Effects Of Restoration Project On Macrobenthos Community And Food Web Structure In The Yellow River Delta Wetland

Under the influence of climate change and human activities,the Yellow River Delta wetland is seriously fragmentized,and its ecological function is extremely impaired.The ecological restoration projects started in early 2019 and will last for five years until 2024.During early restoration,the physical,chemical and biological characteristics of the wetland will be restored through dredging and injecting fresh water,so as to restore and rebuild the degraded wetlands.Scientific and accurate evaluation of the restoration effect and ecological effect of ecological restoration projects can provide an important theoretical basis for wetland restoration and reconstruction.This study mainly investigated the region of vegetation at the initial stage of the project.Environmental factors,macrobenthos community and food web structure in the area were investigated and analyzed before construction（2019.01）,after dredging of sediment,the first fresh water release（T1:2019.11,T2:2020.05）and the second fresh water release（T3:2020.09,T4:2020.11）.The study aim to identify the changing trend of environmental factors and the secongdary succession process of macrobrnthos community and the reconstruction process of food web before and after the project implementation.In order to provide data support for ecological restoration project effect evaluation,and provide theoretical basis for the Yellow River Delta wetland restoration.The main research results are as follows:1.Silty sediment was the main component before and after the restoration project,accounting for about 70%of the total sediment.After the implementation of the project,the contents of TC and TN in sediments decreased,and the concentrations of nitrogen and phosphorus decreased too in interstitial water nutrients except for silicon.Principal component analysis of environmental factors shows that nitrogen and phosphorus in clearance water has been the main environmental factor in the survey area before and after the project implementation.2.The community structure of macrobenthos changed significantly before and after the restoration project.With the implementation of the restoration project,the number of macrobenthos species gradually increased,from one species of Tanypus chinensis before the restoration project,to 24 species in T4 stage.The abundance and biomass showed an increasing trend.The dominant species in the community consists of a single Tanypus chinensi before the restoration project,and increased to 5 species in T4 stage,including Lapnome sp.,Ceratopogonidae,Neomysis orientalis,Chironomid larvae and Radix pereger.Biodiversity index analysis showed that the diversity and richness of macrobenthos community in the study area increased,and the evenness tended to be stable.ABC curve analysis showed that the wetland restoration area was in a moderate disturbance state.Redundancy analysis showed that the distribution of macrobenthos community was mainly related to the nitrogen and phosphorus elements in interleaved water environment.3.Food web structure analysis in T3 and T4 stages showed that there were no significant changes in the range ofδ¹³C andδ¹⁵N values between T3 and T4 stages.The trophic levels of T3 and T4 were 0.23-2.64 and 0.63-3.19,respectively.In T3 period,the energy flow path was:chinococcus and zooplankton→omnivorous fish,aquatic insects→carnivorous fish,aquatic insects;The energy flow in T4 can be divided into two parts:（1）zooplankton→tiny aquatic insects,shrimp→large aquatic insects,shrimp→fish,（2）zooplankton→large aquatic insects,shrimp→fish.The results showed that the implementation of ecological restoration project had a significant impact on the environmental factors,macrobenthos community and food web structure in the region.After sediment dredging and fresh water releasing,the grain size distribution of sediments in the Yellow River Delta wetland was changed.The content of TC and TN in the sediment environment decreased to a low nutrient state.The species number,abundance,biomass of macrobenthos increased,the dominant species of macrobenthos community changed significantly,and the diversity of macrobenthos tended to be improved basically.At the same time,the structure of the food web of macrobenthos became more and more complex,the main food source of the macrobenthos changed from algae to zooplankton,the trophic level of the same species increased gradually,and the energy and carbon flow pathways of the food web became more and more complex.The research results have theoretical reference value for the implementation and effect evaluation of ecological restoration projects,and have guiding significance for the protection and artificial restoration of wetland ecosystem in the Yellow River Delta.