Impacts of climate variability on wetland salinization in the North American prairies

U. Nachshon,S. R. Davies,A. Ireson,H. S. Wheater,G. van der Kamp

doi:10.5194/hess-18-1251-2014

Abstract

Abstract. The glaciated plains of the North American continent, also known as the "prairies", are a complex hydrological system characterized by hummocky terrain, where wetlands, containing seasonal or semi-permanent ponds, occupy the numerous topographic depressions. The prairie subsoil and many of its water bodies contain high salt concentrations, in particular sulfate salts, which are continuously cycled within the closed drainage basins. The period between 2000 and 2012 was characterized by an unusual degree of climatic variability, including severe floods and droughts, and this had a marked effect on the spatial distribution, water levels and chemical composition of wetland ponds. Understanding the geochemical and hydrological processes under changing environmental conditions is needed in order to better understand the risk and mitigate the impacts of future soil and water salinization. Here we explore salt dynamics in the prairies using field observations from St. Denis, Saskatchewan, taken mostly over the last 20 years. Measurements include meteorological data, soil moisture, soil salinity, groundwater levels and pond water volume, salinity, and chemical composition. The record includes periods of exceptional snow (1997, 2007) and periods of exception rainfall (2010, 2012), both of which resulted in unusually high pond water levels. Measurements indicated that severe pond salinization only occurred in response to extreme summer rainfall. It is hypothesized that since rainfall water infiltrates through the soil towards the depressions, while snowmelt water flows mainly as surface water over frozen soils, they have markedly different impacts on salt transport and pond salinization. Whilst this hypothesis is consistent with our conceptual understanding of the system, it needs to be tested further at a range of field sites in the prairies.

Highlights

Surface water and shallow groundwater salinization is a problem affecting agriculture, water resources and ecosystem health in many areas of the world, including Australia (Dehaan and Taylor, 2002; Rengasamy, 2006), the Aral Sea region (Micklin, 2007), playas and sabkhat environments (Tyler et al, 2006) and many other areas (Rengasamy, 2006)
A important factor is prefreeze of soil moisture content: if the soils are very wet when they freeze they have a very low infiltration capacity, and runoff over frozen soils during the subsequent melt period is more intense. This mechanism explains the widespread flooding in Saskatchewan and Manitoba in 2011, which was attributed to high rainfall in the summer of 2010, leading to high antecedent soil moisture
In concurrence with the conceptual model of Nachshon et al (2013), it was shown that under wet conditions associated with rainy summers, large fluxes of salts from the subsurface are flushed into the ponds

Summary

Introduction

Surface water and shallow groundwater salinization is a problem affecting agriculture, water resources and ecosystem health in many areas of the world, including Australia (Dehaan and Taylor, 2002; Rengasamy, 2006), the Aral Sea region (Micklin, 2007), playas and sabkhat environments (Tyler et al, 2006) and many other areas (Rengasamy, 2006). Salt dynamics are driven by hydrological processes, which cycle seasonally and change over long timescales as a result of climate variability and change, and changes in land use and land management practices. This paper takes the salt-rich glaciated plains of North America, known as the prairie pothole region, as a case study to explore how recent climate variability has dramatically affected the salinity of ponds. The region supports a diverse community of wildlife species and major

Methods

Results

Conclusion