Phosphorus release of metazoan zooplankton in two bays with different trophic status in Lake Taihu (China)

The contribution of metazoan zooplankton to internal phosphorus (P) cycling was investigated in Meiliang and Wuli Bays of Lake Taihu, a eutrophic, shallow lake in China by determining biomass and biomass specific P release rates. The zooplankton community of eutrophic Meiliang Bay was dominated by cladocerans, particularly Daphnia spp. and copepods, while dominant groups in hypereutrophic Wuli Bay included rotifers, copepods, and cladocerans. Release rates of PO43--P ranged from 0.20 to 0.57 mg·g (dry weight)-1·h-1 in Meiliang Bay and 0.20 to 0.76 mg·g-1·h-1 in Wuli Bay. In most cases, P release rates were higher in Wuli Bay than Meiliang Bay. Phosphorus fluxes from zooplankton excretion varied from 5.34 to 57.41 mg·m-2·d-1 in Meiliang Bay and 8.20 to 70.02 mg·m-2·d-1 in Wuli Bay. Since P released by zooplankton in this study was in a form available to phytoplankton, zooplankton may represent a significant source of P contributing to high phytoplankton biomass in Lake Taihu.