Abstract: Arsenic pollution is a major environmental problem in Yangzong Lake, one of the largest lakes located in Yunnan Province of southwest China. However, its impact on zooplankton remains unknown. To evaluate the ecological risk of arsenic contamination to zooplankton in Yang zong Lake, we conducted seasonal investigations of rotifers and crustaceans (i.e. cladocerans and copepods) during 2015 and 2016. A total of 32 zooplankton species was recorded, which were mainly cosmopolitan ones. The total abundance of zooplankton ranged from 2 to 18 ind·L^-1, with a mean of 8.5 ind·L^-1. Among the three taxonomic groups, rotifers had the highest abundance, while copepods dominated community biomass. There was a significant difference in zooplankton abundance and biomass among seasons (P<0.05), but no difference among sampling sites (P>0.05). Crustaceans (excluding nauplii) had a mean body length ranging from 180 to 1780 μm, and were dominated by small-sized individuals. In particular, cladocerans were all small-sized species. Results of RDA analysis showed that water total phosphorus, total nitrogen, pH, arsenic concentration, chlorophyll a, and cyanobacteria biomass were the main factors driving seasonal and spatial variations in zooplankton community. Compared to previous records from Yangzong Lake and neighboring lakes with similar trophic states, zooplankton species richness and abundance were significantly lower during 2015 to 2016, reflecting the detrimental effect of arsenic contamination on zooplankton in Yangzong Lake.

Key words: plateau lake, zooplankton, arsenic pollution, ecosystem health, eutrophication, fish predation.