Characterisation And Impact Analysis Of Carbon And Water Fluxes In The Ice/Water-Gas Multimedium Of The Ulansu Sea

Most of the existing flux studies in inland lakes lack high frequency long series monitoring,lack of water quality and meteorological contemporaneous data,it is difficult to analyse carbon and water fluxes at half-hourly scales,and often put H₂O fluxes in a subordinate position,so there is a lack of exploration of its influence mechanism.In the assessment of carbon sinks of inland lakes in China,the exchange of CO₂ fluxes between ice and air during the freezing period is less considered,which can have a great impact on the assessment of carbon sinks in lakes.In order to investigate the characteristics and influencing factors of carbon and water fluxes between ice/water-gas multi-media in shallow lakes in the cold and arid plateau,a carbon and water flux study was conducted in the Ulansu Sea.The vorticity correlation method was used to calculate,interpolate and split the 2018-2019 flux data in conjunction with meteorological data.A spatial and temporal analysis of the footprint of the flux-contributing area was conducted,and diurnal and carbon cycle analyses of CO₂ fluxes were carried out.The TLI method was applied to classify the eutrophication class of the waters near the eddy station,and the influence of eutrophication on CO₂ fluxes was explored.Using flux,meteorological and water quality data,statistical analyses of carbon and water fluxes were carried out separately to establish a regression model for H₂O fluxes during the non-freezing period-early freezing period,and to calculate water surface evaporation,and to filter out the main component indicators of environmental factors affecting carbon and water fluxes.The results are as follows:The flux contributing area is mainly influenced by the northwest wind direction.（1）There is diurnal variation in CO₂ fluxes and monthly variation in the carbon cycle.During the monitoring period,the Ulansu Sea absorbed15.72×10⁷ Kg of CO₂,plant primary production consumed 21.06×10⁷ Kg of CO₂ and ecosystem respiration produced 6.10×10⁷ Kg of CO₂,of which1.04×10⁷、1.33×10⁷ and 1.12×10⁷ Kg of CO₂ were consumed by primary production from January to March during the freeze-thaw period,respectively.CO₂ fluxes are mainly influenced by water and salt temperature and pressure,latent heat of evaporation and shortwave radiation sensible heat index.The changes in monthly cumulative NEE and GPP values during the monitoring period correspond to changes in eutrophication with a lag,with increasing eutrophication corresponding to decreasing monthly cumulative NEE and GPP values or a slowing of the original trend,and decreasing eutrophication corresponding to increasing monthly cumulative NEE and GPP values,while the carbon sink capacity of the lake decreases during both the first ice and melt periods.RECO values rise rapidly from August to September during the non-freeze-out period-early ice,then fall rapidly from September to November,and then show a steady decline as we enter the freeze-out period-melt.（2）The H₂O flux has seasonal variations and is mainly influenced by the water salt temperature,wind heat,wind speed,evaporation,water purity and air pressure indicators during the non-ice out-early ice out period,and the regression model explains 86.5%of the variation in H₂O flux.The cumulative evaporation of the Ulansu Sea during the non-freezing period and the first freezing period was1333.5 mm,and the total evaporation of the lake was 2.77～3.68×10⁸ m³,which was calculated by the eddy station as 1.91×10⁸ m³.（3）H₂O fluxes are linked to CO₂ fluxes through the solubility pump,carbonate pump and biological pump respectively,and there is a temporal difference between the two,that is,CO₂ fluxes do not stagnate throughout the year,while H₂O fluxes are only active during the non-freezing period.