Reemission of inorganic pollution from permafrost? A freshwater hydrochemistry study in the lower Kolyma basin (North‐East Siberia)

Permafrost regions are under particular pressure from climate change resulting in widespread landscape changes, which impact also freshwater chemistry. We investigated a snapshot of hydrochemistry in various freshwater environments in the lower Kolyma river basin (North‐East Siberia, continuous permafrost zone) to explore the mobility of metals, metalloids and non‐metals resulting from permafrost thaw. Particular attention was focused on heavy metals as contaminants potentially released from the secondary source in the permafrozen Yedoma complex. Permafrost creeks represented the Mg‐Ca‐Na‐HCO₃‐Cl‐SO₄ ionic water type (with mineralisation in the range 600–800 mg L⁻¹), while permafrost ice and thermokarst lake waters were the HCO₃‐Ca‐Mg type. Multiple heavy metals (As, Cu, Co, Mn and Ni) showed much higher dissolved phase concentrations in permafrost creeks and ice than in Kolyma and its tributaries, and only in the permafrost samples and one Kolyma tributary we have detected dissolved Ti. In thermokarst lakes, several metal and metalloid dissolved concentrations increased with water depth (Fe, Mn, Ni and Zn – in both lakes; Al, Cu, K, Sb, Sr and Pb in either lake), reaching 1370 μg L⁻¹ Cu, 4610 μg L⁻¹ Mn, and 687 μg L⁻¹ Zn in the bottom water layers. Permafrost‐related waters were also enriched in dissolved phosphorus (up to 512 μg L⁻¹ in Yedoma‐fed creeks). The impact of permafrost thaw on river and lake water chemistry is a complex problem which needs to be considered both in the context of legacy permafrost shrinkage and the interference of the deepening active layer with newly deposited anthropogenic contaminants.