Identification Of Sediment Pollution Characteristics And Key Driving Factors In Typical Inflow Rivers Of Taihu Basin

Taihu basin,one of the most developed regions in China,is located in the lower reaches of the Yangtze River Delta.The river network within Taihu Basin is complex,with a high density of rivers.The water pollution and eutrophication in Taihu Basin is accelerating with rapid economic development and urbanization.Since the 1980s,large quantities of pollutants have been discharged into the lake.With properties of assimilating or carrying off municipal and industrial wastewater and runoff from agricultural land,rivers also plays an important role in contributing main pollutants to Taihu Lake.As the carrier of contaminants,sediments are not only the reservoirs of contaminants,but also the potential secondary sources of contaminants in aquatic ecosystem.River sediments,therefore,are important and fundamental subjects for the assessment of human-induced contamination in an area.The inflow rivers in the heavy polluted region(Northern and Western region)of Taihu Basin was chosen to investigate the nutrient,heavy metal contents and macrobenthic community in sediment.The objective of this dissertation was to indentify the sources of sediment pollution,key pollutants,and the critical scale of human impacts.And then,a systematic methodology to evaluate functional assessment in aquatic ecosystem were provided.Those results will be useful for understanding the driving mechanism of pollution in Taihu Basin,meanwhile,provide important insights for a better management.The results indicated that:(1)The results show that the distribution of heavy metals and nutrients in sediment were heterogeneous for the whole study area,and also indicated that different levels of pollution owing to excessive nutrients and heavy metal emissions.Principal components analysis and correlation analysis revealed two groups of elements:TN,OM and Cd,Hg,Pb;TP and Cu,Cr,Co,Ni,Zn,had analogous sources from anthropogenic activities.We also found most of the inflow rivers in the vicinity of metropolis and industrialized rural areas presented serious sediment pollution,while in all the metropolis have relatively low nutrient content due to well-run municipal sewage treatment system.The EF analysis confirmed Mn mainly derived from terrestrial weathering supply(EF<1).According to the following sequence,the mean value of EFCo(1.7)<EFHg(2.2)<EFNi(3.4)<EFpb(4.0)<EFCu(4.8)<EFCr(5.2)<EFZn(5.4)<EFCd(8.3),confirmed the study area was significantly contaminated with Cd,Cr and Zn.From the EF distribution maps,most of sampling sites were survayed as moderate,even high contamination in the study area.Our results confirmed that the inflow rivers in north and west region was the predominant pollutant contribution to Taihu lake.(2)This investigation of macrobenthic community assemblage and its correlation to pollutant concentrations in sediment showed that almost all regions were quite impoverished or even void of macrobenthos,with lower species diversity and richness.And the ABC plot also implied that the macrobenthic community under disturbed states and was dominated by r-selected species that were fast-growing,small or opportunistic species,such as oligochaetes and chironomids.Sediment pollution may cause structural changes in macrobenthic community,due to different species' stress tolerances.The present work showed that nutrients pollution(TN,TP and OM)make greater contributions than heavy metals.For the abundance data,76.8%of the total variances in macrobenthic communities were explained by the TP,TN,OM,Cd and Zn(P<0.05).Our study also revealed that macrobenthos exhibit species-specific responses to specific contaminants.For example,the oligochaetas(e.g.L.hoffmeisterxi,L claparedeianus)were identified to be significantly positively related with TP and Zn concentration.the chironomidaes(e.g.C.plumosus,T.chinensis)was tolerant to TN and Cd,while the chironomidaes(e.g.P.scalaenum,C.plumosus)were identified to be significantly negatively related with OM concentration.The species-specific responses of macrobenthos to sediment pollutants confirmed that TP,TN,OM,Cd and Zn are the key pollutants affecting the community structure and species composition of macrobenthos.(3)The relationship between land use and sediment pollution were explored in buffers at multiple spatial scales.The results of this study suggest no single land use type was able to describe the overall sediment pollution.Agricultural land(including paddy field and dry farmland),human-settlement(including urban and rural residential),build-up and vegetation are the most important predictors for sediment pollution variability.The influences of land use on sediment pollution changed with the different sizes of buffer zones.Vegetated land cover has strong negative correlation with all considered variables,especially in 1000 m and 1500 m buffers,and 500m scale was identified as human disturbances spatial critical scale for TN,OM,Cd,Hg and Pb.Buffer analysis can provide a effective method to determine the critical scale.According to the regulations of Jiangsu on prevention and control of water pollution in Taihu Basin,3-grade protected regions were divided to improve water quality,and the 1000m buffers on each side of rivers were confirmed as prior protective region.And our study indicated that the protection the 1000m buffers on each side of rivers is effective to aquatic environmental protection and management.(4)Based on aquatic eco-function assessment,the specific category representing comprehensive functions in each of the different regions can be identified and further classified into three groups with the same function condition,including good,average and good condition.The results showed only one region in the Yili River drainage area is under an good condition in its comprehensive functions,which is including Xijiu,Tuanjiu,Dongjiu lake in Yixing city.There are four regions falls into the average function condition.The hilly and mountainous regions,located in the southern area of Yixing,water source area along the Yangtze River,around Gehu Lake,and lakeside zone of Taihu Lake,are all in average condition.It can also be observed that the poor function almost occurred in metropolis and highly developed township,where have rapid urbanization and industrialization,such as Wuxi city,Changzhou city,Yixing city,Jiangyin city and the highly developed countryside.Human disturbance has seriously affected the aquatic ecosystem function,and their actions eventually resulted in serious pollution and poor eco-function.In general,although a series of water pollution prevention regulations were made to improve the water quality,the aquatic environmental situation in Taihu Bain is still far from being optimistic.Current problems of environmental management seems to be too macroscopic,and need to look at more details and distinctions among the different regions.From our findings,there is a serious pollution and environmental degradation in the urban-dominated region,so more attention should be paid to environmental protection,in particular,reduce industrial and household discharges.