Tiller, Brett L., J.D. Marco and W.H. Rickard. “Metal Concentrations, Foraging Distances, and Fledging Success of Great Blue Herons Nesting Along the Hanford Reach of the Columbia River.” Environmental Monitoring and Assessment 104: (2005) 71-79. (reviewed by Allyson Goldstein)
Summary:
This study examines metal concentrations in pre-flight herons in the Hanford Reach of the Columbia River in order to determine if great blue herons in the region are at risk of potential metal ingestion from contaminated river biota, especially fish. Tiller et. al studied nesting sites along three different parts of the Columbia River. One was upstream of all nine retired plutonium production reactors, one was downstream of all of the reactors, and the third was in the middle. They analyzed both excrement and liver samples from the pre-flight herons in order to determine cadmium, chromium, lead, zinc and copper levels in the birds. They wanted to discover if birds nesting along different places along the Columbia River had ingested food with different metal concentrations.
Researchers also visibly tracked herons to see how far they flew to look for food for the pre-flight birds. In addition, researchers measured fledging success and eggshell thickness as indicators of the health of the local heron population. They discovered that the Hanford Reach has significantly higher fledgling success than heron colonies elsewhere in the United States.
Metal concentrations in heron excrement were consistent with metal concentrations in nearby sediment samples, which means that heron excrement is a useful indicator for metal contamination in a heron's diet. Researchers found little difference in metal levels in the three different populations along the Columbia River. However, mercury concentrations in heron livers on the Hanford Reach were approximately ten times higher than Oak Ridge herons. The study concludes that the great blue herons of the Hanford Reach are one of the healthiest populations in the continental U.S.
Critique:
While many studies focus on fish, in particular salmon, in the Columbia River, this study is useful because it demonstrates how river contamination can affect species outside of the river itself. The study's conclusions, however, seem a bit hastily drawn, and though the study states a very specific methodology, it never really explains why the authors think the great blue heron population in the Hanford Reach is one of the healthiest in the continental U.S.
Stylistically, the article is very readable and easy to follow. It presents the statistics in a clear and concise matter, and explains why researchers did the study. It also provides a helpful introduction about the history of the Hanford reach and a map of the region.
One of the article's shortcomings is that the U.S. Department of Energy funded the study. Because the Department of Energy is major stakeholder in the cleanup of the Hanford reach, its conclusions about the success of the cleanup need to be examined
(see another review by Bethany Parkyn)
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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