Permafrost hydrology in changing climatic conditions: seasonal variability of stable isotope composition in rivers in discontinuous permafrost

Abstract

Role of changing climatic conditions on permafrost degradation and hydrology was investigated in the transition zone between the tundra and forest ecotones at the boundary of continuous and discontinuous permafrost of the lower Yenisei River. Three watersheds of various sizes were chosen to represent the characteristics of the regional landscape conditions. Samples of river flow, precipitation, snow cover, and permafrost ground ice were collected over the watersheds to determine isotopic composition of potential sources of water in a river flow over a two year period. Increases in air temperature over the last forty years have resulted in permafrost degradation and a decrease in the seasonal frost which is evident from soil temperature measurements, permafrost and active-layer monitoring, and analysis of satellite imagery. The lowering of the permafrost table has led to an increased storage capacity of permafrost affected soils and a higher contribution of ground water to river discharge during winter months. A progressive decrease in the thickness of the layer of seasonal freezing allows more water storage and pathways for water during the winter low period making winter discharge dependent on the timing and amount of late summer precipitation. There is a substantial seasonal variability of stable isotopic composition of river flow. Spring flooding corresponds to the isotopic composition of snow cover prior to the snowmelt. Isotopic composition of river flow during the summer period follows the variability of precipitation in smaller creeks, while the water flow of larger watersheds is influenced by the secondary evaporation of water temporarily stored in thermokarst lakes and bogs. Late summer precipitation determines the isotopic composition of texture ice within the active layer in tundra landscapes and the seasonal freezing layer in forested landscapes as well as the composition of the water flow during winter months.

Land Cover Change in the Lower Yenisei River Using Dense Stacking of Landsat Imagery in Google Earth Engine

“…However, World Meteorological Organization station records from Igarka and Norilsk show significant air temperature increases since 1985 [29,40]. These trends, representative of the northern and southern portions of the study area, suggest that the detected regional vegetation change can at least partially be associated with regional climatic warming.…”

“…For example, throughout the study area, the closed forest and tundra landscapes are interwoven in a complex pattern. Such spatial heterogeneity is controlled by highly variable permafrost conditions, reflective of a complex history of sedimentation and landscape development [29].…”

“…Warming permafrost and increasing active-layer thickness, which can potentially promote shrub expansion, were reported for several regions in Russia (e.g., [29,[58][59][60]). There are no long-term direct permafrost observations on undisturbed natural landscapes within the study area currently available through international open access sources such as the Global Terrestrial Network on Permafrost.…”

“…There are no long-term direct permafrost observations on undisturbed natural landscapes within the study area currently available through international open access sources such as the Global Terrestrial Network on Permafrost. However, the Igarka weather station has documented soil temperature at 3.2 m depth increasing from −0.5 • C in the late 1970s to +2.5 • C in 2014, and a corresponding lowering of the permafrost table to about 5 m depth was reported for an artificially grass-seeded surface nearby [29]. Similar observations from the Norilsk weather station revealed a progressive increase in active-layer thickness at a rate of 0.05-0.06 m/year over the 1999-2013 period [29].…”

Response of seasonal soil freeze depth to climate change across China

“…Due to global climate warming, significant efforts have been devoted to permafrost research, such as permafrost variations on the hemispheric-scale permafrost temperature changes (Wu and Zhang, 2008;Guglielmin and Cannone, 2012;Streletskiy et al, 2014;Wu et al, 2015), permafrost degradation (Jorgenson et al, 2006;Ravanel et al, 2010;Sannel and Kuhry, 2011;Streletskiy et al, 2015a;Park et al, 2016), hydrological processes in permafrost regions Wang et al, 2009;Park et al, 2013;Streletskiy et al, 2015b;Ford and Frauenfeld, 2016), feedbacks to climate change (Schuur et al, 2008;Park et al, 2015;Abbott et al, 2016), and other aspects. The increasing thickness of the active layer has been indicated by many observations in permafrost regions at high latitudes and altitudes (Brown et al, 2000;Frauenfeld et al, 2004;Zhang et al, 2005;Fyodorov-Davydov et al, 2008;Wu et al, 2010;Zhao et al, 2010;Callaghan et al, 2011;Liu et al, 2014a, b;Stocker et al, 2014).…”