The Bonaparte River, located in British Columbia's southern interior, is a main tributary to the Thompson River (Figure 1). River water quality is important for uses such as drinking water, recreation, irrigation, and livestock watering, as well as for aquatic life and wildlife. Water quality is affected by ranching and agriculture, two sewage treatment plants, two landfill sites, urbanisation and forestry. Previous studies on this river have observed high levels of fecal coliforms, suspended solids, turbidity and algae.
In this report, 10 years of data (1985-1995), obtained under the Canada - B.C. Water Quality Monitoring Agreement, were assessed for trends and concerns in water quality. Monitoring was carried out monthly at the mouth of the river from 1985 - 1995 for 47 variables. These variables were graphed, and then compared to Approved and Working Criteria for Water Quality (Nagpal et al., 1995) and to site-specific objectives set by the Ministry of Environment, Lands and Parks. Related sites within this watershed include: Thompson River at Spences Bridge, South Thompson River at Kamloops, and North Thompson River at Kamloops.
The main conclusions of this study are:
· No environmentally significant trends in water quality were detected through visual assessment of the data.
· Fecal coliforms at times exceeded the site-specific objective designed to permit drinking water use after partial treatment and disinfection. It appears that complete water treatment and disinfection are needed, and that consumption during spring freshet should be avoided.
· Periphyton chlorophyll-a (a measure of attached algal growth) consistently exceeded the site-specific objective to protect recreation and aquatic life. Dissolved phosphorus levels were elevated, indicating an ample supply to support algal growth.
· Non-filterable residue (suspended solids) and turbidity were often elevated during spring freshet, and site-specific objectives were regularly not met. Turbidity removal (complete water treatment) and disinfection are needed before drinking water use.
· The pH was slightly high for drinking water, possibly affecting chlorination effectiveness and causing encrustation and scaling.
· The river was well buffered against acid and metal inputs.
· Hardness levels during the winter were poor for drinking water aesthetics but still tolerable.
· The variables that exceeded criteria during spring freshet were: aluminum, chromium, copper, iron, manganese, titanium and zinc. These metals were largely associated with high levels of turbidity and suspended sediments, suggesting that the metals were in particulate form, probably not biologically available, and would be removed by the drinking water treatment needed to remove turbidity.