Reemission of inorganic pollution from permafrost? – a freshwater
hydrochemistry study in the lower Kolyma basin (North-East Siberia)
Abstract
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-HCO 3-Cl-SO
4 ionic water type (with mineralisation in the range
600-800 mg/L), while permafrost ice and thermokarst lake waters were the
HCO 3-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 have we detected dissolved
Ti or Hg. 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 Cu,
4610 µg/L Mn, and 687 µg/L Zn in the bottom water layers.
Permafrost-related waters were also enriched in dissolved phosphorus (up
to 512 µg/L 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.