| Liuxi River is located in the northwest of guangzhou conghua district,as an important drinking water resource area for Guangzhou,the water quality plays a vital role for the safety of drinking water.Therefore,the long-term monitoring and health assessment of the water environment of the Liuxi River are the basic guarantee for maintaining the health of the people in Guangzhou and an important way to protect the rivers' aquatic life.Zoobenthos plays an important role in the river ecosystem,the change of the number of species and community structure characteristics has a close connection of the water environmental factors(including physical and chemical indicators,riverbed sediment types,riparian vegetation types,etc.),and due to its relatively long life,limited migration ability,and easiness of be collected,so the study of river benthonic animals gradually became the research hot spot.Because Liuxi River belongs to the typical subtropical climate of urban rivers,the distribution of biological and ecosystem in the watershed has a strong regional characteristics.In addition,by the rapid development of the city,the natural environment within the basin by the degree of human interference is becoming increasingly serious.Therefore,this study is based on the monitoring of the water quality and zoobenthos in Liuxi River,analyses the spatial and temporal characteristics of water environment and the community structure of zoobenthos in the watershed,evaluate the health status of the ecosystem by constructing benthic Animal Integrity Index(B-IBI)evaluation system.And choose ecological restoration pond in subtropical region as research object,and analyse the effect on zoobenthos in the process of repairing water ecological environment by submerged plant.In this study,we have enriched the basic data of benthic fauna in large and medium-sized rivers in southern China,and provided a model reference for the biology evaluation method of benthic fauna as the core.The main results and conclusions of this paper are as follows:(1)The water quality of 14 sections of the Liuxi River was investigated in level period(April),high-water period(July),and drought period(October).The water quality of the Guangzhou reach was gradually deteriorated from the upstream source to the downstream(DO 3.28-8.95 mg/L,EC 40.8-327.7 ?s/cm,TN 0.11-6.46 mg/L,NH4+-N 0.04-5.29 mg/L,TP 0.01-3.06 mg/L,CODMn 1.0-5.6 mg/L,BOD5 0.6-4.9 mg/L).The results show that the source of the upper reaches of the Liuxi River is low by the degree of external disturbance,the water quality is I-II water standard,and the tributary water quality is superior to the main stream.The downstream river,the domestic sewage discharge and the industrial pollution increase,the water quality is reduced to IV-V Water standards,and the mainstream water quality is better than tributaries.(2)A total of 144 species were found in the benthic fauna survey,belonging to 4 families,8 orders,22 orders,52 families and 134 genera.The average density and biomass of benthic fauna in the watershed were 217.35 ind./m2 and 20.38 g/m2,respectively.The number of species in the upper reaches was the highest,and the number of species in the lower reaches was gradually reduced,and the pollution-tolerant groups were dominant.The differences in biomass and density of benthic fauna between the sites showed that there were more benthic fauna than that of the main stream.The diversity index showed that the number of upstream species was abundant.The correlation between the biota and the environmental parameters of the benthic fauna showed that the density of the habitat was negatively correlated with DO at the end of April and positively correlated with CODMn.The density of the habitat was positively correlated with BOD5 at the end of July(P <0.05)There was a significant positive correlation between animal density and EC.The results showed that there were differences in the environmental factors affecting the distribution of benthic fauna in different periods.In general,upstream and downstream,with the decrease of DO content,the increase of EC and nutrient content and the significant negative effects on the diversity of benthic fauna.(3)According to feeding methods and object classification,there are 19 kinds of existing snipers,10 species of food,64 species of direct collectors,10 species of filter recipients and 41 species of predator.The total average density of each feeding group is between 5 and 2098 ind./m2,with the largest number of direct collectors.The total average biomass was 0.05-228.28 g / m2,with the largest number of scrapers and the least.On the spatial scale,the decrease in the overall number of functional feeding groups was mainly affected by the reduction of the diapirics and filter feed collectors,and the pollution of the lower reaches was increased,and only the oligosaccharides(waterworms)Collectors.5 kinds of functional feeding groups were found in the tributaries,and only four kinds of mainstream,indicating that the missing food is reflected in the mainstream water quality and habitat degradation of the important indicator group.From the upstream to the downstream,the species composition,diversity and biomass of the benthic fauna were significantly reduced,indicating that the current Liuxihe ecosystem affected by the decline of water quality and the degradation of coastal habitat.(4)The B-IBI system of the Liuxi River was constructed using five key indicators,including total biomass,individual percentage of sensitive groups,and taxa number for EPT,Chironomidae,and tolerant groups.Health standards are: B-IBI value> 3.24 for the health;3.24-2.43 for the sub-health;2.43-1.62 for the general;1.62-0.81 is poor;0.81-0 is very poor.The number of health sites in the river basin accounted for 14.3%,sub-health accounted for 50.0%,generally accounted for 21.4%.The number of EPT taxa and the% of the sensitive group contributed the highest to the B-IBI value in the upper reaches,which indicated that the health status was good,and the number of the pollutants in the lower reaches was the highest,reflecting the deterioration of the health status.There was a significant positive correlation between B-IBI and dissolved oxygen concentration(P <0.01),and negatively correlated with total nitrogen,ammonia nitrogen,total phosphorus concentration and conductivity(P <0.05).The results show that,as a typical urban river,the middle and lower reaches of the Liuxi River are seriously affected by human disturbance and water pollution,and the ecological health status is deteriorating,especially in the downstream dry and tributary river.Compared with the application of different geographical areas,B-IBI system has good applicability in tropical and subtropical regions.(5)A total of 11 species of benthic fauna were found during the restoration process,which belonged to 3 families,4 orders,6 orders,9 families and 10 genera.Submerged plants before planting,the zooplankton only 4 kinds of pollution-tolerant groups,after six months of repair,can be collected to 11 kinds of medium-resistant population.The results of correlation analysis showed that NH4 +-N,TP,CODcr and Chl.a had significant effect on the community structure of benthic fauna,which indicated that the diversity index of benthic fauna was also increased with the improvement of water quality.In general,the species,biomass and species diversity of the benthic fauna were significantly increased before and after the restoration of the submerged plants,and there was a significant positive correlation with the change of the submerged plant biomass(P <0.05)Indicating that submerged plant cultivation significantly improved the demonstration project area of water quality and biological conditions. |
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