| Food web is the most important carrier of material circulation and energy flow in the ecosystem.Species in the food web interact and influence each other through competition and predation,and the outbreak or extinction of one species often affects other species through the interaction between species.Aquatic ecosystem is a kind of ecosystem that is closely related to human life and relatively fragile.Its main producer(phytoplankton)and consumer(zooplankton)are small in size,fast in reproduction,short in growth cycle,sensitive to environmental changes,and easy to fluctuate in food web structure.The main environmental factors and aquatic organisms were sampled and monitored every two months from August 2018 to June 2020 in the River Taizicheng,a mountain river in the core area of the Winter Olympic Games in Chongli District,Zhangjiakou.The spatial and temporal distribution characteristics of species composition,density and biomass of producers,primary consumers and predators communities in the food web were studied to construct the food web structure of River Taizicheng.Multivariate statistical analysis was used to study the effects of environmental factors on trophic organisms of the food web,and the water purification effect of the food web in River Taizicheng was calculated based on the theory of ecological metabolism.The stability of each trophic level of the food web and the stability of the whole food web were calculated by the heterogeneity index of community turnover,and the effects of environmental factors on the stability index of each trophic level of the food web were studied by multivariate statistical analysis.The main results and conclusions are as follows.(1)The structure of the food web in River Taizicheng is relatively simple,in which the main producers are phytoplankton,including Diatoms,Euglysophyta,Chlorophyta,Cyanophyta,Cryptosophyta,Dinoflagellates and Xanthophyta,as well as macroaquatic plants in the wet meadow in the shallow water of the river,and the main dominant species is Diatoms,which can account for 73%of the biomass.The primary consumers are mainly zooplankton,including Protozoa,Rotifers,Cladoceras and Copepods.Cladoceras are the dominant species,accounting for 49%of the biomass.Predators are mainly composed of benthic organisms,including Annelids,Mollusks and Arthropods.Mollusks are the dominant species,accounting for 81%of the biomass,and fish are almost extinct.Phytoplankton individual size ranges from 10-3 mg/ind to 10-13 mg/ind.Phytoplankton individual size presents a normal distribution.Zooplankton with different individual sizes have little difference in density and relatively uniform distribution.The complexity of food web structure in the main stream(T2)and the downstream(T3)of River Taizicheng was higher than that in other regions.Food structure also varies in different time scales,with high biodiversity in summer and autumn and more complex food web structure.(2)The results of Canon corresponding analysis showed that dissolved oxygen and various forms of nitrogen and phosphorus were the main environmental factors affecting food web producers in River Taizicheng,and zooplankton and benthic organisms were mainly affected by water temperature and nutrient concentration.Food web has the certain water purification.With the increase of temperature,the individual growth rate of producers and the predation rate of consumers increase,and the absorption and removal of nutrients and water purification effect are enhanced.Food web in the downstream River Taizicheng(T3)has the best water purification effect.Theoretically,the absorption effect of nitrogen in water is about twice that of the food web in other regions.(3)The stability of each trophic level of the food web in River Taizicheng was different under the fluctuation of environmental factors.The stability of phytoplankton community replacement in T2 and T3 is lower than that in other regions,the stability of zooplankton in T1 and T5 is higher,and the stability of benthos in T3 and T5 is lower.The overall food web replacement stability index(BC=0.618)was high and the food web stability was poor.The stability of the food web in T1 region(BC=0.489)was higher than that in other regions,and the stability of the food web in T2 region was the worst(BC=0.789).The influence of environmental factors on the community stability is more significant,the producer community stability is mainly affected by dissolved oxygen,ORP and nitrogen and phosphorus nutrients,and the consumer community stability is mainly affected by water temperature and nutrient concentration.The results and conclusions of this paper are of great significance for understanding the spatiotemporal changes of food web structure,species composition,density and biomass in mountain rivers.The calculation method of food web water purification based on the theory of ecological metabolism plays an important role in the study of water purification measures of water ecosystem.At the same time,the exploration of food web stability is of great significance to maintain the health and stability of water ecosystem. |
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