| As the important carbon and nitrogen stock, soil has the important status in the globalcarbon and nitrogen cycle, which affect directly the greenhouse gas emissions of terrestrialecosystem and global climate change. Correct Estimating the soil organic carbon (SOC) andtotal nitrogen (TN) level and its change，is the important content of studying global climatechange, is also the hot fields of international geological and ecological community in recentyears. The Loess Plateau is the main ecological regions. Along with the implementation ofreturning farmland to forest and grass, it is one of the important contents of environmenteffect evaluation that studying the distribution characteristics, stock estimation and futuredevelopment trend of SOC and TN. In this paper, Zhi Fanggou is taken as the study area,where belongs to typical small catchment in the Loess Plateau. The area is studied to exploreits spatial variation, distribution characteristics and influencing factors of soil organic carboncontent (SOCC) and total nitrogen content (TNC) under the condition of different land usetypes, by using GPS to even the stationing of the whole catchment, combined with thetraditional statistics, geostatistics and GIS. Through study, it is revealed that theSpatial-Temporal Variability of SOC and TN in the catchment during20years. And,catchment-scale SOC is simulated and predicted with Century model, which is one dynamicmodel of SOC. The main research results as follows:1. The average SOCC and TNC in depth of0-100cm are3.08g·kg-1,0.32g·kg-1respectively. SOCC and TNC decreases with the increase of soil depth, the relationship ofwhich can be expressed by power function. Every layer’s SOCC and TN belong to mediumintensity variation, and conform to logarithmic normal distribution, which can be fitted withdifferent theoretical model. SOCC has medium spatial correlation above40cm, affected byrandom and structural factors together. And it has strong spatial correlation under40cm,mainly affected by structural factors. TNC has strong spatial correlation in the two layers of 0-10cm,40-60cm, mainly affected by structural factors. And it has medium spatialcorrelation in the remained4layers, affected by random and structural factors together.These spatial distribution differences about the catchment have a close relationship withfactors such as the terrain, land use and human activity. The situation of SOC spatialdistribution can be directly reflected by ordinary Kriging interpolation.2. In depth of0-100cm, the content and density of SOC and TN are as follows: shrub>forest> grassland> farmland, and the soil bulk density is in the order: farmland> grassland>forest> shrub. The soil bulk density of farmland in each layer is significantly higher thanthat of other land use type. The depth is not obvious effect on soil bulk density. Therelationship between the soil bulk density and SOCC can be represented by a power function.Under different land use types, there are extremely significant linear correlation (p <0.01)between SOC and TN. From big to small, The C/N is in the order: forest> shrub> farmland>grassland. C/N of grassland, forest and farmland decreases with the increase of soil depth,but that of shrub is not obvious. SOCC of8°-15°slope is significantly higher than that ofother slope (p>0.05), while <5°slope significantly lower than other slope. TNC of15°-25°slope is significantly lower than that of other slope, and the difference between other slopesis not significant. SOCC and TNC in different aspects are shown as: cloudy slope> sunnyslope> half sunny slope> half cloudy slope. It is showed the similar trends that SOCC andTNC vary with the change of altitude: with the increase of altitude, first increased, and thendecreased. In vertical direction, the average level is higher for the profile distribution ofSOCC and TNC above60cm, and the trend reduced with the increase of the depth isobvious. The average SOCC and TNC below60cm are low and stable.3. In0-100cm depth of Zhi Fanggou catchment, the average soil organic carbon density(SOCD) and total nitrogen density (TND) are2.63kgC·m-2and0.267kgC·m-2respectively,and soil organic carbon stock (SOCS) and total nitrogen stock (TNS) are21.62×106kgC,2.20×106kgN respectively. SOCD has strong spatial correlation, affected by structuralfactors. And TND has medium spatial correlation, affected by random and structural factorstogether. SOCD and TND are fitted with semivariance function, whose curve tendencyaccords with the index and spherical model respectively. They show the ladder-like andannular pattern in the spatial distribution. The different land use type、landforms and soiltexture is important influence factor to distribution characteristics of SOCD and TND. Itcan be expressed by power function that the relationship between soil depth and SOCS andTNS. The soil area account about65.58%and59.75%of the total area, whose SOCD andTND are less than average value. These show that SOCC and TNC of most area is low in thecatchment, and soil total SOCS and TNS are small. 4. In recent two decades, SOCC and TNC of0-20cm are increased2.37g·kg-1and0.12g·kg-1respectively. SOCS and TNS compared to1992increase by78%and30%respectively. Two phase data belong to medium variability and conform to logarithmicnormal distribution. In2010, the variation coefficient and spatial correlation degree of SOCand TN are higher than ones in1992. Range data shows that the spatial distributionuniformity is abated in the study area, small scale variation is enhanced, and the overalldistribution is more complex during the past20years. Spatial distribution show that the highvalue area from the catchment periphery of higher terrain to low-lying area of relatively flatterrain. It is the main reason for spatial-temporal variation that the land use change andhuman activity caused by returning farmland to forest and grass.5. In this paper, the Century model is first used in the Loess Plateau, with which thesimulation and prediction in catchment scale are made. The results show that the Centurymodel can be applied to simulate the SOC dynamic changes of the catchment in the LoessPlateau. In the balance status of Century model running, the total SOC pool in the study areais1.792kgC·m-2, and the active, slow and passive SOC pool are respectively3%,68%and29%of the total. After the balance was destroyed, the total SOC has the change trend of“increasing-reduction-increasing”, and final more than the original natural state ofequilibrium. the change of each component SOC pool has a close relationship with the landuse type and agricultural management mode. Simulated with Century model, in2110, SOCDand SOCS in depth of0-20cm are1.86kgC/m2,15.4×106kgC respectively. Under variedland use types, SOC increase in different degree, which shows obvious soil "carbon sink"effect. In the study area, land use and landform will affect the spatial distribution of SOC fora long time. |
PDF Full Text Request