Influence Of Tides On Water-heat Balance And Carbon Fluxes In Mangrove Wetland

The mangrove wetland ecosystem is a contributor to the blue carbon sink,which makes an important contribution to mitigating global warming by virtue of its strong ability to regulate water and heat balance and carbon sequestration.In recent years,mangrove water-heat balance and carbon fluxes have gradually become hot research points.As a special environmental factor in the mangrove wetland ecosystem,tides have an impact on both energy balance and carbon cycle.However,the study on the impact of tides on energy and carbon fluxes in mangrove wetlands is very limited,and there are few studies on the influence of water level and salinity.In this paper,we take Zhangjiang Estuary Mangrove Wetland Ecosystem as the research site,and the eddy covariance technique was used to observe the carbon fluxes and meteorological factors,and the wavelet analysis method was used to explore the effects of water level and salinity change on mangrove energy balance and carbon fluxes at different time scales.The main findings and conclusions are as follows:(1)The annual energy closure ratio of this study is 0.78.There are differences in energy closure levels in different seasons,with the lowest degree of energy closure in summer and the highest degree of energy closure in winter.Regardless of the degree of energy closure from the annual or seasonal scale,the degree of energy closure is within the reported range,so the flux data obtained by the eddy covariance method is accurate and reliable,and can be used for the study of carbon water fluxes.(2)Both energy fluxes and carbon fluxes have obvious daily and seasonal variations.In the daily variation,the maximum time of net radiation,sensible heat and latent heat occurs when the solar radiation is the largest in a day,and the maximum time of soil heat flux appears 2 to 3 hours behind other energy fluxes.Latent heat flux accounts for the largest proportion of energy distribution,followed by sensible heat,and soil heat flux accounts for the smallest proportion.During the study period,the mangrove wetland ecosystem in the Zhangjiang Estuary showed strong carbon sinks throughout the year.The carbon fluxes were higher in spring and summer and lower in autumn and winter.(3)When the carbon fluxes and energy fluxes are in different water levels or salinity ranges,there is a difference in fluxes.But because the environmental factors that primarily affect energy fluxes and carbon fluxes change are also changing with the seasons,so the impact of the tides is different across months.This paper lacks research on the causes of this difference.(4)Discrete Wavelet Transform was used to study the effects of water level and salinity on carbon fluxes and energy fluxes at different time scales.We found that water level and salinity have the greatest impact on carbon fluxes and energy fluxes on multi?day scales,with less impact on the daily scale,and the effect of salinity is greater than the impact of water level.Using cross-wavelet analysis and wavelet coherence analysis,we found that the water level and salinity are closely related to the carbon fluxes and energy fluxes in the frequency-time region,but the distribution law is different and the localization characteristics are obvious.These search results show that the tidal activity has different effects on the carbon fluxes and energy fluxes of the mangrove wetland ecosystem in the Zhangjiang Estuary.The wavelet analysis method is suitable for the study of the relationship between tides and carbon fluxes and energy fluxes.This has important practical significance for a comprehensive understanding of the carbon cycle and energy exchange process of the mangrove wetland ecosystem,understanding its driving mechanism,and better accomplishing the mangrove conservation and planning work in the protected area.