Study On The Health And Biological Integrity Mechanism Of Lake Ecosystem Based On M-IBI And P-IBI

The ecological security of lakes has become a major environmental issue that restricts the sustainable economic and social development of the urban area.Ecosystem health and biological integrity mechanisms are the hot spots of current research on lake ecology.Through sampling and field research conducted locally at Balihe Lake in Anhui Province in November 2016 and April 2017,the P-IBI and M-IBI ecosystem health assessment system was established respectively to analyze the applicability of biological integrity index method in the freshwater ecosystem health evaluation and the selection of environmental factors on the impact of lake plankton and microorganisms.The main conclusions are as follows:(1)The P-IBI ecosystem health assessment system was established based on four parameters:M4 cladocerans and copepods units,M18 green algae abundance,M20 diatom quotient and M27 zooplankton/phytoplankton density ratio.The results showed that the regions with poor P-IBI value appeared in the area of the Wulihu tributary into the Balihe Lake and the connection area of upperlake and lowerlake.In November,the P-IBI value showed a trend of increasing along the water flow.The pollution from upper tributaries of the study area was the main reason for the decrease of P-IBI value.The concentration of pollutants introduced by the upstream tributaries decreased in April and the impacts of human activities became more obvious.(2)The Spearman correlation analysis showed that P-IBI value was significantly and positively correlated with WT(water temperature),C(water conductivity)and pH(p<0.05),while significantly and negatively correlated with NH4+-N(concentration of ammonia nitrogen in water)and TP(concentration of total phosphorus in water)(p<0.01).The RDA analysis between the distribution of plankton community and environmental factors showed that all environmental factors could explain 78.4%of the total plankton community distribution.The first axis of ordination explained 52.0%cumalative variance of species data and 66.4%cumalative variance of species-environment relation,indicating that the first axis represented the main environmental factors affecting the distribution of plankton community and the main influencing factors on plankton community distribution are WT,C,pH and TUR(water turbidity).(3)The results of Spearman correlation analysis between the OTU(Operational Taxonomic Units)matrix rankig top 35 absolute abundence and the environmental factor matrix of each microbial samples showed that the distribution of microbial community was significantly related to STN(total nitrogen of sediments),NO2--N(concentration of nitrite nitrogen in water),TP,C,d(water depth),pH,of which there were significant positive correlations between NO2--N,TP and most of the species while C,d and pH were negatively correlated with most of the species.(4)M-IBI biological integrity assessment system was constructed based on four parameters:T14 relative abundance of Bacteroidetes,T18 relative abundance of β proteobacteria,T20 relative abundance of δ proteobacteria,T31 relative abundance of Legionella.The assessment results are as follows:In November,the range of M-IBI value in Balihe Lake ranged from 2.1325 to 2.5913,and M-IBI value increased along the water flow,the sub-health point(M12)and moderate point(M6)were located along the lakeshore area;In April,the range of M-IBI value ranged from 1.6407 to 3.2230 and M-IBI value increased along the water flow.The region with the lowest M-IBI value(Ml,M2)was located in the region where the Third Lake Ditch flew into the lake.Poor points(M1,M2)and moderate points(M5,M6,M7)are mainly distributed in the upper lake.In general,the spatial variation trend of M-IBI value was consistent with that of P-IBI,both of which were increasing along the water flow and reached the highest at the water outlet of Balihe Lake,but there were certain differences in small area.(5)The Spearman correlation analysis between the relative abundance of microorganisms at class level with occurrence frequency>1/3 in the sampling spots in November and April 2016 and 12 environmental factors was conducted.The result showed that there was no significant correlation between M-IBI values and all environmental factors.Besides,the RDA analysis result between microbial community structure distribution and environmental factors also showed a poor explanation amount of 52.8%on plankton community distribution,Combining the correlation analysis result with RDA analysis result,it could be found that the chosen 12 environmental factors can barely influence the biological integrity of sediment microorganisms.In this paper,through two biological integrity assessment system(P-IBI and a M-IBI)established at Balihe Lake,the impacts of key environmental factors on IBI values were analyzed,the mechanism of how environmental factors acting on the biological integrity of sediment microorganisms and plankton was explored from the perspective of IBI values.The research results can provide theoretical basis for the ecological restoration of lakes and wetlands protection.