Effects Of Vegetation Restotation And Check-dam On Soil Organic Carbon Storage In Small Watersheds In The Hilly-gullied Region Of The Loess Plateau

Vegetation restoration and check-dam have been recognized as the main measures to control soil erosion and also as critical driving forces in regional carbon cycle in the hilly-gullied region of the Loess Plateau in China.Studying characteristics of changes in soil carbon storage under the circumstance of combination of the two measures may help improve the estimation of regional soil carbon budget and the arrangement of different control measures.This study was conducted in check-dam controlled Fangta watershed and Manhonggou watershed which are located,respectively,in loess area and sandstone area and are characterized by different erosion environments.Through investigating,monitoring,and sampling in the field and determining in the laboratory,we analyzed the accumulate,store and loss characteristics of soil organic carbon in response to vegetation restoration implemented on hillslopes,organic carbon store in response to check-dams,and contributions of vegetation restoration and check-dam on soil organic carbon storage in the watersheds.The main results are as follows:(1)As abandoned sloping croplands were restored in a natural way,soil organic carbon began to act as a sink from the very preliminary stage when acting as a source;tree and shrub communities in the middle and late stages of artificial restoration played important roles in carbon sink.Robinia pseudoacacia forestation could increase or significantly increase soil organic carbon accumulation and storage under both the two erosion environments relative to natural vegetation restoration.Moreover,the ability of the same plant communities to accumulate and store soil organic carbon differed in the two erosion environments due to their different climatic and substrate conditions.Artificial tree and shrub communities could accumulate and store more soil organic carbon in check-dam controlled Fangta watershed in loess area than in check-dam controlled Manghonggou in sandstone area,and natural herbaceous communities could accumulate and store more soil organic carbon in check-dam controlled Fangta watershed in loess area and in check-dam controlled Manghonggou in sandstone area,respectively.(2)In a natural way of restoring abandoned sloping croplands,the soil erosion intensity was moderate at the preliminary stage and with time,it decreased and became mild at the late stage(Sophora davidii communities);the soil organic carbon loss decreased with time,but significantly increase was observed at the late stage.As abandoned sloping croplands were afforested with Robinia pseudoacacia,the soil erosion intensity became mild,and soil organic carbon loss decreased significantly as well.(3)Check-dams at different functioning periods all played important roles in carbon sink.Organic carbon storage in the check-dams was affected by erosive rainfall amount and substrate conditions of check-dam controlled catchment area.The contents of sediment organic carbon in the check-dams all changed in a fluctuating way,and they increased as a result of decomposition of organic debris in the sediments,high moisture contents of sediments and the compaction force.In check-dam controlled Fangta watershed in loess area,from the period of 1975~1989 to the period of 1990~2009,as area proportions of cropland and grassland decreased and that of forestland increased,sedimentary organic carbon rate decreased from 96.25 t yr-1 to 26.12 t yr-1.In check-dam controlled Manghonggou in sandstone area,from the period of 1976~1984 to the period of 1985~2007,grassland was the main land use type and had small changes in area proportion,sedimentary organic carbon rate had no distinct changes as well.(4)Woodland(forest and shrub land)and terrace and grassland were considered as the most effective types of land use in accumulating and storing 0~20 cm soil organic carbon for check-dam controlled Fangta watershed in loess area and check-dam controlled Manghonggou watershed in sandstone area,respectively.During the period of about 38 years,restoration-caused land use changes and check-dams all played important roles in carbon sink,and they were considered as the main driving forces increasing total organic carbon storage for check-dam controlled Fangta watershed in loess area and check-dam controlled Manghonggou in sandstone area,respectively.