Effect of Shoreline Subsidence and Anthropogenic Activity on Northwest Territories’ Lakes.

Abstract

Thawing permafrost – in the form of shoreline retrogressive thaw slump events – influence adjacent arctic tundra lake systems near Inuvik, NT. Slump-affected lakes demonstrated lower organic matter and key nutrients such as phosphorus (P), as well as greater water clarity. Key terrestrial permafrost soil indicators such as U, Sr, and Li, were identified to be elevated in slump-affected lakes, while other more biologically important metals (e.g. Fe, Mn) were significantly lower in affected lakes. These physical-chemical changes led to increasing P-limitation for both phytoplankton and periphyton, resulting in lower phytoplankton biomass (Chl-a). Using P as covariate in ANCOVA analysis, slump-affected lakes were also lower in phytoplankton biomass (Chl-a) relative to other study landscapes across the Canadian low-Arctic. Slump-affected lakes also exhibited lower organic matter leading to lower overall Hg concentrations within slump-affected lakes. However, this same reduction in dissolved organic carbon (DOC) has also led to an increase in bioavailable Hg, and increased bioaccumulation of Hg in both periphyton as well as macroinvertebrate species in our most disturbed lakes with DOC concentrations less than 6 and 9 mg DOC/L, respectively. A negative correlation between Hg bioaccumulation and DOC above these concentrations was also observed, and is the typical condition within reference lakes. The legacy impacts of mining were also observed in lakes within 25 km of the Giant Mine roaster stack in the Yellowknife region. Increases in both arsenic (As) and methyl mercury were measured in lakes nearer to the mine, with As concentrations well above water quality guidelines in lakes within 17 km of the roaster stack. This research highlights the necessity of baseline environmental monitoring prior to resource development, as well as the potential for compounded influences of such development within sensitive permafrost regions exposed to thawing.