Study On Geographical Distribution Characteristics Of Carbon And Nitrogen Stable Isotopes And Elemental Of Lake Primary Producers And Zooplankton In Eastern Yunnan

Phytoplankton,zooplankton,and aquatic plants,as the main primary producers and primary consumers,play an important role in the absorption and transmission of carbon,nitrogen and other elements in the lake ecosystem,and the stable isotope composition and elemental change characteristics help to uncover the composition of lake food webs and the transfer processes for biogeochemical cycling.In this study,a spatial survey of ten lakes and a seasonal survey of four lakes in Eastern Yunnan was conducted through analyzing carbon and nitrogen stable isotopes and elemental composition for zooplankton,phytoplankton and aquatic plants.Through statistical methods to identify the key environmental driving factors of the spatial and seasonal carbon and nitrogen stable isotopes characteristics for zooplankton,phytoplankton and aquatic plants.This survey provided important scientific basis data for ecosystem evaluation and ecological restoration of lakes in Yunnan.The dominating findings and results from this thesis include:?1?There were significant differences of the carbon and nitrogen stable isotopes for zooplankton,phytoplankton,submerged macrophyte and floating plant in Eastern lake.The submerged plants had the most positive carbon isotope value?-12.04±4.57‰?,and the floating plants had the most negative carbon isotope value?-28.99±0.86‰?.Phytoplankton and zooplankton were characterized by similar carbon isotope values,with the average value being-21.88±2.97‰,-20.85±2.70‰.Which might be driven mainly different carbon sources in lakes.In the field of nitrogen isotope,the primary producers,including floating plants?5.58±7.38‰?,submerged plants?5.43±5.84‰?and phytoplankton?7.26±3.83‰?,showing similar nitrogen isotope values.While the nitrogen isotope values of primary consumer,zooplankton?11.02±3.18‰?,was significantly higher than phytoplankton,and the spatial averaged enrichment coefficient by 3.46‰,reflecting the effect of nitrogen isotope fractionation across trophic levels in Eastern lakes.?2?On the spatial scale,phytoplankton and zooplankton were characterized by same variation carbon isotope values,and the carbon isotope was mainly affected by water temperature,pH and water depth.The water temperature affected the composition of dissolved inorganic carbon in the water and the pH.The dissolved CO₂ concentration decreases with the increase of water temperature,which leading to phytoplankton use more HCO₃^-and the carbon isotope of phytoplankton became more higher.Similarly,phytoplankton was one of main carbon sources of zooplankton.These factors also had an indirect effect on carbon isotope of zooplankton.In addition,the carbon isotope of zooplankton influenced by different lake depths.The different habitat habits,which affects the contribution of planktonic and benthic carbon sources for living things.The carbon isotope of submerged plants was correlated with transparency of lakes.Having low biomass and high transparency in low-nutrient lakes,the phytoplankton absorbs and uses less CO₂ and HCO₃^-dissolved in water.Submerged plants can absorb large amounts of dissolved CO₂ and HCO₃^-in water,leading to a positive?¹³C value of submerged plant.In the field of nitrogen isotope,the nitrogen isotopic changes of phytoplankton,zooplankton and submerged plants were synchronous,and gradually increase with the increase of nutrient level?total phosphorus,total nitrogen?of lake water.?3?On the seasonal scale,the carbon isotope of phytoplankton and zooplankton had obvious seasonal variation trend in the four lakes,and the carbon isotope of phytoplankton and zooplankton in rain season?June,September?was more positive than the dry season?December,March?.The seasonal variation of phytoplankton carbon isotope might be related with water temperature and the growth rate.The low water temperature leaded to the concentration of CO₂ had increased and the growth rate of phytoplankton bacame slow,these factors affected the carbon isotope signals of phytoplankton was negative.At the same time,the seasonal variation of zooplankton carbon isotope was mainly affected by its food?phytoplankton?,and might be related to rainfall,terrestrial inorganic matter,predation habits and so on.Basin brings more positive carbon sources and HCO₃^-in rainy season,which leads to the positive carbon isotope value of zooplankton,while the rainfall became less during dry season,resulting in the negative carbon isotope value of zooplankton.In spring,the nitrogen isotope of plankton was more positive than other seasons.It might be affected by spring drought,that had more windy weather,air became dry and higher evaporation,leading light?¹⁵N escapes with evaporation and denitrification leaving heavier?¹⁵N,resulting in nitrogen isotope of water became rise,and nitrogen isotope of plankton in the corresponding was also positive.?4?The percentage of carbon in submerged plants and floating plants was significantly higher than phytoplankton and zooplankton,while the percentage of nitrogen was opposite.The ratio of carbon to nitrogen of submerged plants and floating plants was significantly higher than phytoplankton and zooplankton,and the percentage of carbon and nitrogen elements in submerged plants in Eastern lakes was high,which might reflect the karst bedrock background in Yunnan,the water body was rich in carbonates,resulting in aquatic plants absorbs more carbon from the water.In summer,the total carbon content of zooplankton and phytoplankton was the highest in summer,and the minimum in winter and spring,while the percentage of total nitrogen had no obviously change,which might reflect the influence of solar radiation on biological growth.The strong growth of solar radiation in summer and autumn promotes the absorption of macroeletics in water,which makes the carbon element show seasonal trends.The carbon-nitrogen ratio had obvious seasonal variation characteristics,the summer carbon-nitrogen ratio was the largest,and the winter and spring were the smallest.The temporal and seasonal distribution of elemental content indicates that phytoplankton was more susceptible to external climate and environmental factors and the chemical stability of phytoplankton was lower than that of zooplankton.The C/N of aquatic organisms were less than 20,and it defined the shift between autochonous and allothonous of organic matter in lakes.