Cordova students present scientific poster

Published on February 4th, 2010

By CRAIG BAILER, JENNY RANKIN AND JESSICA SMYKE

The following is an excerpt from a scientific poster created by the students and displayed at the 2010 Alaska Marine Symposium in Anchorage.

Baseline data is data that is used to document the current state of an ecosystem and can be used for comparison with data collected in the future. Having baseline data of the sediment in the Southcentral Alaska will allow for comparison between what the sediment was like prior to any damage versus what it's like if there was ever to be a catastrophic event.

The Exxon Valdez oil spill that occurred March 24, 1989, created appalling damages in Prince William Sound. However, there wasn't baseline data that they could be use to find out how much damage really was done. Since this event, organizations in Prince William Sound are collecting baseline data.

The Prince William Sound Regional Citizens' advisory council was established as a result of the Exxon Valdez oil spill. They sample 10 sites in Prince William Sound to monitor the presence of petroleum hydrocarbons and assess the ongoing impacts of routine tanker and terminal operations. Another example of a monitoring program is Mussel Watch, where samples are collected around the country to analyze 100 organic and inorganic pollutants in sediment, mussels and oysters. Since 1986, Mussel Watch participants have analyzed contaminant trends at 300 sites.

After the Exxon Valdez spill, the Auke Bay lab in Juneau created a hydrocarbon database to maintain a record of hydrocarbon signatures for the Prince William Sound region. This database maintains signatures for hydrocarbons from natural seeps or previous spills. A hydrocarbon signature is the ratio of the different types of hydrocarbon molecules found in a sample. Every hydrocarbon deposit has a unique ratio; therefore a hydrocarbon sample can be traced back to its source.

Hydrocarbon signatures are commonly identified using a gas chromatograph. The sample is injected into a tube containing an inert carrier gas, which carries it through an oven. The heat separates the hydrocarbon molecules according to their boiling point so that when the sample exits the oven a detector can output the precise percent composition of each hydrocarbon.

Samples collected for this project consist of both beach sediment and mussels living in the area. Sediments will show what hydrocarbons have reached the area and settled out of the water. Mussels, as filter feeders, collect hydrocarbons in their tissue when filtering the water to collect food. They can also show how hydrocarbons are retained by organisms after initial contamination.

We collected mussel and sediment samples from two sites to be analyzed to find out if they contained any traces of hydrocarbon and to determine the unique signature of the hydrocarbons. The sites were the Cordova Boat Harbor and the mouth of the Bering River. After analysis, the results will be added to the hydrocarbon database for the State of Alaska, maintained by NOAA's Auke Bay Lab in Juneau.

We found that the samples with the most hydrocarbons were in the Cordova Boat Harbor. Considering the harbor is constantly being polluted, this was expected. Samples taken by the pilings at Chilkat had some, but not a lot, and the samples taken by river spit were mostly free of hydrocarbons. Preliminary review suggests the signature found at Chilkat can be linked to the Bering Coal Fields. Modeling weathering of oil on these samples could provide us with a better understanding of the sources of hydrocarbons found in these samples.

This project taught us about the baseline conditions of the Bering River on the eastern edge of the Copper River delta. We can use the data we collected to compare hydrocarbon signatures from different sources. If there was to be a contamination in the future, the data could be used for differentiating the spilled oil from what was there before.

We would like to thank Auke Bay lab for their help, especially Jeep Rice, Mandy Lindeberg and Marie Larsen. This project was made possible by support from the Education Legacy Fund and the Prince William Sound Science Center. For more information on this project, please contact Kate Alexander, kalexanderpwssc@gmail.com.