| The mangrove wetland ecosystem is an important blue carbon ecosystem located in the sea-land transition zone.It has attracted more and more attention from people because of its strong carbon sink capacity and its role in mitigating climate change.While mangrove wetland absorbs CO2,it also emits CH4 and other greenhouse gases,which makes the study of its carbon budget more complicated.The sustained global warming potential(SGWP)of CH4 is 96 and 45 times that of CO2 at the 20-year and 100-year scales,respectively.Therefore,it is important to understand the dynamics of CH4 emissions.In recent years,the research on the greenhouse gas fluxes of mangrove wetland ecosystems has gradually become a research hotspot.However,there are still relatively few related studies on the simultaneous observation of CO2 and CH4 greenhouse gas fluxes in mangrove wetlands.There is great uncertainty about how it is controlled by environmental factors.In order to accurately examine the temporal variations of mangrove wetland net ecosystem exchange(hereinafter referred to as the NEE)and net methane exchange(hereinafter referred to as the NME),this study focus on a subtropical estuarine mangrove wetland as the research area by conducting 1.5-year measurements of meteorology and eddy covariance.The aim is to explore the dynamics of NEE and NME under different time scales,and how each is influenced by environmental factors,especially salinity.The main research results of this paper are as follows:(1)NEE experienced a U-shaped diurnal pattern with low values around noon and high values in early morning and late afternoon,which is opposite to the pattern of PAR and vapor pressure deficit.The diurnal pattern of NME has two troughs the first of which is at around 7 AM and the second is at around 3 PM,and an intraday peak at around 6 PM.(2)NEE shows a consistent pattern for related environmental factors in both dry and wet seasons.During the daytime,NEE has a significant negative correlation with PAR,and its sensitivity is higher in the dry season.There is an obvious positive correlation between night NEE and temperature,with higher sensitivity in the wet season compared with the dry season.The NME-salinity correlation appears to be negative,and the difference between dry season and wet season is not obvious;NME has an obvious positive correlation with soil temperature,and its sensitivity is higher in the dry season.(3)The mangrove wetland in Zhangjiang estuary is a net greenhouse gas sink(this study only considers two greenhouse gases CO2 and CH4)of CO2 sink(-1075.8 g CO2C m-2 a-1)and CH4 source(3.1 g CH4-C m-2 a-1).The CH4-induced warming effect can offset 9.8%(4.6%)of the CO2-induced cooling effect at a 20-year(100-year)time horizon using the metric of sustained-flux global warming potential.In the case that climate change will cause temperature to rise and sea level rise,which will cause salinity to rise in the future,the artificial neural network model is used to conduct sensitivity analysis.The results show that the carbon cycle of the mangrove wetland in Zhangjiang estuary will be slowed down and the inhibitory effect on global warming will also weaken.The above research results show that the mangrove wetland in Zhangjiang estuary is a net greenhouse gases sink and plays an important role in slowing down global warming,but this mitigation effect may be weakened in the future.Environmental factors such as temperature have different effects on NEE and NME on different time scales.In the special habitat of coastal wetlands,salinity has an important effect on greenhouse gas fluxes. |
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