TRANSPORT OF AGRICHEMICALS TO GROUND AND SURFACE-WATER IN A SMALL CENTRAL INDIANA WATERSHED

The occurrence, distribution, concentrations, and pathways of agrichem icals in water were investigated in the Sugar Creek watershed, a poorl y drained agricultural watershed typical of many watersheds in the mid western USA, Water samples from Sugar Creek, two the drains, and 11 we lls along a groundwater flowpath to Sugar Creek were collected between May 1992 and August 1996 and analyzed for N and pesticide compounds, Nitrate was the principal N species and pesticides were common in allu vial water-bearing units in the Sugar Creek floodplain. In the confine d stratified drift aquifers, ammonia was the principal N species and p esticides were rare. Tile drains directly affected the water quality i n Sugar Creek by transporting soil pore water and shallow groundwater containing high concentrations of nitrate (NO3) and pesticides to the creek. When tile drains were flowing (typically December through July) , elevated NO3 concentrations (2-10 mg/L NO3N) in the creek correlated with high NO3 concentrations (2-23 mg/L NO3N) in tile drains discharg ing to the creek. Likewise, with concentrations of atrazine and atrazi ne metabolites, seasonal trends in the tile-drain effluent were simila r to seasonal trends in Sugar Creek. When tile drains went dry, NO3 co ncentrations in the creek were low, indicating most groundwater discha rge to the creek consisted of old or denitrified water. Trace levels o f pesticides in the creek at low flow probably were the result of seep age from alluvial water-bearing units.