| Wetland protection and restoration are important contents and goals of national ecological civilization construction and the "Dual carbon" strategy.In the past few decades,Hongze Lake has been almost surrounded by aquaculture ponds,posing a serious threat to regional water ecological security and the sustainable development of cities around the lake.From 2020,Hongze Lake began to implement comprehensive protection measures to "ban and retire".The comprehensive prohibition and restoration of aquaculture ponds around the lake will undoubtedly have a positive impact on the ecological environment protection of Hongze Lake.Wetland sediment organic carbon(SOC)stability is not only the foundation for ensuring wetland ecology and environmental functions,but also the core content of carbon sink assessment and enhancement technology research in wetland ecosystems.In the past,there have been many studies on the effects of aquaculture on lake water quality,and significant progress has been made.However,the systematic evaluation of its effects on wetland SOC stability is not sufficient.From the perspective of cost and technological speed of retirement,almost all aquaculture ponds are directly restored to natural water surfaces.According to the current situation of land use/cover change in Hongze Lake wetland,reed wetland is a type with more natural cover,and poplar and willow artificial forests are common human use methods.In addition to directly restoring to natural water surfaces,theoretically there is also an option to restore aquaculture ponds to reed wetlands and artificial forests.Therefore,actively evaluating the impact of different rehabilitation and restoration plans on the stability of wetland SOC will provide theoretical and practical basis for the protection and ecological function of Hongze Lake wetland.This paper takes the Hongze Lake wetland as the object,selecting typical cover and land use types such as 10 and 20 year crab ponds(CP10,CP20),return to the lake wetlands(natural water surface,RP),natural reed wetlands(RL),poplar artificial forest(PF),and willow artificial forest(WF).By analyzing the active components of SOC(DOC,EOC,MBC),DOC spectral characteristics,content,and proportion,The mineralization rate and temperature sensitivity of SOC,bacterial community structure and diversity,and the impact of actual land use conversion methods on the stability of wetland SOC in the study area,such as pond aquaculture(RL→CP10/CP20)and pond restoration to natural water surface(CP10/CP20→RP),as well as the conversion of pond to poplar or willow ecological forest(CP10/CP20→PF/WF),were studied The impact of potential restoration schemes such as reed wetlands and ecological forests(RP→RL,RL→PF/WF)on the stability of SOC in natural water surface wetlands.The main results and conclusions drawn in this paper are as follows:(1)When wetlands were reclaimed and utilized as aquaculture ponds,the SOC content significantly increased(P<0.05).Among them,the SOC content under CP10 treatment increased by 42.75% compared to before reclamation,while under CP20 treatment,it increased by 4.50 times.However,the total proportion of active SOC components increased from 26.34%before reclamation to 34.47%-47.62%.This indicates that the reclamation of wetlands into crab ponds significantly increased the content of wetland SOC,but its stability decreased.After restoring the crab pond to a natural surface wetland,if further restored to a reed wetland,the SOC content will significantly decrease;After the conversion of reed wetlands into ecological forest land,especially in poplar forests,the SOC content will significantly increase(P<0.05).(2)The results of three-dimensional fluorescence spectroscopy analysis of DOC indicate that when wetlands are used as crab ponds,the stability of sediment DOC increased.When crab ponds were restored to natural surface wetlands,the stability of DOC rapidly decreased.Under different land use/cover modes,humus and humus like high molecular weight aromatic organic matter components accounted for the highest proportion,HIX was the highest,BIX was the lowest,and stability was the best in the DOC composition of PF treatment.When the crab pond is converted to ecological forest land,the stability of DOC will be significantly improved.(3)The results of SOC mineralization rate indicate that after wetland reclamation into crab ponds,the sediment SOC mineralization rate significantly increased.At different temperatures,the difference in mineralization rate between CP10 treatment and other treatments were relatively small,while CP20 treatment significantly increased mineralization rate.At 15℃,the mineralization rate of CP20 treatment increased by an average of 2.49 times compared to other treatments,and was 3.16 and 3.23 times at 25 and 35℃,respectively.It can be seen that the longer the reclamation time,the higher the mineralization rate of SOC and the more sensitive it is to temperature.In addition,the cumulative mineralization under different temperatures showed the highest variation under CP20 treatment,followed by WF treatment.It is worth noting that the cumulative mineralization of soil SOC in willow plantations is significantly higher than other types with increasing temperature.(4)When the crab pond is converted to artificial forest,the temperature increases by 10℃(15-25℃),and the temperature sensitivity of SOC increases by 16.34%-34.81%.However,when the temperature increases from 25℃ to 35℃,the temperature sensitivity of SOC decreases by 23.59%-38.96%,and SOC becomes more stable.This indicates that in terms of SOC stability,this conversion mode is more suitable for future global warming changes.(5)Compared with RL treatment,CP10 and CP20 treatment had a significant change in sediment dominant bacteria at the genus level,ranging from 89.47% to 94.74%.Obviously,reclamation has almost completely changed the structure and diversity of native microbial communities in sediment.When the crab pond is restored to a natural surface wetland,5bacterial genera(26.32%)will return to the RL treatment level.In comparison,when the crab pond is converted to artificial forests,36.84%-47.37% of the bacterial genera can return to the RL treatment level(6)At the genus level,the clustering analysis of bacterial communities showed that RP treatment had higher community similarity with CP10 and CP20 treatment,while PF treatment was closer to WF treatment.Reclamation significantly reduced the diversity of bacterial/carbon fixing bacteria communities,and no significant changes in community diversity were observed after the aquaculture pond was restored to a natural surface wetland.The conversions of crab ponds to artificial forests,as well as the restoration of natural water surface wetlands to reed or ecological forest wetlands,have increased the diversity of bacterial/carbon fixing bacterial communities(7)Functional gene correlation analysis shows that the changes in the dominant bacterial genus for carbon fixation are manifested as follows: under RL treatment,it is Methylibium,Sulfuricella and unclassified＿c＿Gammaproteobacteria under CP10 and CP20 treatment,respectively.In comparison,under PF treatment,it is unclassified＿f＿Sterolibacteriaceae,The dominant bacterial genus under WF treatment is Hydrogenophaga.In summary,this paper evaluates the impact of different restoration schemes based on SOC stability(content,composition,spectrum,mineralization,function and related microorganisms).It was found that reclamation and aquaculture significantly alter the structure and diversity of wetland native microbial communities reduced the stability of SOC.At present,the restoration of crab ponds to natural surface wetlands and then to reed fields did not significantly improve SOC stability.However,the conversion of crab ponds to artificial forests can not only restore the native microbial communities of the system to a greater extent,significantly improving SOC stability,but also make this conversion mode more adaptable to future global warming changes. |
