Dissolved Cu concentrations in the Strait of Georgia: trends, speciation, and accumulation by local calanoid copepods

Most research on the effects of copper (Cu) on marine ecosystems has focused on benthic organisms and Cu concentrations in the sediments. In contrast, little is known about the effects of dissolved copper (dCu) in pelagic food webs. In most marine waters, more than 99.9% of dCu is bound to organic ligands. These ligands diminish dCu toxicity to aquatic organisms by lowering the concentrations of inorganic dCu, the most bioavailable species of Cu. For the past year, we have studied seasonal trends of dCu concentrations in the Strait of Georgia and have measured and characterized its speciation in seawater. Measurements taken in 2016 ranged from 5.4 to 23.3nM dCu, which are comparable to those found in San Francisco Bay and Puget Sound. Additionally, the highest concentrations were measured when the Fraser River flow rates were the fastest. Dissolved Cu levels were highest in the surface layer (0-50m), followed by the deep layer (200m to the bottom), with the lowest levels occurring in the intermediate waters. The concentrations in the intermediate layer coincide with those in the incoming low dCu- waters from the Pacific Ocean. Furthermore, using 64Cu as a radiotracer, we have measured uptake rates of Cu, from the dissolved and the particulate fractions, by local calanoid copepods exposed to in situ Cu levels. Our data show that copepods can easily accumulate Cu from the dissolved phase. This research provides much-needed information on dissolved Cu in a region historically known to harbor smelting and mining activities, and currently active maritime trade