Mass Balance Model To Quantify Atrazine Sources, Transformation Rates, and Trends in the Great Lakes

A dynamic mass balance model for atrazine was constructed for the Great Lakes to estimate in situ transformation rates and the relative importance of sources. Annual atrazine inputs ranged from ∼1 ton/yr in Lakes Superior to 10−25 ton/yr in Lakes Erie and Ontario. Annual inputs were <10% of lakewide atrazine inventories in all lakes except Erie. Tributaries plus connecting channel inputs account for >75% of the total load to Lakes Erie, Ontario, Huron, and Michigan. Atmospheric inputs account for 95% of the inputs to Lake Superior. Internal transformation rates are similar throughout the Great Lakes, ranging from ∼0.05 to 0.13 yr - 1 . Internal transformation and outflow produce an atrazine water column residence time of ∼2 yr in Lake Erie and >5 yr in the other lakes. Approximately 5−10% of the lakewide atrazine inventory is lost annually through internal transformation.