Mercury trends in colonial waterbird eggs downstream of the oil sands region of Alberta, Canada.

Mercury levels were measured in colonial waterbird eggs collected from two sites in northern Alberta and one site in southern Alberta, Canada. Northern sites in the Peace-Athabasca Delta and Lake Athabasca were located in receiving waters of the Athabasca River which drains the oil sands industrial region north of Fort McMurray, Alberta. Temporal trends in egg mercury (Hg) levels were assessed as were egg stable nitrogen isotope values as an indicator of dietary change. In northern Alberta, California and Ring-billed Gulls exhibited statistically significant increases in egg Hg concentrations in 2012 compared to data from the earliest year of sampling. Hg levels in Caspian and Common Tern eggs showed a nonstatistically significant increase. In southern Alberta, Hg concentrations in California Gull eggs declined significantly through time. Bird dietary change was not responsible for any of these trends. Neither were egg Hg trends related to recent forest fires. Differences in egg Hg temporal trends between...