Incorporating forage grasses in riparian buffers for bioremediation of atrazine, isoxaflutole and nitrate in Missouri

Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation approaches to alleviate nonpoint source agricultural pollution in heavily fertilized systems. However, highly concentrated herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass (Dactylis glomerata), smooth bromegrass (Bromus inermis), tall fescue (Festuca arundinacea), timothy (Phleum pratense), and switchgrass (Panicum virgatum) ground covers to atrazine and Balance™ (isoxaflutole) plus their capacity to sequester and degrade these herbicides and their metabolites. Their ability to remove soil nitrate was also quantified. Concentrations of atrazine, Balance™ and their metabolites in the leachate, soil and plant samples were determined by solid phase extraction followed by high performance liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in the system was calculated using a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites to parent herbicide plus metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass treatments to the bare ground control. Based on this herbicide tolerance, bioremediation data and shade tolerance determined in a previous study, it was established that switch grass, tall fescue and smooth bromegrass are good candidates for incorporation into tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance™ and nitrate.