Streamlevels of agrichemicals during a spring discharge event

Levels of agrichemicals were monitored during a spring runoff event in Shell Creek, an eastern tributary of the Platte River, which drains a 700 km² watershed of predominantly row-cropped corn. Discharge during the runoff event ranged from 19 to 781 cfs. Maximum levels of atrazine, cyanazine, and alachlor of 89, 76, and 46 μg/L, respectively, occurred prior to the peak in stream discharge. Other residues detected at low concentrations during the peak in stream discharge include the herbicides- butylate, EPTC, metolachlor, metribuzin, propachlor, and trifluralin, and one insecticide- disulfoton. Suspended sediment levels (max = 19.7 g/L) correlated with pesticide levels, while nitrate-N concentrations (max = 6.3 mg/L) did not.