The Disturbance Of Floods On The Carbon Sink Function Of Wetlands Ecosystems

Wetland ecosystem is the most biodiversity rich ecosystem in nature,which has the functions of purifying water quality,flood control,mitigating climate change,maintaining ecosystem stability,etc.It is also an important part of the global carbon cycle,and plays a key role in controlling the terrestrial carbon cycle.Under the background of global warming,climate change has become an important disturbance factor of wetland ecosystem carbon cycle.Wetland ecosystems are highly sensitive to changes in hydrological conditions,and frequent floods seriously threaten the normal operation of the lake wetland ecosystem carbon cycle.Therefore,it is crucial to accurately predict the carbon balance of wetlands under climate change and improve their carbon sequestration capacity by carrying out the disturbance of floods on the carbon sequestration capacity of wetland ecosystems.This paper takes the Honghu Wetland Nature Reserve as the research object.Firstly,used the daily rainfall data of Honghu from 2000 to 2019,the long-term flood occurrence in the study area was evaluated,and the flood characteristics of Honghu Wetland from2013 to 2019 were analyzed based on the evaluation results;Secondly,based on the data of 117 GF-1 WFV remote sensing images from 2013 to 2019,combined with the research results of existing literature,the vegetation biomass,lake dissolved organic carbon(DOC)concentration,soil organic carbon density(SOCD)in the study area were estimated,and the vegetation carbon storage,water carbon storage and soil carbon storage were calculated;Finally,typical representatives of different levels of floods from 2013 to 2019are selected seasonally to explore the impact of floods on carbon storage and carbon sink,which can provide scientific basis for the protection,utilization and ecological restoration of Honghu wetland ecosystem.The main conclusions are as follows:(1)The seasonal distribution of flood disasters in the study area from 2000 to 2019showed significant differences,with the highest frequency of flood days occurring in spring;A total of 136 flood events were identified.A detailed analysis of the flood characteristics from 2013 to 2019 shows that 2018 had the highest number of flood events and 2017 had the longest total duration of floods;From the seasonal scale analysis analysis,the typical years of spring floods are 2015 and 2017;The typical years of summer floods are 2015,2016,and 2017;The typical years of autumn floods are 2013and 2014;The typical years of winter floods are 2014,2015,and 2018.(2)From 2013 to 2019,the annual variation trend of vegetation biomass and carbon storage of Honghu wetland was increased firstly and then decrease.The vegetation biomass and carbon storage were high in summer,and vegetation carbon storage reached the highest in August 2019.As the inundation area of the lake gradually increases,the vegetation biomass in spring and summer gradually decreases,the high biomass areas in autumn and winter gradually decrease,the low biomass areas in autumn show a trend of first decreasing and then increasing,and the low biomass areas in winter gradually expand.Without the influence of flood,the order of vegetation carbon storage in four seasons is spring>summer>autumn>winter.With the increase of the degree of flooding,the vegetation carbon storage shows a trend of gradual decrease in spring and summer,and decreasing first and then increasing in autumn,and increasing first and then decreasing in winter.(3)From 2013 to 2019,the fluctuation of DOC concentration in the study area was significant,with an annual trend of increasing first and then decreasing.Without the influence of flood,the order of DOC concentration of Honghu Wetland in the four seasons is spring>summer>autumn>winter,and the order of DOC storage is autumn>summer>winter>spring.Floods have a certain increasing effect on the DOC storage in the study area,with an increase range of summer floods>autumn floods>spring floods>winter floods.(4)During the study period,the annual changes of SOCD and soil carbon storage of Honghu Wetland showed a trend of increasing first and then decreasing.The values of SOCD and soil carbon storage were higher in summer and lower in winter.From the perspective of interannual changes,the peak value of SOCD in 2016 was relatively low,mainly due to the frequent and significant occurrence of flood disasters in the study area in the summer of 2016,which had a certain impact on the SOCD value.Without the influence of flood,the SOCD and soil carbon storage of the study area in the four seasons are spring,summer,autumn and winter from the largest to the smallest,and the change range is small.The occurrence of flood led to the decrease of SOCD and soil carbon storage in Honghu wetland,with the largest decrease in spring and the smallest in winter.(5)The maximum total carbon storage of Honghu wetland during the study period is4.31×10~4t,appeared in August 2019.The carbon storage of wetland ecosystem is obviously affected by seasonal changes.During the study period,the annual change of carbon storage showed a trend of increase first and then decrease,and the wetland carbon storage value in summer was the highest.Spring floods,summer floods and autumn floods reduced the total carbon storage of Honghu wetland,and winter floods increased the total carbon storage.(6)Among the three carbon sinks of vegetation,soil,and water,the proportion of vegetation carbon sink capacity to total carbon sink is the highest,with vegetation carbon sink accounting for over 50%in spring and summer.Between 2013 and 2019,the maximum values of total carbon sequestration capacity,vegetation carbon sequestration capacity,and soil carbon sequestration capacity of Honghu Wetland all occurred in August 2019,while the maximum value of water carbon sequestration capacity reached in July 2016.The trend of total carbon sequestration capacity within a year is increasing first and then decreasing,with significant fluctuations.Under no flood conditions,the total carbon sequestration capacity in spring,summer,autumn,and winter is 73.00g/m~2,65.15g/m~2,36.63g/m~2,and 24.31g/m~2,respectively.As the degree of flooding continues to increase,the total carbon sequestration capacity gradually decreases in spring,showing a trend of increasing first and then decreasing in summer and winter,and a trend of first decreasing and then increasing in autumn.Overall,floods have a significant reduction in vegetation carbon sequestration capacity,an increase in water carbon sequestration capacity,and a decrease in soil carbon sequestration capacity,but the reduction is relatively small.