SOURCES, DISTRIBUTION AND TRANSPORT OF ATRAZINE IN THE ST-LAWRENCE-RIVER (CANADA)

A Lagragangian sampling strategy was chosen in order to evaluate the m ain sources of atrazine to the St. Lawrence River, Canada. Lagrangian sampling was carried out during six sampling trips, one at every hydro logical season except winter from the period of the summer low flow of 1990 to the spring freshet of 1992. Loadings of atrazine are subject to annual variations induced by different climatic and hydrological co nditions. Loadings of atrazine are also dependent on season. Results e mphasize the persistence of atrazine as it was found in significant am ounts at the end of the growing season and in the following spring. Va riations in loadings of atrazine along the river as well as the latera l distribution of atrazine concentrations in a downstream direction su ggest inputs within the province of Quebec. The Great Lakes and the in ternational corridor of the St. Lawrence River contribute 68% of the l oading exported to the estuary, while Quebec tributaries account for 8 % of the inputs. The importance of the unmeasured sources within the r iver itself (24%) stresses the need for further research on internal p rocesses and contaminant transfer in the aquatic environment.