Mobilization of Geochemical Elements to Surface Water in the Active Layer of Permafrost in the Russian Arctic

The predicted increase of ground temperatures in the Arctic results in the deepening of the active layer and intensification of geochemical processes. Determining the responses of riparian soil systems to surrounding hydrological flows is important for understanding seasonal changes in hydrological processes. In this study, one soil core from a polygon rim (close to the Taz River, TA) and two soil cores from a riverine terrace (close to the Syoyakha River, SY and Murtyyakha River, MU) in Western Siberia, Russia, and their suprapermafrost water, adjacent surface flows, and river water were sampled for analysis of geochemical elements. Results showed that most elements above their respective detection limits began accumulating in the underlying gleyed layer during September-October in response to the deepest thaw in the active layer. This study focused on the highly mobile elements in the deepest layer; and found that the transport of organic matter in the upper layer carried these elements to both surface water ponds/flows and suprapermafrost water, and further, to the rivers. The efflux of released elements from surface soil to surrounding surface water appeared to be low. The best linear correlation for both surface flows and river water was with Mn; therefore, Mn may be a proxy for predicting the processes occurring within the active layer during the annual summer-autumn thaw. Moreover, landscapes with different ice contents may experience changes in the elements transported to surface waters. A general conceptual model for the response of elements to the thawing-freezing process of the active layer is established. Plain Language Summary The rapidly increasing atmospheric temperature in the Arctic has led to the feedback of permafrost thawing, which increases the depth of the active layer and accelerates chemical weathering. These processes may cause a further release of chemical substances to adjacent aquatic landscapes. Here, we investigated the horizontal and vertical transport of geochemical elements through surface flow and suprapermafrost water to river water from three cryogenic soil cores in the Arctic tundra. The results showed that most elements accumulated in the gleyed layer, which was deepest in the active layer during the thawing season. Mn, Ca, Mg, Al, and Ti showed the highest mobility from soil to suprapermafrost water to the surface flows/rivers, while Mn was the only element that could migrate from topsoil and suprapermafrost water to surface water and river water, indicating that Mn may be a proxy for predicting the processes occurring in the active layer during summer-autumn thawing.