16 Apr 2024

The Use of Rhodamine Water Tracer (RWT) Dye to Improve Submersed Herbicide Applications

Abstract: The inert fluorescent dye rhodamine water tracer (RWT) has been widely used in freshwater aquatic systems for many years to quantify bulk water exchange patterns and as a tracer for submersed herbicide movement. The dye is well-suited for tracer work due to its high solubility and detectability in water (<0.01 μg/L). Federal guidelines limit the aqueous concentration 0f RWT to <10 μg/L at drinking water intakes. The dye has proven to be harmless to aquatic organisms and humans in low concentrations and is relatively inexpensive. Since 1991, RWT has been used by Engineer Re-search and Development Center (ERDC) researchers to simulate aqueous herbicide applications in large, hydrodynamic systems in over 12 states. Such simulations have improved the effectiveness of herbicide treatments by linking in situ water exchange processes with appropriate herbicide selection and application rates. Understanding these parameters can be critical for mitigating herbicide exposure in environmentally sensitive settings and around potable water and irrigation intakes. A data-based estimate of water exchange patterns usually results in successful submersed herbicide applications—both with target-plant efficacy and limited injury to nontarget vegetation. Using RWT dye to simulate submersed herbicide applications is an important predictive and real-time tool in both experimental and operational settings.