Monitoring 13 years of drastic catchment change and the hydroecological responses of a drained thermokarst lake

Catastrophic drainage of thermokarst lakes transforms portions of former lakebed to terrestrial settings, which have largely unknown consequences for the remaining aquatic habitat. Old Crow Flats, northern Yukon (Canada), is a lake-rich area that has recently experienced a climate-driven increase in lake drainage frequency. A notable example occurred during June 2007 when Zelma Lake (originally 12 km2) lost over 80% of its volume. Here we integrate remote sensing techniques with in situ hydrological and limnological measurements over 13 years following drainage to (1) monitor water surface area and terrestrial land cover change and (2) identify associated effects on aquatic conditions. An airborne drone system was used to provide training data for land cover classification of AVIRIS-NG data, which indicated that tall willow shrubs covered 30.8% of the former lake area by 2017. Lake water isotope-derived deuterium excess increased during the 13-year record indicating that hydrological input increased with greater snowpack accumulation within encroaching vegetation. Limnological conditions were highly variable and eutrophic during the first few years following drainage but became more stable as vegetation colonized the former lakebed. This long-term study provides insight into aquatic responses to thermokarst lake drainage and shrub vegetation proliferation, which are increasing in many Arctic and subarctic landscapes.