To the editor:
Some of the variability observed between studies of mercury impact on loons may be due to a complication in Adirondack geology.
Adirondack geology places granitic and limestone-marble-rich soils in relatively close proximity, given the bands of complex faults and geology. Some acidic lakes are quite close to other lakes buffered by limestone and other calcium-carbonate-rich rocks and soils. Mercury is carried from the same sources as the acid in the acid rain that did so much damage to the 'Dacks. However, non-acidic soils do a much better job of buffering mercury and reducing mobility, which may modify its impact on loon populations. If the soil type associated with the various lakes were included as a regression variable in the analysis of loon procreation, it may show significant interactions with mercury content and might resolve some of the differences between studies.
Daniel E. Platt