1. INTRODUCTION
Permafrost loss has been observed widely in the Northern Hemisphere since the second half of 20th century (Streletskiyet al. , 2015) and it has impacted markedly both terrestrial and aquatic environments (Mann et al. , 2022; Vonk et al. , 2015). Further significant changes are predicted in permafrost environments during the 21st century (Smith et al. , 2022; Streletskiy et al. , 2021; Teufel & Sushama, 2019) as the climate warms (Overland J., 2017; Overland et al. , 2014). Such changes will be both vertical and horizontal, resulting in deeper active layers (Abramov et al. , 2021), shrinking permafrost extent, and the retreat of its respective zones (Lim et al. , 2019; Streletskiy, 2021). The progressing permafrost degradation leads to important and lasting changes in geomorphological processes (Rudyet al. , 2017; Tananaev & Lotsari, 2022), hydrological phenomena (Rudy et al. , 2017; Suzuki et al. , 2021) and biogeochemical cycles (Grosse et al. , 2016; Mann et al. , 2012; Vonk et al. , 2015).
Hydrochemical changes in permafrost regions are increasingly probable, leading to both temporary and permanent hazards to the surface water quality in the Arctic (Brubaker et al. , 2012; Gunnarsdóttiret al. , 2019). Permafrost active layer deepening and the formation of new thermokarst lakes, taliks and drainage pathways (Dzhamalov & Safronova, 2018; in’t Zandt et al. , 2020; Tananaev & Lotsari, 2022) all lead to changes in the migration of chemical compounds (Frey & Mcclelland, 2009; Monhonval et al. , 2021) both horizontally and vertically (Ji et al. , 2021; Tananaev et al. , 2021). The newly formed drainage pathways may leach chemical compounds from layers previously disconnected from groundwater flow (Jiet al. , 2021; Lim et al. , 2019). Thermoerosion phenomena lead to intense erosion and thaw slump formation. Such phenomena impact the fluvial transport of suspended sediment and chemical compounds along the main hydrological pathways, to the estuaries and the ocean (Chalovet al. , 2018; Frey & Mcclelland, 2009; Kokelj et al. , 2013; Toohey et al. , 2016). Both natural and antropogenic chemical compounds may become mobilised from permafrost into surface waters (Kosek et al. , 2019; Lehmann-Konera et al. , 2018), and the anthropogenic compounds may be of both local and long-range-transport origin (Potapowicz et al. , 2019; Szopińskaet al. , 2016).
The studies on the hydrochemical impacts of climate change in Siberian Arctic rivers have focused mainly on the organic carbon (OC) transport, including the dissolved OC (DOC), suspended particulate OC (POC) and riverbed sediment OC (SOC) (e.g., Holmes et al. , 2012; Jonget al. , 2022; Mann et al. , 2012; Wild et al. , 2019). Compared to the research on OC, the recognition of inorganic elements transport, including heavy metals, is relatively poor and limited to selected elements (Ji et al. , 2021; Kuchmenko et al. , 2002; Lim et al. , 2019). Systematic research on the potential accumulation of heavy metals in permafrost has only been conducted on mercury (Wang et al. , 2022). Therefore, we present a study on the possible release of contaminants from permafrost into freshwater. Our objective was to perform a detailed hydrochemical assessment of permafrost thaw impact on the inorganic chemicals occurrence in the lower Kolyma River basin. We investigate this question in various freshwater environments: thermokarst lakes, permafrost ice, permafrost thaw creeks, and in watercourses representing various proportions of permafrost thaw supply.