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Prior to 1980 there was no systematic collection
of precipitation for chemical analysis for the southern Rocky Mountains.
Thus, we use lake sediment paleolimnological techniques to reconstruct
trends in deposition over time from the mid-1800s to the present
(Baron et al. 1986). Lake sediments are cored and analyzed for metals
and diatom community assemblages. Sequential layers from the sediment
cores are radiometrically dated to reconstruct patterns of metal
deposition that could be attributed to an increase in industrial
emissions. Diatoms have very specific pH preferences, which are
well documented, so that knowledge of diatom community changes over
time can be used to interpret lake chemical composition over time
(Charles and Norton 1986).
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