Effects of land clearing techniques and tillage systems on runoff and soil erosion in a tropical rain forest in Nigeria

This work reports runoff and soil loss from each of 14 sub-watersheds in a secondary rain forest in south-western Nigeria. The impact of methods of land clearing and post-clearing management on runoff and soil erosion under the secondary forest is evaluated. These data were acquired eighteen years after the deforestation of primary vegetation during the ‘ West bank’ project of the International Institute for Tropical Agriculture (IITA). These data are presented separately for each season; however, statistical analyses for replicates were not conducted due to differences in their past management. Soil erosion was affected by land clearing and tillage methods. The maximum soil erosion was observed on sub-watersheds that were mechanically cleared with tree-pusher/root-rake attachments and tilled conventionally. A high rate of erosion was observed even when graded-channel terraces were constructed to minimize soil erosion. In general there was much less soil erosion on manually cleared than on mechanically cleared sub-watersheds (2.5 t ha⁻¹ yr⁻¹ versus 13.8 t ha⁻¹ yr⁻¹) and from the application of no-tillage methods than from conventionally plowed areas (6.5 t ha⁻¹ yr⁻¹ versus 12.1 t ha⁻¹ yr⁻¹). The data indicate that tillage methods and appropriate management of soils and crops play an important role in soil and water conservation and in decreasing the rate of decline of soil quality.     

Terraced fields and Mediterranean landscape structure: An analytical case study from Antikythera, Greece

Terraces are important capital investments in a range of agricultural landscapes worldwide, typically enduring well beyond any single farming cycle and over many human generations. This paper begins by emphasising that, while human population growth may often be loosely linked to terrace construction efforts, the association is by no means a straightforward one. We then argue that the choice of which parts of the landscape to terrace is driven by a range of cultural and environmental priorities that are most usefully explored by a combination of global, local and auto-correlative modelling, as well as via simulation-based methods. The results demonstrate that surficial geology, terrain slope, pre-existing terraces and pre-existing patterns of human habitation are all important structuring features. We also consider terraces as method for soil conservation, question the uncritical use of meso-scale erosion models and argue that patterns of catastrophic soil loss are often overstated in Mediterranean contexts. However, erosion modelling can, if deployed cautiously and comparatively, nonetheless be used to explore ways in which terraces do indeed manage localised soil movement in agriculturally favoured parts of the landscape, with our results suggesting that a substantial proportion of the erosion in this regions is indeed ameliorated by such measures.     

典型铁路工程水土流失情况调查研究

在我国水力侵蚀亚区内选取几条施工中铁路进行现场水力侵蚀实验调查,对铁路施工期水力侵蚀情况调查和研究,并在我国5个水力侵蚀亚区内的铁路施工期水力侵蚀进行人工降雨试验和侵蚀沟调查,研究结果得出5个侵蚀亚区内各铁路工程类型施工期水土流失等级、加速侵蚀因子和侵蚀模数。结论表明,交通工程边坡水力侵蚀程度受施工工程特点影响非常明显,新型构造物的形成将引发严重的土壤侵蚀现象。     

乌鲁木齐市烟尘控制区验收监测结果分析

通过对验收监测结果的分析，找出了乌鲁木齐市烟尘控制区的烟尘排放特点并提出了相应的建议。     

Coastal flood protection: What perspective in a changing climate? The THESEUS approach

Coastal areas are vital economic hubs in terms of settlement, industry, agriculture, trade and tourism to mention some key sectors. There are already many coastal problems including erosion, flood risk and long-term habitat deterioration. As economies continue to develop the asset base at risk will grow, while accelerating climate change will increase the likelihood of damaging extreme events, as well as accelerate habitat decline. Existing coastal management and defence approaches are not well tuned to these challenges as they assume a static situation.THESEUS project is developing a systematic approach to delivering both a low-risk coast for human use and healthy habitats for evolving coastal zones subject to multiple change factors. The project examines innovative mitigation and adaptation technologies and integrate the best of these technical measures in a strategic policy context through overarching guidelines. THESEUS activities are carried out within a multidisciplinary framework using 8 study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located.This paper describes THESEUS approach, and specifically: the Source-Pathway-Receptor-Consquence model for coastal risk assessment; the engineering, social, economic and ecological mitigation measures under analysis; the participatory approach with end users and coastal authorities for the selection and identification of the appropriate defence strategy to be planned in sudy sites.     

Evaluation of the efficiency of some sediment trapping methods after a Mediterranean forest fire

Forest fires are common in Mediterranean environments and may become increasingly more frequent as the climate changes. Destruction of the forest cover and litter layer leads to greater overland flow and increased erosion rates. The greatest risk occurs during the first rainstorms following a major fire, so local authorities must act quickly to put erosion control methods in place in order to avoid excessive post-fire sediment loads in river channels. Deciding on which methods to use requires accurate knowledge of their impact on sediment load and an estimate of their cost efficiency. The objective of this study was to evaluate the efficiency of Log Debris Dams (LDDs) and a sedimentation basin for their effectiveness in trapping sediments. Paired sub-catchments were studied to quantify the amount of sediments trapped in stream channels by a series of LDDs and a sedimentation basin. Cost efficiency was evaluated for each of the measures as a function of the cost per unit volume of sediments trapped. In addition, grain size analyses were performed to characterise the nature of the sediments trapped. A third sediment trapping method, Log Erosion Barriers (LEBs) was evaluated more superficially than the first two and conclusions regarding this method are tentative. LDDs trapped a mean volume of 1.57 m³ per unit (median = 1.28 m³); mean LDD height was 105.4 cm (std. dev. = 21.9 cm), and mean height of trapped sediments was only 50.0 cm (std. dev. = 22.9 cm), showing that the traps were only half filled. Sediment height was limited by the presence of gaps between logs or branches that allowed runoff to flow through. Comparison of the textural characteristics of slope and trapped sediments showed distinct sorting: particles greater than 20 mm were not mobilised from the slopes during the study period, sediments in the medium to coarse sand size fractions were trapped preferentially by the LDDs, and sediments in the sedimentation basin were enriched by clay and silt sized (<0.050 mm) particles as coarser sediments were trapped upstream by the LDDs. Cost efficiency of LDDs was estimated at about 143 € m⁻³ for the LDDs and 217 € m⁻³ for the sedimentation basin at the time of sampling. The LDDs are therefore a cost effective method of trapping sediments, but they can only be used when pine trees or straight-trunked trees are locally available. In this case, they should be combined with LEBs, which had a cost efficiency estimated at about 250 € m⁻³. Installation of the LEBs had not been optimised and they have the advantage of trapping sediments on the slopes where they can continue to play an ecological role, so this method can give better results with more care. Sedimentation basins can be emptied if necessary and are useful in areas where pine trees are not available and where the site can be secured.     

Socioeconomic Factors Affecting Farmers’ Perceptions of Land Degradation and Stonewall Terraces in Central Palestine

Land degradation by soil erosion is a socioeconomic and environmental problem facing many developing countries. Application of stonewall terraces for soil moisture conservation is vital to reducing the environmental impacts of this phenomenon. To this end, a field plot experiment was conducted in the study area along with the use of a closed-ended questionnaire. The object of the experiment was to study the socioeconomic impacts of soil erosion on local farmers and their adoption of the stonewall terrace technique. The study showed a higher net profit in areas that had implemented terrace conservation practices than in areas that had not (i.e., 3.5 to 6 times higher net profit). Correlation analysis indicated that the farmers’ perceptions, land ownership, and geomorphology were significantly related to the farmers’ incentives and willingness to adopt terraces as soil conservation measures (P < 0.05), although the correlations were negative. Smallholder farmers (52% of the interviewed farmers) were involved in the sale of the agricultural land for urban uses, largely because of the high price and immediate returns offered. However, the associated land use changes warrant greater involvement of both the private and public sectors. This cooperation may be accomplished through the introduction of a long-term agricultural loan system and the development of proper legislation accompanied by a comprehensive and durable infrastructure and service system with the goal of reducing the negative impact of land use changes and encouraging sustainable use of resources.     

大连市水土流失控制模拟研究

从控制大连市水土流失出发,结合大连市地表总体状况,根据水土流失通用方程,利用拉格朗日中值定理分析原理,模拟计算了土壤有机质含量、地面覆盖类型、地面覆盖率和水土流失控制距离等方面对水土流失造成的影响;分别计算了不同地表条件下控制水土流失的理论经济点和理论敏感点;定量分析了不同地表作用因子对控制水土流失的影响程度.模拟结果表明:对水土流失影响最大的地表作用因子是土壤有机质含量,其次依次为地面覆盖率、地面覆盖类型和水土流失控制距离;控制水土流失最基本的地表条件是,土壤有机质含量不得低于1.78%,地面覆盖率不得低于41%,地面不得裸露,最基本的植被覆盖类型是草地,水土流失控制距离不得低于3　603 m.依据模拟结果,提出了控制大连市水土流失的措施.      

Towards a common Mediterranean framework for beach nourishment projects

Integrated Coastal Zone Management as a strategy for achieving conservation and sustainable multiple use of the coastal zone includes various types of management initiatives. Due to natural phenomena such as tides and winds and to social and economic activities, coastal areas undergo transformation. Coastal erosion and the disappearance of beaches as a result of wrong planning decisions and lack of effective legislation are among the most damaging effects and to reverse them requires application of a series of engineering techniques. Beach nourishment projects as a way towards shore protection and utilization through recreational purposes in the Spanish and Italian coasts are noteworthy in this respect. In beach nourishment projects, the roles of various entities, both public and private, should be clearly indicated and in the evaluation and execution stage a series of questions should be answered for the successful completion of any nourishment project. Past projects in the Mediterranean and experiences from recent Italian projects in Anzio and Nettuno confirm this. For example, dredging of the entrance channel of the port of Anzio enabled middle-sized ferryboats once again to enter the port (which had not been possible before). This will in turn increase the tourism potential of the town. Nourishment of two beaches at these sites prevented further erosion and provided more area for recreational purposes. Expected economic contribution of beach nourishments to the regional authority was estimated for Nettuno and Anzio; the resulting theoretical payback period was found to be 3 yr for the former and 15 yr for the latter.     

Does Tephrosia candida as fallow species, hedgerow or mulch improve nutrient cycling and prevent nutrient losses by erosion on slopes in northern Viet Nam?

Agroforestry is considered to be a promising alternative to short-fallow shifting cultivation or other monocropping systems. An on-farm experiment was established in 1996 in northern Viet Nam to examine the contribution of the leguminous bush Tephrosia candida (Roxb.) D.C. as a fallow or hedgerow species and as a mulch producer to improve nutrient cycling and prevent nutrient losses by erosion. The systems tested were upland rice monocropping (Mono), natural fallow (NaFa), fallow of Tephrosia (TepFa), hedgerow intercropping with upland rice (Oryza sativa L.) and internal mulching using pruned Tephrosia biomass (TepAl), and upland rice with external mulching using Tephrosia biomass (TepMu). Over two cropping seasons, from April 1996 to April 1998, nutrients recycled and inputs and exports were recorded, as well as changes in C-, N- and P-pools, and in pH in the 0–5 cm topsoil layer.The Tephrosia systems (TepFa, TepAl, TepMu) prevented nutrient losses by erosion effectively. Compared to the NaFa system, the TepFa system accumulated 34% more N in the above-ground plant parts and increased topsoil N by 20%, probably due to N-fixation. There was a trend that the less labile P-pools (NaOH-P) were reallocated into the more labile P-pools (Bicarb-P) in the soil of the TepFa system. Burning released significant amounts of the inorganic P-pools in both the NaFa and TepFa systems and this effect seemed to be more pronounced in the TepFa than in the NaFa. Organic input to crop export ratios for N and P were >1 in the TepAl and TepMu treatments. This was due to a sufficient quantity and quality of the Tephrosia mulching material. However, moderately labile NaOH-extractable organic P seemed to be depleted in the topsoil due to high P uptake in the TepMu treatment. Thus, nutrient cycling and nutrient balances were improved under the Tephrosia systems. But for long-term P sustainability, there is a belief that a combined use of mulching and mineral P fertiliser is needed.