Researchers Study Herbicide Persistence in Tailwater Recovery Systems
Pumping rates of groundwater in the Mississippi River Alluvial Valley exceeds its natural ability to recharge, leading to unsustainable water use. With this in mind, farmers throughout the region are looking into options that will allow them to reduce their reliance on groundwater, such as installing tailwater recovery systems which can capture and store runoff from the fields in ditches and ponds. However, using water from tailwater recovery systems might not be so simple, as this water can contain potential contaminants like herbicides and pesticides.
Dr. Cammy Willett from the Department of Crop, Soil, and Environmental Sciences at the University of Arkansas along with collaborator Dr. Deborah Leslie from the Department of Physical Sciences at Arkansas Tech University set out track and monitor six commonly used herbicides through tailwater recovery systems within the Cache River critical groundwater area. The goals of this study were to test recovered tailwaters for herbicide concentrations that could lead to cross-crop injuries and determine the suitability of the stored water for artificial groundwater recharge.
Drs. Willett and Leslie found that herbicides were found in both the tailwater ditches and ponds, but concentrations were greater in the ditches. This is because herbicides may break down during transport to the ponds, and because concentrations become more diluted with more water in the ponds. Unsurprisingly, herbicide concentrations were greatest in the spring after crops were planted and herbicides were applied, because rainfall runoff during this “spring flush” carries chemicals from the field to water sources.
This research shows that water recovered from agricultural fields can contain herbicides. While more research is needed to understand how other crops will respond to irrigation water that contains leftover herbicides, this study does highlight a few important recommendations for farmers who plan to reuse tailwaters. First, irrigation water should only be sourced from the reservoirs rather than the ditches. Second, if the recovered water is used for groundwater recharge, it should happen during the non-growing season, when herbicide concentrations are much lower in the tailwater ponds.
This research was funded by the U.S. Geological Survey 104B program through the Arkansas Water Resources Center and was published in the 2018 Arkansas Bulletin of Water Research.
Image caption: On-farm water storage pond, from Mississippi State Extension.
