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.

Abstract: This study used the Denitrification-Decomposition (DNDC) model to calculate greenhouse gas emissions from a paddy rice cultivation in ​​Nam Dinh province. The results show that the total CH4 emission from paddy rice field in Nam Dinh province ranges from 404 to 1146kg/ha/year. Total N2O emissions range from 0.8 to 4.2 kg/ha/year; The total amount of CO2e varies between 10,000 and 30,000 kg CO2e / ha / year. CH4 emissions on typical salinealluvial soils, light mechanics are the highest and lowest on alkaline soils. Alluvium, alkaline soils have the highest N2O emissions and the lowest is the typical saline soils. The study has also mapped CH4, N2O and CO2e emissions for Nam Dinh province. Keywords: DNDC, Green house gas, agricultural sector, Nam Dinh,  GIS. References: [1] Bộ Tài nguyên và Môi trường, Báo cáo kỹ thuật kiểm kê quốc gia KNK của Việt Nam năm 2014, NXB Tài Nguyên Môi trường và Bản đồ Việt Nam, Hà Nội, 2018.[2] D.L. Giltrap, C.Li, S. Saggar, DNDC: A process-based model of greenhouse gas fluxes from agricultural soils, Agriculture, Ecosystems & Environment 136 (2010) 292–300. https://doi:10. 1016/j.agee.2009.06.014.[3] Viện Thổ nhưỡng Nông hóa, Báo cáo kết quả đề tài: “Nghiên cứu, đánh giá tài nguyên đất sản xuất nông nghiệp phục vụ chuyển đổi cơ cấu cây trồng chính có hiệu quả tại tỉnh Nam Định”, 2017.[4] Trung tâm Khí tượng thủy văn quốc gia – Bộ TN&MT, Số liệu thống kê khí tượng thủy văn các trạm khí tượng Văn Lý, Nam Định, Ninh Bình, Thái Bình năm 2014, 2015.[5] Niên giám thống kê tỉnh Nam Định, 2015.[6] T. Weaver, P. Ramachandran, L. Adriano, Policies for High Quality, Safe, and Sustainable Food Supply in the Greater Mekong Subregion. B.T.P. Loan, N.H. Son, M.V. Trinh, N.T. Thuy, D.T.P. Lan, Chapter 7, ADB, Manila, Philippines, 2019, pp. 178-204.[7] Mai Văn Trịnh, Sổ tay hướng dẫn đo phát thải khí nhà kính trong canh tác lúa. NXB Nông nghiệp, Hà Nội, 2016.

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.

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.  

Abstract. This paper attempts to examine the changes in surface water environment and community based coastal resources management activities in the Tam Giang Lagoon, Central Vietnam. The results show that the lagoon’s surface water has been polluted. BOD５, COD and nutrient concentration have increased in the lagoon’s surface water environment. It proved that there was a present of organic substances. Due to the globalization of seafood products and changes in lagoon’s water quality by aquaculture development; the local government has issued many regulations to manage lagoon’s resources. Among those policies, the establishment of fisheries association and/or self-management team is considered as appropriate solution to develop aquaculture and capture aquatic resources in the lagoon. However, the benefit and power of the resource users have not been stipulated for both fisheries association and self-management team. Instead of this, it is only member’s responsibilities and duties in using lagoon’s water surface areas. As a result, most of resource users in the study area have not participated in these organizations as their members. The resource user must do all activities in relation to aquaculture by themselves, without supporting from above organizations.Keywords: Community Based Resource Management, Biochemical Oxygen Demand, Chemical Oxygen Demand, Surface Water Environment, Self-management Team, Tam Giang Lagoon.

The study estimates plastic waste generation and leakage to the environment and the sea in Hai An ward, Thanh Hoa province. The study uses a material flow analysis model, field samplings (include plastic waste sorting and weighing), and secondary data collection and analysis. The plastic waste generated is estimated to be 77.01 ton/year, of which the plastic waste from domestic sources and other sources, including agriculture and aquaculture (fishing), are 71.17 ton/year and 5.84 ton/year, respectively. Research results show the composition of plastic waste from domestic sources is diverse, with bottles being the highest (28.4%), followed by plastic bags (23.1%). The findings of the study also indicate that the plastic waste leakage to the environment is 9.63 ton/year, of which 6.4 tons are from the uncollected plastic waste and 3.23 tons are the plastic waste lost during the collection, transportation, and treatment process. The research also estimates that the plastic waste leakage to the sea accounts for about 7.24 ton/year, plastic waste retained on land is about 2.16 ton/year, and the plastic waste openly burnt is 0.23 ton/year.  

With an advantage of relatively wide area, diversified terrain, Ha Giang province is considered to have a great potential to develop grass-fed livestock. However, in Ha Giang, there are now many difficulties in ensuring the provision of green food for cattle, especially in cold winter season. In order to contribute to the development of livestock feed supply in the area, this study aims to select suitable tree and grass species for ecological conditions in Ha Giang, contributing to the sustainable development of livestock in the area. Selected research results from 11 plants and grass varieties, including: VA06; Panicum maximum TD58; Guatemala; Brachiaria Brizantha, B. Mulato II; The Florida Elephant; Pakchong; Maize NK4300; Maize LCH9; local Sorghum in Lao Cai; imported Sorghum BMR6 shows that Pakchong, VA06, TD58 and maize variety NK4300 have good growth and yield. The Pakchong elephant grass is capable of yielding 188.6 tons / ha / year, VAO6 177.8 tons / ha / year, Panicum maximum TD58 is 126.6 tons / ha / year and maize variety NK4300 was 70.4 tons / ha / 2 crops of Summer and Autumn. Based on the results of field experiments, the study has selected the Pakchong elephant grass, VA06, Panicum maximum TD58 and maize variety NK4300, which have good growth, high yielding and suitable for the ecological condition in Ha Giang province.  

Trong bài báo này, chúng tôi đề cập đến việc sử dụng kết hợp phương pháp giá trị thông tin và phương pháp phân tích thứ bậc cho mục đích thành lập bản đồ nguy cơ trượt lở đất tỉnh Bắc Kạn. Theo đó, bản đồ hiện trạng trượt lở được thành lập dựa trên các kỹ thuật giải đoán ảnh lập thể (ảnh vệ tinh độ phân giải cao và siêu cao chồng phủ lên mô hình số độ cao) kết hợp với điều tra thực địa. Nguy cơ trượt lở được tính thông qua phân tích mối tương quan giữa hiện trạng trượt lở tại khu vực nghiên cứu với các nhân tố ảnh hưởng đến sự phát sinh tai biến trượt lở cũng như phân tích mức độ quan trọng giữa các nhân tố gây trượt lở với nhau. Bản đồ nguy cơ trượt lở được kiểm chứng bằng phương pháp diện tích dưới đường cong cho giá trị AUC = 0,78.Keywords: Landslide, information value, AHP.

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.