Soil Carbon Content And Density In Soil Profiles Of Natural Wetlands And Their Consequent To Cultivated Croplands

Wetland is a unique ecosystem which plays an important role in the global terrestrial C sink which is related to global warming.Compared with other terrestrial ecosystems, wetlands preserve a larger organic carbon pool with much higher carbon density.In recent years,due to improper landuses,wetlands have been declined rapidly and C releases from degraded wetlands have been inceased resulting in enhanced CO₂ emissions.Therefore,it's important to maintain and improve the function of carbon storage of wetland greenhouse gas emission.Wetlands along the Changjing River reaches of Anhui Province are typical fresh marsh wetlands.In this study,profilesof freshwater marshes and their reclaimed croplands at 5 locations(Longgan Lake,Daguan Lake,Po Lake,Shengjin Lake and Qingtong River) were sampled.Soil total organic carbon(SOC) were determined and the stable portions of DOC1 and DOC2 were analyzed.Results of C densities and the changes after cultivation were presented and the imolication of C density decline was discussed.Research results are as follows:1.Carbon density of marshes was 45-60 tC·hm^-2 in the surface soil layer and 80-90 tC·hm^-2 in the whole profile of 0-100cm,while for the cultivated croplands its,22-50 tC·hm^-2 and 40-80 tC·hm^-2 in the whole profile,respectively.After reclamation,SOC decreased by 36%in the surface and in the profile,but the variability increased.It indicated that wetland soil was superior to the cropland on carbon sequestration.Besides,OC and carbon density of cultived upland was notably lower than paddy soil and wetland soil.2.SOC content of surface soil was higher in marsh than other kind of soil in Wanjiang drainage area.There was also large amout of OC at the deeper layer.There was obvious less SOCand greater variability in cropland,than that in the wetland.Carbon loss at the surface layer was about 18 tC·hm^-2,and nearly 30 tC·hm^-2 within the profile of 0-100cm. The percentage OC loss reached up to 40%.It was estimated that the loss of OC in wetland can be up to 4Tg.It's infered that agricultural utilization of wetland is the main cause of carbon pool elimination.3.Among the 3 kinds of OC,content of recalcitrant carbon was the most,with percentage above 50%,and DOC1 and DOC2 came in sequence.DOC1,DOC2 and recalcitrant carbon were positive correlated with TOC(R=0.683,p＜0.05).After reclamation,the 3 items all fell to only about 55%of their former level.This tudy demonstrated that C loss due to the degraded and cultivated wetlands may be of great concern in the soil C pool in China.Therefore the protection of these marsh wetlands could be an important a measure for enhancing the C sink effect to climate change in China.