Sulfate salt dynamics in the glaciated plains of North America

The semiarid glaciated plains of the North American continent, known as the prairies, are characterized by an undulating terrain rich in sulfate salts in the subsurface, with ephemeral streams and large numbers of wetlands containing seasonal or semi-permanent ponds. Salinization is a potential concern for the diverse community of vegetation, aquatic ecosystems, wildlife and agricultural production supported by the prairies, especially as a result of land use changes and climate change. In this paper, a literature review of prairie salt dynamics and distribution is presented. On the basis of observations from past field studies, a conceptual model describing prairie sulfate salt dynamics is proposed, which identifies a number of important zones of salt accumulation in the subsurface and in surface water. As is the case in any other environment, the distribution of salts is determined by the hydrological conditions, in particular subsurface flow pathways and evapotranspiration front locations. However, the semi-arid climate and glacial geology of the region result in unique and characteristic hydrological conditions and distributions of accumulated salts. The hydrology of the prairies is sensitive to land use, with the major changes over the past 100. years or so being conversion of prairie grasslands to annual dryland crops and drainage of wetlands. Moreover, in semi-arid environments the hydrological system is highly sensitive to climate variability and change. Hence, even small hydrological changes may result in mobilization of salts concentrated in the shallow subsurface, and, if sustained, may generate ground surface, wetland and surface water salinization. However, these changes are difficult to predict, involving multiple interacting processes, and it is therefore necessary to develop an improved, quantitative understanding of the coupled hydrological and geochemical processes in order to manage or adapt to future changes.