Remediation of atrazine in irrigation runoff by a constructed wetland

Graduation date: 2001Presentation date: 2000-12-01Due to its frequent use in agriculture and its frequent detection in surface water,\ud atrazine was chosen as a model compound to study the treatment capability of a surface flow wetland used to remediate irrigation runoff at a container nursery near Portland, Oregon. Further evaluation of treatment of atrazine was performed under controlled conditions using static wetland microcosms. The potential to enhance microbial degradation of atrazine in the constructed wetland was investigated using bioaugmentation with an atrazine spill-site soil containing a large population of atrazine-degrading microorganisms. For the first five field experiments conducted in 1998 and 1999, the percent atrazine recovered at the outlet of the constructed wetland during a 7-d period ranged from 16 to 24% and several degradation products (deethylatrazine (DEA), deisopropylatrazine (DIA)) were detected in runoff water. Changes in total flow or frequency and intensity of runoff events did not affect treatment. However, for a sixth experiment, when runoff events were\ud longer in duration treatment was compromised. Static water-sediment column experiments suggested that sorption is an important mechanism for atrazine loss from water passing through the constructed wetland. Less than 12% of the atrazine applied to static wetland microcosms remained in the water column after 56 d. Atrazine degradates were observed in water and sediment, with hydroxyatrazine (HA) the predominant degradate. The presence of a large population of atrazinedegrading organisms was not observed in wetland sediment, suggesting that\ud microbial degradation of atrazine in the constructed wetland was inconsequential.\ud Wetland sediment bioaugmented with spill-site soil (1: 100 w/w) was shown to rapidly degrade 30% of atrazine added, and most probable number (MPN) assays confirmed growth of microorganisms in bioaugmented wetland sediment. Enhanced atrazine degradation using bioaugmentation into static wetland microcosms was successful when atrazine treatment in the water column of microcosms was employed. Results of these studies indicated that this constructed wetland effectively reduced overall atrazine concentration in irrigation runoff by\ud sorption, abiotic degradation, and possibly by plant uptake. Due to the limited presence of atrazine-degrading microorganisms in wetland sediment, bioaugmentation provides the best opportunity for enhancing microbial degradation of atrazine in sediment in this wetland system