Water Quality and River Nutrient Load in the South Saskatchewan River Basin, SK, Canada

The South Saskatchewan River is arguably one of the most important river systems in western Canada. Due to its central location in the arid Prairie Provinces, the large population it supports, and its proximity to industrial and agricultural activities, the South Saskatchewan River Basin is one of the most utilized river basins in Canada. However, reoccurring water quality issues present a risk to the use of the river for agriculture, drinking water, and recreation. These issues include contamination from municipal and industrial effluents, urban stormwater runoff, and irrigation return flows; elevated mercury concentrations and fecal coliforms; and high sodium, chloride, and sulphate concentrations. It is crucial that we improve our understanding of the state of water quality in the South Saskatchewan River so that we may identify potential threats to the continued use of this river for people and ecosystems. A basin-scale assessment of water quality in the South Saskatchewan River Basin was carried out on historical data for 22 water quality parameters sampled at 16 locations from 1966-2009 along the South Saskatchewan River and its major tributaries (Bow River, Oldman River, Red Deer River). Water quality parameters included physical/chemical characteristics; nutrients; dissolved metals/metalloids; and biological parameters. Particular focus was given on nitrogen and phosphorus as key indicators of ecosystem health and water quality degradation. Current water quality state was determined by applying provincial and federal guidelines for aquatic ecosystem protection. Water quality ‘state’ was defined as the risk for each parameter to exceed guidelines based on the number of exceedances during the study period. Trends in water quality that may indicate decreasing or degrading water quality over time were identified based on historical data using a Mann-Kendall (M-K) test for monotonic trend in a two-phase approach that included water quantity-quality modelling, and M-K testing. Water quality risk was “high” or “very high” for concentrations of dissolved fluoride, total zinc, total copper, fecal coliforms, dissolved organic carbon, total phosphorus, and total nitrogen. Total nitrogen and total phosphorus concentration had the highest risk rating. Increasing trends were identified at all sampling locations for pH, total dissolved solids, conductivity, sodium, sulphate, and chloride concentration. Temperature, turbidity, and organic carbon concentration were generally decreasing over time. No significant trends were detected for dissolved oxygen concentration. Insufficient sample size resulted in test error for zinc, copper, and lead. Total nitrogen concentration was increasing for most sampling locations on the Bow River, with weakly decreasing trends on the Red Deer River and Oldman River. Total Phosphorus concentration was decreasing over time for all sampling locations, on all river reaches. Spatial and temporal patterns of three non-point sources (land use, population density, and agriculture) and one point source (municipal wastewater effluent) of nutrient loading to river systems were selected through literature review for further analysis. GIS data for these sources were obtained from various provincial and federal research programs: landcover data; crop and livestock production; phosphorus runoff risk; population data; and municipal wastewater effluent sources. Quantitative changes over time and space were assessed across the maximum contributing area for each incremental sub basin using thematic mapping tools in ArcGIS. Key nitrogen sources included crop-based agricultural production along the Red Deer River; livestock production along the Red Deer and Bow Rivers; and wastewater generated from large urban centers (City of Saskatoon, City of Calgary, and City of Red Deer). Phosphorus runoff risk was highest in the south-west portion of the basin along the upper reaches of the Oldman River. Agricultural production was linked to in-stream phosphorus loading through spatial correlation (co-location) analysis using phosphorus runoff risk and in-stream phosphorus loads. Agricultural production intensity was linked to in-stream nitrogen concentrations using the spatial correlation between livestock and crop production, and total nitrogen exceedance risk. Total phosphorus runoff risk and total phosphorus loading were temporally related, while both spatial and temporal correlations were apparent for total nitrogen concentration and high-intensity agricultural production. Total nitrogen and total phosphorus loading contributions from municipal wastewater effluent were then estimated for City of Calgary and City of Saskatoon as the largest potential contributors from municipal sources in the basin. The City of Calgary was the largest contributor of both nitrogen and phosphorus, and was responsible for approximately 72% of downstream total phosphorus loading in the Bow River, and 73% of downstream total nitrogen loading compared to 15% and 35% from the City of Saskatoon respectively. Estimated agricultural and municipal nutrient loading was then compared for each sub-basin within the study area. From a basin perspective, it was concluded that agricultural inputs of nitrogen and phosphorus were greater than municipal inputs for most portions of the basin, but that both were significant potential contributors to in-stream nutrient loading