Macrobenthic Community In Lakes From Wuhan And Their Response To Heavy Metals And Other Environmental Stress

Eutrophication and heavy metal pollution in freshwater lakes,which seriously affect important ecological service functions such as freshwater supply and biodiversity maintenance in lakes,have become one of the most prominent ecological and environmental problems in the world.Wuhan is an important pilot city for the Yangtze River protection strategy.The safety of water quality within the city will directly affect the implementation of the strategy and the regional sustainable development.It is undoubtly crucial to clarify the ecological status of water quality in lakes and the driving factors of ecological environment changes during the rational formulation and implementation of lake protection and restoration measures.Macrobenthos are an important part of the lake food web,and their community composition is very sensitive to environmental changes within the lake,and thus often be used to assess the ecological quality of aquatic freshwater.This study analyzed the composition of macrobenthos in more than 30 representative lakes in Wuhan,and evaluated their ecological status in 2019 and 2021 based on the fauna community.The correlation between benthic animals and environmental factors was analyzed through ordination analysis to reveal the impact of human activities on aquatic ecological environment.Given the seriously pollution of heavy metals in thses lakes,we also evaluated the ecological risk of heavy metals via analyzing the contents of heavy metals in surface sediments.This will provide effective scientific support for the lake restoration and management.To clarify the dose-effect relationships bettwen metals and specific macrobenthos,the physiological traits of chironomids,a typical benthic group,were experimentally tested under the effects of heavy metals（eg.Pb and Zn）as well as other environmental stresses.（1）In 2019 and 2021,the zoobenthos in lakes from Wuhan were dominated with highly pollution-tolerant species Limnodrilus and Tanypus chinensis and medium tolerant species Bellamya purification.It is found that the community abundance in suburban lakes increased in 2021 compared with that in 2019,reflecting improved water quality with time.Of urban and suburban lakes,only two lakes（Donghu Lake and Dugong Lake）showed slightly increased in the number of species in 2021 compared with 2019.As to the spatial characteristics of lakes,cluster analysis verified that these studied lakes distributed as circulars along a pollution-tolerant species to median tolerant taxa from the city center.Ordination analysis identified that lake location（distance from the city center）and water productivity determined the spatial structure of benthic fauna in lakes from Wuhan;（2）Assessment of ecological quality based on macrobenthos showed that these lakes were generally at a moderate level in pollution during 2019 to 2021.During the study period,the ecological quality shows a similar spatial pattern,that is,the farther from the city center,the higher of Shannon-Wiener index and Margalef index and meanwhile the lower BI index,indicating improving water quality with distance from the city center;（3）The distribution of heavy metals in lakes from Wuhan has obvious spatial heterogeneity,and the risk of heavy metals in suburban lakes is relatively low.The overall heavy metal content in 2021 will be lower than that in 2019,especially elements such as Zn,Cr,and Pb.Although the pollution levels of Cu,Zn,Cr,Pb,As,and Mn were relatively low,Cd and Hg pollution was prevalent in lakes from Wuhan.In particular,Cd pollution in Jiangxia and Hongshan-Wuchang District was prominent,therefore has become the main source of ecological risk of heavy metals in these areas.The accumulation of Hg and Zn exerted significantly impacts on lake benthos in the density and biomass.These two metals should be highly concerned in the future governance and restoration of lakes;（4）Laboratory toxicity test showed that the growth rate of chironomids and the dry weight of adults decreased with the increase of population density,but not the case of emergence rate.Meanwhile,all these life historical traits decreased when the content of organic matter in the sediment decreased.Both the increase of population density and the decrease of sediment organic matters had the most obvious effects on the dry weight of chironomids adults than other physiological traits.The toxicity of combined Pb²⁺and Zn²⁺was higher than the each metal alone,expect for the dry weight of some male adults,the emergence and development rate decreased and dry weight of adults lowered under the combined effects of two metals.Therefore,it is necessary to consider the increase in the sensitivity of benthic animals to stressors caused by environmental stress and the combined effect of heavy metals in the future environmental monitoring and ecolgical risk assessment of heavy metals.