Mercury concentrations in northern pike (Esox lucius) from boreal lakes with logged, burned, or undisturbed catchments

We measured total Hg and stable isotopes (delta C-13 and delta N-15) in nor thern pike (Esox lucius) from 19 Boreal Shield lakes with undisturbed, logg ed, or burned watersheds. Average Hg level in standard 560-mm northern pike , on a dry weight basis, was significantly higher in logged lakes (3.4 mug. g(-1)) than in reference lakes (1.9 mug.g(-1)). Average Hg concentrations i n burned lakes (3.0 mug.g(-1)) did not differ significantly from those in l ogged and references lakes. Concentrations of Hg normalized to trophic posi tion determined from isotopic composition yielded similar results. Mercury levels were above the WHO safe consumption limit in all logged lakes. Mercu ry in northern pike was correlated with methyl mercury in zooplankton (+), total N (+), pH (-), alkalinity (-), sulfate (+), dissolved organic C loadi ng (+), and light attenuation in lake water (+). Stepwise multiple regressi ons explained 79% of the variability in Hg in fish and included methyl merc ury in zooplankton, pH, and sulfate as independent variables. Explained var iability increased to 92% when a second-order lake with an exceptionally la rge drainage area was excluded. Our results suggest that extensive logging activities may disrupt the natural cycling of Hg in watersheds and increase Hg levels in the aquatic biota.