Submitted to: Clean Water Clean Environment 21st Century Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 5, 1995
Publication Date: N/A
The landscape of central Iowa is characterized by low ridges surrounding closed depressions (potholes), which are often drained by subsurface tiles. Our objectives were to quantitate the amount of atrazine leaching through the soils in this landscape and to relate the leaching pattern to sorption and degradation processes. Atrazine concentrations in subsurface tile drain water were normally below 1 ppb with a maximum concentration of 12 ppb. Deeper groundwater samples were typically devoid of atrazine above the 0.2 ppb reporting limit. Atrazine sorption (binding to soil) was greatest in surface soils within the pothole and least in shoulder slopes and backslope soils. Atrazine sorption decreased with depth, but substantially more atrazine was sorbed to subsurface soils in the pothole than other subsoils. Atrazine was degraded in subsurface soils, but the rates were much lower than in surface soils. The greater capacity of the soils in the depressional areas to adsorb atrazine appears to retard atrazine leaching sufficiently that concentrations in tile drains remain small. Atrazine may leach through less sorptive soils on the shoulders and summits on the ridges surrounding the potholes and move laterally towards the tile drains. However, the longer flowpath to the tile drain in conjunction with subsurface biodegradation would reduce the impact of atrazine leaching at these landscape positions.