SALEM, Ore. Most people know that tree rings tell stories about the age of the tree, the history of rainfall or drought in an area.
But growth increments on Pacific Northwest river mussels, some of which are as old as 50 years, can also tell the tales of the water quality of the streams and creeks where they live.
"There is a ton of information in here," researcher Jason Dunham said about the mussel shells. "It is basically a stream of data. We just have to figure out what it is telling us."
Scientists are hoping to unlock a decades-long, accurate record of the health of aquatic areas.
Consistent information about temperature, for example, is only known for about a handful of sites in Oregon and only for as long as 20 years. Researchers are hoping that freshwater mussels can fill in the gaps, providing historical data from periods before any water sampling was done.
Dunham, a scientist with the U.S. Geological Survey in Corvallis, has collected about 450 mussels from streams across Oregon, including the Willamette Valley, and into central Idaho.
Researcher Bryan Black now is examining cross-sections of those mussel shells at Oregon State University's Hatfield Marine Science Center in Newport.
"Tree rings are one of the leading indicators for global change and climate history," Black said. "We are hoping that clams and mussels and long-lived fish will give us comparable records for aquatic systems."
The first step for scientists is to ensure that the growth increments on shells directly relates to the temperature data in streams. After that, they can use the shells to determine the water temperature for areas and time periods where that information wasn't collected.
A historical look at Oregon's streams could also help scientists understand more about salmon. Freshwater mussel populations would not survive long without salmon, which nourish mussel larvae for several weeks.
For Ray Kinney, the decline of mussels along Deadwood Creek, which feeds into the Siuslaw River, is directly related to fewer salmon and other marine species returning to the area.
Kinney, a director for the local soil and water conservation district, guesses that mussels are suffering because fewer salmon and maybe even lamprey are bringing marine nutrients, especially calcium, back to the creek.
He now is documenting the rate at which they are dying in Deadwood Creek and comparing that to healthy populations in Steamboat Creek on the North Umpqua River.
"There used to be tons and tons of salmon here," Kinney said. "Marine-derived nutrients like calcium was brought up with the salmon. But now with the salmon decline, that is not happening."