Multiple land use activities drive riverine salinization in a large, semi-arid river basin in western Canada

Salinization is increasingly recognized as a global issue. However, the relative importance of different drivers across a broad range of ions and ecosystems is not well understood. This study examined spatial and temporal dynamics in riverine salinity (conductivity, Ca2+, Mg2+, Na+, K+, SO42-, Cl- and HCO3-) in the South Saskatchewan River Basin (SSRB), a semi-arid, mixed land use watershed in Alberta, Canada. A significant temporal increase (p < 0.05) in the concentration of one or more ions was observed at all 12 study sites. While all ions exhibited a significant increase in concentration over time, the rate of change was generally highest for Cl- (approximate to 1.4-3.0% yr(-1)). The observed increase in riverine Cl- loading downstream of a large urban center (approximate to 1700 tonnes yr(-1)) was attributed to increasing inputs from road salt (approximate to 1800 tonnes yr(-1)) and to a lesser extent municipal wastewater (approximate to 400 tonnes yr(-1)). For most other salts, spatial variation was driven not by urbanization but by the proportion of salt affected soils and/or cropland. A distinct Na2SO4 signal was observed at stations draining salt affected soils which strengthened over time at 7/12 sites indicating temporal trends in Na+ and SO42- have been driven largely by soil processes. A strong relationship between cropland and salt chemistry across the basin suggests agricultural activities have also contributed to observed trends. Therefore, in regions with similar climatic and anthropogenic characteristics to the SSRB, multiple stressors are likely to be operating and as such, these systems may be at particular risk from salinization.