Bi-phasic trends in mercury concentrations in blood of Wisconsin common loons during 1992-2010.

We assessed the ecological risk of mercury (Hg) in aquatic systems by monitoring common loon (Gavia immer) population dynamics and blood Hg concentrations. We report temporal trends in blood Hg concentrations based on 334 samples collected from adults recaptured in subsequent years (resampled 2-9 times) and from 421 blood samples of chicks collected at lakes resampled 2-8 times 1992-2010. Temporal trends were identified with generalized additive mixed effects models and mixed effects models to account for the potential lack of independence among observations from the same loon or same lake.

Bioaccumulation patterns and temporal trends of mercury exposure in Wisconsin common loons.

A long term field study was initiated by the Wisconsin Department of Natural Resources in 1992 to elucidate patterns of common loon (Gavia immer) mercury (Hg) exposure. Analysis of loon blood and feather samples collected from recaptured adult loons in Wisconsin 1992-2000 found evidence of a decline in overall body burdens of mercury in common loons for this region. The interval between sampling individual loons spanned 2-8 years, a sufficient length of time to observe a change in tissue Hg concentrations.