Changes And Factors Of Soil Carbon Storage In The Sanjiang Plain, Northeast China From1980s To2010

Small changes of soil carbon stock could make the sinks-source "or" source-sink"conversion in ecosystem carbon, it plays a major impact on global biogeochemicalcycles. Accurate estimatting of soil organic carbon and revealing the distributionpattern of soil carbon stock and its dynamics will help us to predict a feedbackrelationship of terrestrial ecosystems to climate change. Sanjiang Plain is the largestfreshwater wetland distribution in China and one of the most development area in thepast50years. The ecological balance of the Sanjiang Plain has been broken, as aresult, the change and the distribution of the total reserves of the soil organic carbonin the Sanjiang Plain are being affected. So we use the remote sensing and GIStechnology, combined with statistical and geostatistical methods to estimate theSanjiang Plain soil organic carbon reserves in1980s and2010. We determined thecontrolling factors of soil organic carbon density, and analyzed the dynamic variationand influencing factors. That helps us understand the carbon source of the SanjiangPlain. It is important for us to protect Wetlands in Sanjiang Plain, help the governmentmacro making decision and research agricultural area of the soil organic carbon cycleresearch. The main conclusions are as follows:1.The density of soil organic carbon and controllable factors in Sanjiang Plain. Theaverage of the different vegetation types (0-30,0-60,0-100cm) soil organic carbondensity in descending order are as follow: wetlands> woodland> grassland> paddy>upland of Sanjiang Plain in1980s and2010. The average marsh soil organic carbondensity in Sanjiang Plain (0-30,0-60,0-100cm) from1980s to2010are reduced. Soiltexture is an important environmental factor that affect the spatial distributioncharacteristics of soil organic carbon density in the Sanjiang Plain, soil clay had thegreatest impact. The average annual temperature and average annual cumulativerainfall impact on soil organic carbon density.2. The vertical distribution characteristics of the Sanjiang Plain soil organic carbonand its influencing factors. The trend of different types of soil organic carbon contentand density of the vertical distribution of characteristics in1980s and2010from thetop to down were decrease. Soil organic carbon density and content were moreconcentrated on the surface. The ratio of surface soil organic carbon accounted for1m depth from1980-2010showed a significant downward trend. Dry farmland (0-30cm)accounted1m depth total soil organic carbon (54%) was significantly greater than inthe paddy field topsoil (0-30) organic carbon accounting the1m depth proportion ofthe total (53%) in1980s. The ratio of marsh in0-30cm and30-60cm accounted1mdepth were decreased in2010, which were50%and28%respectively. Soil organiccarbon density in Sanjiang Plain increased by the soil depth, and its correlation withenvironmental variables was on the wane. It is significant positive correlation (P<0.01) for the topsoil organic carbon density and annual cumulative rainfall, soil claysoil silt, but it is a significant negative correlation (P <0.01) with the average annualtemperature and soil sand. The total proportion of soil silt content of soil organiccarbon density was a significant positive correlation in1980s and2010.3. The space-time dynamic of soil organic carbon storage in the Sanjiang Plain. Itshowed a decreasing trend from1980s to2010. The topsoil organic carbon pool of theSanjiang Plain had decreased19.84%during the three decades. The1m soil organiccarbon pool in1980s in Sanjiang Plain was2930.46Tg C. And it was2324.34Tg Cin2010. It had reduced606.11Tg C of soil organic carbon reserves during the threedecades. Topsoil organic carbon pool accounts for about50%of its1m soil organiccarbon pool in1980s and2010. Woodland was the largest and grass was the minimumin different land cover types of soil organic carbon reserves in1980s. But in2010thesoil organic carbon of woodland was the highest, the value was near dry farmland.Judging from space, it is obvious for the difference between soil organic carbon fortwo periods of time. There are more than60%pixels in the1m soil organic carbondensity of Sanjiang Plain in the study area are reduced, These in the south-east werehigher than the western region, more than40kg/m2. The most increasing area was inin Northeast of Sanjiang Plain and in a maximum of more than10kg/m2.4．Factors of dynamic changes in soil organic carbon of the Sanjiang Plain. Land usewas large changing from1980s to2010which is more dramatic occurs mainlybetween farmland and other land use types. The area of dry farmland in northeastincreased most. The reclamation of marsh、woodland and grassland are the majorreason of the decrease of soil organic carbon stocks. Our studies have shown that thereclamation of soil organic carbon reduction is mainly reflected in the topsoil.1mSanjiang Plain marsh reclamation led to the loss of soil organic carbon reserves of86.84Tg C, it is also one of the main reasons for northeastern in different depth ofsoil organic carbon reduction. The reclamation of woodland and grassland led to the loss of soil organic carbon reserves of24.78Tg C and2.01Tg C. Dry farmland tomarsh and returning farmland to forests may increase the Sanjiang Plain soil organiccarbon stocks. From1980s to2010, dry farmland into wetlands led to the increase by19.02Tg C in soil organic carbon reserves. Dry farmland to marsh and to woodlandare more conducive to the increase of the topsoil organic carbon. Chemical fertilizer,the proportion of paddy in land and irrigation methods affect the Sanjiang Plain soilorganic carbon is also an important factor in three kinds of farmland management.