Socio-ecological dimensions of infectious diseases in Southeast Asia

One critical concern for Thailand reservoirs which are used for irrigated agriculture (mainly paddy rice) and aquaculture is the lack of information on contamination from trace metal element (TME) in waters and biological compartments of the reservoirs. TME are both from natural and anthropogenic origins and may affect the quality of lake waters and food chain. The goal of this study was to evaluate the contamination in TME and study their transfer between the different compartments in and downstream of the reservoir. Fourteen TME have been measured in water column (dissolved phase), fishes, and sediments of the Mae Thang Reservoir (northern Thailand) as well as soil and rice grains of irrigated area. Analyses were performed by inductively coupled plasma-mass spectrometer (ICP-MS). This 2-year study showed that TME concentrations in water were lower than standards for irrigation and aquatic life. However, localized values of Fe and Mn were higher than the standard in the bottom of the reservoir in dry season. TME in sediments were relatively high compared to pristine lakes. Two species of fish were contaminated in As and Ni. Soils exceeded standard values for Cr, Ni, and Cu, while rice grains showed contamination in Ni that indicated a transfer between soil and rice grain. The accumulation of TME in sediments showed that upstream cultivated areas may have contributed to bring TME in the reservoir. TME concentrations in fishes were thus affected and should be controlled. Accumulation of TME in soils of paddy field due to the use of pesticides and fertilizer may increase contamination of rice in the long term

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

Seasonal effect on trace metal elements behaviour in a reservoir of northern Thailand

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