From peaks to prairies: a time-of-travel synoptic survey of pesticides in watersheds of southern Alberta, Canada

A time-of-travel synoptic survey was conducted in August 2014 to assess pesticide occurrence in major river subbasins of southern Alberta, Canada. We collected 155 water samples from Alberta's South Saskatchewan River Basin (Bow, Oldman, Red Deer, and South Saskatchewan river subbasins) and analysed them for 106 pesticides. Samples were collected from mainstems (rivers) as well as tributaries and effluents (point sources) discharging into the rivers in an estimated time-of-travel to capture agricultural and urban contributions as the water flowed eastward from headwaters in the Rocky Mountains. The aim of the study was to assess point-source contributions of pesticides to Alberta's South Saskatchewan River Basin mainstems during low flow conditions. In addition to examining differences in pesticide contributions among source type and subbasins, the cumulative effect of inputs on the mainstem rivers, the influence of land use, and seasonality of pesticides in select effluents was analysed. We detected 17 pesticides and 1 metabolite, reflecting runoff from agricultural and urban land use. Pesticide detection frequency was significantly higher in effluents than in tributaries and mainstems, and pesticides were detected in effluents in summer and winter. Our evaluation of land-use relationships highlighted the influence of agriculture on pesticide occurrence in these aquatic agroecosystems. To our knowledge, this is the first watershed-wide time-of-travel survey of pesticides conducted in southern Alberta to measure contributions of pesticide loads from effluents and tributaries to the mainstems in all regions of Alberta's South Saskatchewan River Basin.