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

Statistical analysis of long-term series rainfall data: a regional study in Southeast Asia

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

Statistical analysis of long series rainfall data: A regional study in Southeast Asia

In IWMI SOUTHEAST ASIA, KU ? IWMI Seminar on Scientific Cooperation, Kamphol Adulavidhaya Conference Room, Kasetsart University, Bangkok, Thailand, 26 March 200

The off-site effect of soil erosion: a case study of the Mae Thang Reservoir in Northern Thailand

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

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

Impact of land use change and rainfall on sediment and carbon accumulation in a water reservoir of North Thailand

The lifespan of many tropical water reservoirs is limited by siltation due to soil erosion in the watershed. The objectives of this study were to determine, the amount of catchment-derived organic carbon accumulated in sediments of a reservoir of North Thailand and to relate it with the history of cultivation and rainfall regime in the watershed. Over a twelve-years period (1995-2006) since impoundment sediment delivery was high (ca. 19.6 Mg ha(-1) yr(-1)). The yearly supply of catchment-derived material was composed of coarse sediment deposits near the main inlets and of fine laminated sediment accumulations in deep-water environments. Their stable carbon isotope composition indicated that soil organic matter was the main source of organic carbon preserved in sediments (ca. 83 wt.%). Fine sediments derived from suspended loads exported from the watershed by runoff and stream waters were related to erosive rainfall, to the extent of area under annual cropping and to crop change with a marked increase after the replacement of beans by maize. However, sediment accumulation did not respond linearly to extreme rainfall events, as shown by the supply of nearly 48% of the total amount of sediments by a single exceptional flood. Total organic carbon storage in sediments reached ca. 23.8 MgC ha(-1) yr(-1) in 2006, twelve years after impoundment, falling in the upper range of small to medium size reservoirs with agricultural catchments

Soil erosion under land use change from three catchments in Laos, Thailand and Vietnam

Unpublished repor