Soil Erosion under Land Use Change from Three Catchments in Laos, Thailand and Vietnam

Abstract: The systems often identified as "traditional" undergo rapid changes as a response to demographic, economic, political and cultural drivers. These transitional periods are often most critical for soil erosion. The on-site impacts of soil erosion reduce the soil chemical fertility through nutrient and organic depletion, and acid subsoil exposure. Erosion also damages the physical fertility by removing surface soil, reducing the soil depth and water holding capacity, and exposing gravel and rocks. These combined processes result in less productive soils, hence lower farm income. To obtain the initial crop yield prior to erosion, increased amounts of inputs are needed, which is most often beyond the economic capacity of the small holders. To study the impact of land use change upon erosion, concurrent case studies, as seen with a dynamic perspective, can compensate for long-term monitoring studies. This approach provides data, which can be used for prediction soil erosion based on global change scenarios. The main objective of this study was to assess the influence of the rapid change of cropping systems on water erosion from three small catchments in three countries of South-East Asia (Laos, Thailand, Vietnam), using a multidisciplinary approach. These three catchments were selected because of their similar biophysical components (very steep slopes on shales; Janeau et al., submitted) and their land use intensification gradient. This investigation was conducted under the auspices the Management of Soil Erosion Consortium (MSEC) started in 1998 (Amado et al., 2002). Water discharge and soil erosion were monitored during three years at the outlet of each catchment using weirs. These data were used to calibrate and validate the PCARES model (Predicting Catchment Runoff and Soil Erosion for Sustainability) in each cachment. This GISbased model was developed in the Philippines for very steep slope condition

The use of Slingram EM38 data for topsoil and subsoil geoelectrical characterization with a Bayesian inversion

International audienceWe use the Bayesian method to invert a simple two-layer pedological horizon (1-D with a topsoil and a subsoil) of a surveyed site to be assessed. We show how the Bayesian method is well suited to the determination of topsoil/subsoil features, and can be used in particular as a tool for the analysis of parameters to be retrieved in terms of information content. Our approach is devoted mainly to the assessment of topsoil thickness, and of topsoil and subsoil conductivities, which are provided in terms of probability density functions. We first summarize the methodology implemented with the Geonics EM38-MK2 conductivity meter, and discuss the adaptation of field procedures and post-processing methods to mitigate the effects of drift and bias. We briefly review some non-Bayesian approaches, and then develop the Bayesian approach for the context of our geophysical survey, highlighting its merits. Positivity constraints (on thickness and conductivity) are included in the form of log parameters. A priori knowledge, based on an objective choice made by the geophysicist, is naturally included in the Bayesian scheme. We discuss the equivalence problem associated with the application of the Slingram method to soil structure analysis. The survey of a luvisol at the Kwazulu-Natal (South Africa) site of Potshini is used to illustrate an ecological application of the Slingram and Bayesian methods, used to define the geo-electrical structure of the near-surface soil. These algorithms have demonstrated their usefulness in mapping the clay content of the Bt horizon associated with the control of encroaching trees. (C) 2013 Elsevier B.V. All rights reserved

Seasonal variability of faecal indicator bacteria numbers and die-off rates in the Red River basin, North Viet Nam

International audienceThe Red River is the second largest river in Viet Nam and constitutes the main water source for a large percentage of the population of North Viet Nam. Here we present the results of an annual survey of Escherichia coli (EC) and Total Coliforms (TC) in the Red River basin, North Viet Nam. The objective of this work was to obtain information on faecal indicator bacteria (FIB) numbers over an annual cycle and, secondly, to determine the die-off rates of these bacterial indicators. Monthly observations at 10 stations from July 2013–June 2014 showed that TC and EC reached as high as 39100 cfu (colony forming units) 100 ml−1 and 15300 colonies 100 ml−1, respectively. We observed a significant seasonal difference for TC (p < 0.05) with numbers being higher during the wet season. In contrast, no significant seasonal difference was found for EC. The FIB die-off rates ranged from 0.01 d−1 to a maximum of 1.13 d−1 for EC and from 0.17 d−1 to 1.33 d−1 for TC. Die-off rates were significantly higher for free bacteria than for total (free + particle attached) bacteria, suggesting that particle attachment provided a certain level of protection to FIB in this system

Development and validation of the PLER (Predict and Localize Erosion and Runoff) Model

In Maglinao, Amado R.; Valentin, Christian; Penning de Vries, Frits (Eds.), From soil research to land and water management: Harmonizing people and nature ? Proceedings of the IWMI-ADB Project Annual Meeting and 7th MSEC Assembly. Bangkok, Thailand: IWM

Catchment approach to combating soil erosion in Thailand

In Annual report 2003. IWMI Southeast Asia Regional Office, Bangkok, Thailan

The indirect impact of encroaching trees on gully extension: a 64 year study in a sub-humid grassland of South Africa

Lettere En WysbegeerteGeografie En OmgewingstudiePlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

Rainfall simulation to identify the storm-scale mechanisms of gully bank retreat

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff). during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h(-1) for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m(2) buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m(-2) h(-1). Runoff erosion proved to be the dominant mechanism and amounted to 450g m(-2) h(-1), followed by splash and fall down of aggregates (about 170 g m(-2) h(-1)). Gully bank retreat occurred at a rate of 0.55 mm h(-1) and assuming that the soil bulk density is 1.3 g cm(-3), this corresponds to a retreat of 8.8 mm y(-1). Extrapolations to the watershed level, where about 500 m(2) of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha(-1) y(-1). These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm