Effect of different types of site restoration on soil erodibility in Wenchuan seismic area, China
Large earthquakes can increase land substrate erodibility through shattering of rock mass and coalescence of cracks, which may further produce soil and slop instability leading to landslides. Thus, it is an important and necessary target to employ suitable technology for speeding restoration in seismic areas in order to avoid or reduce serious soil erosion. In this study, soil physical, chemical and hydraulic properties were measured in four restored sites on a seismic area in Wenchuan County, China, where a large earthquake (measured at 8.0 Ms) occurred in May of 2008. The four restored sites were: (1) a bare slope site with no vegetation cover (as L1); (2) a natural restored site covered by scattered shrubs and grasses with a vegetation coverage rate of about 40% (L2); (3) an artificial restored site, where several economic plant species were planted with a vegetation coverage rate of about 60% (L3); and (4) a control site, where soils were not damaged by the earthquake with a vegetation coverage rate of about 90%. Three plots (each with a size of 10m×10m) were selected for each of the four sites and a soil profile (50cm×50cm×cm in size) was dug out from each plot. The overall objective of the project was to evaluate the soil anti-erodibility under different restored approaches in a seismic area.
The results showed that 1) all factors making contribution to soil anti-erodibility in the studied sites can be grouped into eight categories: inorganic clay, water stable aggregate, micro-aggregate, porosity, organic matter, soil nutrient, soil water infiltration, and plant species diversity; (2) the most important variables affecting soil anti-erodibility were sand particle content (2-0.05mm in size), silt particles content (0.05-0.002mm in size), micro-aggregate fractal dimension, total porosity, total N, total P, available K, stable infiltration rate, and total infiltration water within initial 75min; 3) the soil anti-erodibility in the four restoration sites decreased in an order of L4> L3 > L2 > L1; 4) soil nutrient states, such as total N, total P and available K were the appropriate indicators to evaluate soil anti-erodibility at the early stage of restoration in seismic area, while organic matter and water states, such as SOM and water stable aggregate were the more suitable ones at the later stage. Our research results provide scientific reference to choose an effective approach for protecting soil erosion and to better understanding of soil anti-erodibility in the seismic region.