3.3. Metals, metalloids and non-metals
Elemental concentrations exhibited a large variability (Figure 5), with maxima typically found in P1-P2 (Duvanny Yar) samples (Be, Co, Sb, Se, Sr, V), in the lower layers of lake waters (As, Cd, Cu, Fe, Mn, Ni, Si, Zn) or in single samples from Kolyma river (Ba, Li, Mo). Only Al showed the highest concentration in permafrost ice (sample P3). Multiple heavy metals showed much higher concentrations in permafrost creeks and ice (As 1.24-4.23 µg L-1, Cu 1.82-11.4 µg L-1, Co 0.57-3.99 µg L-1, Mn 122-1300 µg/L, µg L-1Ni 3.36-16.5 µg L-1) than in Kolyma and its tributaries (As 0.22-0.81 µg L-1, Cu 0.70-5.72 µg L-1, Co 0.01-0.05 µg L-1, Mn 0.61-14.1 µg L-1, Ni 0.2-1.87 µg L-1(Suppl. Mat. 2 ). Permafrost samples also contained metals that were not typically found in other samples: Ti (15.7-30.3 µg L-1) and Hg (0.128-0.131 µg L-1). In the lakes, several metals concentrations increased with water depth: Fe, Mn, Ni and Zn concentrations did so in both lakes; Al, K, Sr in Lake 1, and Cu, Pb, Sb in Lake 2. The only instances of an opposite direction of change were Mo, Na and Sb in Lake 1. The highest concentrations of selected elements in this study were observed in lake bottom waters, e.g. [Cu] = 1370 µg/L, [Mn] = 4610 µg/L, and [Zn] = 687 µg/L. Bottom lake waters, permafrost creeks and ice were also enriched with phosphorus (up to 34.7 µg/L in Lake 2, up to 512 µg/L in creeks and 43.3 µg/L in ice) (Suppl. Mat. 2 ).
Enrichment factors (EF) of all the collected samples indicate significant or higher enrichment in heavy metals (As, Cd, Co, Cu, Mn, Ni, Pb and Zn). The highest EFs in the dataset were found in lake bottom waters for As, Co, Cu, Mn, Ni, Pb and Zn (Suppl. Mat. 1, Table S4 ). Noteworthy is also the extremely high enrichment of the permafrost ice and creeks, as well as Maly Anyui (A2) sample in Hg. Furthermore, the concentration level of Cd was higher in the collected samples connected to permafrost than elsewhere: in permafrost creeks, permafrost ice, lower layers of lake water and in a few samples from the Kolyma river in the K3 cross section. In that particular cross section, the enrichment in Cd was higher in the mid-stream (samples K31 and K32) than in the river bottom waters (K31b, K32b), testifying to the limited mixing of dissolved elements in the vertical profile of the river, suggesting their local supply.