Gleysolic soils of Canada: Genesis, distribution, and classification

Abstract

Bedard-Haughn, A. 2011. Gleysolic soils of Canada: Genesis, distribution, and classification. Can. J. Soil Sci. 91: 763–779. This review examines the pedogenesis of Gleysolic soils, including how they affect and are affected by land use and climate change. In the Canadian System of Soil Classification, the Gleysolic Order includes all those soils with morphologic features that provide dominant physical evidence of oxidation-reduction processes or gleying. Gley features include dull coloured soil matrices and/or brightly coloured mottles, which arise due to periodic or permanently saturated conditions. Under saturated conditions, oxygen is rapidly depleted and alternative terminal electron acceptors (such as iron, Fe3+) are used by microorganisms in the decomposition of organic matter. Gleysolic soils are found throughout Canada, either in low-lying landscape positions in association with better-drained soil orders (e.g., Prairie Pothole region), or as the dominant soil type where topography and/or a slowly permeable substrate prolong the period of saturation (e.g., Clay Belt of northern Ontario and Quebec). These soils are often highly fertile agricultural land and are commonly drained for production, altering the soil-forming environment. Gleysolic soils have also been found to be potentially significant sources of greenhouse gas emissions due to high levels of denitrification and methanogenesis under their characteristic reducing conditions. Given their economic, ecologic, and environmental significance, further research is required to refine our understanding and classification of Gleysolic soils, particularly with respect to (1) how Gleysols are affected by human- or climate-change-induced changes to the drainage regime (either progressing towards reducing conditions or regressing to a non-redoximorphic state), (2) classification of carbonated and saline Gleysols, and (3) pseudogley versus groundwater Gleysols.