| As the basic food source of the food web,the food source plays an important role in the material circulation and energy flow of the food web.The total area of lakes in the Qinghai-Tibet Plateau is about 41831 km2,accounting for about 50%of the national lake area.Due to the high altitude,long illumination time,high ultraviolet intensity,large daily temperature difference,thin oxygen,complex climate conditions,human activities has less impact,and it is a region with more and special aquatic biodiversity in southwestern China,which has formed a unique plateau ecosystem.However,there are relatively few studies on the food web of the plateau ecosystem.This study conducted a systematic survey of Lake Basomtso bait organisms in May2018?dry season?and August?flood season?,and combined the physical and chemical indicators of the water body to analyze the correlation between the biological distribution characteristics of the bait and the physical and chemical indicators of the water body;the application is stable Isotope technology is used to construct the food web structure in different hydrological periods,and the Bayesian mixed model is used to estimate the contribution rate of different food sources to consumers in Lake Basomtso.,and then to analyze the impact of hydrological changes on Lake Basomtso.1. Physical and chemical indicators of water quality:The water depth in the flood season was significantly greater than that in the dry season.The differences in water temperature and dissolved oxygen in different hydrological periods were not significant.The transparency in the flood season was significantly lower than that in the dryr flood season,and the p H was significantly lower than the dry season.Compared with the dry season,the ammonium nitrogen and total nitrogen in the water were significantly higher than that in the dry season,and the nitrate nitrogen was significantly reduced.The difference between nitrite nitrogen,soluble phosphorus and total phosphorus was not significant,and the content of chlorophyll a Significantly increased.2. The survey results show that there were 3 genera and 23 genera found in the attached algae,with an average annual density of 54.34Χ104 cell/m2.The density of the attached algae in the flood season is significantly higher than that in the dry season?p=0.007?.There was no significant difference between sampling points.A total of 5 genera and 18 genera were found in phytoplankton.The density and biomass in the flood season were lower than those in the dry season,with an average annual density of 0.45Χ104 cell/L.The density and biomass at point 5 were higher than other points.A total of 9 genera of zooplankton were found.The density and biomass in the flood season were significantly higher than in the dry season,with an average annual density of 1.91 ind/L.There was no significant difference in density and biomass between the sampling points.A total of 4 genera and 6 genera were found in benthic animals.The density in the flood season was 0.221 mg/m2,and the density in the dry season was 0.073 mg/m2.There was no significant difference,and there was no significant difference between the sampling points.3. The Pearson correlation analysis of bait organisms and environmental factors showed that the density of algae attached to Lake Basomtso has a significant negative correlation with the content of nitrate nitrogen and nitrite nitrogen in the water?p<0.05?,and it was extremely significant with the transparency of the water Negative correlation?p<0.01?,which had a significant positive correlation with the content of chlorophyll a in the water?p<0.05?;the density and biomass of phytoplankton were extremely significant with the depth of the water and the nitrite nitrogen content in the water Negative correlation?p<0.01?;zooplankton density and biomass were significantly negatively correlated with water transparency and total phosphorus content?p<0.05?,which was extremely significant with water nitrate nitrogen content Negative correlation?p<0.01?.4. Based on the stable isotope technique,the characteristics of the LakeBasomtso food web were described.The results showed that during dry season,?13C varied from-28.66to-13.57,and the?15N value ranged from 0.01to10.50.During the flood season,?13C changed from-27.15to-12.19,and the?15N value ranged from 0.97to 10.08.The difference between the dry season and the flood season was not obvious.There were four food sources in the Lake Basomtso food web:attached algae,particulate organic matter,terrestrial plants,and wet plants.The average value of?13C of particulate organic matter was-24.48;the average value of?13C of attached algae was-22.73;the average value of?13C of wet plants was-24.85;the average value of?13C of terrestrial plants was-26.63.The average value of?15N of particulate organic matter POM was 5.08;the average value of?15N of attached algae was 5.19;the average value of?15N of wet plants was 2.42;the average value of?15N of terrestrial plants was 2.07.There were significant differences in carbon and nitrogen isotope values of the four food sources?p<0.05?.5. The Bayesian mixed model was used to calculate the contribution rate of four food sources in different seasons of Lake Basomtso to consumers of water bodies?fish and water invertebrates?.The results showed that the attached algae was the main food source in the dry season of the Lake Basomtso food web.;The contribution of the four food sources to the consumers of the water body was relatively balanced during the flood season.The four food sources were divided into endogenous food sources and exogenous food sources according to the source.The results showed that:the exogenous food source was the main food source in each hydrological period of the Lake Basomtso.Food web,of which the omnivorous fish is dry.The season was mainly dominated by endogenous food sources,while the flood season was transformed into an exogenous food source. |
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