Seasonal Loadings of Atrazine and Metolachlor to a Southeastern Ontario River from Surface Runoff and Groundwater Discharge

Abstract The Payne River in the South Nation River basin in eastern Ontario was continuously sampled for atrazine and metolachlor from April to October during 1991 and 1992, using a modified Quality Environment Ltd. automatic liquid sampler. The objectives of the study were to determine weekly flow...

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Bibliographic Details
Published in:CONTAMINATION OF GROUNDWATER BY PESTICIDES IN CANADA 1995-01, Vol.30 (3), p.533-553
Main Authors: Fischer, J D, Apedaile, B E, Vanclief, L K
Format: Article
Language:English
Subjects:
Freshwater
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Summary:Abstract The Payne River in the South Nation River basin in eastern Ontario was continuously sampled for atrazine and metolachlor from April to October during 1991 and 1992, using a modified Quality Environment Ltd. automatic liquid sampler. The objectives of the study were to determine weekly flow proportional concentrations and loadings to the river, and to assess loadings during dry weather periods for evidence of contributions from groundwater discharge. In 1992, samples were also analyzed for desethylatrazine, the predominant residue of atrazine. The site southeast of Ottawa represented a watershed area of 182 km2. The maximum concentration of atrazine were recorded for the weeks ending May 29, 1991 (0.83 µg/L), and July 30, 1992 (1.20 µg/L. These values were approximately half the Canadian Water Quality Guideline for the Protection of Freshwater Aquatic Life (2 µg/L). Maximum concentrations of metolachlor were also recorded for these dates. Values were 0.43 µg/L and 0.26 µg/L, respectively, well below the Canadian Water Quality Guideline of 8 µg/L for the Protection of Freshwater Aquatic Life. Discharge data were used to calculate weekly loadings from the watershed, and seasonal loadings were compared with the results of a pesticide usage survey. Atrazine loadings to the Payne River as a percentage of atrazine applied during both cropping seasons were the same (0.13%) despite different discharge patterns. Metolachlor loadings were similar for both years and less than the value for atrazine. In 1991, 0.01% of the metolachlor applied to the study area reached the river during that cropping season. The corresponding value for 1992 was 0.03%. Atrazine loadings associated with carry-over from the previous cropping season were an important factor during the study period. Observed atrazine loading before application in a given year exceeded the loading for the entire cropping season of that year. The compounds were also present in river water under dry weather conditions, suggesting that in addition to surface runoff, groundwater is also a significant source of pesticides to the Payne River.
ISSN:1201-3080
2408-9443
DOI:10.2166/wqrj.1995.041