Effects Of Conversion Of Marshes Into Aquaculture Ponds On Storage,composition And Mineralization Rate Of Soil Organic Carbon In The Min River Estuary

In order to reveal the impact of the transformation of tidal marsh wetlands into aquaculture ponds on carbon storage,organic carbon composition and organic carbon mineralization potential rates in the Minjiang Estuary,this study quantified and compared the carbon storage of tidal marshe cosystem and aquaculture pond sediment,soil/sediment physicochemical properties,soil/sediment organic carbon composition the soil/sediment extracellular enzyme activity,and also calculated the carbon emission per unit area caused by the transformation of different dominant plant marsh wetlands into aquaculture ponds in the Minjiang Estuary.The results show that:（1）In the vertical direction,with the increase of depth,there was no significant change in soil p H and water content in Phragmites australis marsh,Cyperus malaccensis marsh and Spartina alterniflora marsh;The soil bulk density of P.australis marsh and short leaf wetland increased gradually;The soil conductivity of P.australis marsh and S.alterniflora marsh decreased with the increase of soil layer in the range of 0～100 cm;There was no significant difference in soil particle size within 0～100cm of swamp wetland with different vegetation types in Minjiang Estuary.After the reclamation of coastal swamp wetland into aquaculture pond,the p H value,bulk density and electrical conductivity of soil/sediment increased significantly,and the moisture content of soil/sediment decreased significantly.The reclamation had little impact on the soil particle size of swamp wetland.（2）The change trend of SOC content in marshes dominated by three plant communities in the range of 0～100 cm soil layer is that it decreases with the increase of depth,and the SOC content of aquaculture pond sediment transformed by swamp wetland does not change significantly with depth.The difference between the organic carbon content of aquaculture pond sediment and that of tidal flat swamp wetland before reclamation shows that the difference between the surface and bottom is large,The effect of reclamation on soil/sediment SOC decreases with the increase of depth.（3）There was no significant difference in the contents of DOC,EOC and MBC in soil/sediment of 0～30cm soil layer between the three vegetation types of swamp wetland in the Minjiang Estuary and the reclaimed aquaculture pond.The contents of DOC,EOC and MBC in soil/sediment decreased after swamp wetland was reclaimed as aquaculture pond;There was no significant difference in the ratio of DOC/SOC and MBC/SOC before and after reclamation,but the ratio of EOC/SOC increased significantly after the three vegetation types of swamp wetlands were reclaimed into aquaculture ponds.The content of Ca SOC in sediments increased after reclamation as aquaculture pond;After the P.australis wetland and S.alterniflora wetland were reclaimed as aquaculture ponds,the content of Fe（Al）-SOC in sediments changed significantly,while the content of short leaf grass did not change significantly.The ratios of Ca-SOC/SOC and Fe（Al）-SOC/SOC increased as a whole and the ratio of residual SOC/SOC decreased as a whole after the marsh was reclaimed as a breeding pond.After the swamp wetland was transformed into aquaculture pond,the content of Ca SOC in soil/sediment increased significantly and the content of Fe（Al）-SOC decreased significantly.At the same time,it is likely to be accompanied by the decrease of soil/sediment mineralization stability.（4）The changes of Soil/sediment extracellular enzymes activities ofβG,CBH,and PEO after the P.australis marsh converting into the aquaculture ponds were most greatest.The CH₄and CO₂production rates of soil/sediments significantly increased after the P.australis wetland,C.malaccensis wetland and S.alterniflora wetland converting into the aquaculture ponds.