Your search found 24 records
1 Vigiak, Olga; Ribolzi, O.; Pierret, A.; Sengtaheuanghoung, O.; Valentin, Christian. 2008. Trapping efficiencies of cultivated and natural riparian vegetation of northern Laos. Journal of Environmental Quality, 37: 889–897.
Riparian vegetation ; Sedimentation ; Rivers ; Runoff ; Control methods ; Sloping land ; Cultivation ; Rice ; Vegetables ; Teak ; Bananas ; Bamboos / Laos / Houay Pano Catchment
(Location: IWMI HQ Call no: IWMI 631.7.5 G708 VIG Record No: H040503)
In northern Laos, intensification of cultivation on sloping land leads to accelerated erosion processes. Management of riparian land may counteract the negative impacts of higher sediment delivery rates on water quality. This study assessed water and sediment concentration trapping efficiencies of riparian vegetation in northern Laos and the effect of cultivation of riparian land on water quality. Runoff flowing in and out of selected riparian sites was monitored by means of open troughs. In 2005, two native grass, two bamboo, and two banana sites were monitored. In 2006, adjacent to steep banana, bamboo, and native grass sites, three upland rice sites were established and monitored. Water trapping efficiency (WTE) and sediment concentration trapping efficiency (SCTE) were calculated on an event basis; means and 95% confi dence intervals (CIs) were estimated with a bootstrapping approach. Confidence intervals were large and overlapping among sites. Seepage conditions severely limited trapping efficiency. Native grass resulted in the highest WTE (95% CI, -0.10 to 0.23), which was not significantly different from zero. Banana resulted in the highest SCTE (95% CI, 0.06–0.40). Bamboo had negative WTE and SCTE. Median outflow runoff from rice sites was nine times the inflow. Median outflow sediment concentration from rice sites was two to five times that of their adjacent sites and two to five times the inflow sediment concentration. Although lowtillage banana plantation may reduce sediment concentration of runoff, cultivation of annual crops in riparian land leads to delivery of turbid runoff into the stream, thus severely affecting stream water quality.
2 Sengtaheuanghoung, O.; Valentin, Christian; Ribolzi, Olivier; de Rouw, Anneke; Thiebaux, Jean-Pierre. 2007. The impact of rapid land use changes upon sediment yields from agricultural catchments in northern Lao PDR. Actes des JSIRAUF, Hanoi, Vietnam, 6-9 novembre 2007. 5p.
Catchment areas ; Sedimentation ; Land use ; Cropping systems ; Shifting cultivation ; Rain ; Runoff / Laos / Houay Pano catchment
(Location: IWMI HQ Call no: IWMI 333.91 G708 SEN Record No: H040865)
To provide data that are lacking at the catchment scale, outflow and sediment yield have Been monitored from 8 small (0.5-64 ha) rural catchments since 2001 in northern Lao PDR. Soil conservation strategies have been developed and tested on three of these catchments. Results clearly show that sediment yields can be reduced from 5-11 Mg ha-1 yr-1 under the current slash and burn system to nearly nil when appropriate practices are selected. These include improved fallow systems based on legumes. These innovative practices rehabilitate degraded land and enhance water quality.
3 Mousques, C.; Sengsoulychanh, P.; Sengtaheuanghoung, O.; Latchackack, K.; Ribolzi, O.; Pierret, Alain. 2007. Relevance of Payments for Environmental Services (PES) for watershed management in northern Laos. Keynote address at the 2nd International WEPA Forum on Water Environmental Governance in Asia. The Water Environment Partnership in Asia (WEPA), 3-4 December 2007, in Beppu City, Oita Prefecture, Japan. 6p.
(Location: IWMI HQ Call no: IWMI 333.91 G708 MOU Record No: H041516)
(0.46 MB)
In this paper we discuss the main results of a feasibility study for the implementation of Payments for Environmental Services (PES) in a small watershed of northern Laos. The aim of the work was to assess the relevance of such a scheme as a way to control both the quality and flow of a small mountain stream. We found that the PES concept, with some adaptations, may offer interesting avenues as a means to maintain water quality through an improved control of soil erosion in the upper catchment: Willingness-To-Pay (WTP) within the sampled population was approx. USD 0.3/month/household which would be sufficient to abate the negative impact of soil erosion. At the whole catchment scale, major impediments to the immediate implementation of a PES scheme were i) the lack an unequivocal relationship between environmental services, users and providers, ii) insufficient WTP to maintain water quality along the stream through waste management and iii) absence of a critical mass of buyers. A precondition of successful implementation of PES in the area is to increase the awareness of environmental issues in the concerned communities.
4 Sengtaheuanghoung, O.; Valentin, Christian; Ribolzi, Olivier; de Rouw, Anneke; Thiebaux, Jean-Pierre. 2007. Enhancing water quality through better land management of degraded upland regions in northern Laos. In Gebbie, L.; Glendinning, A.; Lefroy-Braun, R.; Victor, M. (Eds.). Proceedings of the International Conference on Sustainable Sloping Lands and Watershed Management: Linking Research to Strengthen upland Policies and Practices, National Agriculture and Forestry Research Institute of Lao PDR (NAFRI), Vientiane, Lao PDR, 2007. Vientiane, LAO PDR: National Agriculture and Forestry Research Institute of Lao PDR (NAFRI) pp.47-58.
Land management ; Water quality ; Erosion ; Sedimentation ; Rainfall-runoff relationships ; Soil conservation ; Shifting cultivation ; Catchment areas / Laos
(Location: IWMI HQ Call no: IWMI 333.91 708 SEN Record No: H041510)
http://www.nafri.org.la/documents/SSLWM/SSLWMpapers/chapter1/ch1_04_oloth.pdf
https://vlibrary.iwmi.org/pdf/H041510.pdf
https://vlibrary.iwmi.org/pdf/H041510.pdf
5 Vigiak, Olga; Ribolzi, Olivier; Valentin, Christian; Sengtaheuanghoung, O.. 2007. Hillslope sediment trapping by natural or cultivated riparian vegetation in northern Laos. In Gebbie, L.; Glendinning, A.; Lefroy-Braun, R.; Victor, M. (Eds.). Proceedings of the International Conference on Sustainable Sloping Lands and Watershed Management: Linking Research to Strengthen upland Policies and Practices, National Agriculture and Forestry Research Institute of Lao PDR (NAFRI), Vientiane, Lao PDR, 2007. Vientiane, LAO PDR: National Agriculture and Forestry Research Institute of Lao PDR (NAFRI) pp.121-129.
(Location: IWMI HQ Call no: IWMI 333.91 708 VIG Record No: H041511)
http://www.nafri.org.la/documents/SSLWM/SSLWMpapers/chapter2/ch2_01_vigiak.pdf
https://vlibrary.iwmi.org/pdf/H041511.pdf
https://vlibrary.iwmi.org/pdf/H041511.pdf
6 Planchon, O.; Orange, Didier; Pierret, Alain; Boonsanner, A.; Nguyen, D. P.; Sengtaheuanghoung, O.; Valentin, Christian. 2008. Relevance and feasibility of PES to combat soil erosion and solve catchment management issues in the Mekong Region. In Humphreys, E.; Bayot, R. S.; van Brakel, M.; Gichuki, F.; Svendsen, M.; Wester, P.; Huber-Lee, A.; Cook, S. Douthwaite, B.; Hoanh, Chu Thai; Johnson, N.; Nguyen-Khoa, Sophie; Vidal, A.; MacIntyre, I.; MacIntyre, R. (Eds.). Fighting poverty through sustainable water use: proceedings of the CGIAR Challenge Program on Water and Food, 2nd International Forum on Water and Food, Addis Ababa, Ethiopia, 10-14 November 2008. Vol.3. Water benefits sharing for poverty alleviation and conflict management; Drivers and processes of change. Colombo, Sri Lanka: CGIAR Challenge Program on Water and Food. pp.69-74.
Erosion control ; Soil conservation ; Catchment areas ; Watershed management ; Environmental management ; Environmental protection ; User charges ; Farmers ; Stakeholders ; Sloping land ; Crop production ; Case studies / South East Asia / Vietnam / Thailand / Laos / Mekong Region
(Location: IWMI HQ Call no: IWMI 333.91 G000 HUM Record No: H041852)
http://cgspace.cgiar.org/bitstream/handle/10568/3708/IFWF2_proceedings_Volume%20III.pdf?sequence=1
https://vlibrary.iwmi.org/pdf/H041852.pdf
https://vlibrary.iwmi.org/pdf/H041852.pdf
(0.15 MB)
7 Huon, S.; Ribolzi, Olivier; Aubry, E.; Soulileuth, B.; Longchamp, M.; Angeli, N.; Sengtaheuanghoung, O.. 2008. Iron and manganese concentration levels in watercress cultivated within the main stream of the Houay Pano catchment, northern Lao PDR. Lao Journal of Agriculture and Forestry, Special issue no.17:113-128.
Catchment areas ; Watercress ; Metals ; Sedimentary materials ; Swamps ; Environmental effects / Laos / Houay Pano catchment
(Location: IWMI HQ Call no: e-copy only Record No: H041772)
(0.46 MB)
8 Vigiak, Olga; Ribolzi, Olivier; Pierret, Alain; Sengtaheuanghoung, O.; Chaplot, Vincent; Valentin, Christian. 2008. Estimation of runoff curve number (CN) of some Laotian land use types. Lao Journal of Agriculture and Forestry, 16:49-60.
(Location: IWMI HQ Call no: e-copy only Record No: H041781)
(0.34 MB)
9 Mousques, C.; George, A.; Sengsoulichanh, P.; Latchackack, K.; Sengtaheuanghoung, O.; Ribolzi, Olivier; Pierret, Alain. 2008. Relevance of Payments for Environmental Services (PES) for watershed management in northern Lao PDR. Lao Journal of Agriculture and Forestry, Special issue no. 17:129-148.
(Location: IWMI HQ Call no: e-copy only Record No: H041947)
http://www.nafri.org.la/documents/newsletter/Journal/journal_17/section7.pdf
https://vlibrary.iwmi.org/pdf/H041947.pdf
https://vlibrary.iwmi.org/pdf/H041947.pdf
(0.72 MB)
10 Vandervaere, J. P.; Ribolzi, Olivier; Valentin, Christian; Lapetite, J. M.; Miscioscia, J. M.; Sengtaheuanghoung, O.. 2008. A new tension infiltrometer to measure the soil hydrodynamic properties on steep slopes. Lao Journal of Agriculture and Forestry, Special issue no.17:73-90.
(Location: IWMI HQ Call no: e-copy only Record No: H041778)
(0.61 MB)
11 Lacombe, Guillaume; Pierret, Alain; Hoanh, Chu Thai; Sengtaheuanghoung, O.; Noble, Andrew. 2010. Conflict, migration and land-cover changes in Indochina: a hydrological assessment. Ecohydrology, 3(4):382–391.
Hydrology ; River basins ; Land cover ; Forests ; Evapotranspiration ; Rainfall-runoff relationships ; Time series analysis ; Models / Southeast Asia / Laos / Myanmar / Thailand / Vietnam / Mekong River Basin / Indochina
(Location: IWMI HQ Call no: e-copy only Record No: H043213)
(0.35 MB)
The Indochinese section of the Mekong Basin has been subjected to major environmental disturbances over the last half century. The Vietnam War is invoked as a central explanation for the extensive deforestation in specific areas while conflictinduced exoduses caused the abandonment of cultivated lands, followed by forest regeneration. Although the socio-economical consequences of these episodes have been analysed, their hydrological impacts remain unknown. This paper investigates hydrological changes in two catchments of the lower Mekong Basin that were either heavily bombed (in southern Laos) or depopulated (in northern Laos). This analysis is based on the widely and independently recognized fact that vegetation, via evapotranspiration, is a central driver of basin water yield. The analysis of the most complete Vietnam War air mission database and of available hydro-meteorological data over the period 1960–2004 reveals a sharp runoff increase in the southern catchment when bombing climaxed in the early 1970s while no hydrological change is observed in the northern catchment over the same period. From 1995 onwards, the northern and southern catchment’s runoff productions are significantly lower and higher than in the pre-war conditions, respectively. Although causalities could not be ascertained because of data limitations, these short- and long-term hydrological shifts were found to be consistent, in terms of occurrence, spatial distribution and magnitude, with the expected changes in the vegetation cover, either denser in the north (in response to abandonment of cultivated lands) or sparser in the south (as a result of bomb-induced deforestation and soil degradations).
12 Lacombe, Guillaume; Hoanh, Chu Thai; Pierret, Alain; Sengtaheuanghoung, O.; Smakhtin, Vladimir; Noble, Andrew. 2010. Climate change versus land-cover change: a comparative analysis in the Mekong Basin. In Herath, S.; Wang, Y.; Liang, L. (Eds.). Meeting climate change challenges in transboundary basins: role of sciences. Tokyo, Japan: United Nations University (UNU). Institute for Sustainability and Peace (ISP). pp.29-31. (Climate and Ecosystems Change Adaptation Research (CECAR) 4)
Climate change ; Land cover ; Analysis ; River basins ; Catchment areas ; Rainfall-runoff relationships / South East Asia / Mekong River Basin
(Location: IWMI HQ Call no: e-copy only Record No: H043309)
(4.77 MB)
13 Lacombe, Guillaume; Pierret, Alain; Hoanh, Chu Thai; Sengtaheuanghoung, O.. 2010. Hydrological consequences of armed conflicts and massive migrations in the Lower Mekong Basin over the second half of the 20th Century. [Abstract only]. Paper presented at the Hydrology Conference 2010, San Diego, California, USA, 11-13 October 2010. 2p.
(Location: IWMI HQ Call no: e-copy only Record No: H043383)
(0.17 MB)
We investigated whether the Vietnam War bombing and conflict-induced exodus could have altered the hydrological behaviour of the Mekong Basin. The rainfall-runoff relationship was analysed in 2 catchments over period 1960-2004 (figure 1). In each catchment, rainfall and runoff time series together with potential evapotranspiration were used as input to run GR2M monthly water balance model whose robustness is adapted to data-scarce conditions. The space-time distribution of densities of bombs dropped during the war was derived from UXO-NRA database which records the amount and type of ordnances and the aircraft types and numbers per US Air Force sorties from 1965 to 1973. Bomb-induce damages inflicted on vegetation was estimated using the Bomb Damage Assessment Report. We found that the delivery of about 1.5 million tons of high-explosive ordnances likely caused profound damage to one third of the southern catchment whose runoff increased by >365 mm/year during at least 4 years after bombing climaxed in 1972. The magnitude of this increase was found to be consistent with usual tropical forest transpiration rates over the bomb-cleared surface area. No hydrological change was observed during this period in the 30-fold-less bombed catchment located in the North. From 1995 onward, southern and northern catchments’ runoff productions are significantly higher and lower than in pre-war conditions, respectively. These hydrological shifts are most likely attributed to permanent changes in the vegetation cover, either denser in the northern sub-catchment (in response to the extensive abandonment of cultivated lands) or sparser in the southern catchment (as a result of bomb-degraded soil conditions). These results illustrate the high responsiveness of flow regime to forest cover changes in tropical areas where deforestation is expected to perpetuate at a high rate over the coming decades.
14 Ribolzi, O.; Cuny, Juliette; Sengsoulichanh, Phonexay; Mousques, Claire; Soulileuth, Bounsamai; Pierret, Alain; Huon, S.; Sengtaheuanghoung, O.. 2010. Land use and water quality along a Mekong tributary in northern Lao P.D.R. Environmental Management, 47(2):291-302. [doi: https://doi.org/10.1007/s00267-010-9593-0]
Land use ; Water quality ; Measurement ; Water pollution ; Rivers ; Highlands ; Wastewater ; Surveys / Laos / Mekong Basin tributary / Houay Xon Stream / Luang Prabang Province
(Location: IWMI HQ Call no: e-copy only Record No: H043454)
(0.65 MB)
Improving access to clean water has the potential to make a major contribution toward poverty reduction in rural communities of Lao P.D.R. This study focuses on stream water quality along a Mekong basin tributary, the Houay Xon that flows within a mountainous, mosaic land-use catchment of northern Lao P.D.R. To compare direct water quality measurements to the perception of water quality within the riparian population, our survey included interviews of villagers. Water quality was found to vary greatly depending on the location along the stream. Overall, it reflected the balance between the stream self-cleaning potential and human pressure on the riparian zone: (i) high bacteria and suspended load levels occurred where livestock are left to free-range within the riparian zone; (ii) very low oxygen content and high bacteriological contamination prevailed downstream from villages; (iii) high concentrations of bacteria were consistently observed along urbanized banks; (iv) low oxygen content were associated with the discharge of organic-rich wastewater from a small industrial plant; (v) very high suspended load and bacteria levels occurred during flood events due to soil erosion from steep cultivated hill slopes. Besides these human induced pollutions we also noted spontaneous enrichments in metals in wetland areas fed by dysoxic groundwater. These biophysical measurements were in agreement with the opinions expressed by the majority of the interviewees who reported poor and decreasing water quality in the Houay Xon catchment. Based on our survey, we propose recommendations to improve or maintain stream water quality in the uplands of northern Lao P.D.R.
15 Mekuria, Wolde; Sengtaheuanghoung, O.; Hoanh, Chu Thai; Noble, A. 2012. Economic contribution and the potential use of wood charcoal for soil restoration: a case study of village-based charcoal production in Central Laos. International Journal of Sustainable Development and World Ecology, 19(5):415-425. [doi: https://doi.org/10.1080/13504509.2012.686070]
Wood ; Trees ; Charcoal ; Fuelwood ; Case studies ; Production possibilities ; Chemicophysical properties ; Economic aspects ; Profitability ; Biomass ; Energy consumption ; Soil improvement ; Water availability ; Forestry ; Developing countries ; Rural areas ; Income / Laos
(Location: IWMI HQ Call no: e-copy only Record No: H044884)
(0.65 MB)
Wood charcoal production provides affordable energy in many developing countries and has substantially contributed to the economy through the provision of rural incomes. In several countries, charcoal production leads to overexploitation of forests due to inefficiencies in processing. This study was undertaken in central Laos to (1) examine and document traditional charcoal production systems; (2) investigate the production capacity, recovery efficiencies and economic gains of existing traditional charcoal production methods; (3) characterize the chemical properties of wood charcoal and investigate the potential for soil restoration and (4) investigate local charcoal producers’ perception on forest degradation and their species preferences. Through a socio-economic survey, a cost-based method for economic valuation was undertaken on a range of charcoal production methods currently being used. Laboratory chemical analyses were performed on wood charcoal samples. Results indicated that the traditional mud charcoal mound was used by the majority (82%) of charcoal producers. Total charcoal production per production cycle varied between 400 (produced from 2.7 m3 of wood) and 1600 kg (produced from 18 m3 of wood), with a mean of 938 kg (±120) for traditional mud charcoal mounds. The volume of the traditional mud charcoal mounds correlated positively and significantly with total charcoal production (R2 = 0.45, p = 0.03), whereas correlated negatively and significantly with the recovery efficiency (R2 = 0.58, p = 0.01). On average, the local producers receive a total net benefit of 457,272 Lao kip (USD 57.2) in 17 days. We also identified a rice husk mound method of charcoal production, which may not encourage further deforestation while producing rice husk biochar that can be used for soil restoration. Furthermore, we found that there are significant differences (p < 0.05) between the sampled wood charcoals in chemical properties, indicating that the potential of using wood charcoal for the restoration of degraded soils varies from charcoal to charcoal.
16 Mekuria, Wolde; Noble, Andrew; Hoanh, Chu Thai; McCartney, Matthew; Sengtaheuanghoung, O.; Sipaseuth, N.; Douangsavanh, Somphasith; Langan, Simon; Getnet, Kindie. 2014. The potential role of soil amendments in increasing agricultural productivity and improving the livelihood of smallholders in Lao PDR. Paper presented at the 15th National Agriculture and Forestry Research Institute Anniversary Symposium on Agriculture and Forestry Research for Development, Vientiane, Lao PDR, 8-10 April 2014. 15p.
Agricultural production ; Water productivity ; Soil amendments ; Smallholders ; Living standards ; Maize ; Nutrient uptake ; Biomass ; Economic aspects ; Case studies / Lao People's Democratic Republic
(Location: IWMI HQ Call no: e-copy only Record No: H046433)
The present study was undertaken in Lao PDR to investigate the impacts of organic and clay-based soil amendments on maize yield, total nutrient uptake and crop water productivity (CWP), and analyze the economic return of such interventions. Structured field experiments were established over two consecutive years (2011 and 2012) with maize as the test crop at the Veunkham and Naphok sites. Ten treatments were applied in a Randomized Complete Block Design with three replications. The treatments were control, rice husk biochar (applied at a rate of 10 t ha-1), bentonite clay (10 t ha-1), compost (4 t ha-1), clay-manure compost (10 t ha-1), rice husk biochar compost (10 t ha-1), and their combinations. All treatments were applied in 2011. CWP and the soil water balance of the various treatments were determined using the AquaCrop model. To determine the costs and benefits of soil amendments over the two cropping seasons a cost-based valuation method was applied. Significant (p < 0.05) treatment effects in maize grain yields, total nutrient uptake and CWP were observed. At Veunkham, differences in yield between the control and amended soils ranged from 0.9 to 3.3 t ha-1 in 2011 and from 0.2 to 1.3 t ha-1 in 2012, whereas differences at Naphok varied between 0.2 and 2.2 t ha-1 in 2011 and from 0.2 to 1.7 t ha-1 in 2012. Differences in CWP between the amended and control plots at Veunkham varied between 0.3 and 1.0 kg m-3 in 2011 and from 0.05 to 0.29 kg m-3 in 2012, whereas differences at Naphok varied between 0.1 and 0.6 kg m-3 in 2011 and from 0.1 to 0.4 kg m-3 in 2012. Differences between the control and amended soils in yield and the associated CWP can be attributed to the improvements in total N and P uptake, soil pH, exchangeable Ca++ and Mg++, and CEC following the application of soil amendments. At both sites, in most of the treatments, yields and CWP in 2012 were significantly (p < 0.05) lower than 2011. This difference can be attributed to late season drought. Over the two cropping seasons , the enhancement of maize yield due to soil amendments resulted in net revenues ranging from -794 to 841 and -331 to 1391 US$ ha-1 at Naphok and Veunkham, respectively. The study found that soils amended with low-cost amendments such as compost, rice husk biochar, rice husk biochar compost, and clay-manure compost were economically viable within the first cropping season. In contrast, soils amended with higher-cost amendments such as bentonite clay required up to 5 years to be economically viable. Such variations indicate that maize yield revenues alone are an insufficient incentive for farmers to adopt higher-cost soil amendments. The results of this study confirm that soil amendments can be effective in improving crop yield and the associated CWP. In addition, the income of smallholders can be improved using locally available low-cost soil amendments. These findings provide important information for decision makers wishing to improve agricultural productivity and food security through sustainable intensification.
17 Mekuria, Wolde; Noble, Andrew; Sengtaheuanghoung, O.; Hoanh, Chu Thai; Bossio, D.; Sipaseuth, N.; McCartney, Matthew; Langan, Simon. 2014. Organic and clay-based soil amendments increase maize yield, total nutrient uptake, and soil properties in Lao PDR. Agroecology and Sustainable Food Systems, 38:936-961. [doi: https://doi.org/10.1080/21683565.2014.917144]
Soil amendments ; Soil properties ; soil organic matter ; Maize ; Rice husks ; Clay ; Nutrients ; Food security ; Food production ; Agricultural production ; Smallholders ; Bentonite ; Composts ; Biomass ; Land degradation / Lao People's Democratic Republic / Veunkham / Naphok
(Location: IWMI HQ Call no: e-copy only Record No: H046584)
(0.29 MB)
In the Lao People’s Democratic Republic (PDR), increasing food security remains a challenge since smallholder agricultural systems, which are the main source of food production, are under serious threat due to poor soil fertility and climate variability. This study was undertaken in Lao PDR to investigate the impacts of organic and clay-based soil amendments on maize yield, total nutrient uptake, and soil properties. Structured field experiments were established over two consecutive years (2011 and 2012) with maize as the test crop at the Veunkham and Naphok sites. Ten treatments were applied in a randomized complete block design with three replications. The treatments were control, rice husk biochar (applied at a rate of 10 t ha-1), bentonite clay (10 t ha-1), compost (4 t ha-1), clay-manure compost (10 t ha-1), rice husk biochar compost (10 t ha-1), and their combinations. All treatments were applied in 2011. Significant (p < 0.05) treatment effects in maize grain yields, total nutrient uptake, and soil properties were observed. At Veunkham, differences between the control and amended soils in yield ranged from 0.9 to 3.3 t ha-1 in 2011 and from 0.2 to 1.3 t ha-1 in 2012, whereas differences at Naphok varied between 0.2 and 2.2 t ha-1 in 2011 and from 0.2 to 1.7 t ha-1 in 2012. At both sites, in most of the treatments, yields in 2012 were significantly (p < 0.05) lower than 2011; this was attributed to a late season drought. Differences between the control and amended soils in yield can be attributed to the improvements in total N and P uptake, soil pH, exchangeable Ca++ and Mg++, and cation-exchange capacity following the application of soil amendments. The results of this study confirm that the soil amendments under consideration can be effective in improving agricultural productivity, while improving key soil properties indicating that soil amendments could be an option for intensification of agricultural productivity.
18 Lacombe, Guillaume; Ribolzi, O.; de Rouw, A.; Pierret, A.; Latsachak, K.; Silvera, N.; Pham Dinh, R.; Orange, D.; Janeau, J.-L.; Soulileuth, B.; Robain, H.; Taccoen, A.; Sengphaathith, P.; Mouche, E.; Sengtaheuanghoung, O.; Tran Duc, T.; Valentin, C. 2015. Afforestation by natural regeneration or by tree planting: examples of opposite hydrological impacts evidenced by long-term field monitoring in the humid tropics. Hydrology and Earth System Sciences Discussions, 12:12615-12648. [doi: https://doi.org/10.5194/hessd-12-12615-2015]
Afforestation ; Plantations ; Tectona grandis ; Hydrological factors ; Humid tropics ; Ecosystem services ; Land use ; Soil conservation ; Water conservation ; Catchment areas ; Rain ; Runoff ; Models / Lao People s Democratic Republic / Vietnam / Houay Pano Catchment / Dong Cao Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H047340)
http://www.hydrol-earth-syst-sci-discuss.net/12/12615/2015/hessd-12-12615-2015.pdf
https://vlibrary.iwmi.org/pdf/H047340.pdf
https://vlibrary.iwmi.org/pdf/H047340.pdf
(3.39 MB) (3.39 MB)
The humid tropics are exposed to an unprecedented modernization of agriculture involving rapid and highly-mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability controlling habitats, water resources and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydro-meteorological variables has been operating in several headwater catchments in tropical Southeast Asia since 2001. The GR2M water balance model repeatedly calibrated over successive 1 year periods, and used in simulation mode with specific rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses and trend detection tests allowed causality between land-use changes and changes in seasonal flows to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow, led to intricate flow patterns: pluri-annual flow cycles induced by the shifting system, on top of a gradual flow increase over years caused by the spread of the plantation. In Vietnam, the abandonment of continuously cropped areas mixed with patches of tree plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration or planting) led to opposite changes in flow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation.
19 Lacombe, Guillaume; Ribolzi, O.; de Rouw, A.; Pierret, A.; Latsachak, K.; Silvera, N.; Dinh, R. P.; Orange, D.; Janeau, J.-L.; Soulileuth, B.; Robain, H.; Taccoen, A.; Sengphaathith, P.; Mouche, E.; Sengtaheuanghoung, O.; Tran Duc, T.; Valentin, C. 2016. Contradictory hydrological impacts of afforestation in the humid tropics evidenced by long-term field monitoring and simulation modelling. Hydrology and Earth System Sciences, 20:2691-2704.
Humid tropics ; Hydrological factors ; Afforestation ; Natural regeneration ; Plantations ; Monitoring ; Simulation models ; Land use ; Land cover change ; Ecosystem services ; Forest conservation ; Catchment areas ; Rainfall-runoff relationships ; Stream flow ; Cropping systems ; Water conservation ; Soil conservation ; Soil surface properties ; Tectona grandis / Lao People's Democratic Republic / Vietnam / Houay Pano Catchment / Dong Cao Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H047644)
http://www.hydrol-earth-syst-sci.net/20/2691/2016/hess-20-2691-2016.pdf
https://vlibrary.iwmi.org/pdf/H047644.pdf
https://vlibrary.iwmi.org/pdf/H047644.pdf
The humid tropics are exposed to an unprecedented modernisation of agriculture involving rapid and mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability which controls habitats, water resources, and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydrometeorological variables has been operating in several headwater catchments in tropical southeast Asia since 2000. The GR2M water balance model, repeatedly calibrated over successive 1-year periods and used in simulation mode with the same year of rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses, and trend detection tests allowed causality between land-use changes and changes in seasonal streamflow to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow led to intricate streamflow patterns: pluri-annual streamflow cycles induced by the shifting system, on top of a gradual streamflow increase over years caused by the spread of the plantations. In Vietnam, the abandonment of continuously cropped areas combined with patches of mix-trees plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration vs. planting) led to opposite changes in streamflow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation.
20 Huon, S.; Evrard, O.; Gourdin, E.; Lefevre, I.; Bariac, T.; Reyss, J.-L.; des Tureaux, T. H.; Sengtaheuanghoung, O.; Ayrault, S.; Ribolzi, O. 2017. Suspended sediment source and propagation during monsoon events across nested sub-catchments with contrasted land uses in Laos. Journal of Hydrology: Regional Studies, 9:69-84. [doi: https://doi.org/10.1016/j.ejrh.2016.11.018]
Rivers ; Catchment areas ; Suspended sediments ; Organic matter content ; Fallout ; Radionuclides ; Nitrogen ; Particle size ; Electrical conductivity ; Stream flow ; Monsoon climate ; Rain ; Flooding ; Soil erosion ; Storm runoff ; Hydrological factors ; Land use / Lao People's Democratic Republic / Houay Xon Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H048044)
http://www.sciencedirect.com/science/article/pii/S221458181630204X/pdfft?md5=7e7b3f476faa5301eb5701c1798aa8d9&pid=1-s2.0-S221458181630204X-main.pdf
https://vlibrary.iwmi.org/pdf/H048044.pdf
https://vlibrary.iwmi.org/pdf/H048044.pdf
(4.55 MB) (4.55 MB)
Study region: Houay Xon catchment in northern Laos.
Study focus: Because agricultural headwater catchments of SE Asia are prone to erosion and deliver a significant proportion of the total suspended sediment supply to major rivers and floodplains, the potential sources of sediments and their dynamics were studied for two successive storm flow events in June 2013. Characterization of suspended sediment loads was carried out along a continuum of 7 monitoring stations, combining analyses of fallout radionuclides, particle borne organic matter and stream water properties.
New hydrological insights: Radionuclide activities showed that remobilization of soil particles deposited during the previous rainy season or supplied by riverbank erosion is the dominant process, although pulses of surface-soil derived sediments also propagate downstream. This interpretation is supported by suspended organic matter data that also fingerprints the mixing of surface soil vs. subsurface particles. The study moreover highlights the advantages and the drawbacks of combining fallout radionuclides, particle borne organic matter composition and stream water characteristics to discriminate and quantify sediment sources and dynamics in rural areas undergoing urban sprawl.
Study focus: Because agricultural headwater catchments of SE Asia are prone to erosion and deliver a significant proportion of the total suspended sediment supply to major rivers and floodplains, the potential sources of sediments and their dynamics were studied for two successive storm flow events in June 2013. Characterization of suspended sediment loads was carried out along a continuum of 7 monitoring stations, combining analyses of fallout radionuclides, particle borne organic matter and stream water properties.
New hydrological insights: Radionuclide activities showed that remobilization of soil particles deposited during the previous rainy season or supplied by riverbank erosion is the dominant process, although pulses of surface-soil derived sediments also propagate downstream. This interpretation is supported by suspended organic matter data that also fingerprints the mixing of surface soil vs. subsurface particles. The study moreover highlights the advantages and the drawbacks of combining fallout radionuclides, particle borne organic matter composition and stream water characteristics to discriminate and quantify sediment sources and dynamics in rural areas undergoing urban sprawl.
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