Low doses of earthtec QZ ionic copper used in effort to eradicate quagga mussels from an entire pennsylvania lake

Abstract

A liquid formulation of acid-stabilized ionic copper called EarthTec QZ was used in an effort to eradicate invasive quagga mussels (Dreissena rostriformis bugensis) from an entire 12-hectare lake in Pennsylvania in fall of 2017. The treatment consisted of three separate applications of ionic copper delivered over a period of 37 days with the intent to minimize likelihood of spreading invasive mussels during a one-time water transfer event planned for later that year, from the treated lake to an adjacent river. Mussel mortality was estimated through use of caged adult mussels that were suspended at different locations and depths throughout the lake. Adult mussels began to die within 3 days of the initiation of treatment, particularly in the top 6 meters of the water body. The death of the last caged mussel was confirmed 40 days after the initiation of treatment, in a cage that had been placed in the metalimnion at a depth of 9 meters below the surface. Both biological and physicochemical data collected during the treatment period revealed that there was a pronounced thermocline at 8-11 meters depth. The layer of water in the thermocline resisted mixing, suggesting an explanation for why mussels located above and below this metalimnion were eradicated quickly, yet those within the metalimnion required targeted treatment techniques and 40 days to succumb to 100% mortality. Visual inspection of the shoreline after partial pump-down of the quarry in early November revealed high densities of empty shells from dead adults, and no live adults were found. Analysis of eDNA samples taken in December of 2017 and again in July 2018 concluded no mussel eDNA was detectable. Plankton tows collected and analyzed by microscopy in July, August and September 2018 were rich with zooplankton but no live mussel veligers were found. The cumulative sum of product applied throughout the entire course of treatment totaled 13,500 liters, which is equivalent to 0.44 mg/L as copper as calculated on the full volume of the lake - noteworthy because it is less than half the concentration EPA allows (1.0 mg/L) in a single algaecide treatment. This experience illustrates that low doses of acid-stabilized ionic copper can have profound effects on invasive mussel populations and are a viable management tool. If future sampling confirms that this eradication effort was successful, it will be the first recorded instance of eradicating quagga mussels from an entire lake.