Effects of Road Construction on Soil Degradation in Mountainous Area, West of China.
Xu Pei, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, #.9, Block 4, Renmingnan Road, Chengdu, Sichuan 610041, China
One of the important tasks to implement large-scale development in Western China is to speed up the construction of infrastructure. The total investment in the construction of traffic systems in 2000 reached as high as RMB 170 billion yuan in Sichuan province with an attempt to solve the problem of “Traffic Inaccessibility in Sichuan”. While the road network has brought about huge benefits to human society, the adverse impacts of road development on environment such as disturbance and destruction of ecosystems have become more and more obvious. Unfortunately, such adverse impacts have long been neglected. Great attention should be paid to this problem, and urgent work should be undertaken on the control of soil degradation along road. The Sichuan-Xizang(Tibet) highway is a representative of important road projects in the mountainous areas of western China, which crosses different geological and morphological units, and ecological areas and segments with different structures and functions. The Mingshan-Ya'an-Tianquan segment of the Sichuan-Xizang highway was selected as the key area of this study. This study area is located in the transitional zone between the first-grade Qinzang Plateau and the second-grade Yangtze River Mid-Lower Reaches Plain, where rainfall is plenty, geological fragmentation is serious. In addition, purple argillaceous shales, which are easily weatherable, extensively expose in the region. So it encourages soil erosion and degradation. By employing the space landscape and soil morphological series comparative method, and selecting the same type of soil that has developed in the area with identical or similar landscape to that of the study area, but unaffected by anthropogenic activities as a control, we evaluated the diagnostic soil horizons, diagnostic features and soil system classification in the area., In addition we measured the physico-chemical and biochemical variations of soils in unaffected areas, and the same soil variations in the areas damaged during and after road project construction. We also investigated the characteristics and mechanism of soil degradation in a typical area under the influence of road engineering construction. Five research sections with obvious effects of road construction and contrasts research sections along Tibet highway were selected. The results from this study are summarized below: 1) The degradation of soils in the destroyed and damaged areas due to road engineering construction is of mutability. In accordance with the systematic classification of soils on a quantitative basis, it can be seen clearly that the soil diagnostic horizons and diagnostic features have changed from complex and top-grade to simple and low-grade, with a reduction in diversity of soil type. 2) Obvious changes have taken place in the properties of soils in the destroyed and damaged segments, as mirrored by the degradation of physical properties, trophicity and biological features of soils. More noticeably, soils displayed compactability, coarse aggregation or high viscosity-density and other physical degradation phenomena with low contents of organic matter, nitrogen in soil other soil nutrients The degradation of physico-chemical properties of soil was accompanied by biodegradation and the reduction of soil microorganisms and enzyme activity. The microbial biomass carbon and nitrogen that were significantly and positively correlated with organic matter and total nitrogen in soil were decreased to varying extent. 3) The project of Sichuan-Xizang highway was implemented in a ecosystem background vulnerable to damage and destruction. It is process in which human activities have most strongly influenced the eco-environment. Vulnerability of the eco-environment is an important external factor, leading to soil degradation. In road engineering construction, the structures and characteristic features of soil layers have been artificially interfered and destroyed, thus giving an impetus to water loss and soil erosion, and causing induced effects of mountain hazards, as well as the reduction of forest coverage percentage and the destruction of bio-diversity. All these are the leading factors responsible for the degradation of soils along the line of road engineering construction.