黔北山区坡面基岩出露特点及与坡面特征的关系

Characteristics of exposed slope boulders and its relationship withslope features in the mountainous region of North Guizhou

以基岩大面积出露地表为特征的石漠化,是西南喀斯特地区最严重的生态环境问题。为揭示坡面基岩出露特点,进而为石漠化相关研究提供依据,选择贵州遵义典型潜在石漠化坡面,系统调查坡面出露基岩的空间分布、走向、出露高度及其影响因素。结果表明:1)与坡面侵蚀程度和土壤厚度相对应,中坡部位基岩出露数量高于上坡和下坡部位;2)调查区基岩平均出露高度为(0.35±0.25)m,且在0~15°坡度范围内,基岩出露高度随坡度增大呈幂函数形式增大;3)基岩走向多与坡向斜交,垂直走向的基岩出露高度(0.43±0.23)m,显著大于斜交和平行走向,在坡面上发挥着重要的蓄水拦沙作用;4)农地上基岩出露高度(0.32±0.26)m,小于林草地(0.37±0.18)m,印证了岩溶地区“原生林草地农地石漠次生林草地”土地演变模式。研究结果可为认识喀斯特地区石漠化坡面基本特征以及坡面土壤侵蚀研究提供数据支撑。

[Background]Rocky desertification is the most serious eco-geologically environment problem in the karst area of Southwest China.The surface exposed by outcropped boulders is a special landscape feature of rocky desertification slopes in karst regions of Southwest China.At present,there are few studies on the morphology,outcropping state and spatial distribution characteristics of outcropped boulders on the slope.This work aims to explore the outcropping characteristics of the outcropped boulders,and then provide a basis for the related researches on rocky desertification.[Methods]A typical rocky desertification slope in Zunyi city,Guizhou province was taken as the survey area.A full-slope carpet field survey was conducted,and a total of 375 exposed boulders were investigated.Firstly,We systematically investigated the spatial distribution,the direction of the outcropped boulders,and the heights of the outcrops as well as their influencing factors,such as slope gradient,altitude,slope aspect,and land use type.Then by using SPSS18.0 software(Statistical Product and Service Solutions 18.0),we explored the relationship between the exposed heights of boulders and the slope gradient.[Results]1)The number of exposed boulders was the most in the middle of the slope(183 boulders),1.63 times and 2.29 times of that on upslope and downslope,respectively.The reason was that the middle part of the slope suffered from more severe erosion and the soil thickness was relatively thinner.2)The average height of exposed boulders on the slope was(0.35±0.25)m.In contrast,the influence of slope gradient on the height of exposed boulder was greater than that of other factors.With the increase of slope gradient(0°-15°),the height of exposed boulders increased in the form of a power function.3)The direction of most boulders was crossed with the slope aspect,and there were significant differences in exposed height between different directions,following a descending order of the vertical direction(0.43±0.23)m>the oblique cross direction(0.33±0.28)m>the parallel direction(0.26±0.20)m.The exposed boulders,striking vertically to the slope aspect,played an important role in retaining overland runoff and sediment.4)The exposed height of boulders on agricultural land(0.32±0.26)m was smaller than that on secondary forest and grassland(0.37±0.18)m,confirming the land changing model of“native forest and grassland-farmland-rocky desertification land-secondary forest and grassland”under the influence of mankind in karst areas.[Conclusions]The number and height of exposed boulders are closely related to the characteristics of the rocky slope.This study provides a useful reference for understanding the basic characteristics of outcropped boulders on rocky desertification slopes in karst area and carrying out relevant studies on soil erosion and earth surface processes more scientifically in Southwest China.