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.

Controlled slow release fertilizer (CRF) in this study was produced by mixing Silica-Biochar (SB), Bentonite (B), and Diatomite (D) at different ratios with N, P, K form customized crystal membrane to control the dissolution of N, P, K into water. Research results show that the mixing rate of SB and B significantly affects the pelleting process, decay rate, hardness, and air hygroscopicity of CRF fertilizer. The decay rate is more than 20% after 13 and 5 days and greater than 80% after 17 and 9 days, respectively with SB mixing ratio of 30 and 40%. The maximum hardness of CRF fertilizer was 3.2 kg/cm2 and the smallest was 1.6 kg/cm2 respectively with the SB used ratio of 30 and 40%. With the mixing rate of SB at 30%, the resulting CRF fertilizer has the smallest hygroscopicity. With the mixing rate of B at 5%, the resulting decay rate of CRF was the smallest. The mixing rate of B did not affect the air hygroscopicity of CRF fertilizers. The different mixing rates of diatomite used did not affect the decay rate, hardness, and air hygroscopicity of CRF fertilizers.  

Understanding of community responsiveness on climate change and the natural hazards is an essential component of urban planning and adaptation strategies. The coastal cities are seriously affected by the impact of rising sea levels and climate change-induced hazards. In this paper, we investigate the urbanization level on climate change and natural hazards awareness of local communities at the households’ level in Da Nang city, the largest municipality in Central Vietnam using 1903 surveyed households. The results showed that the urbanization level significantly influenced the local communities' responsiveness to climate change. Communities with robust infrastructure and strong economic status demonstrate greater resilience and awareness of climate change and natural hazards compared to others. Therefore, it is recommended to prioritize enhancing local people’s responsiveness to develop bottom-up climate change response strategies and policies, instead of enforcing top-down decisions.

Reservoirs system in upstream of Ba River has been affecting to the hydrology and sediment regime at the downstream. Sediment imbalance causes consequences such as erosion at river bank, lack of sediment supply to downstream areas and deposition/erosion in estuaries. This study focused on a quantitative assessment of the impact of Ba Ha reservoir and Song Hinh reservoir on sediment regime at the Cung Son hydrological station (12 km downstream of Ba Ha reservoir and 45 km from the mouth of the Da Dien river). Research used analytical and statistical methods with flow and suspended sediment data measured at the Cung Son hydrological station from 1977 to 2016. The results show that the system of these two reservoirs has a huge impact to the sedimentation regime, especially after the operation of Ba Ha reservoir. The average amount of sediment in the period before and after 2008 significantly reduced from about 2.5 million to about 1 million tons per year.

Abstract: The expansion of perennial crops area plays an important role for supporting the human livelihood in the Central Highlands, so have negative impacts on deforestation and sustainable development. Remote sensing and GIS were used to analyze the trajectories of perennial crops cover change in relationship with deforestation. The Logistic regression models were used to analyze proximate reasons and spatial changing determinants of main land cover changes for the period 2004-2016 of Bảo Lâm district. The result show that the perennial crops changes are indicator for deforestation in Bảo Lâm district with high deforestation rate 0,8% per year caused by the expansion of annual crops, blind area and the expansion of perennial crops. The facile accessed forest and suitable forest area for perennial crops have more destroyed. The trajectories of perennial crops and forest cover changes are important scientific towards sustainable development.  

This study examines impacts of climate change and natural disasters on livelihoods in Dien Bien province, located in Northern Mountainous Region of Vietnam. Based on meteorological data, household surveys, interviews, and focused group discussions conducted across four communes, the research finds that Dien Bien is experiencing more frequent and intense extreme weather events, including heavy rainfall, landslides, and droughts. These changes are severely impacting agriculture-dependent ethnic minority communities, with over 60% of households reporting arable land and crop productivity losses of 40-65% in 2022 alone. Income losses are the most pronounced in remote areas, where 62% of households lost over half of their annual income. While social welfare and climate-smart agriculture programs exist, the coverage and adoption rates vary widely across communes. The findings highlight the disproportionate impacts on marginalized populations and the need for tailored, culturally-sensitive adaptation strategies. The study recommends promoting multipurpose tree planting, establishing community-based nurseries, diversifying livelihoods through small-scale family activities, and expanding inclusive financial mechanisms to enhance resilience. Findings from this study provide new insights into the complex vulnerabilities of ethnic minority communities in mountainous regions and offers targeted interventions to safeguard their livelihoods under accelerating climate change.  

Tóm tắt:Bài báo giới thiệu một số kết quả nghiên cứu ứng dụng phần mềm CALROADS VIEW để mô phỏng lan truyền ô nhiễm bụi PM10 từ hoạt động giao thông trên tuyến đường Trường Chinh - Hà Nội. Kết quả nghiên cứu cho thấy ảnh hưởng của hoạt động giao thông đường bộ đến nồng độ bụi PM10 tại khu vực dân cư dọc theo tuyến đường là khá đáng kể. Nồng độ bụi trung bình 24h lớn nhất là 95,6µg/m3 xấp xỉ bằng 63,6 % so với quy chuẩn cho phép hiện hành. Với hướng gió chủ đạo là Đông Nam (tần suất 33%) thì khu vực chịu ảnh hưởng lớn nhất do lan truyền bụi PM10 trong không khí là khu vực dân cư phía quận Đống Đa bên cạnh đường Trường Chinh. Kết quả của mô phỏng bằng mô hình đạt 79% kết quả quan trắc thực tế.  Từ khóa:Mô hình hóa, PM10, Calroads view.

Pesticides containing organophosphate (OP) compounds in general and Chlorpyrifos   (CPF) in particular are used to control insects and pests. However, they have been proven to be highly toxic not only to some insects and wild animals but also have negative impacts on the environment and human health. This study provides an assessment of the effectiveness of using microbial product (MP) to degrade CPF in a large- and small-scale tea cultivation environment. The research results show that in some farming areas, residual CPF exists both in the soil and in agricultural products. When using the MP, the CPF content in tea decreased by 77.66%; the efficacy of CPF treatment in the soil reached 72-76% in the small scale . Additionally, the use of MP also increased the total microbial density in the net house scale from 106 to 107 CFU/g and beneficial microorganisms in the soil, stimulating growth and productivity for tea plants.

From the field survey research between 2012 and 2021, we herein provide a list of 39 threatened species of amphibians and reptiles from Son La Province. Of these, the following species have high conservation values: two species are listed in the Governmental Decree No. 64/2019/ND-CP, 12 species are listed in the Governmental Decree No. 84/2021/ND-CP, 12 species are listed in the CITES Appendices, 22 species are listed in the Vietnam Red Data Book (2007), and 24 species are listed in the IUCN Red List (2022). In addition, 21 species are being exploited for food and wildlife trade by local people. Major threats to the habitat and populations of amphibians and reptiles in the study areas include deforestation, slash-and-burn cultivation, hunting activities, exploitation of forest products, quarrying, hydropower and road construction, as well as overharvesting for food and trade. The research results provide a scientific base for conservation and management of amphibians, reptiles and biodiversity of Son La Province.