How phytoplankton biomass controls metal(loid) bioaccumulation in size-fractionated plankton in anthropogenic-impacted subtropical lakes: A comprehensive study in the Yangtze River Delta, China

Abstract

Phytoplankton biomass can significantly affect metal(loid) bioaccumulation in plankton, but the underlying mechanisms are still controversial. We investigated the bioaccumulation of eight metal(loid)s (As, Co, Cu, Hg, Mn, Pb, Se, and Zn) in three size categories of planktonic organisms – seston (0.7–64 μm), mesozooplankton (200–500 μm), and macrozooplankton (>500 μm) – sampled from six freshwater lakes in two seasons in the Yangtze River Delta, China. Our results highlight phytoplankton biomass is the major driver on metal(loid) bioaccumulation in the studied anthropogenic-impacted subtropical lakes, mainly via affecting site-specific water physiochemical characteristics and plankton communities. However, such impact is highly dependent on chlorophyll a (Chl-a) concentration. The bioaccumulation of metal(loid)s in size-fractionated plankton declined significantly with increasing phytoplankton biomass when Chl-a was below ∼50 μg L−1, mainly owing to the reduced metal(loid) bioavailability and subsequent bioaccumulation at more productive sites (with elevated pH and dissolved organic carbon), rather than algal bloom dilution. To a lesser extent, phytoplankton growth dilution and the smaller body-size of zooplankton at more productive sites also contributed to the lower metal(loid) bioaccumulation. The bioaccumulation of metal(loid)s was enhanced under severe algal bloom conditions (when Chl-a concentration was higher than ∼50 μg L−1). Although the underlying mechanisms still require further investigations, the potential risks of metal(loid) bioaccumulation under severe algal bloom conditions deserve special attention.