Fig. 4. (A, B) Shows the temporal variation of the concentration ratio of atrazine to cyanazine (ACR) among ACR categories for the Delaware River, KS and the Iroquois River, IL. (C, D) Discrimination diagram showing the influence of the ACR on the temporal variation of the concentration ratio of deethylatrazine to deisopropylatrazine (D²R) among discrimination fields for the Delaware River, KS and the Iroquois River, IL, 1990.