Does Palsa Thaw in Northern Finland Contribute to Remobilisation of Metals Accumulated in Peat Into Surface Waters?

ABSTRACT Permafrost is rapidly degrading in the sporadic zone, including palsa mires in Scandinavia. Peatlands in the area have likely accumulated heavy metals from atmospheric deposition of industrial contaminants in the wider region. As the palsa mire chemical composition is not well known, and in other permafrost regions the permafrost thaw may contribute elevated heavy metal concentrations in surface waters, we hypothesized that palsa mires may act as a source of inorganic input to the local aquatic environment. We verified this hypothesis in a short‐term study of water and sediment composition in the area of Skalluvaara palsa mire in northern Finland. During a time of likely palsas thaw, we compared the physical and chemical parameters in the collected water and aquatic sediment samples from the Skalluvaara palsa mire and its drainage to other streams, rivers, and lakes (in the area facing Varanger Fjord that is, the Jääräjoki‐Nuorgam area). The determined levels of water temperature, conductivity, pH, oxidation–reduction potential (ORP), and isotope ratios (δ 17 O, δ 18 O, and δ 2 H), and the elemental and ionic concentrations, total organic carbon (TOC), and chlorophyll a concentration showed clear differences for objects related to the Skalluvaara palsa mire and outside of it, as revealed in the principal component analysis (PCA). In particular, elevated rock weathering indices and anomalous concentrations of Ni, Zn, and Hg were found in these aquatic environments. However, the highest concentrations of several metals and metalloids, including heavy metals, were found in the water not impacted by palsa mires, and their concentrations correlated with TOC concentrations. We conclude that other sources are more important inorganic inputs in the area, and it may be possibly connected to the erosion of peat or soil, which requires further investigation.