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.

22 Sep 2021

Chemical Management Strategies for Starry Stonewort: A Mesocosm Study

Abstract: US Environmental Protection Agency (USEPA) approved algaecides and herbicides are frequently utilized to manage nuisance algae and aquatic macrophytes. However, there is limited information available on the effectiveness of these products for the management of starry stonewort. Thus, the goal of this research was to discern effective chemical control products for later growth stages of starry stonewort using mesocosm studies. Eleven treatments were evaluated using various combinations of four copper-based products, endothall, diquat, and carfentrazone – all with USEPA registrations for use in aquatic sites. To assess treatment efficacy, water quality, photophysiology, biomass changes, and bulbil viability were evaluated. Nine of the eleven treatments yielded lower dissolved oxygen concentrations and higher specific conductance when compared to the control. Photophysiological response varied by condition, but seven of eleven treatments resulted in significantly lower fluorescent and maximum fluorescent yield. Five of these also exhibited significantly lower average photosynthetic yields, with combination treatments resulting in more drastic decreases. Ten of the eleven treatments had significantly less biomass compared to the control when measured via wet weight; however, only four treatments were significant when measured via dry weight. Lastly, all conditions utilizing copper-based products significantly reduced bulbil viability while non-copper products had no impact.