Effect of permafrost on geochemistry in a Canadian peat plateau bog

Abstract

Permafrost is a common feature in the Canadian Subarctic, resulting in the development of distinctive wetland forms, such as peat plateaux, which are perennially frozen peatlands. The geochemistry of a peat plateau bog in East Little Bear River Valley, Northwest Territories, is discussed, including variations in botanical and mineralogical composition, and the influence of permafrost. The riparian margin of the plateau bog is unfrozen, but permafrost occurs at 0.68 m depth 10 m inland. Cores taken in these 2 sites exhibit variations in peat stratigraphy, but possess a similar C-shape ash distribution. In the core not affected by permafrost, most elements studied (Al, Ba, Cr, Fe, K, Mg, Na, Si, Th, Ti, V) also display a C-shape distribution, and their concentration can be explained in terms of mineral matter abundance and variety. Halogens (Cl, I, Br), on the other hand, are mainly associated with the organic fraction, whereas Ca and Se appear to be associated with both the organic and inorganic fraction. In the permafrost-affected core, all elements, independently of their organic or inorganic affinity, exhibit a substantial enrichment immediately above the permafrost table, whereas they are depleted immediately below. This is inferred to be the result of solute redistribution linked with ice formation caused by upward permafrost growth and downward seasonal freezing.