Insecticide and nutrient transport in water, related to agricultural land use of a stream basin in Ontario, Canada.

Transport by stream water of insecticides and nutrients in Big Creek, Norfolk County, Ontario, Canada, was examined by combining concentrations of substrates with flow data. Big Creek has its headwaters in dairy cattle country, its central basin area is mainly devoted to tobacco growing, and its lower reaches contain mixed farming, corn and vegetables, etc., before it flows into Lake Erie. Three sampling sites were chosen to represent these 3 different land uses. Generally concentrations of substrates in the water were quite uniform at the 3 sites resulting in transport of quantities in proportion to stream flow. Certain anomalies occurred and are discussed. The 2 chief insecticides found were DDT and dieldrin. Analyses for potassium, calcium and magnesium indicated that these nutrient losses into the stream were area-rather than usage-dependent. Midseason variations in loss of nitrogen and phosphorus may be the result of agricultural practices in the three areas represented in this study. The largest quantities of all nutrients lost occurred early in the season before crops were established.