The Spatial Structure of Zooplankton Communities of Pedu Reservoir, Malaysia

A total of 22 species of zooplankton were identified from 8 sampling stations located in the limnetic zone of Pedu reservoir.The zooplankton community was dominated by rotifers (11 species),followed by cladocerans (9 species) and copepods (2 species).Four species of zooplankton comprised of 3 rotifers,Brachionus quadridentata,Brachionus caudatus and Keratella cochlearis and one cladoceran,Ceriodaphnia cornuta were present at all sampling stations.Species richness was highest at Station 2 (17 species) followed by Station 4 and Station 8 (14 species),Station 5 (15 species),Station 7 (11 species),Station 6 (10 species),Station 3 (9 species) and Station 1 (7 species).With an exception of water transparency,all other water quality parameters such as temperature,dissolved oxygen,conductivity,pH and total dissolved solids were not significant when compared between sampling stations.The study found that station 5 which was located in a calm strait,protected from strong wave and wind was a suitable area for zooplankton growth and establishment.Factors supporting the findings included highest water transparency (3.4 m),rich in species numbers (15 species),high diversity index (0.950) and evenness index (0.808).     

Geothermobarometry and fluid inclusions of dioritic rocks in Bangladesh: Implications for emplacement depth and exhumation rate

Application of hornblende thermobarometry and fluid inclusion studies to the Palaeoproterozoic (1.7 Ga) basement rocks from Maddhapara, NW Bangladesh, provide information on the pressure and temperature (P–T) conditions of crystallization, the emplacement depth and composition of magmatic fluid. The basement rocks are predominantly diorite or quartz diorite with a mineral assemblage of plagioclase, hornblende, biotite, quartz, K-feldspar, titanite, and secondary epidote and chlorite. The calculated P–T conditions of the dioritic rocks are 680–725 °C and 4.9–6.4 kbar, which probably correspond to crystallization conditions. Fluid inclusion studies suggest that low- to medium-salinity (0–6.4 wt.% NaCl_eq) H₂O-rich fluids are trapped during the crystallization of quartz and plagioclase. The isochore range calculated for primary aqueous inclusions is consistent with the P–T condition obtained by geothermobarometry. The basement rocks likely crystallized at a depth of 17–22 km, with a minimum average exhumation rate of 12–15 m/Ma during Palaeoproterozoic to Lopingian time. Such slow exhumation indicates low relief continental shield surface during this period.     

Vertical distribution and source identification of polycyclic aromatic hydrocarbons in anoxic sediment cores of Chini Lake, Malaysia: Perylene as indicator of land plant-derived hydrocarbons

Four anoxic sediment cores were collected from Chini Lake, Malaysia in order to investigate the variability of polycyclic aromatic hydrocarbon (PAH) and perylene concentrations. The study also determined significant differences of perylene concentrations in different sediment layers. Total PAH concentrations ranged from 248 to 8098 ng g⁻¹ in the samples. Diagnostic PAH ratios such as methylphenanthrenes/phenanthrene (MP/P), phenanthrene/anthracene (P/A) and fluoranthene/(fluoranthene + pyrene) (Fl/(Fl + Py) revealed a dominance of pyrogenic influences and partial petrogenic inputs to the top sediment layers. Perylene concentrations were high in the top layers (<12 cm) and increased with increasing depth. There is a significant positive correlation (r = 0.705, p = 0.01) between perylene concentrations and TOC. Analysis of variance (ANOVA) and LSD revealed significant differences (p < 0.05) in TOC-normalized perylene concentrations between the upper (<12 cm) and bottom layers (>12 cm). The average perylene concentrations accounted for 26–50% (0–12 cm) and 50–77% (12–36 cm) of pentacyclic-aromatic hydrocarbon isomers (PAI) present whereas it made up 10–34% (0–12 cm) and 46–66% (12–36 cm) of the total PAH. The average pyrene concentrations decreased with increasing depth and accounted for 62% (0–3 cm), 20–23% (3–12 cm) and 3–1.4% (12–36 cm) of perylene present. The results of hierarchical cluster analysis based on these ratios suggested different input sources for the top and bottom layers. It is concluded that the activity of termites on woody plants produced perylene which is supplied to the lake by run-off from the heavy and frequent rains in this Asian tropical climate. In addition, there was also in situ formation of perylene in the bottom layers due to diagenetic processes.     

Effect of mercury and cadmium on early life stages of Java medaka (Oryzias javanicus): a potential tropical test fish

Several organisms have been used as indicators, bio-monitoring agents or test organisms in ecotoxicological studies. A close relative of the well established Japanese medaka, the Java medaka (Oryzias javanicus), has the potential to be a test organism. The fish is native to the estuaries of the Malaysian Peninsula, Thailand, Indonesia and Singapore. In this study, newly fertilised eggs were exposed to different concentrations of Cd and Hg. Observations were done on the development of the embryos. Exposure to low levels of Cd and Hg (0.01-0.05 ppm) resulted in several developmental disorders that led to death. Exposure to ≥1.0 ppm Cd resulted in immediate developmental arrest. The embryos of Java medaka showed tolerance to a certain extent when exposed to ≥1.0 ppm Hg compared to Cd. Based on the sensitivity of the embryos, Java medaka is a suitable test organism for ecotoxicology in the tropical region.     

Solubility of Fe2(OH)3Cl (pure-iron end-member of hibbingite) in NaCl and Na2SO4 brines

Pure-iron end-member hibbingite, Fe₂(OH)₃Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe₂(OH)₃Cl(s), the pure-iron end-member of hibbingite (Fe^II, Mg)₂(OH)₃Cl(s), and Fe(OH)₂(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe₂(OH)₃Cl(s) + 3H⁺ ? 3 H₂O + 2 Fe²⁺ + Cl^?,the solubility constant of Fe₂(OH)₃Cl(s) at infinite dilution and 25 °C has been found to be log₁₀ K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)₂(s) + 2H⁺ ? 2 H₂O + Fe²⁺,the solubility constant of Fe(OH)₂ at infinite dilution and 25 °C has been found to be log₁₀ K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe₂(OH)₃Cl(s) and Fe(OH)₂(s), the Na⁺–Fe²⁺ pair Pitzer interaction parameter θ_{Na⁺/Fe²⁺} has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)₂(s) to Fe₂(OH)₃Cl(s). Additionally, when Fe₂(OH)₃Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations.     

Rain induced attenuation studies for V-band satellite communication in tropical region

Satellite communications operating at 10 GHz and above in the tropics suffer severe signal degradation due to rain. Attenuation due to rain at 38 GHz had been measured for a period of 20 months in Malaysia. Analyses carried out include seasonal variations, diurnal effects and the annual cumulative distributions. Obtained results were compared with several established prediction models including the ITU-R. The rain fade characteristics were also investigated in determining the levels of signal loss and fading. In addition, the studies highlight several potential fade mitigation techniques that can be embarked. These fundamental aprehensions are very critical for future earth space communication link design and can be exploited as preliminary groundwork plan for the researchers as well as engineers.     

Geotechnical modeling of fractures and cavities that are associated with geotechnical engineering problems in Kuala Lumpur limestone,Malaysia

This study presents a modified geotechnical model of subsurface cavities and fractures that are associated with foundation and pilling problems. The topographical model was used to automatically extract minimum surface curvature, slope, and pits. The image processing shows that more than fourteen regional faults, trending NE, SW, and WNW affect the Kuala Lumpur limestone bedrock and the surface topography from South to North. These fractures often show higher probability of piling and constructions problems. The faults are tensional, low lying, and wrench of length 10–20 km. Opencast ex-mining pond floors (bathymetry) are good indicators of subsurface fractures and cavities that affect the limestone bedrock. The LANDSAT image (band one) shows that the fractures of opencast ex-mining pond floors have the same trend as the regional faults. These techniques can help geotechnical engineers to predict subsurface fractures and cavities, especially in areas adjacent to ex-mining ponds. In brief, most of the subsurface cavities and ex-mining ponds, for example the Phong Fatt pond, are located on and along fault zones.