Study On Effect Of Carbon Source On Carbon Sequestration Capacity Of Dominant Algae In Pengxi River

Excessive carbon emissions have posed a huge threat to the current human living environment,among which microalgae plays an important role in global carbon cycle.However,there were few researches have paid attention to the environmental influence on the algae and assessment of carbon flux.In this research,Gaoyang lake,which belongs to a part of Pengxi River was the study area,and the native algae communities in the Pengxi River were the research object,the in-situ monitoring and experiment were conducted.Then,the same water sample and microalgaes were collected and cultivated using continuous flow containing different inorganic and organic carbon to study the effects of different carbon resources on the carbon sequestration ability of algae.In addition,the Fridlyand model and the carbon flow conversion model were used to simulate the response of carbon sequestration ability to inorganic carbon and organic carbon,respectively.By analyzing the change of carbon sequestration ability by micro level,aiming to explore the relationship and response mechanism between the algae in the reservoir environment and the carbon cycle of the environmental system,and to provide a reference for the carbon footprint and management of the Three Gorges Reservoir.（1）6 Na HCO₃gradients were used to cultivate algae collected from the Pengxi River by using the continuous flow.The effects of inorganic carbon concentrations on water quality indexes,biological indexes and carbon fluxes were investigated.The results are as follows:1)When Na HCO₃concentration was 20 mg·L^-1,it was suitable concentration for native microalgae producing chlorophyll a.When Na HCO₃concentration was 25 mg·L^-1,it was suitable concentration for algae to grow.And the concentration of caro was postive to the input Na HCO₃concentrations.2)With the increasing of Na HCO₃concentration,the cyanobacteria proportion would increase gradually.3)The cell size surged significantly with the increasing of Na HCO₃concentrations.4)F_V/F_Mincreased significantly with the increasing of Na HCO₃concentration;5)The activities of external carbonic anhydrase（e CA）activity and internal carbonic adhydrase（i CA）decreased with the Na HCO₃concentration increasing.When the Na HCO₃concentration was 30 mg·L^-1,the Ru Bis CO activity showed highest value;6)p CO₂increased with the increasing of Na HCO₃concentration and the results of“carbon source”or“carbon sink”would not change with the increasing of Na HCO₃concentration.（2）6 types of organic carbon with the concentration of 5 mg·L^-1were used to cultivate algae from Pengxi River using continuous flow.The effects of organic carbon types on water quality indexes,biological indexes and carbon fluxes were also investigated.The results are as follows:1)When the organic carbon was biological carbon,the average TIC concentration was the highest.When the organic carbon was heteroauxin,the TOC concentration was the highest.2)Both cell density and chlorophyll concentration increased when the organic carbon was sodiumα-naphthylacetic acid or heteroauxin.3)The input of glucose,α-naphthylacetic acid,heteroauxin or biological carbon were beneficial to Chlorophyta.Sodium acetate contributed to the competition of cyanobacteria.4)When the organic carbon was sodium acetate,the cell size of microalgae was the largest.5)When the organic carbon was biological carbon,the net photosynthetic rate of algae was the lowest.6)When the organic carbon type was glucose,the activities of e CA and i CA were the lowest.When the organic carbon was biological carbon andα-naphthylacetic acid,the activity of e CA and i CA was the highest,respectively.When the organic carbon was sodium acetate,the activity of Ru Bis CO was the highest.7)The effect of“carbon sink”was more prominent during the organic treatment,and the degree of CO₂“carbon sink”declined after the inputting of organic carbon.When the organic carbon was heteroauxin,the phenomenon of“carbon source”appeared on the first day.Therefore,different organic carbon types inputting may transform the“carbon sink”into“carbon source”by increasing the CO₂pressure in the water through inhibit the growth of algae or increasing the algal respiration at night.（3）The effects of water flow（including the changing of daily input or output of algae species,nutrient and carbon concentration,and water disturbance of the Pengxi River）on water quality index,biological index and carbon flux were investigated by in-situ monitoring and experimental culture of native algae in Pengxi River using in-situ equipment.The results are as follows:1)The algae in the Pengxi River and in-situ devices would not experience the 4 growth stages,and the algae growth tendency was influenced by the changing environment;2)Water flowing would be more conducive to the preservation of Microcystis rather than Sciophyta.3)The cell size in the Pengxi River were lower than that in the in-situ devices on account of the shear force produced by water flowing.4)TIC concentration would inhibited e CA activity on in-situ condition;5)Because of the heavy rainstorm occurred in upper reaches in the Gaoyang Lake on day2,the turbidity and DOC concentration increased and the transparency of Gaoyang lake decreased,causing the phenomenon of“carbon sink”to become“carbon source”.（4）2 different models were employed to calculate the carbon sequestration capacity of algae during the inorganic and organic carbon treatments.The results are as follows:1)When Na HCO₃concentration was 40 mg·L^-1,the single cell net HCO₃^-fixation ability and carbon sequestration ability in the device reached peaks.With the increasing of Na HCO₃concentration,algae would reduce their CCM efficiency to allow the energy utilization level to fail in a reasonable range;2)The change of organic carbon type would influence algae to obtain different types of carbon.When the organic carbon was heteroauxin,it was suitable for the growth of Chlorophyta.CCM efficiency reached its highest point when organic carbon was biological carbon.When the organic carbon was glucose,the carbon sequestration ability of single cell was the highest;3)CCM model was mainly used for microscopic modeling,and could be applied to investigate the carbon sequestration rate of pure algae and the mechanism of carbon sequestration.And the carbon flow transformation model could be applied to macroscopic modeling and to determine carbon sequestration ability of water body.Therefore,in view to explore the carbon sequestration rate of the native algae in Pengxi River,the carbon flow transformation model was more accurate;4)11 kinds of important variables were amassed using the multi-factor modeling（p H,TIC and TOC,total phosphorus,total nitrogen,cell density,Chl.a,F_V/F_M,e CA,i CA and Ru Bis CO activity）,and carbon sequestration ability were analyzed.The results showed that the index explained 87%of the carbon sequestration ability change.Therefore,environmental and biological indicators measured in laboratory experiments could response the carbon sequestration ability of algae in the field.The results showed that the calculated value of river water was close to the measured value,but must be based on the condition that the algae genus in the field and indoor were the same.