Study On The Oriental White Stork Food Web Structure And Heavy Metal Accumulation Characteristics In Wetland-Farmland Edge Habitat Of Sanjiang Plain

The expansion of agricultural farmland in the Sanjiang Plain has exposed a greater proportion of edge habitats between wetlands and farmland habitats.The emergence of"edge effects"has led to changes in the living environment and food resources of birds in wetlands represented by the oriental white stork（Ciconia boyciana）.The exposure of heavy metals to edge habitats has posed a serious threat to the survival and reproduction of birds in wetlands.In this study,the large endangered waterbird oriental white stork was taken as the research object,and its preferred wetland-farmland edge habitat of the Sanjiang Plain was used as the research site.Samples were collected from June to July 2021-2022 for two consecutive years,mainly including feather of oriental white stork chicks,fish and shrimp,amphibians,insects,snails,zooplankton,particulate organic matter,and aquatic plant.Based on stable carbon and nitrogen isotope techniques,the oriental white stork food web was constructed in the wetland-farmland edge habitat of the Sanjiang Plain,and its internal structure and material flow characteristics were explored.On this basis,the contents of four heavy metals Hg,Pb,Cu,and Zn in various species were measured,and their enrichment characteristics in the food web were quantitatively evaluated,with a view to providing new ideas for bird protection in the context of habitat changes caused by agricultural development.The main research contents and results are as follows:（1）The results of carbon and nitrogen stable isotope values of various species in the wetland-farmland edge habitat of Sanjiang Plain were significantly different（p<0.01）.Divide the nodes of the food web based on feeding habits,and the range of trophic levels at each node is 1-2.101,with a narrow width.Based on Mix SIAR,the oriental white stork food web of wetland-farmland edge habitats in the Sanjiang Plain was quantitatively constructed.The results showed that the edge effect made insects,amphibians,shrimp,and snails a good supplementary food source for the oriental white stork.The prominent feature of edge habitats in this study is that insects contribute more than 35%to the food supply of each predator,occupying a key position in the entire food web.（2）The content of Hg,Pb,Cu,and Zn in each node of the wetland-farmland edge habitat in the Sanjiang Plain was significantly different（p<0.01）,with Zn content being the highest and Hg content being the lowest overall.The pollution levels of four heavy metals such as insects and snails,which contribute a higher proportion to the potential food sources of oriental white stork chicks,are relatively consistent,indicating that the content of heavy metals in oriental white stork is affected by the content of heavy metals in the food source species and the proportion of food sources.（3）The Metal Pollution Index（MPI）was used to comprehensively evaluate the pollution degree of each node,and the results showed that the comprehensive pollution degree of each node showed a significant positive correlation with the content of Pb,Cu,and Zn（p<0.05）.The particularity of edge habitats leads to the highest comprehensive pollution level of POM and zooplankton,and among the other nodes,the oriental white stork has the highest MPI.In addition,the feeding habits and growth parameters of fish can also affect their heavy metal pollution levels.（4）Based on the Trophic Magnification Factor（TMF）,the enrichment characteristics of four heavy metals in the food web were evaluated.Hg showed significant bioamplification in the edge habitat food web（TMF>1）,while Pb,Cu,and Zn showed significant biodilution（TMF<1）.The calculated results of the Bioamplification Factor（BMF）can well explain this feature,namely,Hg exhibits biomagnification in most of the transport relationships of the oriental white stork’s predatory food web,while Pb,Cu,and Zn exhibit biodilution in most of the transport relationships.The BMF_PScorrected by quantifying the proportion of food sources exhibits similar characteristics to TMF and BMF,indicating that the content of heavy metals in the food source species and the proportion of food sources significantly affect the enrichment characteristics of heavy metals in the food web.