REGIONAL AND TEMPORAL PATTERNS OF TOTAL SOLUTES IN THE SASKATCHEWAN RWER BASIN1

Abstract

ABSTRACT: In the Saskatchewan River Basin (365,000 km2), which drains the Canadian prairie from the Rocky Mountains east to Manitoba, concentrations of total solutes are usually within the range of 100 to 1000 mg/L. Total solutes levels in tributaries increase markedly from west to east across the basin, as mountain snowmelt and dilute surface runoff are replaced by ion‐rich ground water and concentrated prairie runoff as the major influences on solute concentrations. In contrast, total solutes concentrations in main‐stem rivers are nearly constant, ranging 200–300 mg/L, with only a small increase across the basin. Dilute mountain runoff dominates solute concentrations in main‐stem rivers, despite the influx of increasingly ion‐rich water from tributaries.The principal long‐term trends in total solute concentrations across the basin, as revealed by linear and sine‐curve regressions, were due to the construction of reservoirs, which depress the natural winter maximum in solute concentrations and disrupt the sinusoidal annual pattern, while sharply reducing seasonal variation. These regression methods did not show anticipated anthropogenic increases in salt load in the Red Deer or South Saskatchewan Rivers, but a trend of slowly increasing solutes concentrations (2 mg/L/yr) was detected for autumn flows in the lower Bow River. Municipal wastes from the City of Calgary or irrigation return flows are probably responsible for this increase.