ИСТИНА

Hillslope water tracks are landmark features of permafrost landscapes, yet their origin and future evolution are debated. Water track networks are believed to be fully developed fluvial networks constrained by permafrost. Hence one potential evolution scenario under future climate is rapid thermo-erosional development of water tracks. Permafrost tundra environment near Vorkuta, European Russian Arctic, N67°17’, E63°39’, is a model ecosystem for this scenario, developing under changing climate and permafrost degradation. Field works at the study site were carried out in September 2017 and repeated in 2021. Local streams and groundwater, from both boreholes and soil pits, were sampled for dissolved organic carbon (DOC) and nitrogen (DON), major ions, stable water isotopes and trace elements. Electrical resistivity tomography (ERT) was used to study permafrost distribution. First-order water tracks are minor linear depressions, occupied by Betula nana and rarely expressed in local topography, hosting fast subsurface runoff. Initial stages of permafrost perturbation, these forms are major pathways of DOC export from permafrost slopes, with mean DOC content is 29 ± 2 mg/L. Channelized runoff appears farther downslope, at the slope bend. Increased input from supra-permafrost groundwater is traced by Ca2+ increase, and rapid decline in DON content, from 0.1-0.3 mg/L to zero. At toeslopes adjacent to the Vorkuta R., larger streams coexist with polygonal depressions dissecting otherwise flat riverine terrace. In streams, the DOC content decreases to 12 ± 1.5 mg/L, while in depressions, it raises to 38-39 mg/L. Terrain perturbation by water tracks provides initial slope drainage and promotes fast DOC export from slope soils and its potential microbial consumption. Permafrost is discontinuous, and open taliks are present under water tracks and polygonal depressions, as shown by ERT survey. Taliks allow upward groundwater movement and drainage to the fluvial network. Sub-permafrost groundwaters