| Arsenic(As)is a kind of contaminant similar to metal,which can exist in the environment for a long time and cause continuous harm.The pollution to the natural ecology is immeasurable.Under the action of human activities,a large amount of arsenic is released into the environment,and much arsenic enters rivers or lakes through river basins,posing a threat to the health of water ecosystems.For example,arsenic pollution is one of the most prominent environmental problems in Yangzong Lake and Datun Lake,two important plateau lakes in Yunnan province.Arsenic pollution not only directly endangers aquatic life,but also can harm human health through drinking water and the food chain.However,studies on the effects of arsenic on aquatic organisms have long focused on ecotoxicology such as toxicity,toxicology mechanism,bioenrichment and amplification,and lack of studies on the effects and mechanisms of arsenic on aquatic ecosystems.In order to scientifically evaluate the effects of arsenic pollution on aquatic ecosystem health and explore its mechanism,the effects of arsenic concentration on zooplankton community were studied by microcosmic experiments.Arsenic free control group,low arsenic group and high arsenic group were set up in the experiment.0 μg/L,50 μg/L and 150 μg/L sodium arsenite were added,respectively.The arsenic concentration selected for the experiment was set according to the arsenic concentration in Yangzonghai,a lake seriously polluted by arsenic in Yunnan Province.A total of 12 experimental units were set up with 4 replicates per treatment,and a 48-day simulated control experiment was conducted.The experimental results show that:(1)During the experiment,28 species of zooplankton belonging to 22 genera and 11 families were identified,including 14 species of rotifers,accounting for 50%,9 species of cladicornis,accounting for 32.1%,and 5 species of copepods,accounting for 17.9%.(2)In terms of zooplankton diversity,the number of zooplankton species in the arsenic-free group,the low-arsenic group and the high-arsenic group fluctuated the same,and there was no significant difference in the number of zooplankton species among the three groups during the experiment period(p>0.05).The Shannon-Wiener diversity index fluctuated during the experiment,but was similar to the initial condition.There was no significant difference in Shannon-Wiener index among the three arsenic concentrations(p>0.05).(3)In terms of zooplankton abundance,the variation trend of zooplankton abundance of the three groups under the three arsenic concentrations was basically the same,and there was no significant difference(p>0.05).The abundance of dominant species of zooplankton in the low arsenic and high arsenic groups showed the same trend as that in the control group without arsenic,and there was no significant difference in the abundance of dominant species under different arsenic concentrations during the experiment(p>0.05).(4)In terms of zooplankton biomass,there were no significant differences in total zooplankton biomass,cladhorn biomass,copepods biomass and rotifer biomass under different arsenic concentrations during the experiment(p>0.05).The biomass of dominant species of zooplankton in the low arsenic and high arsenic groups showed the same trend as that in the non-arsenic control group,and there was no significant difference in the biomass of dominant species under different arsenic concentrations during the experiment(p>0.05).(5)The body length of the crustaceans(excluding anoplinae)ranged from220-1700 μm,and the daphnia was mainly composed of the smaller Daphnia rotunda.The body length of most of the cladicans was between 160-600 μm,and that of the copepods was between 400-1500 μm.The zooplankton were mainly copepods in the early stage,and the abundance of the copepods increased in the later stage,and the daphnia were mainly composed of the smaller daphnia.Crustaceans larger than 600μm,mainly copepods.There was no significant difference in the body length of crustaceans(excluding anoplast larva)between the low arsenic group,high arsenic group and no arsenic group(p>0.05).(6)During the experiment,the abundances of the three groups of zooplankton in the arsenic-free group,the low-arsenic group and the high-arsenic group showed the same trend.The PRC analysis of cladicorns,copepods,and rotifers showed that although there were fluctuations during the experiment,they all returned to pre-experiment levels or higher at the end of the experiment.T test showed that there was no significant difference between treatment groups after adding arsenic.Through the redundancy analysis of environmental factors and zooplankton,it was found that the main environmental factors driving the change of zooplankton community structure were total chlorophyll,chlorophyll less than 35 μm and total phosphorus.Arsenic was not a significant factor affecting the zooplankton community structure.A separate redundancy analysis of arsenic concentration and the abundance of the three categories of zooplankton showed that arsenic was positively correlated with the abundance of the three categories of zooplankton,but the effect was not significant.Arsenic had no obvious promotion or inhibition effect on the zooplankton community.These results showed that arsenic had no significant effect on the dominant species,abundance,biomass,diversity index and body length of crustacean zooplankton at environmental concentrations.With the progress of the experiment,the abundance biomass increased compared with the beginning of the experiment.Therefore,the effect of arsenic on zooplankton in arsenic polluted lakes may be less than that of other environmental factors in the field.The results of this study have important significance to reveal the mechanism of arsenic pollution on lake ecosystem. |
