hydrological.net

Underlying much of the Arctic is permafrost: sediment or soil which has remained below 0°C for at least two years. Permafrost acts as an aquiclude, restricting the flow of water. Aquifers in permafrost may be located above, within, or below the frozen layer. The active layer is the topmost layer of permafrost which thaws during the summer, allowing organic processes to occur. As it often becomes saturated, the active layer is prone to mass wasting. Thermokarst landscapes can develop as permafrost melts. The presence of permafrost causes Arctic basins to behave like impermeable catchments, as the frozen ground cannot absorb runoff and contribute to base flow to any significant degree. Below large lakes, however, taliks often develop. These areas of unfrozen ground can link lakes with subpermafrost aquifers. Significant amounts of organic material have collected in permafrost due to cryoturbation, a process which moves organic materials down the active layer to the unfrozen permafrost.

Permafrost is warming along with the rest of the Arctic. A study of Arctic lakes in Siberia observed that many lakes have disappeared or shrunk in the last 30-40 years. Lakes in areas of continuous and discontinuous permafrost experienced the most shrinkage, likely due to permafrost degradation allowing them to drain to the subsurface. As warming continues, some regions of the Arctic will see shifts in the type of permafrost they experience (continuous to discontinuous, or discontinuous to sporadic) and deepening of the active layer, accompanied by changes in vegetation and sedimentation. Thawing permafrost could release more sediment into waterways, increasing turbidity and decreasing light availability for photosynthetic organisms. At the same time, more nutrients are likely to be released from the permafrost. Permafrost degradation will also affect the distribution and size of peatlands and other wetlands, which are important productive areas of the Arctic.

The active layer is normally leached of nutrients but often has high organic carbon content. Nutrients and other minerals may be concentrated in permafrost below the active layer. As warming occurs, this deeper permafrost will start to melt and release salts and nutrients. What impacts will this have on aquatic organisms? Very high concentrations of calcium and sulfate were found in thaw slumps, where slumping of the active layer exposed deeper permafrost to the surface and allowed it to begin thawing. Some research has been done on pairs of Arctic lakes to determine the affect that slumping has on Arctic lake biota. Slumped lakes were found to have lower levels of dissolved organic carbon than their unslumped counterparts, higher ion concentrations, as well as slightly lower levels of nutrients in the water column, which was not expected. No significant change in planktonic chlorophyll content was observed. Macrophytes and bacteria might be responsible for the lower levels of nutrients, and research is continuing.