Central Cambodia Research Articles

Evapotranspiration during the late rainy season and middle of the dry season in the watershed of an evergreen forest area, central Cambodia

AbstractIn this study, we measured evapotranspiration in an evergreen broadleaf forest watershed in the Kampong Thom Province of central Cambodia with the aid of a 60‐m high meteorological observation tower. The main vegetation species at the study site were Myristica iners and Vatica odorata. The mean tree height in the upper crown layer at the study site was 27·2 m, and the maximum tree height was 45·1 m. A heat balance method, which incorporated the Bowen ratio, was used to calculate the energy balance above the forest canopy; this value was subsequently used for the calculation of evapotranspiration. All the equipment necessary for the measurement of meteorological variables was installed in the observation tower. Data were collected during two distinct sampling periods: October 2003, in the late rainy season, and March 2004, in the middle of the dry season. Daily variations in evapotranspiration were strongly correlated with the measured amount of net radiation above the canopy layer. On the basis of our measurements, the mean evapotranspiration levels of the forest watershed during the late rainy season and the middle of the dry season were 4·3 and 4·6 mm/day, respectively. No significant differences in soil moisture were observed between the middle of the dry season and the late rainy season, probably due to the shallow depth of the water table. The results of this study suggest that the high levels of evapotranspiration recorded during the middle of the dry season reflect the presence of sufficient soil moisture (derived from the shallow water table) and a high vapour‐pressure deficit. Copyright © 2008 John Wiley & Sons, Ltd.

Comparison of soil physical properties in evergreen and deciduous forests in central Cambodia

We investigated soil physical properties in three forest types in tropical lowland monsoon forests in central Cambodia under the same climatic conditions, i.e., Kanhaplic Haplustults in dry evergreen forest (KH-E), Arenic Haplustults in dry deciduous forest (AH-D), and Arenic Ultic Alorthods in mixed evergreen–deciduous forest (AA-M), to clarify the relationship between forest types and soil physical properties. The clay content was correlated with water content at ψ = −9.8 and −1500 kPa (WC10 and WC1500), available water capacity (AWC), and the van Genuchten (vG) parameter N (P < 0.01). vG parameter N was in the order AH-D > AA-M > KH-E whereas vG parameter α had a high value in KH-E soil at 0–100 cm in depth. The cumulative AWC (AWCcl, mm) at a soil depth of 0–200 cm was higher in the AH-D than in the KH-E, and was not considered a major factor affecting the distribution of different forest types under the same climatic conditions. The unsaturated hydraulic conductivity (K) at 0–100 cm in depth, estimated by use of models, was higher in AH-D than in KH-E mostly at matric potential ψ > −10 kPa. The low K in KH-E at ψ > −10 kPa was considered favorable for evergreen trees to retain the soil water for the transpiration in the dry season, and the matric potential in KH-E showed more gentle decreases in the early dry seasons than AH-D. Thus the differences in K among generally sandy soil types could possibly affect the establishment of different forest types in the study area with the same climate.

Comparison of soil moisture effects on surface conductance between late dry and rainy seasons in an evergreen forest of central Cambodia

Some forests in the Asian monsoon region are reported to transpire actively, even in the late dry season. The evergreen forest in central Cambodia is included in them. The surface conductance was estimated for an evergreen forest in central Cambodia in the late dry (May) and rainy (August) seasons, and the effects of environmental conditions on surface conductance were compared between seasons. The effects of soil moisture did not differ between seasons, indicating that soil water drought in the late dry season does not limit transpiration from the entire forest community. Evergreen forests in central Cambodia are thought to transpire actively in the late dry season.

Preliminary study of flow regimes and stream water residence times in multi-scale forested watersheds of central Cambodia

To elucidate the water cycle in lowland forests of the Mekong River basin, our research group established four experimental watersheds in the Stung Chinit River basin in Kampong Thom Province, Cambodia. The drainage areas of these experimental watersheds ranged from small (4 km2) to mesoscale (3,659 km2). Here, we present the first preliminary results of our rainfall-discharge observations and analyses of temporal variations of stable isotope ratios in rainfall, stream water, and groundwater. This paper focuses on the following three main topics: annual rainfall, discharge, and water balance; stormflow generation and dominant flow pathways; and flow regimes and stream water residence times. All stream water residence times (τ = 1.7–7.5 months) for the four experimental watersheds were shorter than the residence time of the groundwater (τ = 9.4 months) through the soil and regolith layers, implying that the stream waters consisted of not only the groundwater-flow component, but also younger-aged flow components such as saturation-excess overland flow. The smallest (4 km2; O Toek Loork) watershed had longer residence time (τ = 7.5 months) than the three larger watersheds (126–3,659 km2; τ = 1.7–3.9 months). This may suggest differing contributions of the groundwater and younger-aged flow components in the stream water in each watershed. Our approach of multi-scale watershed observation might better contribute to the needs of physically based models and aid in predictions for ungauged basins.

Seasonal fluctuation of groundwater in an evergreen forest, central Cambodia: experiments and two-dimensional numerical analysis

This study of a water cycle was conducted in an evergreen forest located in the Mekong River Basin in central Cambodia. At the observation site, we measured the dynamics of the spatial distribution of groundwater levels. The groundwater movement was analyzed two-dimensionally using boundary conditions and parameters that had been observed in the field. The climate in the research area is dominated by two seasons, which occur annually: a rainy and a dry season. The groundwater levels are generally high during the rainy season and low during the dry season. Groundwater levels were measured along a stream, which flowed through the study site. The streambed was visible at the head of the stream in January. At the next downriver well point, the streambed appeared in March. Finally, it became visible at all well points in April, meaning that surface runoff had disappeared temporarily and instead flowed underground during the ensuing dry period. Groundwater levels of the studied lateral flow perpendicular to the stream that seeped and infiltrated into the stream were 1.2–2.5 m deep (in April), which was the lowest level recorded for the year. During that period, the depth of the groundwater of the studied lateral flow fell by as much as 56 mm per month. In addition, the lateral flow groundwater infiltrated into groundwater of the stream during that period. The groundwater level fluctuation was estimated based on a two-dimensional analysis of lateral flow perpendicular to the stream using a numerical simulation model with soil physical parameters and observed boundary conditions. The observations of ground water fluctuations were well reproduced. Deep seepage of groundwater was estimated using a uniform boundary condition that allowed efflux through the bottom, estimated as being approximately 30 mm per year. The simulated deep seepage rate was considered plausible considering other hydrological components such as soil water storage fluctuation.

Blindness and Eye Disease in Cambodia

Purpose: To assess the prevalence and etiology of blindness and low vision and to assess the prevalence of common eye diseases in central Cambodia. Methods: In this cross-sectional, population-based study, 6,558 residents of Kandal Province, Cambodia were registered, and 5,803 (88.5%) were interviewed and examined. This house-to-house survey was conducted by a team consisting of a senior ophthalmologist, a Cambodian eye doctor, and eight Cambodian eyecare workers. Results: The prevalence of bilateral blindness (visual acuity <3/60) is 1.1% (95% confidence interval [CI], 0.9–1.4), and an additional 4.4% (95% CI, 3.9–5.0) have low vision (visual acuity < 6/18, ≥3/60 in the better eye). The major causes of bilateral blindness are cataract (67.4%), phthisis (6.1%), uncorrected refractive error (6.1%), corneal scar (5.3%), uncorrected aphakia (3.0%), trachoma corneal scar (3.0%), optic atrophy (3.0%), and others (6.1%). The major causes of low vision are uncorrected refractive error (49.8%) and cataract (42.7%). The prevalence of unilateral blindness is 1.2% (95% CI, 0.9–1.4), often caused by cataract, corneal scar, or phthisis. Trauma due to landmine explosions and war-related injuries was frequently the underlying etiology in subjects with phthisis, corneal scarring, or other pathology.Conclusions: The prevalence of blindness and low vision in Cambodia is relatively high compared to other developing countries. Most of the causes of blindness and low vision are treatable or preventable. Landmines and other war-related injuries are an important cause of ocular injury. These results will assist in developing a national plan for the prevention of blindness in Cambodia.

Acrisols and adjacent soils under four different forest types in central Cambodia

Acrisols and adjacent soils under four different forest types in central Cambodia

The Holocene history and development of the Tonle Sap, Cambodia

The Tonle Sap, the ‘Great Lake’ of central Cambodia, is the central component of wetland ecosystems in the lower Mekong River basin, and is of enormous conservation value. The lake's unusual hydraulic relationship with the Mekong River, and its consequent sensitivity to monsoon variability, makes the Tonle Sap sensitive to climate change. Exploring the dynamics and development of this system under different climate regimes of the past offers a perspective on possible future impacts, which is critical for sound management. Biostratigraphic and sedimentological data derived from cores of lake sediment indicate that during the period >7000 to ca. 5500 14C years Before Present the lake was less variable than present in terms of depth during the annual cycle of flood, and may have been strongly influenced by saline tidal waters associated with higher-than-present seas levels. As regional environments became drier and more seasonal in the late Holocene, more sediment was re-suspended during the increasingly marked dry season lake level minimum, lowering the effective sediment accumulation rate. Contrary to current interpretations of the history of the lake and associated wetland ecosystems, the data presented here imply that regional hydraulic connections between the lake and the Mekong River existed from at least the early Holocene.

A geographic information systems model for mapping risk of fasciolosis in cattle and buffaloes in Cambodia

A geographic information systems (GIS) model for mapping the risk of fasciolosis in cattle and buffaloes was developed for the Kingdom of Cambodia using determinants of inundation, proximity to rivers, land use, slope, elevation, and the density of cattle and buffaloes. Determinants were subjectively weighted according to their perceived relative importance before combining them to produce a risk-map of fasciolosis. The model estimates that 28% of Cambodia is potentially at risk of fasciolosis with areas of high and moderate risk concentrated in southern and central Cambodia. The estimates of risk reflect the actual prevalence of fasciolosis in most districts surveyed, suggesting that the epidemiological determinants and weightings used to produce the model were appropriate. These results will be progressively refined as more detailed field surveys are completed to fully validate the model.

A geographic information systems model for mapping risk of fasciolosis in cattle and buffaloes in Cambodia

A geographic information systems (GIS) model for mapping the risk of fasciolosis in cattle and buffaloes was developed for the Kingdom of Cambodia using determinants of inundation, proximity to rivers, land use, slope, elevation, and the density of cattle and buffaloes. Determinants were subjectively weighted according to their perceived relative importance before combining them to produce a risk-map of fasciolosis. The model estimates that 28% of Cambodia is potentially at risk of fasciolosis with areas of high and moderate risk concentrated in southern and central Cambodia. The estimates of risk reflect the actual prevalence of fasciolosis in most districts surveyed, suggesting that the epidemiological determinants and weightings used to produce the model were appropriate. These results will be progressively refined as more detailed field surveys are completed to fully validate the model.

Eco-ethological heterogeneity of the members of the Anopheles minimus complex (Diptera: Culicidae) in Southeast Asia and its consequences for vector control.

The presence of cryptic species within Anopheles minimus s.l. Theobald, one of the most widespread malaria vectors in Southeast Asia, was suggested on the basis of behavioral heterogeneities observed within this taxon. Subsequently, two species, A and C, were recognized. However, the existence of these cryptic species did not explain all observed behavioral heterogeneities within this complex. Besides, data on the behavior of vectors are essential to understand the dynamics of disease transmission and thus evaluate the appropriateness of vector control measures. Different collection methods were used to collect Anopheles species from several localities in Southeast Asia to assess the inter- and intraspecific behavioral divergences of An. minimus A and C. Collection results were subjected to a correspondence analysis. The members of the An. minimus complex were identified by use of the octanol dehydrogenase allozyme profiles or the polymerase chain reaction-restriction fragment length polymorphism assay. Large intraspecific behavioral differences were observed among populations of An. minimus A. These populations belong to the same species on the basis of the applied genetic markers. In northern Vietnam, species A tended to be more zoophilic, whereas in the study sites of south central Vietnam, Cambodia, and Laos it showed marked antropophilic behavior when cattle were scarce. In the most northern study site, An. minimus A showed noteworthy endophilic behavior. An. minimus C was primarily zoophilic and based on this behavior, its role in malaria transmission is questionable. However, it was only found in one locality, so that intraspecific behavioral variation could not be assessed. An. minimus A is able to change its host preference in function of local situations in host availability. Hence, its role in malaria transmission can differ from region to region. Similarly, the impact of vector control on this species may differ between localities. In conclusion, intraspecific behavioral differences in Anopheles species can occur and these behavioral heterogeneities, albeit important for disease transmission and control, are not a priori indicative for the presence of cryptic species.

Schistosomes in the Xe Kong river of Cambodia: the detection of Schistosoma mekongi in a natural population of snails and observations on the intermediate host's distribution.

A natural population of Neotricula aperta (Gastropoda: Pomatiopsidae) in the Xe Kong river of Cambodia was found to be infected with Schistosoma mekongi--apparently the first time this parasite has been found in snails outside the Mekong river. Only 0.14% of the N. aperta collected were found infected. Potential habitats for N. aperta were examined in selected rivers of central and southern Laos and Cambodia, so that the density of N. aperta at each site could be estimated. At survey sites where sufficient snails were collected, the population was also screened for infection with S. mekongi. The geographical distribution of N. aperta outside the Mekong river is shown to be much greater than previously documented; this is in agreement with predictions based on palaeo-geographical models and the evolutionary history and historical biogeography (phylogeography) of the species. The Xe Kong river is identified as a potential source of N. aperta colonists entering Cambodia from Laos. The findings, which indicate that there is a risk of human infection with S. mekongi in areas distant from the Mekong river, have important implications for schistosomiasis-control strategies in the region.

Rice Remains in the Prehistoric Pottery Tempers of the Shell Midden Site of Samrong Sen: Implications for Early Rice Cultivation in Central Cambodia

La découverte de restes de riz parmi les dégraissants des poteries du site de Samrong Sen et ses implications sur l'histoire de la culture du riz dans le centre du Cambodge. II est fort possible que la culture et la domestication du riz dans les plaines inondables du centre du Cambodge remontent à la préhistoire. Certaines fouilles archéologiques menées par l'auteur sur le site de Samrong Sen, situé dans la zone inondable du Tonle Sap, ont montré que la balle de riz était, parmi d'autres sous-produits agricoles, utilisée comme dégraissant dans les poteries. Les restes analysés pourraient remonter à 3 600 ans au plus tard. En 1999, l'analyse de quelques centaines de tessons mis au jour sur le site a permis d'identifier pour la première fois un certain nombre de spécimens de grains de riz entiers. L'analyse morphologique de chaque spécimen a révélé que certains d'entre eux présentaient des traits caractéristiques de la sous-espèce Oryza indica et de certaines variétés d'Oryza sativa. Le présent article présente les résultats de l'analyse des restes de riz mis au jour à Samrong Sen, examine l'histoire de l'apparition du riz dans la zone du Tonle Sap et suggère quelques pistes de recherche dans le domaine du riz à l'époque préhistorique au Cambodge.

Seroepidemiologic evidence for murine and scrub typhus in Malang, Indonesia.

Indonesian military personnel stationed in Malang, East Java were among troops deployed to central Cambodia as part of the United Nations' Transition Authority Cambodia peace-keeping operation in 1992. Predeployment blood samples obtained from a cohort of Indonesian soldiers indicated a high prevalence of antibodies to antigens of Rickettsia typhi or Orientia (formerly Rickettsia) tsutsugamushi, the etiologic agents for murine and scrub typhus, respectively. To evaluate the potential risk of these rickettsial diseases in the Malang area, a subsequent seroepidemiologic survey was conducted. This study involved civilian personnel residing within one of three Malang kelurahans (neighborhoods) representing urban, suburban, and rural communities. The heads-of-households from 197 homes completed a detailed epidemiologic survey. In addition, blood samples were collected from 464 individuals residing within the households surveyed. Examination of civilian blood samples disclosed that 34.7% and 1.3% of the study participants were seroreactive to R. typhi and O. tsutsugamushi, respectively. These results were similar to those obtained earlier from the military samples. In addition, assessment of 78 blood samples obtained from peridomestic rodents trapped from within or near the households surveyed showed that 28 were reactive to R. typhi antigens and four were reactive to O. tsutsugamushi antigens. These data indicate that military and civilian personnel living in the Malang area of East Java are at risk of infection with rickettsiae that are antigenically indistinguishable from those that cause murine and scrub typhus.

Geographic variation in Australasian microtektite concentrations: Implications concerning the location and size of the source crater

Geographic variations in the concentration of Australasian microtektites in 42 cores from the Indian Ocean, western equatorial Pacific Ocean, and the Philippine, Celebes, and Sulo Seas were used to predict the location of the Australasian tektite source crater and to estimate its size. The location that seems to best explain the geographic variations in microtektite concentrations is located in central Cambodia at about 12°N latitude and 106°E longitude. The diameter of the source crater is estimated to be between 32 and 114 km based on thickness of the microtektite layer at each site and distance from the predicted source area in Cambodia. The large range in estimated size of the source crater is due to a lack of knowledge about the value of the exponent that describes the radial decrease in ejecta thickness. Additional microtektite/ejecta‐bearing sites closer to the source region could help resolve this problem.

The distribution of the Hb Constant Spring gene in Southeast Asian populations

The distribution of the hemoglobin Constant Spring (Hb CS) gene in eight populations in Southeast Asia (including Assam) was determined using oligonucleotide hybridization. Hb CS was absent in two Assamese populations with a high prevalence of Hb E. The Hb CS gene frequency was 0.033 in northern Thailand and near 0.01 in central Thailand and Cambodia. High frequencies, between 0.05 and 0.06, were observed in northeastern Thailand. The present data and a similar study in Laotians suggest that the Lao-speaking populations of the Mekong River basin in northeastern Thailand and Laos have the highest frequencies of the Hb CS gene in Southeast Asia.

Societies and Academies

Societies and Academies