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[en] Thorium activity concentrations were measured in seven marine sediment cores taken from Sabah-Sarawak coast on 2004 by using a gravity box corer. Collected sediments were generally homogenous mud which contained much more mixture of silt and clay compared to sand and relatively low content of organic carbon (i.e. less than 5% at all sampling stations). The results found that activity concentrations of 230Th, 232Th and ratios of 230Th/232Th were ranged from 6.5-20.4 Bq/kg dry wt., 6.8-27.8 Bq/kg dry wt. and 0.69-0.92, respectively. It seem that, 232Th activity concentrations are slightly higher than 230Th at all sampling stations and both radionuclides were generally high at Sabah compared to Sarawak coastal waters. 230Th activity concentrations in sediment core appear to be correlated with the activity concentrations of 232Th at some sampling station. These indicating both radionuclides were supplied from the same of environment and source origin of detrital from terrestrial and shallower water. The low 230Th/232Th activity ratio which is less than unity suggesting that 232Th was actively and rapidly regenerated compared to 230Th from 234U. It also can be attributed to less efficiently scavenge of 230Th onto particles prior deposited at the marine sediment bed. (author)
[en] The radioactive tracers, modern elements which make possible infinity of studies, are nowadays one of the main tools in the human activity. The radioisotopes, are used in medicine, industry, special programs, etc. This project is about the use of radioactive tracers in the study of the movement of solid material in the bottom of the rivers. This study is important, because it allows to make conclusions on the characteristics of material transport in the bottom, and from there, to establish certain deposit areas or the thickness of the layer of transport. The general principle of the method is the immersion or launching, in a previously established place, of a radioactive material whose characteristics are identical to those of the natural silt of the area in study, followed by an accompaniment to know the migration of this silt by means of a radiation detection equipment. Later on the traditional methods based on empiric formulas will be compared, to confront them with this method and to determine the reliability in the process
[en] There The problems facing the area of Kuala Kemaman are siltation and erosion at shoreline. The objectives of study are to assess the best alignment of the groyne alignment, to ascertain the most stable shoreline regime and to investigate structural measures to overcome the erosion. The scope of study are data collection, wave analysis, hydrodynamic simulation and sediment transport simulation. Numerical models MIKE 21 are used - MIKE 21 NSW, for wind-wave model, which describes the growth, decay and transformation of wind-generated waves and swell in nearshore areas. The study takes into account effects of refraction and shoaling due to varying depth, energy dissipation due to bottom friction and wave breaking, MIKE 21 HD - modelling system for 2D free-surface flow which to stimulate the hydraulics phenomena in estuaries, coastal areas and seas. Predicted tidal elevation and waves (radiation stresses) are considered into study while wind is not considered. MIKE 21 ST - the system that calculates the rates of non-cohesive (sand) sediment transport for both pure content and combined waves and current situation
[en] Radioisotopes can be applied to hydrological studies in two principal ways: as a tracer to identify water, or as an age measuring device. Applications of each method are discussed in the paper. Other applications such as the possibility of using sand labelled with radioisotopes for measuring of transport of silt and sand has been investigated
[en] Dating by radiation damage methods of eolian and fluviatile sediments preferentially deposited during glacial periods is meanwhile a routine. Automated devices allow a high throughput of TL/OSL (thermoluminescence, optically stimulated luminescence) analyses while the most time-consuming work remains the separation of pure mineral fractions, their chemical and physical treatment, the calibrated radiation and last but not least the evaluation and interpretation of raw results in order to get absolute dates. Beside many widely and continuously studied basic physical phenomena, fundamental questions are not yet satisfactorily answered. For an example the influence of palaeohydrological changes to the accuracy of the absolute dates. One of the reasons may be the limited precision of TL and OSL dates. A recently introduced technique to date single-aliquots may overcome at least some of these problems. (author)
[en] Highlights: • Seagrass species compositions in 2012 were compared with those in 1995. • Between two observations, the culture of milkfish was proliferated. • Species richness decreased at the sites affected by milkfish culture. • Seagrass disappeared at a site, where both siltation and nutrient load are heavy. - Abstract: Effects of fish culture can alter the adjacent ecosystems. This study compared seagrass species compositions in 2012 with those in 1995, when fish culture was less intensive compared to 2012 in the region. Observations were conducted at the same four sites around Santiago Island, Bolinao: (1) Silaqui Island, (2) Binaballian Loob, (3) Pislatan and (4) Santa Barbara, and by using the same methods as those of Bach et al. (1998). These sites were originally selected along a siltation gradient, ranging from Site 1, the most pristine, to Site 4, a heavily silted site. By 2012, fish culture had expanded around Sites 2, 3 and 4, where chlorophyll a (Chl a) was greater in 2012 than in 1995 by one order of magnitude. Enhalus acoroides and Cymodocea serrulata, which were recorded in 1995, were no longer present at Site 4, where both siltation and nutrient load are heavy
[en] Past studies have focused on carbon variation in the upper 1 m of the soil profile. However, there is limited information on carbon variation at deeper depths (e.g., 0–4 m) and mathematical functions to extrapolate carbon content at these depths. The objective of this study was therefore to assess the vertical variation in SOC (reached 4 m) of the Tarim River floodplain in northwestern China. The vertical distribution in SOC was described by exponential and power functions based on (1) soil depth, (2) soil depth and silt content, (3) soil depth and SOC at the shallowest and deepest depths, (4) soil depth, silt content, and SOC at the shallowest and deepest depths, and (5) soil depth and SOC at the shallowest depth. We found SOC content decreased with depth from 6.82 g kg−1 at 0–0.2 m to < 1.0 g kg−1 below 3.2–3.4 m averaged across five locations along the floodplain. Both the power and exponential functions provided a good fit to the measured data in the upper 1 m of the soil profile, whereas the power function provided a better fit to the data when extrapolating to a depth of 3–4 m. The power function describing SOC as a function of soil depth, silt content, and SOC at the shallowest and deepest depths best portrayed the distribution in SOC with depth. Considering the cost and labor in measuring soil properties, our results suggest that SOC at the shallowest depth can provide good estimates of the vertical distribution in SOC in a floodplain.
[en] The ore of a uranium deposit in the south of China is a high-content-type ore, with a series of problems, such as low permeability, low leaching rate and long leaching period. This study through the agitation leaching test, explores reasonable technical parameters. It achieved satisfactory results. Through carrying out agitation leaching to high mud weight cataclastic granite type uranium ore, reasonable technology parameters and the optimized conditions were obtained, uranium leaching rate reached 95% above, which laid the foundation for the future field enlarged experiment and is significant for shortening the leaching time, improving the leaching rate,recovery rate and economic benefit. (authors)
[en] Uranium concentration varies from 9.01 to 12.7, 8.03 to 11.5, 9.1 to 14.0 and 10.1 to 14.2 mg/kg in grab sediment, coarse sand fraction, fine sand fraction, silt and clay fraction respectively. Thorium concentration varies from 20.0 to 29.4, 17.3 to 28.6, 19.6 to 30.4 and 21.1 to 35.9 in grab sediment, coarse sand fraction, fine sand fraction, silt and clay fraction respectively. Uranium and thorium concentrations vary in different size fractionated sediment samples like silt and clay fraction > fine sand fraction > coarse sand fraction. (author)
[en] Erosion and the production of sediments effect the siltation of reservoirs and create large environmental problems. This work calculates the volume of sediments caused by erosion in a hydrological basin using the Revised Universal Soil Loss Equation 2 (USLE–RUSLE2), applying, or not, the sediment delivery ratio, and is compared with the volume of sediments transported using the Lawrence method. The USLE–RUSLE2 method is validated in the study area, the Jerte Valley, using the geographic information systems. The result obtained showed an erosion of 7 Tm/ha year and low risk of siltation, which suggest that the Plasencia reservoir has a long life expectancy.