Water Resources Research Act Program

Details for Project ID 2019AR009B

Herbicide Mitigation Potential of Tailwater Recovery Systems in the Cache River Critical Groundwater Area

Institute: Arkansas
Year Established: 2019 Start Date: 2019-06-01 End Date: 2020-05-31
Total Federal Funds: $25,008 Total Non-Federal Funds: $51,080

Principal Investigators: Cammy D. Willett

Abstract: Current unsustainable agricultural water usage has led to drawdown of Arkansas aquifers, including the Mississippi River Valley Alluvial Aquifer. Producers are constructing on-farm reservoir-tailwater recovery systems to reduce reliance on groundwater by an estimated 25-50%. At this time, little is known about how these systems interact hydrologically with the surrounding landscape, impact water quality, or affect persistence and accumulation of herbicides. These systems may conserve surface water quality by preventing off-site movement of nutrients, sediment, and herbicides. But, residual herbicides could also injure crops upon reapplication of tailwater as irrigation. On-farm storage water has also been proposed as a suitable supply for enhanced aquifer recharge. Further investigation of on-farm reservoir-tailwater recovery systems as sustainable water management strategies is needed to address these questions. The objective of the proposed research is to provide information to determine how on-farm reservoir tailwater recovery systems can be managed to effectively remove herbicides by 1) creating a seasonal herbicide monitoring data record for 7 on-farm storage reservoir-tailwater recovery systems in the Cache Critical Groundwater Area to determine appropriate timing for irrigation reuse or for artificial aquifer recharge, 2) identifying system design components that enhance the mitigation of herbicides, and 3) supporting innovative use of on-farm reservoir-tailwater recovery systems for responding to water quality and quantity concerns. Tailwater ditch and reservoir grab samples will be collected weekly during production months and biweekly during off-production months. Samples will be shipped on ice overnight, processed by vacuum filtration within 48 hours of receipt, and stored at -20°C until analysis. Samples will be analyzed for glyphosate, clomazone, 2,4-D, dicamba, metolachlor, propanil, and quinclorac. The selected herbicides were selected based on widespread application and dominant usage in the region. Glyphosate will be analyzed using enzyme-linked immunosorbent assay kits with photometric detection. For all other herbicide compounds, samples will be concentrated and purified using solid phase extraction and analyzed using high performance liquid chromatography with photodiode array detection. Herbicide concentrations will be statistically compared with established risk assessment benchmark concentrations for drinking water within the general population using linear or non-linear regression and correlation analyses. Reservoir herbicide concentrations will be qualitatively assigned a risk of high to low based on crop sensitivity data compiled by University of Arkansas weed scientists. Differences in herbicide concentrations and reservoir characteristics will be assessed using the general linear and non-parametric model procedures and least significance tests at 95% confidence level. Kruskal-Wallis non-parametric tests will be used for group comparison between reservoir sites and associated ditches.