Potential Impacts of Increased Thermokarst Activity on Aquatic Ecosystems in Arctic Landscapes

Recent observations suggest that thermokarst formation has increased in the area near the Toolik Lake Field Station in the foothills region of the Brooks Range on the North Slope of Arctic Alaska. This area has been the subject of continuous observation and research since the early 1970's and few thermokarsts had been observed here until the last few years. In August 2003 a thermokarst formed catastrophically on a slope in the headwaters of the Toolik River after an intense rainfall in the area. The mode of failure was unusual. The area lies in a region with silt-rich deposits which apparently also contain extensive ice wedges. Prior to the hillslope failure, a large ( ∼ 0.75 m x 2 m) tunnel formed ∼1 m below the surface, extending at least 50 to 100 m down slope. The initial failure occurred when the roof of this tunnel collapsed. Subsequently, peat and soil continued to erode from the site leading to a displacement of ∼4000 m ³ of sediment by August 2004. Macronutrients (in particular NH ₄ and PO ₄) and suspended sediments in the water draining the thermokarst have increased by 1 to 2 orders of magnitude. The impacts of this thermokarst formation on aquatic ecosystems are uncertain. On the one hand, our previous research has shown that even minor increases in nutrient loading (especially PO ₄) stimulate primary and secondary production in these streams. However, the massive increase in sediment loading could smother benthic communities and negate the positive impacts of increased nutrient delivery. We have calculated that the mass of sediment mobilized by this individual failure is sufficient cover a 20 to 40 km length of the river with sediment to a thickness of 0.5 cm. During the 2004 field season we noted at least 2 new thermokarsts with failure modes similar to the one observed in 2003 along with numerous slip failures. Although the terrestrial area impacted by these thermokarsts is limited, the aquatic habitat altered by these failures is extensive. It is likely that warming in the Arctic foothills region will lead to additional and perhaps accelerated thermokarst formation which may have considerable impacts on aquatic ecosystem over wide areas and at least decadal time scales.