The Attenuation of Atrazine and its Major Degradation Products in a Restored Riparian Buffer

Abstract

The fate and transport of atrazine and three of its major degradation products were studied in a restored forested riparian buffer system in southern Georgia to examine the effectiveness of the system in attenuating the chemicals. Atrazine was applied to a 10 100 m strip immediately upslope from the buffer system, and atrazine, deethylatrazine, deisopropylatrazine, and hydroxyatrazine were monitored in groundwater, soil, and runoff water for 11 months following application. Atrazine removal from groundwater was very effective, with the calculated 3810 mg entering the upslope position being reduced to 174 mg exiting the streamside landscape position. Each of the landscape positions (0, 8, 13, 18, 28, and 38 m from the application strip) in the buffer system contributed significantly to the atrazine concentration reduction in the initial three months following application, when the majority of atrazine was measured. Deethylatrazine is the primary result of biotic degradation and was the predominant degradation product in groundwater, with approximately 10% (379 mg) as much estimated to have entered the upper interface of the buffer system as did the parent atrazine. The riparian buffer system was successful in significantly reducing concentrations of deethylatrazine in groundwater in both the initial three months following application and in the final eight months of the study. Adsorption of the analytes to subsurface soils was minimal in this system. Deethylatrazine was also the predominant degradation product in the runoff water, but hydroxyatrazine was predominant in conjunction with runoff sediments. Removal efficiency of analyte mass loads in surface runoff water ranged from 92% to 100% as the chemicals were transported through the buffer system. While the mass load of atrazine associated with sediment was only 8% of that measured for the water phase, the mass loads of deethylatrazine and deisopropylatrazine (approximately 40%) and particularly hydroxyatrazine (75%) in sediments were proportionally much higher. About 98.6% of measured runoff water and sediment phase transport of atrazine occurred within the first few days following application as a result of an extended rainfall event. In contrast, roughly 45% of the deethylatrazine and deisopropylatrazine and only 16% of the hydroxyatrazine were measured in the first rain event sample. The results of this work indicate that riparian buffer systems can be successfully used to intercept atrazine and the studied degradation products in order to minimize contamination of natural water systems. Riparian buffers can provide year round attenuation, particularly for deethylatrazine. The importance of timing atrazine application to correspond with periods when there is no threat of rainfall is also emphasized.