Food Web Structure Of The East Taihu Lake Aquatic Ecosystem Based On The Stable Isotope Analysis

Taihu Lake is a large-scale shallow lake with the most typical human activities intervention in the middle and lower reaches of the Yangtze River in China.With its good water quality and rich bait resources,it has become one of the most developed and utilized water resources in China.Its ecological environment is closely related to human economic production activities.However,frequent economic production activities have also seriously affected the water ecology of Taihu Lake.The relationship between fish bait organisms,community structure and food network has changed significantly.The structure of fishery resources has developed towards miniaturization and simplification.In addition,the eutrophication of Taihu Lake has not been solved,and some part of the waters have even increased.Controlling the decline of fishery resources in Taihu Lake and optimizing fish community structure,and forming a more complete fishery management policy and restoring a good lake ecological environment are urgent problems to be solved.In this thesis,the stable isotope technique was used to study the food web structure of the Dongtai Lake aquatic ecosystem.The main findings are as follows:1.The trophic level and energy source of aquatic organisms in Dong Taihu Lake in spring of 2018 were analyzed,and also the structure of aquatic food web was constructed.In all samples,the fish δ15N value was 8.88‰～16.86‰,the zooplankton δ15N value was 8.71‰,and the δ15N values of Particulate Organic Matter(POM)and Vallisneria natans are 6.71‰ and 7.11‰,respectively;the fish δ13C value is-27.59‰～-21.14‰,the zooplanktonδ13C value is-28.16‰,and the δ13C values of Particulate Organic Matter(POM)and Vallisneria natans are-26.65‰ and-22.59‰,respectively.The results show that fish is the consumer of this ecosystem,among which the carnivorous fish,Mortusmbelus aculeatus,has the highest trophic level of 4.12;the Particulate Organic Matter(POM)and Vallisneria natans have the lowest trophic level,1.13 and 1.23 respectively,are the producer of the ecosystem;the δ13C value of some consumers is outside the range of producers of Particulate Organic Matter(POM)and Vallisneria natans,so it is inferred that exogenous nutrients enter the ecosystem.According to the analysis of the research results,the Dong Taihu Lake ecosystem has four trophic levels,five energy transfer pathways,and energy transfer through 3-4 links.2.The carbon and nitrogen stable isotope determination of fish fins and white muscle samples from the Taihu Lake in the winter of 2018 was carried out.The feasibility of the fin samples as a substitute for muscle samples was analyzed,and a linear regression model was constructed.The results showed that there were significant differences in the carbon and nitrogen stable isotope values of muscle and fin,but there was a strong linear relationship between them(R2C-13=0.8579,R2N-15=0.9).A linear regression model of fins and muscles was constructed for some fish species.Except for the low correlation of the carbon linear regression model of Protosalanx hyalocranius(R2=0.2685),all the other models showed high correlation(R2>0.7).Therefore,when using the stable isotope analysis to study the fish food web,fish fins can be used instead of the white muscle as a sample,but the δ15N and δ13C values need to be corrected during use.3.The structure of the aquatic food network of the Dong Taihu Lake in the winter of 2018 was constructed again.The results showed that the average value of δ13C in fish ranged from-26.36‰(Aristichthys nohilis)to-21.02‰(Mugilogobius myxodermus),and the average value of δ15N ranged from 11.02‰(Aristichthys nobilis)～18.38‰(Mugilogobius myxodermus).The fish with the highest trophic level are the Mugilogobius myxodermus(4,22),while the fish with the lowest trophic level are Aristichthys nobilis(2.06).There is a certain seasonal change in the aquatic food network of the Dong Taihu Lake.The trophic level of the secondary consumers varies greatly,but the overall food network structure tends to be stable.The factors that cause seasonal changes in fish community food webs are seasonal changes in producers in the ecosystem and seasonal changes in fish diet.