黄土高原沟壑区王东沟小流域土壤有机碳空间分布

地貌和土地利用是影响土壤有机碳(Soil organic carbon,SOC)空间变异的重要因素。以黄土高原沟壑区王东沟小流域(8.3 km2)为对象,在考虑地貌单元和土地利用影响的基础上,采集0—20cm样品448个,0—200cm样品33个。研究了地貌单元(塬面、塬坡和沟道)和土地利用方式对SOC含量的影响。结果表明,地貌单元和土地利用对小流域表层和深层SOC的含量分布影响都有显著差异。0—20cm土层的SOC含量,沟道塬面塬坡;塬面表层SOC含量的变化平缓;塬坡和沟道SOC变异大于塬面。0—200cm土层SOC三地貌单元差异达极显著水平(P99.9%),塬面SOC含量最高(5.37g kg-1),塬坡(3.06 gkg-1)最低。不同地貌单元条件下土地利用方式对表层和剖面SOC含量分布的影响也存在明显差异。塬面区,人工草地SOC含量亦明显高于农田和果园,但仅40cm以上土层SOC达到显著差异。在塬坡上,不同土地利用类型间,发生显著差异深度达到140cm。沟道内,林草两种土地利用类型间的SOC含量无显著差异。在估算该地区SOC密度和储量时,需要充分考虑地貌单元和土地利用方式的影响。

SOC spatial distribution at small Wangdonggou watershed in gully region of the Loess Plateau

Patterns of soil organic carbon (SOC) vary widely across the landscape and land uses leading to large uncertainties in the SOC budget especially for agricultural landscapes where water erosion redistributes soil and SOC across the landscape. Samples from 448 sites (0-20cm) and 33 sites (0-200cm) were collected during May 2004 at Wangdonggou watershed in the gully region of the Loess Plateau to measure SOC, and analyzed the effect of land use, landform (tableland, slope land, and gully) and depth on SOC. Soil sampling units were defined on the basis of land form (tableland, slope land, and gully) and land use (arable, orchard, grassland, and woodland). There was significant variation in SOC concentration across the landforms (P > 99.9%). For the top soil of 0-20 cm, SOC concentration was greatest at the gully position (9.1 g kg-1 ), next was at the tableland position (7.8 g kg-1), and least (6.8 g kg-1) at the slope position. For the soil profiles (0-200 cm), the average of SOC concentration was greatest at the table land position, next was at the slope position, and least at the gully position. Land use impact SOC across the three landforms significantly. For the table land position, SOC content in 0-40cm under grassland was significantly higher than crop land and orchard. For slope land position, SOC content in 0-140 cm under grassland and woodland was significantly higher than under crop land and orchard. For the gully position, SOC content across the depth under grass land was not significantly different from woodland. On the tableland, SOC in 0-20 cm varied between 6.49 and 8.56 g kg-1, on the slopleland, the range of SOC concentrations increased (5.79-9.95 g kg-1), and varied most in the gully (5.79-10.64 g kg-1). Our study also indicates that geomorphic position and land use are important for estimating SOC density and stock within a watershed in the region.