Pollution history documented through shell remains provides tool to study ecosystem change

Without destroying endangered freshwater mussels

In the early 1900s, there were 42 species of freshwater mussels in the North Fork of the Holston River in Southwest Virginia. There were 33 downstream of Saltville. Now there are only nine species of mussels downstream of Saltville, and none directly below Saltville. When Virginia Tech geosciences student Megan Brown of Colonial Heights, Va., decided to study the local extinctions of these creatures, some of which have been known to live 200 years and many of which are endangered species, she didn’t want to have to use the traditional means of pulverizing them to measure chemical uptake.

At the joint meeting of the Northeastern and Southeastern Sections of the Geological Society of America, Brown will report on her non-invasive means to determine whether pollution or environmental stresses are threatening freshwater mussels. The GSA meeting is March 25-27 in Tysons Corner, Va.

Brown measured the mercury content in freshwater mussel shells in the river near Saltville, Va., where industry had polluted the river from 1950 until 1972, measured the damage done to the shells, and observed stages of recovery.

She looked at two sites upstream, unaffected by the pollution, at a site at Saltville, the point of the contamination, and at two sites downstream. “There was a very low level of mercury in shells upstream. I had to go 30 miles downstream to find a site with mercury levels at the background levels of the upstream sites,” Brown says

Dead mussel shells reflected the levels of mercury, with high levels directly below Saltville and decreasing levels with increasing distance from Saltville. Brown examined shells to see if those from areas with no living populations looked different from shells in areas with living populations. She observed such characteristics as whether shells were still hinged together, external luster, edge preservation, and how broken they were.

“Wear could have been due to a change in stream gradient, but we found the most destruction was at the site of heaviest contamination and determined the heavy destruction was because there was no input of fresh-dead material,” Brown says. “And wear was present whether the shell was thin or thick.”

By documenting what happened to the mussels near Saltville, Brown has developed a strategy for study of other areas. “We can look at geochemical characteristics of the shell to determine what kind of pollution has impacted a system – to determine whether the local extinction is from pollution or an environmental stress such as heavy sedimentation,” explains Brown. “And we can observe the kinds of destruction, such as the kinds of damage to shells, to help determine how long ago populations were still alive.”

Brown will present the paper, “Using geochemical and taphonomic signatures of freshwater mussel shells to explore industry-related extirpations in the North Fork Holston River, Va. (60-8),” at 10:40 a.m. Saturday, March 27, in the Lord Thomas Fairfax Room of the Hilton McLean Tysons Corner. Co-authors are Virginia Tech geological sciences professor Michal Kowalewski, biology professor Donald Cherry, fisheries and wildlife professor Richard Neves, and geosciences professor Madeline Schreiber.

Brown, who received her undergraduate degree in biology from the University of Virginia, says she undertook the mussel study because “I’m interested in learning about the problems we’ve created and how we can remedy them.” She expects to receive her master’s degree from Virginia Tech in May and would like to work with the Fish and Wildlife Service.