| The green heart of the ChangZhuTan urban agglomeration has important ecological services,but the impact of land use changes on carbon fluxes in the area since the implementation of conservation remains unexplored.This study simulates the carbon flux changes in the green heart of the ChangZhuTan urban agglomeration through the mesoscale weather model WRF-CHEM and VPRM models,and carries out a quantitative study of atmosphere-ecosystem CO2 exchange under the conditions of an urban agglomeration with high summer temperatures and high industrial activity levels.The results are as follows.The results are as follows:(1)The overall difference in carbon flux reduction in the study area through land use change in the comparison tests of the current situation,planning and optimisation scenarios was not significant.From the perspective of landscape ecology,the optimisation scheme of reducing the area of urban construction land in the green heart area can cool the area locally and achieve the ecological effect of an urban green lung.In terms of daily-scale changes,the experiment had a relatively weak impact on the physiological changes of the ecosystem.The optimised solution had some localised cooling effect,but the mechanism of photosynthetic respiration in terrestrial ecosystems under high temperature conditions is currently complex,and the cooling had a minor effect on NEE changes.The slight increase in CO2 concentration suggests that the direct and rapid effect of atmospheric CO2 concentration is not in the land use change part of this experiment,but probably in the fossil fuel part;and the slight decrease in NEE,where the enhanced photosynthesis did not affect atmospheric CO2 concentration in a short period of time,suggests that photosynthetic CO2 uptake,in a slowly mixing atmosphere,has a weak effect;as this experiment The land use change,i.e.the reduction in urban area,was small and did not really affect the atmospheric CO2 concentration.(2)The spatial and temporal distribution of carbon fluxes in the green heart of Chang-Zhu-Tan city cluster was analysed.In terms of time,CO2 concentration showed a diurnal low and night high daily variation;the variation of NEE showed an obvious"single peak" type daily variation trend,which was a weak carbon sink during the day and rapidly changed to a carbon source at night.The daily curve shows a close relationship between NEE and atmospheric CO2 concentration,with anthropogenic emissions being offset by 66%during the daytime in July.The effect of carbon offsetting by carbon sinks is still very obvious.Spatially,a clear high temperature cluster is formed in the eastern part of the green heart(the built-up area of the city);the mountain canyon in the northeast of the green heart is a clear low temperature cluster.CO2 concentrations from industrial emission areas around the urban area of Changsha spread to the northern part within the Green Heart region,showing significant highhigh clustering,while the southern part of the Green Heart,which is further away from the industrial emission areas around Changsha and has a high density of vegetation cover,shows significant low value clustering.The mean NEE distribution within the Green Heart area forms a significant high-high clustering in the built-up area of the town(eastern part of the Green Heart),with an anthropogenic substrate of activity making it a positive NEE(i.e.a carbon source).In the northern part of the green heart,the ecological forested areas show a significant low value of clustering,forming a significant negative NEE area(i.e.carbon sink).(3)The analysis of the 24-day atmospheric CO2 concentration and NEE changes shows that under the conditions of an urban agglomeration with high summer temperatures and high levels of industrial activity,the atmospheric CO2 source areas are distributed in the eastern(Xingsha Industrial Zone and the agricultural area around Dujiaping),southern(Muyun Industrial Zone)and western(Lugu District of Hexi and Ningxiang Industrial Zone)parts of the main urban area of Changsha;the atmospheric CO2 source areas in the Green Heart region are mainly in the northern Muyun Area.The physiological anomalies of the ecosystem are located in the main urban area of ChangZhuTan as well as some of the Muyun area and Yetang area in the Green Heart area,all of which are carbon sources to varying degrees and have certain ecological disturbances.Observing,detecting and locating the CO2 concentration and surface fluxes in the Green Heart area of ChangZhuTan urban agglomeration will be of scientific guidance for further planning of the reclamation and restoration of the Green Heart area.(4)The factor with the greatest influence on carbon fluxes is temperature,with an influence of 0.24,followed by photosynthetic radiation,with an influence of 0.23.The other influencing factors also have some influence on carbon fluxes,with permanent wetlands,urban and built-up areas,grasslands and water bodies having a greater influence on carbon fluxes among the land use types.This indicates that human activities(including human production activities)and water bodies and wetlands have a high impact on carbon fluxes.In summary,the quantification of carbon flux processes in the green heart of the Chang-Zhu-Tan urban agglomeration provides a fuller understanding of the relationship between urbanisation and urban carbon flows,further complements the sample of cities for estimating carbon fluxes,and provides some scientific guidance for low carbon urban planning. |
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