Study On The Characteristics Of Dominant Algal Carbon Utilization During Algal Blooms Of Pengxi River In The Three Gorges Reservoir

Since the Three Gorges Reservoir began to store water in 2003,the intervention of man-made dispatching operation has greatly changed the hydrological characteristics of the original river channel.The flow rate in the backwater area of each tributary is slowed down,and the retention time of the water body is increased,which causes the material transmission rate to slow down.The nutrient salt is largely retained,and the frequent occurrence of the bloom phenomenon has caused widespread concern.The current research is mostly aimed at the succession of dominant algae during the bloom,the relationship between water bloom and environmental factors,and the construction of the model of water bloom,and the relationship between dominant algae and greenhouse gas flux during the bloom The relationship between carbon flow and transformation is less studied.In this study,the water bloom process under three different water level operating conditions was monitored,and the habitat characteristics,algal succession trends,and various carbon forms of the study area during the development of the water bloom were analyzed,and the characteristics of the habitat elements were analyzed.The mechanism of the influence of different dominant algae and different carbon forms;then the simulation of the water bloom process in the field according to the characteristics of wild blooms,and the analysis of the succession trend of dominant algae under the conditions of indoor culture and the habitat factors under the action of phytoplankton The trend of change and the characteristics of flow transformation of various carbon forms.Finally,according to the classical lake carbon cycle theory,the carbon utilization characteristics and carbon flow conversion of dominant algae in different blooms and indoor simulation conditions are analyzed.And explore the similarities and differences between the two,in order to better understand and understand the carbon utilization process under a variety of complex ecological processes.The results of this study mainly lead to the following conclusions:?1?The three water blooms during the different water level operation of the tributary of the Three Gorges Reservoir were monitored,and the following conclusions were obtained:?1?The nutrient concentration during the water bloom was affected by the organism,and the input and output of the material in the study area were exchanged.The effects of various kinds of nutrients and nutrient concentrations monitored during different periods were different,but they all exceeded the threshold of eutrophication.?2?The habitat factors are affected by the external meteorological conditions and various roles in the waters,and their trends and laws are quite different.?3?There are significant differences in DIC and DOC concentrations under different operating conditions.Because of the combined effects of various ecological processes,the fluctuations during the monitoring period are small and there is no obvious law;affected by algal photosynthesis and other external conditions,March The average value of CO₂fluxes detected in April and the performance of“Chongqing”in June were characterized by“Source”in June.The CH₄ flux is positive,and as the water level in the reservoir decreases,the flux of CH₄ continues to increase with the increase in the bubble flux frequency.?4?The Chl.a,algal cell density and biomass during the three water blooms were at different levels,which changed with the change of environmental conditions.The functional groups of dominant algae vary greatly during each bloom,and the overall trend is high water level D/P/X1/X2?discharge period L_M/P/L_O/X2?low water level G/MP/B;According to the algae growth strategy,the phytoplankton algae succession in the sensitive period of water bloom is CR/R/C?S/R/C?CS/CR.?2?Gradient analysis between species?various carbon forms and dominant algae?and habitat factors during blooms:DIC and DOC are affected by various ecological processes,so the correlation between individual factors and individual factors is not clear The CO₂ flux is the result of the carbon flow transfer in the water body,and its variation law will be affected by various physical,chemical and biological effects;in addition to the biological effects,the CH₄ flux is more in the process of transmission.Interference with a variety of physical factors;study the operation state of reservoirs in the waters,the input of light and heat,the concentration of nutrients and the hydrodynamic and hydrodynamic conditions of the waters will select the suitable conditions for survival and superiority under the current conditions through“natural screening”.Algae species.Therefore,under the different habitat characteristics of the waters during the three water blooms,the factors affecting the growth of algae and the degree of influence are also very different.?3?According to the analysis of the indoor simulation experiment established from the in-situ monitoring results,the algae species fully utilize the external nutrient salts and inorganic carbon sources to synthesize their own algae cells for proliferation when the environmental conditions are good.The change trend of algal cell density and algal biomass was the same as that of Chl.a,and it was at a relatively high level.It showed a trend of rapid increase and peaking.The overall growth strategy of algae species is CS/CR/R?CS/S.Except that the ammonia nitrogen is gradually increased and then decreased,the concentration of each nutrient salt in the water is greatly absorbed by algae,and all of them show different degrees of decline.In addition,DIC was consumed by algae in the water during the cultivation process,and the DOC concentration generally increased.The concentration of CO₂ in the device system gradually increased,and the rate of change gradually decreased with the consumption of nutrients.Methane is gradually consumed in an oxygen-rich environment within the device,and its concentration gradually decreases as the simulation time increases.The change trend of DO and pH in the device was similar to that of Chl.a,and the whole body increased first and then decreased.?4?Based on the classical lake carbon cycle,the process of dominant algae carbon utilization characteristics during in-situ monitoring and indoor simulation experiments during water bloom was analyzed,and the specificity of CO₂ flux during the water bloom in June was“source”.After analysis,the following conclusions were obtained:?1?Reanalysis of greenhouse gas flux data during 24h day and night monitoring in situ revealed that the optimal monitoring moments of CO₂ and CH₄ flux during each bloom were not present at the same time,and due to various The influence of exogenous conditions on the range of CO₂ and CH₄ flux is large,and the monitoring of data is more accidental.The contribution of CO₂ flux to“Hui”at all times during the March and April water blooms was positive.The contribution of CO₂ flux to“source”at various moments observed during the water bloom in June was also positive.It is characterized by a net absorption and net emission of CO₂ by water.?2?Through the simplified use of the inorganic carbon model,the calculation results show that only the amount of carbon absorbed or released by the“carbon sink”or“carbon source”is insufficient to support the carbon balance theory,which indicates that the carbon cycle during natural water bloom is not only dependent on The physiological action of algae is driven,and more depends on the interaction of various physical,chemical,biological and other processes.?3?The carbon circulation flow process in the device is relatively simple,and the phenomenon of carbon utilization is slightly different from the phenomenon that the water body absorbs CO₂ gas in the air in situ observation.Through calculation of the carbon-containing components in the system,it was found that 11.32%of the DIC in the water was converted into DOC by complex biological action,and 2.86%of the DIC was transformed into self-algae cells by photosynthesis absorption by the algae,and the remaining DIC concentration was converted into Organic matter in POC and CO₂ gas in the air.?4?The amount of CO₂ released by the water body into the air during the water bloom in June mainly comes from the organic carbon accumulated in the study area and the organic carbon retained in the water during the river transport.The rainfall runoff washes away the organic carbon that enters the water body.Can be ignored.