| Atrazine (2-chloro-4ethylamino-6isopropylamino-s-triazine) contamination has been widely observed throughout agricultural catchments, however, the mechanisms by which atrazine moves through catchments are poorly understood because of a lack of holistic, watershed studies. To understand the complexities of atrazine transport more fully, additional field-based studies under natural environmental conditions are needed. The objective of this study was to investigate how field-applied atrazine is transported through an agricultural watershed. A small agricultural catchment (1.2-km2) was intensively instrumented and all the individual watershed hydrological components (groundwater, streamwater, precipitation, soil water, hyporheic zone water, and overland flow) were intensively sampled for one complete growing season (May through September).; During storms, the concentrations of silica and calcium decreased, the atrazine response was variable, and the concentrations of nitrate, DOC, potassium, chloride, and sulfate increased; the elevated nitrate signal lagged several hours behind the other elevated constituents. Graphical and statistical analyses indicate that a relatively stable spring-fed baseflow was modified by a mixture of overland flow and soil water. A rapid, short-duration overland-flow pulse dominated the streamflow early in the event and contributed most of the potassium, DOC, chloride, suspended sediment, and atrazine. A longer-duration soil-water pulse dominated the streamflow later in the event and contributed the nitrate as well as additional potassium, DOC, sulfate, atrazine, and suspended sediment.; At the upstream monitoring site (along the edge of a cornfield), atrazine and other solutes were rapidly transported from the land surface, through the soil, and into the groundwater. Conceptually, the rapid transport of atrazine and other solutes into the groundwater appears to occur by transport through soil macropores. Quantitatively, atrazine transport to groundwater was modeled with a transfer function model (based on an analysis of time-series data). The transfer function model fit the groundwater data and indicated that the solute transport from the land surface through the soil and into the groundwater was dominated by macropore flow. The macropore flow results in substantial atrazine contamination of the groundwater and may result in significant downgradient contamination of baseflow streamwater. |
