Application of hydropedology to predictive mapping of wetland soils in the Canadian Prairie Pothole Region

• Wetland soils had a predictable spatial pattern of distribution.
• Salt transport occurs through both episodic fill-and-spill events and groundwater.
• The maximum pond water level controls soil distribution in freshwater wetlands.
• The recharge/discharge soil boundary is an enduring record of pond water levels.

Digital soil mapping of wetland soils has met with limited success in part because terrain attributes based on hillslope hydrology are inappropriate for predicting the pedological consequences of wetland hydrology. Our objective is to synthesize recent developments in the hydrology and hydrochemistry of wetlands in the northern Prairie Pothole Region (PPR) and apply this enhanced understanding to the predictive mapping of wetland soils. The landscape-scale distribution of freshwater vs. brackish/saline soils is controlled by salt transport by episodic surface fill-and-spill events and (more rarely) by groundwater–surface interactions. Both sets of hydrological processes lead to ponds in lower-elevation spillways having more saline conditions. At nine freshwater ponds studied at three study areas (Swift Current, St. Denis, and Melfort, Saskatchewan) the elevation threshold between wetland-recharge (i.e., gleyed soils with deep (2- to 5-m) zones of carbonate depletion) and wetland-discharge (i.e., carbonated soils with no B horizon formation) soils corresponds to the maximum water level recorded at the nine ponds over approximately 40 years of water level measurements. The band of discharge soils surrounding the wetland extends for approximately 1 m elevation above of this water level elevation. The spatial distribution of wetland-recharge and wetland-discharge soils in freshwater ponds provides an enduring record of pond hydrological conditions and can be readily adapted to predictive soil mapping in this region.