This paper highlights a preliminary study on the potential of a tipping flush gate to be used in an open storm drain to remove sediment. The investigation was carried out by using a plasboard model of the tipping flush gate installed in a rectangular flume. A steady flow experiment was carried out to determine the discharge coefficients and also the outflow relationship of the tipping flush gate. The velocity produced by the gate at various distances downstream of the gate during flushing operation was measured using a flowmeter and the velocity at all the points was higher than the recommended self-cleansing design available in the literature. A preliminary experiment on the efficiency of flushing was conducted using uniform sediment with d50 sizes of 0.81, 1.53 and 4.78 mm. Results generally showed that the number of flushes required to totally remove the sediment from the initial position by a distance of 1 m increased by an average of 1.50 times as the sediment deposit bed thickness doubled. An equation relating the number of flushes required to totally remove the sediment bed for 1 m with the sediment bed deposit thickness was also developed for the current study.
Studies of naturally occurring radioactive materials (NORM) distribution of (226)Ra, (228)Ra and (40)K in East Malaysia were carried out as part of a marine coastal environment project. The results of measurements will serve as baseline data and background reference level for Malaysia coastlines. Sediments from 21 coastal locations and 10 near shore locations were collected for analyses. The samples were dried, finely ground, sealed in a container and stored for a minimum of 30 days to establish secular equilibrium between (226)Ra and (228)Ra and their respective radioactive progenies. They were counted using a high-purity germanium (HPGe) spectrometer covering the respective progeny energy peak. For (40)K, the presence of this was measured directly via its 1460 keV energy peak. The concentration of (226)Ra, (228)Ra and (40)K in samples obtained from coastal Sarawak ranged between 23 and 41 (mean 30+/-2) Bq/kg, 27 and 45 (mean 39+/-4) Bq/kg and 142 and 680 (mean 462+/-59) Bq/kg, respectively. Meanwhile, the concentration of (226)Ra, (228)Ra and (40)K for samples obtained from coastal Sabah ranged between 16 and 30 (mean 23+/-2) Bq/kg, 23 and 45 (mean 35+/-4) Bq/kg and 402 and 842 (mean 577+/-75) Bq/kg, respectively. For the Sarawak near shore stations, the concentration of (226)Ra, (228)Ra and (40)K ranged between 11 and 36 (mean 22+/-2) Bq/kg, 21 and 65 (mean 39+/-5) Bq/kg and 149 and 517 (mean 309+/-41) Bq/kg, respectively. Meanwhile, the concentration of (226)Ra, (228)Ra and (40)K for samples obtained from Sabah ranged between 9 and 31 (mean 14+/-2) Bq/kg, 10 and 48 (mean 21+/-3) Bq/kg and 140 and 580 (mean 269+/-36) Bq/kg, respectively. The calculated external hazard values of between 0.17 and 0.33 (less than unity) showed that there is little risk of external hazard to the workers handling the sediments.
Valuing sedimentary 'blue carbon' stocks of seagrass meadows requires exclusion of allochthonous recalcitrant forms of carbon, such as black carbon (BC). Regression models constructed across a Southeast Asian tropical estuary predicted that carbon stocks within the sandy meadows of coastal embayments would support a modest but not insignificant amount of BC. We tested the prediction across three coastal meadows of the same region: one patchy meadow located close to a major urban centre and two continuous meadows contained in separate open embayments of a rural marine park; all differed in fetch and species. The BC/total organic carbon (TOC) fractions in the urban and rural meadows with small canopies were more than double the predicted amounts, 28 ± 1.6% and 36 ± 1.5% (±95% confidence intervals), respectively. The fraction in the rural large-canopy meadow remained comparable to the other two meadows, 26 ± 4.9% (±95% confidence intervals) but was half the amount predicted, likely owing to confounding of the model. The relatively high BC/TOC fractions were explained by variability across sites of BC atmospheric supply, an increase in loss of seagrass litter close to the exposed edges of meadows and sediment resuspension across the dispersed patchy meadow.
The investigation of sediment transport in tropical rivers is essential for planning effective integrated river basin management to predict the changes in rivers. The characteristics of rivers and sediment in the tropical region are different compared to those of the rivers in Europe and the USA, where the median sediment size tends to be much more refined. The origins of the rivers are mainly tropical forests. Due to the complexity of determining sediment transport, many sediment transport equations were recommended in the literature. However, the accuracy of the prediction results remains low, particularly for the tropical rivers. The majority of the existing equations were developed using multiple non-linear regression (MNLR). Machine learning has recently been the method of choice to increase model prediction accuracy in complex hydrological problems. Compared to the conventional MNLR method, machine learning algorithms have advanced and can produce a useful prediction model. In this research, three machine learning models, namely evolutionary polynomial regression (EPR), multi-gene genetic programming (MGGP) and M5 tree model (M5P), were implemented to model sediment transport for rivers in Malaysia. The formulated variables for the prediction model were originated from the revised equations reported in the relevant literature for Malaysian rivers. Among the three machine learning models, in terms of different statistical measurement criteria, EPR gives the best prediction model, followed by MGGP and M5P. Machine learning is excellent at improving the prediction distribution of high data values but lacks accuracy compared to observations of lower data values. These results indicate that further study needs to be done to improve the machine learning model's accuracy to predict sediment transport.
Ocean sediments give information on the paleoclimatic evolution in the geological past which gives detailed information on both the age of the sediments and both paleoceanographic and paleoclimatic conditions during sedimentation. One possible way to date sediments is with 210Pb method which can be used to date sediments up to 100 years. In this study, two core samples labelled as JB15 and JB17 were collected using pledging corer, analysed and measured for the activity of 209Po and 210Po using the alpha spectrometer. Applying the methods, average sedimentation rates for JB15 and JB17 were calculated as 0.38 cmyr-1 and 0.43 cmyr-1, respectively. Assuming that the sedimentation rate values are accurate, this might imply that the sediments at the depth of 30 cm were deposited 70 years ago.
Microplastic pollution is a prevalent and serious problem in marine environments. These particles have a detrimental impact on marine ecosystems. They are harmful to marine organisms and are known to be a habitat for toxic microorganisms. Marine microplastics have been identified in beach sand, the seafloor and also in marine biota. Although research investigating the presence of microplastics in various marine environments have increased across the years, studies in Southeast Asia are still relatively limited. In this paper, 36 studies on marine microplastic pollution in Southeast Asia were reviewed and discussed, focusing on microplastics in beach and benthic sediments, seawater and marine organisms. These studies have shown that the presence of fishing harbours, aquaculture farms, and tourism result in an increased abundance of microplastics. The illegal and improper disposal of waste from village settlements and factories also contribute to the high abundance of microplastics observed. Hence, it is crucial to identify the hotspots of microplastic pollution, for assessment and mitigation purposes. Future studies should aim to standardize protocols and quantification, to allow for better quantification and assessment of the levels of microplastic contamination for monitoring purposes.
Surface sediments along the Southern Terengganu coast (≤7 km from the coast) were analyzed for polycyclic aromatic hydrocarbons (PAHs). The concentrations of 16 USEPA priority polycyclic aromatic hydrocarbons (ΣPAH16) ranged from 2.59 to 155 ng g-1 and their respective alkylated ranged between 8.80 and 24.90 ng g-1. Traces of acephenanthrylene, benzo[c]phenanthrene, thiophenic PAH, and benzonaphthofuran were identified. PAH diagnostic ratios and cross-plots revealed that these sedimentary PAH compounds are derived mainly from pyrogenic sources, primarily from biomass burning and petroleum combustion residues with minor petrogenic input. The high correlations between pyrogenic PAHs to total PAHs (r >0.73, p <0.5), and the Bap/Bep ratio to total PAHs (r = 0.88, p <0.5), suggest that atmospheric deposition and urban runoff are the main deposition pathways. The concentrations of the PAHs in the southern South China Sea fall in the moderate contamination range of 100-1000 ng g-1.
Tourism-related activities such as the heavy use of boats for transportation are a significant source of petroleum hydrocarbons that may harm the ecosystem of Langkawi Island. The contamination and toxicity levels of polycyclic aromatic hydrocarbon (PAH) in the sediments of Langkawi were evaluated using sediment quality guidelines (SQGs) and toxic equivalent factors. Ten samples were collected from jetties and fish farms around the island in December 2010. A gas chromatography/flame ionization detector (GC/FID) was used to analyse the 18 PAHs. The concentration of total PAHs was found to range from 869 ± 00 to 1637 ± 20 ng g⁻¹ with a mean concentration of 1167.00 ± 24 ng g⁻¹, lower than the SQG effects range-low (3442 ng g⁻¹). The results indicated that PAHs may not cause acute biological damage. Diagnostic ratios and principal component analysis suggested that the PAHs were likely to originate from pyrogenic and petrogenic sources. The toxic equivalent concentrations of the PAHs ranged from 76.3 to 177 ng TEQ/g d.w., which is lower compared to similar studies. The results of mean effects range-median quotient of the PAHs were lower than 0.1, which indicate an 11% probability of toxicity effect. Hence, the sampling sites were determined to be the low-priority sites.
The current study aims to verify the existing equations for incipient motion for a rigid rectangular channel. Data from experimental work on incipient motion from a rectangular flume with two different widths, namely 0.3 and 0.6 m, were compared with the critical velocity value predicted by the equations of Novak & Nalluri and El-Zaemey. The equation by El-Zaemey performed better with an average discrepancy ratio value of 1.06 compared with the equation by Novak & Nalluri with an average discrepancy ratio value of 0.87. However, as the sediment deposit thickness increased, the equation by El-Zaemey became less accurate. A plot on the Shields Diagram using the experimental data had shown the significant effect of the sediment deposit thickness where, as the deposit becomes thicker, the dimensionless shear stress θ value also increased. A new equation had been proposed by incorporating the sediment deposit thickness. The new equation gave improved prediction with an average discrepancy ratio value of 1.02.
The present study applied the use of sequential extraction technique and simple bioaccessibility extraction test to investigate the bioavailable fractions and the human bioaccessible concentration of metals collected from nine stations in surface sediment of the Bernam River. The concentrations of total and bioaccessible metals from different stations were in the range of 0.30-1.43 μg g(-1) and 0.04-0.14 μg g(-1) for total cadmium and bioaccessibility of cadmium, respectively, 6.20-288 μg kg(-1) and 2.06-8.53 μg kg(-1) for total mercury and bioaccessibility of mercury, respectively, and 9.2-106.59 μg g(-1) and 0.4-2.75 μg kg(-1) for total tin and bioaccessibility of tin, respectively. The chemical speciation of Cd in most sampling stations was in the order of oxidisable-organic > acid-reducible > residual > exchangeable, while the chemical speciation of Hg was in the order of exchangeable > residual > oxidisable-organic > acid-reducible and the chemical speciation of Hg was in the order of residual > oxidisable-organic > acid-reducible > exchangeable. The principal component analysis showed that the main factors influencing the bioaccessibility of mercury in surface sediments were the sediment total organic matter, cation exchange capacity, and easily, freely, or leachable and exchangeable fraction, and the factors influencing the bioaccessibility of tin were the total tin and cation exchange capacity, while the bioaccessibility of Cd in surface sediments was influenced by the only factor which is the easily, freely, or leachable and exchangeable fraction.
The understanding of how the sediment deposit thickness influences the incipient motion characteristic is still lacking in the literature. Hence, the current study aims to determine the effect of sediment deposition thickness on the critical velocity for incipient motion. An incipient motion experiment was conducted in a rigid boundary rectangular flume of 0.6 m width with varying sediment deposition thickness. Findings from the experiment revealed that the densimetric Froude number has a logarithmic relationship with both the thickness ratios ts/d and ts/y0 (ts: sediment deposit thickness; d: grain size; y0: normal flow depth). Multiple linear regression analysis was performed using the data from the current study to develop a new critical velocity equation by incorporating thickness ratios into the equation. The new equation can be used to predict critical velocity for incipient motion for both loose and rigid boundary conditions. The new critical velocity equation is an attempt toward unifying the equations for both rigid and loose boundary conditions.
The geochemistry and distribution of major, trace and rare earth elements (REE's) was studied in the surface sediments of the Lower Baram River during two seasons: the Monsoon (MON) and Post - monsoon (POM). The major geochemical processes controlling the distribution and mobility of major, trace and REE's in the Lower Baram River surface sediments was revealed through factor analysis. The risk assessment of major and trace element levels was studied at three specific levels; i.e. the enrichment level [Contamination Factor (Cf), with the geo-accumulation index (Igeo)], the availability level [metals bound to different fractions, risk assessment code (RAC)], and the biological toxicity level [effect range low (ERL) and effect range medium (ERM)]. The results of all the indices indicate that Cu is the element of concern in the Lower Baram River sediments. The geochemical fractionation of major and trace elements were studied through sequential extraction and the results indicated a higher concentration of Mn in the exchangeable fraction. The element of concern, Cu, was found to be highly associated in the organic bound (F4) fraction during both seasons and a change in the redox, possibly due to storms or dredging activities may stimulate the release of Cu into the overlying waters of the Lower Baram River.
The benthic foraminiferal diversity index was computed from Beypore estuary sediments. The abundance and diversity of Quinqueloculina lata, Textularia agglutinans, Haplophagmoides canariensis, and Quinqueloculina stelligera were dominated by stress-tolerant taxa such as Ammonia tepida, A.parkinsoniana, Nonion grateloupi, and N. scaphum in the estuary. The small-size foraminifera probably perished in a juvenile stage because of the high temperature and low salinity that prevailed in the ecosystem. The dominance of stress tolerant benthic foraminifera and absence of Elphidium species in the estuary suggest the prevalence of hypoxic (low-oxygen) conditions. The consistent low-diversity index of foraminifera indicates that the ecosystem is moderate to highly stressed ecologically in the Beypore estuary. The application of benthic foraminifera as a bioindicator for assessing the environmental stress in the Beypore estuary is key in monitoring these fragile coastal ecosystems.
Bauxite and iron ore mining is the major contributor to metal pollution in Tasik Chini, Malaysia. Deforestation of the protected zone of reserve forest exacerbates the problem. The current study is to understand the speciation of metals spatially in sediment to analyse the risk associated in terms of its mobility and bioavailability. The samples of sediment are collected from Sungai Jemberau, Laut Jemberau, and Laut Gumum of Tasik Chini. Four samplings were conducted for a year, by collecting the surface sediment. Sequential extraction method was followed for speciation of sediment and classified it into exchangeable, reducible, Fe-Mn oxides, organic and residual fractions. The results were also analyzed using principal component analysis (PCA) and cluster analysis (CA). The result reveals that Fe, Al, Mn, Zn, and Pb are the primary constituents of sediment contributing to about 98% of residual fraction. Co, Cd, Cr, As, and Ni are found in trace metal concentration and are identified to be mainly released from anthropogenic sources nearby. Although the individual proportion is less than major metals in exchangeable and carbonate fraction, they possess geochemically significant concentration above the permissible limit. More than 70-80% of all its total concentration proportion is hence found in mobile and bioavailable state. These possess toxic and have chronic effects to aquatic life and public health even in trace elemental concentration. Hence, these metals are the most toxic and bioavailable metals pausing risk for aquatic and public health. PCA analysis highlights that the enrichment of heavy metals in bioavailable fraction is mostly contributed from anthropogenic sources. The same results are emphasized by cluster analysis.
Brunei Bay is one of the most important marine environments of East Malaysia (South China Sea), covering many productive ecosystems with activities including fisheries, tourism, and main shipping lanes for petroleum transfers. Evaluation of the sources and distributions of steroids in the surface sedimentary organic matter was carried out by gas chromatography-mass spectrometry (GC-MS). The concentrations of the total identified sterols (TIS) ranged between 0.81 and 12.69 μg g-1 dry weight, and the total sterones were between 0.11 and 5.66 μg g-1 dry weight. The coprostanol level was comparatively low (<0.10 μg g-1), and the multi-biomarker proxies indicated that the region did not exhibit significant contamination from sewage effluents. Principal component analysis (PCA) revealed the coastal environment of the study area was dominated by allochthonous (mainly terrestrial) organic matter input.
The distribution of aliphatic hydrocarbons in three sediment cores from Brunei Bay was investigated in order to understand their sources and the biogeochemical processes of these hydrocarbons. The total concentrations of C15 to C37n-alkanes ranged from 0.70 to 16.5 μg g-1. Traces of hopanes with C29-C31 carbon homologs were detected in the study area. The carbon preference index (CPI15-37) ranged from 1.23 to 3.42 coupled with the natural n-alkane ratio (NAR19-32) ratios (1.52 to 5.34), and the presence of unresolved complex mixtures and hopanes, suggested slight contamination by anthropogenic hydrocarbons, presumably derived from activities along the coasts. The presence of C27 trisnorhopene and diploptene, as well as their association with long-chain and short-chain n-alkanes, revealed a depositional environment of organic matter in the sediment cores.
The concentrations of 137Cs and 134Cs in Malaysian marine sediments were measured by gamma-ray spectrometry with a high-purity germanium (HPGe) detector connected to a multichannel analyzer. In general, the 137Cs concentration in Malaysian marine sediments has been found to be very low and less than 5 Bq/kg dry weight with the exception of those from a few sampling locations. The concentration of 134Cs was found to be less than the minimum detectable activity for the measuring condition used. Data reported in this paper were found to be comparable with results from within the region and thus can be used as reference data for the country.
This study investigates the textural characteristics of sediments collected at eroded and deposited areas of highly severed eroded coastline of Batu Pahat, Malaysia. Samples were taken from systematically selected 23 locations along the 67km stretch of coastline and are extended to the fluvial sediments of the main river of Batu Pahat. Grain size distribution analysis was conducted to identify its textural characteristics and associated sedimentary transport behaviours. Sediments obtained along the coastline were fine-grained material with averaged mean size of 7.25 ϕ, poorly sorted, positively skewed and has wide distributions. Samples from eroded and deposition regions displayed no distinctive characteristics and exhibited similar profiles. The high energy condition transported the sediments as suspension, mostly as pelagic and the sediments were deposited as shallow marine and agitated deposits. The fluvial sediments of up to 3km into the river have particularly similar profile of textural characteristics with the neighbouring marine sediments from the river mouth. Profiles were similar with marine sediments about 3km opposite the main current and can go up to 10km along the current of Malacca Straits.