VNU Journal of Science: Earth and Environmental Sciences

Abstract

The Gulf of Thailand is a semi-closed Gulf on the west and southwest side of the Indochina Penisula and experiences reversal monsoon.  The object of the present study is to investigate monthly and spatial distributions of the phytoplankton in the Gulf of Thailand during whole El Nino year 2002 by using remote-sensing measurements of chlorophyll-a (Chl-a) and surface wind vectors. Results show that monthly and spatial variations of the phytoplankton blooms are primarily associated with the monsoonal winds. In general, the average monthly Chl-a concentrations were quite low (<0.5 mg m-3) most area of the Gulf, with a belt of higher Chl-a concentrations along the coast during throughout year. Phytoplankton blooms extensively offshore in the near-coastal area of the Gulf in January and February, which is consistent with the winter northeast monsoon. In particular, one peak of Chl-a concentrations was observed in December. Areas with higher Chl-a concentrations along the coast were observed in both winter and summer monsoon months. Keywords: Phytoplankton blooms, Monsoon, Gulf of Thailand, El Nino.

This paper evaluates the ability to forecast monthly and seasonal rainfall in seven climatic regions of Vietnam using the dynamical downscaling method, employing two climate models, clWRF and RegCM, with input data from the global climate model (NCEP CFSv2). The results indicate that the models perform best in the northern regions. However, significant forecast errors occur in the Central Highlands and Southern regions during dry months. The RegCM model provides more accurate rainfall forecasts in the North Central, South Central, and Central Highlands regions, while the clWRF model performs better in the Southern region. Forecast quality varies with lead times. At 5-month lead time, the models show considerably larger errors compared to 1- and 3-month lead times, particularly in September, October, November, and December in the Northwest, Northeast, and Red River Delta regions. Similarly, higher errors happen in January, February, November, and December in the other regions, while in March, April, and May, the models using 5-month lead time exhibit the lowest errors in these regions. The correlation between forecasted and observed rainfall remains low, emphasizing the complexity of seasonal rainfall forecast. Therefore, exploring post-model correction methods is needed to improve forecast quality.  

According to the World Health Organization (WHO), air pollution ranks 6th among the leading causes of death globally. The wet porous membrane filter has been widely used in dust removal, VOCs, and acid gas absorption. The wet filtration solutions need to ensure a low water activity that limits the release of moisture into the air, inhibits microbial growth, and can absorb dangerous gases. This study investigated the water activity of NaCl, NaNO3, K2CO3, KCl, K2SO4, Mg(NO3)2, MgCl2, and CaCl2 solutions at different concentrations to saturation at 25 °C. NaCl and NaOH solutions are not only investigated at different concentrations but also investigated the effect of temperature in the range of 0-40 °C. Some solution formulas are suggested that ensures the following properties: low water activity, antifungal, antibacterial and acid gas absorption.      

In this study, a membrane bioreactor – MBR system at laboratory-scale was designed to remove sulfamethoxazole (SMX) in water. The system consists of a 8-liter aerobic tank combined with a hollow fiber micro filtration membrane (MF). Influent flow rate of wastewater was 15,84 L/day. Affecting factors to treatment efficiencies (organic pollutants and antibiotics) such as contact time and initial antibiotic concentration were investigated. Experimental results indicated that wastewater with initial parameters COD, NH4+, NO3-, PO43- were respectively 240, 9,4, 37,5, 6,3 mg/L, the treatment efficiencies achieved were respectively at 63,4, 89,7, 78,1, and 79,8%. The removal efficiencies of the wastewater containing SMX (concentrations range from 0,052 to 0,268 mg/L) for COD and NH4+ decreased by 4,2 and10,9% respectively, and for NO3- and PO43- increased by about 4,5 and 7,9%, correspondingly. Overall SMX elimination performance is about 49,7%.

In this study, the effectiveness of pH (1-5), hydrogen peroxide concentration (5-10 mM), ion Fe2+ concentration (0,1-0,5 mM), and reaction time on treatment of mononitrotoluen by homogeneous Photo-Fenton process was evaluated. The response surface methodology (RSM) was applied to design the experiment and determine the optimal treatment. The results indicated, at optimized pH=3, C0MNT=100 mg/L, CFe2+= 0.4 mM, CH2O2= 2.5 mM, the MNT treatment efficiency reached 99.4% after 5 minutes.  

Sulfur-oxidizing bacteria are capable of oxidizing various sulfur compounds including sulfide and thiosulfate in the environment. Hydrogen sulfide (H2S), a product of anaerobic decomposition, is highly corrosive. With the typical smell of rotten eggs, the toxic gas H2S causes many harmful effects on the environment and human health. Sulfide:quinone oxidoreductase enzyme (SQR) produced by sulfur-oxidizing bacteria plays an important role in the sulfide oxidation process, contributing to minimizing sulfide toxicity in the environment. In this study, the presence of sqr gene and SQR enzyme in the photosynthetic purple bacterium Rhodopseudomonas palustris (R. palustris) isolated from domestic wastewater was determined by gene amplification (PCR) using specific primer pairs following by sequencing and denaturing SDS-PAGE method combined with sulfide oxidase assay that measures BaSO4 turbidity, respectively. The results showed that the sqr gene has 1254 bp in length, encoding for the SQR protein containing 417 amino acids with a molecular weight of 45.87 kDa and locating on the cell membrane. The enzyme operated optimally under the condition of pH 6.5 and temperature at 30 °C with sulfide oxidation activity recorded up to 20-21 U/ml. The study has initially shown the ability of the R. palustris bacterial strain to oxidize sulfide for further research using sulfur-oxidizing bacteria applied in environmental treatment.  

The Day estuary area is accreting relatively quickly, expanding the land area for Nam Dinh and Ninh Binh provinces. To understand the sediment accreting mechanism in this region, 42 surficial sediment samples were taken and analyzed for grain size to determine the rules of surficial sediment distribution and analyze the net sediment transport pattern. Research result shows that in the Day estuary area: sand is mainly dominated in the east and south, silty sand is distributed in front of the estuary and south of Con Noi, and sandy silt is distributed in the west and center of the study area. The coarsest-grained sediments are distributed in the North and South, while finer-grained sediments occupy the main area in the East and finest-grained sediments are spread out in the West of the study area. Well-sorted sediments are dominated throughout the region, covering the center and the East of the study area, showing that the hydrodynamic regime is relatively stable. Medium-sorted sediments are distributed in the West, North, and South, reflecting a less stable hydrodynamic regime. Poorly-sorted sediments at the Day estuary mouth represent the most complex hydrodynamic conditions here. Sediment tends to be transported from the southeast and west to the central area, causing a strong accretion process to create Con Noi and shallow mild tidal flats in the Day estuary area.

This study presents, for the first time, the dynamical downscaled results at 25 km resolution for Vietnam from a global climate model participating in the Coupled Model Intercomparison Project Phase 6. The regional climate model (RegCM) version 4.7 was used with initial and boundary conditions from the global model CNRM-CM6-1 (referred to as CNRM) under the two Shared Socioeconomic Pathways (SSPs) 2-4.5 and 5-8.5. Simulated rainfall from RegCM and CNRM for the baseline period 1995–2014 is compared with the observation-based Vietnam Gridded Precipitation Dataset. The results indicate that downscaling is particularly effective in complex terrain areas, notably in the Central region during the winter monsoon season. However, in an overall assessment, the downscaled RegCM rainfall has not demonstrated added value compared to the CNRM results, whether in terms of annual variation, rainfall amounts, or spatial distribution. Future projection results until the end of the 21st century show an increase in average rainfall, rainfall intensity, and annual maximum daily rainfall in Vietnam under both SSP2-4.5 and SSP5-8.5 scenarios. The increase is projected to reach approximately 25% in the Northern coastal area in the RegCM experiment under SSP5-8.5. The increase in rainfall intensity is pronounced across most of Vietnam, particularly under SSP5-8.5. Regarding projected maximum daily rainfall, there are discrepancies between the regional climate model and the global model. While CNRM exhibits unclear trends in many areas, RegCM indicates an overall increase in maximum daily rainfall across most of Vietnam under both SSPs scenarios.            

Abstract