Collapsing gully erosion is the main important and specific soil erosion type in the red soil region of tropical and subtropical South China. Knowledge of the soil disintegration characteristics within different weathering profiles (surface layer, red soil layer, sandy soil layer and detritus layer) and its relationships with soil particle size distribution and soil properties is important in understanding the mechanism of the forming process and development of the collapsing gully. In this paper, we conducted an experiment on four collapsing gullies located four counties (Tongcheng County, Gan County, Anxi County and Wuhua County) in the hilly granitic region of southern China. The anti-disintegration ability of the different weathering profiles with two different moisture conditions (the air-dried condition and the natural state condition) were determined by the anti-disintegration index (Kc) and measured by the submerging test. The results show that the coarse particles are higher in the sandy soil layer and the detritus layer of collapsing gully than that in the surface layer and the red soil layer, but the finer particles show the inversed order. The Kc values reduce significantly from the surface layer to the detritus layer. In the surface layer and the red soil layer, the Kc values in the natural state condition are much higher than that in the air-dried condition. The results highlight that, the sandy soil layer and the detritus layer are easily to disintegrate compare with the surface layer and the red soil layer, and in the case of low soil water content, the soil in any layer of collapsing gully is easy to disintegrate. The regression equation shows a very significant and positive relationship between the Kc values and the < 0.002 mm particles contents and the SOM (soil organic matter) (p<0.01), and negative relationship between the Kc values and the contents of other soil particle size. The results revealed that the repulsive force produced by compressed air in the soil exceeds the suction between the soil particles is the predominant factor to soil disintegrate rates in the air-dried state condition. Whereas the soil contained a certain amount of water can reduce the degree of disintegration. The results also indicated that the more contents of the cementation agents (like clay and SOM) in the soil of the different layers of collapsing gully, the higher Kc values (it means the more difficult to disintegrate).
Many measures have been applied to quarry slopes for ecological restoration; however, the performance of these measures has not been clearly evaluated. Thus, research evaluating the effects of the ecological restoration of quarry slopes in Caidian District was carried out to quantify the performance of different ecological restoration methods, to evaluate the effect of ecological restoration projects and to learn the applicability of different restoration technologies in Caidian District. The research can provide a reference for scientific decision-making in the follow-up management of ecological environments in Caidian District. First, the ecological restoration process of quarries in Caidian District was described in detail by visiting the relevant design and construction units. Through observational analysis from the aspects of applicable slope gradient, slope flatness requirements, project cost, the vegetation coverage conditions, the species diversity conditions and construction difficulty, the advantages and disadvantages, as well as the applicability of different ecological restoration technologies were preliminarily clarified. Then, the comprehensive evaluation index system of the ecological restoration effects was established by using the fuzzy AHP method. The ecological restoration effects of each sample plot were evaluated quantitatively based on the data of the evaluation indexes obtained by the field investigation and sampling analysis. Finally, according to the evaluation results, the existing problems in the follow-up management of the ecological restoration of quarry slopes in Caidian District were analyzed, and corresponding countermeasures and suggestions were proposed. The results showed that the quantitative evaluation results obtained by the comprehensive evaluation system of ecological restoration were consistent with the observational analysis results, and the validity of the evaluation system was proven.
Vegetation-concrete is one of the most widely used substrates in ecological slope protection engineering. The porosity of the vegetation-concrete must be high enough to satisfy the growth needs of the plant roots, while the mechanical properties must be strong enough to satisfy the self-stability requirement of the substrates on the slope. It is necessary to balance these two aspects in the design of vegetation-concrete. As one of the main components in vegetation-concrete, organic material has a remarkable effect on both the porosity and the mechanical properties of the substrate. In this paper, four types of common organic materials (rice husks, sawdust, and corn distillers’ and unhulled rice distillers’ grain) are chosen to research the effect of the organic material type and proportion on the porosity and mechanical properties of the substrate. The experimental results show that the porosity of samples containing corn distillers’ grain is clearly higher than those of the other samples types, while situation of the mechanical properties is the opposite. It can be concluded that organic material with a large grain size is not suitable for use in vegetation-concrete directly and needs to be crushed before use to prevent crack formation. The research results also show that the rates of increase in porosity decrease with more organic material added, while the rates of decrease in the unconfined compressive strength and the elasticity modulus increase. From a comprehensive consideration of the required mechanical properties and plant growth, organic material with a small grain size is most suitable for use in vegetation-concrete, and the suitable proportion is between 7% and 9%.
Increasing forest soil organic carbon (SOC) storage is important for reducing carbon dioxide (CO2) emissions from terrestrial ecosystems and mitigating global climate change. Although the effects of altitude, temperature and rainfall on organic carbon have been studied extensively, it is difficult to increase SOC storage by changing these factors in actual forest management. This study determined the SOC, soil physical and chemical properties, nutrient elements, heavy metal elements, soil minerals and microbial biomass in the 0–140‐cm soil layer of the monsoon broad‐leaved forest in the acid red soil region of southwestern China by stratification. We tried to identify the soil factors affecting the SOC storage of the forest in the acid red soil region and determine the weights of the factors affecting the SOC, with the aim of improving the SOC retention capacity in forest management by changing the main soil factors affecting SOC storage. The results showed that the soil factors affecting the forest SOC storage in this area are total nitrogen (N, 22.7%) > soil water content (19.9%) > active iron (including poorly crystalline iron, Feo, 15.5%) > pH (9.5%) > phosphorus (P, 9.4%) > aluminium (Al, 8.9%) > silicon (Si, 7.1%) > sulphur (S, 6.8%). Of these factors, N, the water content, Feo, and P are practical factors for forest management, whereas the pH, Al, Si and S are not. SOC was significantly positively correlated with the soil N concentration, water content, active iron content and P concentration (p < .05). In acidic red soil areas, with active iron as the highlight, N, soil water content, phosphorus and active iron jointly regulate the forest SOC storage capacity. Consequently, in actual forest management, any measures to promote soil N and water content and to activate inactive iron can enhance the storage of SOC, as appropriate input of N and P fertiliser and irrigation in dry years and the dry season. Highlights The soil environmental factors affecting SOC storage in forest soil are quantified Activation of inactive iron helps SOC storage in forest soil Irrigation and N and P input are effective for helping SOC storage in forest soil N, WC, P and Feo jointly regulate SOC in tropical acid red soil forest
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