Comprehensive Pollution Pressure Study Of Sedimentary Environment In Adjacent Waters Of The Yangtze River Estuary (Hangzhou Bay) Based On Typical Benthic Fishery Organisms

The Yangtze River estuary area is one of the most economically and industrially developed areas in China,and it is also an important estuarine ecosystem,an area with complex material sources and complex flux changes,and the Yangtze River estuary and its adjacent continental shelf edge seas are deeply affected by human activities.A certain amount of pollution pressure is unavoidably placed on the marine sedimentary environment as a result of the Yangtze River basin’s rapid economic growth and the ongoing strengthening of coastal development.Numerous pollutants congregate in the estuary of the Yangtze River and the waters nearby in a variety of forms.The seawater quality of the Yangtze River estuary and outer waters,especially Hangzhou Bay,is mainly inferior,and compared with historical data,there is no obvious improvement trend,and on the whole,the health of the marine ecosystem is in an unhealthy state.However,the reaction of organisms to changes in environmental quality is frequently too slow,indicating that conventional methods for assessing the sedimentary environment are somewhat trailing and are unable to give quick and efficient information for managing the marine environment.In a relative sense,biomarkers serve as"early warning"systems and are sensitive to specific types of pollutants.To better reflect the combined effects of multiple pollutants on marine organisms and to satisfy the demands of a thorough environmental quality assessment in a particular sea area,it is important to investigate how to construct a suitable biomarker assessment model.This is because multiple pollutants may exist in the marine environment simultaneously.In this thesis,through the interdisciplinary approach of fisheries resources,pollution ecology,molecular biology,and statistics,the sediment of important fishery waters in the Yangtze River estuary(Hangzhou Bay)is taken as the monitoring and evaluation object,and through field investigation,the important fishery species suitable for building a comprehensive pollution pressure assessment model for the sedimentary environment are selected,the physical and chemical properties of the sedimentary habitat,pollution factors and the activity level of biomarkers of important fishery species are detected and analyzed,and the main pollution factors are identified,analyze pollutant sources,build and optimize integrated biomarker response(IBR)model,and assess the comprehensive pollution pressure of the sedimentary environment.According to the results of IBR pollution assessment and the physical and chemical pollution characteristics of sediments,this study screened the benthic fish Cynoglossus joyneri and the benthic animal Nereis spp.,determined the Nereis spp.as the indicator organism,and used the IBR pollution index of this organism as the final environmental quality assessment result of the monitoring waters.In addition,this study attempts to use the pollution grade of multi-biomarker pollution index(MPI)assessment method to calculate the grade standard of IBR pollution assessment,so as to obtain an effective division of the pollution grade of the study area,intuitively reflect the temporal and spatial differences of the pollution degree,and optimize the existing IBR pollution assessment methods.Furthermore,this paper analyzes the historical trend of the main pollution factors and puts forward corresponding prevention and control measures.The main research results are as follows:(1)Status of benthic organisms in waters near the Yangtze Estuary.A total of 28species of macrobenthic organisms from 4 families were obtained from the spring and autumn surveys in the Yangtze estuary.Among them,there are 1 species of nemerteans,21 species of annelida,2 species of crustaceans,1 species of echinoderms,1 species of prokaryotes,and 2 species of mollusks.There were 6 dominant species in spring,and the dominant degree of Magelona japonica was the highest,and the average Shannon’s diversity index(H’)was 1.05.There are 9 dominant species in autumn,and the dominant degree of M.japonica was the highest,and the average Shannon’s diversity index(H’)was 1.18.The mean values of total habitat density and total biomass of macrobenthos in spring were 51.43 ind./m~2and 0.16 g/m~2respectively.The distribution trend was generally low in the north and high in the south.The mean values of total habitat density and total biomass of macrobenthos in autumn were 64.29 ind./m~2and0.91 g/m~2respectively.The overall distribution trend is patchy.According to the evaluation results of average Shannon’s diversity index(H’)in spring and autumn in the survey area,the habitat in this area is in the"poor"level,indicating that the existing benthos environment has a deteriorating trend.(2)Status of fishery biological resources in the waters near the Yangtze River Estuary.A total of 38 species of fishery organisms were captured in the Yangtze Estuary waters in spring and autumn,including 15 species of fish,9 species of shrimps,11species of crabs and 1 species of shellfish.The species with high economic efficiency accounted for 42.10%.There are 26 kinds of fishery resources in spring and 29 kinds in autumn.The proportion of fish weight is the highest,reaching 74.71%(spring)and68.99%(autumn),and the proportion of shrimp tail is the highest,reaching 60.90%(spring)and 62.80%(autumn).The dominant species in spring and autumn are C.joyneri and Miichthys miiuy.The diversity index in spring is higher than that in autumn.The biodiversity was generally at a"good"level.The proportion of juvenile fishery organisms was high,and the miniaturization is obvious.The proportion of larvae in spring was 59.26%,and that in autumn was 67.24%.Among them,the proportion of fish,shrimp and crab larvae was more than 50%,especially the proportion of crabs is more than 67%.The average resource amount in spring is 221.83 kg/km~2,and the average resource density is 15.55×10~3ind./km~2,the average resource amount in autumn was 92.59 kg/km~2,and the average resource density is 22.66×10~3ind./km~2.The distribution pattern of fishery organisms in the whole survey sea area is patchy.The result of cluster analysis shows that the fishery organisms in the investigated sea area can be divided into two groups,but the distribution is scattered and lacks continuity.There are obvious seasonal changes in species composition of fishery organisms in the northern waters and waters near the mouth of Hangzhou Bay.The fishery biological community has a certain disturbance in spring,and the structure of the fishery biological community is relatively stable in autumn.(3)Sedimentary environment of the Yangtze River Estuary.In spring and autumn,the distribution trend of 6 heavy metals,total petroleum hydrocarbons(TPH)and polycyclic aromatic hydrocarbons(PAHs)in the surface sediments of the Yangtze River estuary is generally decreasing from near shore to far shore,and the content is relatively stable.On the whole,the heavy metal pollution in the surface sediments of the investigated sea areas in spring and autumn is relatively light,and Pb,Cd and AS are polluted to some extent in some survey stations.Only one station in the spring(March)contained petroleum hydrocarbons exceeding the first-class standard in the“Marine Sediment Quality”,while the rest of the stations and the survey stations in the autumn of 2022(October)all met the first-class standard in the“Marine Sediment Quality”.The pollution level of PAHs in the surface sediments of the surveyed sea area is at a medium pollution level,and the content of the vast majority of PAHs monomers in March and October 2022 is lower than the effects range low(ERL)value,and only in March 2022,the FLT monomers at stations 1～8 have potential ecological risks.The heavy metals in the sediments of the investigated sea area mainly originate from land-based transport.Petroleum hydrocarbon pollution is the joint result of land-source input and anthropogenic pollution,mainly from petroleum sources.PAHs are mainly from fossil fuels,biomass incomplete combustion process under relatively high temperature conditions.(4)Response characteristics of biomarkers in two fisheries.Based on the dominant benthic and near-benthic species obtained from field surveys of fishery organisms and benthic organisms,and then combined with the migratory and other ecological activity characteristics of typical benthic species,tolerance to pollutants,sample accessibility and other conditions,C.joyneri and Nereis spp.were selected as assessment objects.The response values of EROD(ethoxyresorufin-O-deethylase,EROD)、SOD(superoxide dismutase,SOD)、CAT(catalase,CAT)、GR(glutathione reductase,GR)、GSH(glutathione,GSH)、GPx(glutathione peroxidases,GPX)、GST(glutathione S-transferases,GST)、GSSG(glutathione oxidized,GSSG)、MDA(malondialdehyde,MDA)in gill tissue and liver tissue of C.joyneri in the Yangtze River estuary and adjacent waters showed some spatial and seasonal differences.The sensitivity of Nereis spp.to the comprehensive pollution toxicity of sediments between stations is higher than that of C.joyneri.The activity of GST enzyme in gill tissue,liver tissue or intestine tissue of C.joyneri has a higher response to pollutants in the sedimentary environment.There was no significant difference in SOD activity between C.joyneri and Nereis spp.which may be the adaptive response of the two organisms to the sedimentary environment.The sensitivity of the same biomarker in different tissues of C.joyneri and Nereis spp.is different.The activity of nine biomarkers of C.joyneri showed obvious tissue differences,among which the activity of SOD,EROD and the content of MDA in liver tissue were higher than those in gill tissue.(5)Construction of IBR evaluation model and evaluation of sedimentary environment pollution.The response of biomarkers in gill and liver tissues of C.joyneri and Nereis spp.to various pollutants showed significant tissue differences.The biomarkers of C.joyneri and Nereis spp.showed significant interspecific differences in terms of space and time.According to the correlation analysis,7 biomarkers of Cynoglossus joyneri and 5 biomarkers of Nereis spp.were screened out.There is a significant correlation between the biomarkers and the Nemerow index of Nereis spp.is selected as the indicator for the assessment of sediment environmental pollution in the study area.According to the optimization of IBR evaluation method,the quality of sedimentary environment in the study area is evaluated by using the biomarkers of Nereis spp.The results show that the study area is located in the central waters of Hangzhou Bay in spring,and there is a polluted and seriously polluted area.The nearshore waters are slightly polluted and the offshore waters are pollution-free.In autumn,the distribution trend of high pollution level in coastal waters and low pollution level in offshore waters.(6)Countermeasures and suggestions for ecological environment management in Yangtze River Estuary and its adjacent waters.Strengthening scientific and technological services,promoting green,low-carbon,and high-quality development,integrating scientific and technological resources,promoting the digital construction of ecological environment,strengthening ecological environmental protection and restoration,highlighting scientific pollution control,strengthening land-based pollution control and management,monitoring sea pollution and sudden environmental risks at sea.