Mercury Temporal Trends in Top Predator Fish of the Laurentian Great Lakes from 2004 to 2015: Are Concentrations Still Decreasing?

TLDR: The Kendall-Theil robust regression with a cluster-based age normalization method to control for the effect of changes in lake trophic status was used by as discussed by the authors to determine the mercury (Hg) concentration trends in top predator fish (lake trout and walleye) of the Great Lakes (GL) from 2004 to 2015.

Abstract: Mercury (Hg) concentration trends in top predator fish (lake trout and walleye) of the Great Lakes (GL) from 2004 to 2015 were determined by Kendall–Theil robust regression with a cluster-based age normalization method to control for the effect of changes in lake trophic status When data from the GLs (except Lake Erie) are combined, a significant decreasing trend in the lake trout Hg concentrations was found between 2004 and 2015 with an annual decrease of 41% per year, consistent with the decline in regional atmospheric Hg emissions and water Hg concentrations However, a breakpoint was detected with a significant decreasing slope (−81% per year) before the breakpoint (2010), and no trend after the breakpoint When the lakes are examined individually, Lakes Superior and Huron, which are dominated by atmospheric Hg inputs and are more likely than the lower lakes to respond to declining emissions from areas surrounding the GL, have significant decreasing trends with rates between 52 and 78% per year f