Tạp chí Khoa học Trái Đất và Môi trường Đại học Quốc gia Thành phố Hồ Chí Minh

The port system of Ho Chi Minh City including 34 ports, serves as the gateway to the South (including the South East and the Mekong Delta) in export and import activities. In which contribute a huge amount of pollutants to the atmosphere in Ho Chi Minh City. The objective of this study is to: (i) Calculating air emissions from ports system in Ho Chi Minh city using the SPDGIZ model which emits a large amount of air pollutants such as sulfur oxide (SOX), nitrogen oxide (NOX), fine dust (PM2.5, PM10), volatile organic compounds (VOC), carbon monoxide (CO) from large ships (Ocean going vessels - OGVs), towing ships (Harbor Crafts - HCs), cargo handling equipment (Cargo handling equipment - CHE) and other vehicles (Heavy trucks – HVs); (ii) Using dispersion model TAPM-AERMOD to assess the impact of port operations to air quality in surouding port area; (iii) Proposing abatement measures based on the results of simulation to reduce emissions/ air pollution levels. The results of emission inventory show that the total port emissions are largely NOX and SOX mainly from large ships (OGVs) and cargo handling equipment (CHE) due to the use of heavy oil and diesel which have high sulfur content. The results show that the time at which a mooring boat is the most time consuming (accounting for over 90% of total emissions from OGVs).

Livestock is one of the main activities of the agricultural sector in Tan Thanh district, Ba Ria – Vung Tau province. Beside of pollution sources such as waste water, solid waste, livestock activity in Tan Thanh district, Ba Ria - Vung Tau province in recent years has caused air pollution in the livestock area and surrounding area. This research was carried out to evaluate the process of air pollution dispersion from livestock activities based on applying the TAPM meteorological model and AERMOD air quality model. The results showed that the maximum concentrations of air pollutants from livestock area such as NH3, H2S and CH3SH exceeded the National Technical Regulation on Ambient Air Quality (average hour) in the centre of Tan Thanh district, such as Toc Tien commune, part of Tan Phuoc and Phuoc Hoa communes, is 505 μg/m3; 57.4 μg/m3 and 111 μg/m3, respectively. Phu My district and other suburban communes (Hac Dich, Song Xoai, Chau Pha, Tan Hoa, Tan Hai, My Xuan, etc.) have distribution of lower concentrations of air pollutants. Base on the present results of modeling, the authors have proposed livestock development scenarios to control air pollution from this activity, contributing to environmental protection for Tan Thanh district.

Plastic debris was separated from Saigon river sediment using a microplastic sediment separator (MPSS) for the first time. A separation fluid of ZnCl2 solution (1.6 kg/L) was used to separate lower density materials (floating on the top) from higher density materials (sinking in the bottom). Plastic and plastic-like materials were collected and analyzed by a FTIR spectrometer to determine plastic composition. The results show that a total of 350 items (0.0485 g) of plastic debris were extracted from 1,500.00 g dry sediment, including 11 items (0.0130 g) of macroplastics (> 5 mm) and 339 items (0.0355 g) of microplastics (0.3–5 mm). Polyethylene (PE), polypropylene (PP), and PE-PP mixture were the most major plastic types with 225, 85, and 21 items, respectively. Others, including polystyrene (PS), polyurethane (PU), silicon, rubber, and nylon were also found in the sediment sample. Fragments were the major shape with 300 items while other shapes of sheets, fibers and beads were also recorded. The advantages of MPSS are high capacity, high separation efficiency, and low-cost operation. The disadvantages of this apparatus are high pollution due to using ZnCl2, bottom stirrer is easily stuck, and uncertain efficiency with small microplastic particles (< 0.3 mm). A significant high number of microplastics in sediment environment indicates that microplastics could be a potential risk for benthic organisms and aquatic food web. Various types and shapes of plastics also suggests that macroplastics and microplastics in sediment could originate from various sources. It is said that, for the first time in Vietnam, plastic debris, particular with microplastics, can be efficiently extracted from a large amount of sediment sample (up to 1.5 kg dry sediment). These findings could be an interesting reference for researchers who may want to obtain a large amount of microplastics for further investigation of microplastic toxicology.

In the present study, Multivariate Statistical Analysis (MSA) such as Principle Component Analysis (PCA) and Cluster Analysis (CA) were applied to determine the temporal and spatial variations of groundwater quality in Tan Thanh district, Ba Ria – Vung Tau province. Groundwater samples were collected from 18 monitoring wells in April (dry season) and October (wet season) during the year 2012. Fifteen parameters (pH, TH, TDS, Cl-, F-, NO3-, SO42-, Cr6+, Cu2+, Ca2+, Mg2+, Na+, K+, HCO3- and Fe2+) were selected for MSA. PCA identified a reduced number of mean three latent factors of groundwater quality. Three factors called salinization, water-rock interaction and anthropogenic pollution explanined 70,5% (dry season) and 71.28% (wet season) of the variances. Cluster analysis revealed two main different groups of similarities between the sampling sites. This study presents the necessity of MSA in order to extract more precise information from a huge minitoring data, which will be usefull to groundwater quality management.

The purpose of this study is to evaluate and analyze the possibility of nitrogen recirculation when applying a closed eco-system for intensive catfish ponds in the Mekong Delta in accordance with the existing available natural conditions in the local area. A closed ecosystem is proposed for optimizing N emissions from intensive pangasius farming on the basis of closed flows of materials, waste, and energy. The entire system is applied to Tran Trung Nhan household in An Binh B ward, Hong Ngu city, Dong Thap province consisting of 6 sub-systems (catfish ponds, composting, rice cultivation, livestock, liquid fertilizer, aquatic ditches) which are designed to be interacted, and Nitrogen in the catfish ponds are used as the main nutrient sources throughout the integrated system. The material flow analysis (MFA) method, which is based on the principle of material flow balance, is applied in the integrated system to analyze the potential of Nitrogen circulation in the whole system. The results show that the input N source is mainly from feed (43.35 kgN), and there are 3 main sources of N emissions from the system: sewage sludge (20.55 KgN), wastewater (3.4 KgN), and hydrolyzed nitrogen from dead fish (3 KgN). The source of N generated from sewage sludge is mixed with other wastes (biomass from rice straw and water hyacinth) in the system to produce compost (26 KgN), and wastewater generated from catfish ponds after aquatic treatment is supplied to agricultural activities (4.9 KgN).

A backarc basin represented by a mafic/ultramafic magmatic ophiolitic sequence has been discovered first time within Vietnam territory. Backarc basin/forearc basin and other features of a convergent tectonic system are being considered as a location of the two geological blocks that almagamated together and preferred as a geological suture. The middle Triassic suture resulted from the welding of the Indochina and Sibumasu blocks has been studied in details and traced from northen Thailand as Nan-Attaradit suture southward to Cambodia as Sra Kaeo suture. After a gap comparable to the territory of Vietnam it reappears in the northern Malaysia and being recognized as Bentong-Raub suture. With this new discovery of a back arc basin of this suture system located within Vietnam, the complete geographical location of the suture between the Indochina and Sibumasu block has been clearly verified and would be valuable information for geological studies in the area.

The problem of studying, calculating, simulating the process of transporting sediment and calculating erosion and accretion in rivers is very complicated. There are many methods that are applied and have shown their own effectiveness. However, at present, the development of a computer system as well as a good data base (especially topographic data) will ensure the ability to apply hydrodynamic models to simulate high results. In the Mekong Delta, there are currently 406 landslide sections, with a total length of 891km, of which An Giang is assessed as one of the localities most severely affected by riverbank erosion. Currently, there are many methods used to assess and predict riverbank erosion through the calculation of sediment content and regime in the river in specific areas, such as: document analysis method. real measurement; physical model; experience formula and mathematical model. Research using 2D Mike 21FM model is being widely used to simulate sediment regime on Tien and Hau river systems and analyze in detail for Long Xuyen city, An Giang province, which is a serious landslide area in recent years. The criteria to evaluate the reliability of the model both in terms of hydrodynamics and sediment at Vam Nao hydrological station show that the set of parameters ensures enough reliability to conduct the simulation of sediment on the system. Simulation results of flow regime and velocity show that the direction of sediment movement is from the right bank to the left bank, and this area has many scour holes and the level of sediment moving away from the shore is up to 50kg/m3. Many locations also clearly show a high risk of landslides in this area. This result will strengthen the scientific basis of the mathematical modeling method along with other methods for simulating finding mechanisms and causes of riverbank erosion, serving the prevention and mitigation of riverbank erosion. damage caused by landslides.

Numerical model is a useful tool in studying the flow and sediment transport, change in river bed and is built on solving governing differential equations. Numerical model has many different levels and three-dimensional model is the highest level, allowing detailed simulation of flow and sediment transport process in 3D space. The paper presents a method calculating three - dimensional flow and sediment transport in the open channel. Water level and flow velocity are solved from three-dimensional equations with hydrostatic hypothesis. Concentration of suspended sediment, bottom sediment and bottom evolution is solved from transport equations. The governing differential equations in the "sigma" transform coordinate system are solved by finite volume method on unstructured grid of quadrilateral elements. Boundary condition of water level or flow will be imposed on open boundary. For suspended sediment concentrations in the injected phase, suspended sediment concentrations are applied and the outflow phase applies free drainage conditions. This method of calculation was tested with the problem of curved channel sediment transport which was studied experimentally by Odgaard and Bergs. Calculation results are quite consistent with the measured data. In order to test the practical applicability, this method is also tested with the problem of sediment transport in Cu lao Pho islet on Dong Nai river. To solve the matter of hydraulic boundary condition of this problem, the model of Cu lao Pho islet is integrated into the Sai Gon - Dong Nai river system model. Results of the calculation of the river bed evolution of the Cu lao Pho islet on the Dong Nai river also show that this calculation method gives results consistent with the rule and can be used in practical research.  

Recently, the Intensity – Duration – Frequency (IDF) relationship of extreme rainfalls in a local area is usually investigated to provide accurate required data for calculating, planning, and developing urban drainage systems, especially in the context of climate change. Traditionally, IDF curves are computed based on a statistical method for analyzing the frequency of occurrence or non-occurrence of annual extreme rainfall events over a return period; or based on a probability distribution function of these events. However, these traditional methods do not take into consideration the relationship between extreme rainfalls of different durations as they only simulate the intensity of extreme rainfall events at each individual duration after generated a large number of parameter sets. Therefore, the results of these methods are inaccurate and much depend on the actual observed data. In this study, a new approach to develop IDF relations was proposed based on the scale-invariance nature of extreme rainfalls at different durations. This method will be examined and compared with traditional methods based on the IDF curves of extreme rainfalls at Tan Son Nhat gauge station (HCMC) from 1980 to 2015. Results have indicated that there is a linear relationship between extreme rainfalls at different time scales and showed that the proposed method is appropriate for estimating the IDF curves with many prominent advantages rather than traditional method.