Evaluation of copper dissipation, exposure factor, and algaecidal efficacy in an irrigation canal following pulse \u2018slug\u2019 application of a chelated copper algaecide

Abstract

Nuisance algal growths pose a significant threat to irrigation canals for water conveyance and flood control. Copper algaecides are routinely used to control algae in moving water. In this research, we monitored an application of a new use pattern of a chelated copper algaecide to a flowing canal and evaluated efficacy using controlled bench-scale study of the field-realized exposure using an alga commonly found in flowing water (Oedogonium sp.). The highest peak copper concentration (3.17 ppm) was measured 0.80 km from the application site though it decreased significantly at each sampling interval to the 9.66 km sampling point and remained at or below 0.2 ppm at 9.66–19.31 km from the application site. Copper mass dissipated with an exponential curve (R2 = 0.9558), and less than 10% of applied copper was recovered at or beyond 9.66 km from application. Peak concentration dissipated by exponential decay (R2 = 0.9922) and was predicted to achieve background concentrations by 20.9 km from application. Scaled laboratory experiments showed control at exposure achieved through 6.44 km from application. This research demonstrates a method to improve operational efficiency of copper use in flowing water to achieve desired algal control, while decreasing overall copper use and complying with applicable discharge levels.