in recent years. These compounds have toxic properties and
have been detected in fish-eating wildlife.
The details of the studies are published in
the science journals Archives of Environmental
Contamination and Toxicology (http://fresc.usgs.gov/products/papers/1880_Henny.pdf)
and Ecotoxicology. Additional information about the
studies and related USGS osprey research is available on the
web at: http://fresc.usgs.gov/.
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