VNU Journal of Science: Earth and Environmental Sciences

Abstract

Abstract. Rapid socio-economic development leads to a great increase in water demand of manysectors and conflicts between water users. Moreover, studies have warned about serious degree ofinfluence of climate change (CC) on Vietnam, particularly on the water resources. Therefore,assess CC impacts on water balances are very necessary task. The Ministry of Natural Resourcesand Environment has com pleted the appropriate clim ate change scenarios in Vietnam [1]. In thisstudy, water balance results will be presented including three scenarios: high emissions scenario(A2), medium emission scenario (B2), and low emission scenario (B1). The water balanced inHong-Thai Binh river basin was calculated, which is one of the largest basins in Vietnam. Thebasin is very complicated: Under the influence of flow regime of international rivers [2], a systemof reservoừs and irrigation structures serving diverse purposes, such as of water supply, irrigation,flood control and hydropower [3-5]. MIKE BASIN model was applied to describe exploitation,utilization and to identify ứie water shortage areas according to the climate change scenarios.Keywfords: climate change, water resources, Hong-Thai Binh river.

Vertical subsurface flow-constructed wetlands (VSF CW) are evaluated in this research as a potentially effective and cost-efficient solution for treating wastewater from Da Mai noodle handicraft village in Bac Giang province. Due to the high pollution load in this type of wastewater, there are concerns about clogging and the stability of the technology. In this study, we explored different sizes of limestone and gravel for the five medium composition formulas in the VSF CW system. The experiments were conducted over a period of three months. We used ANOVA, one-sample T-test, and Pearson correlation analysis methods to evaluate the experimental results, with statistical significance set at 0.05. The results showed a linear correlation between medium size, hydraulic conductivity, and treatment efficiency (p < 0.05). Smaller medium sizes had higher pollutant removal efficiency but lower porosity and hydraulic conductivity. For the same sizes, limestone demonstrated higher treatment efficiency compared to gravel (p < 0.05). The Cp5 formula (comprising sand, 1×2 cm limestone, and 3×5 cm gravel) was selected as the best filter medium for VSF CW, achieving COD, TSS, TN, and TP removal efficiencies of 86.02 ± 1.71%, 81.15 ± 2.24%, 64.46 ± 2.23%, and 69.76 ± 2.68%, respectively. After three months of operation, the treated wastewater consistently met QCVN 40:2011/BTNMT Column B standards, and there were no significant differences in hydraulic conductivity (p > 0.05), indicating stable operation of the VSF CW.

The Ota’s bent-toed gecko (Cyrtodactylus otai) was discovered in isolated karst outcrops of Hang Kia Commune, Mai Chau District, Hoa Binh Province, in 2015 and in Chieng Yen Commune, Van Ho District, Son La Province in 2017, in northwestern Vietnam. This gecko is both an endemic and endangered species of Vietnam, and its known range to date is restricted to a severely fragmented and small regions. Hence, to identify more populations and to better understand the distribution patterns of this cryptic species, we conducted field surveys in surrounding regions of the type localities from 2020 to 2023. We discovered eight new populations for C. otai, and expanded the known range of the species in Van Ho District (Son La Province) and Mai Chau District (Hoa Binh Province). We used species occurrence data from previous studies and our field surveys to model the gecko’s distribution using MaxEnt. The model results showed that the distribution of C. otai may include other nature reserves in surrounding regions, such as Pu Hu and Pu Luong (Thanh Hoa), and Ngoc Son – Ngo Luong (Hoa Binh). Based on the model results, there is a possibility that the Ota’s bent-toed gecko also occur in nearby Lao regions. Therefore, future research and conservation initiatives may focus their efforts in such areas to look for new populations of the Ota’s bent-toed gecko, as well as to assess the distribution, habitat, and ecological patterns of this poorly known reptile.  

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.  

Hoa Vang district in Da Nang city, is frequently affected by floods. This research was conducted to generate a flood map in Hoa Vang District, Da Nang City, during the peak flooding period in 2022, using Sentinel 1 imagery on the Google Earth Engine (GEE) cloud computing platform. The research also aims to assess the impact of this flooding event on the productivity of agricultural land in the district. Based on the Sentinel 1 imagery's backscattering coefficient, the study utilizes the Otsu algorithm for thresholding to determine the flood inundated areas. The results indicated that the optimal Otsu threshold value range from -16.003 to -10.631 dB. In addition, to assess the reliability of the flood mapping results, the study utilizes the in-situ flood inventory data to calculate the overall error and Kappa index. The research findings indicate a high level of reliability with an overall accuracy of 0.89 and a Kappa index of 0.79. Based on this analysis, the study successfully established a flood map for the peak flooding period 2022 in the study area. Furthermore, the study assessed the impact of floods on agricultural land productivity in the communes of Hoa Vang District. The findings showed that the flooded agricultural land area was 1,979.8 hectares, accounting for 77.3% of the total flooded area and 2.7% of the total natural area, primarily concentrated in the southern communes of the district such as Hoa Tien, Hoa Chau, Hoa Phuoc, and Hoa Phong. These findings serve as scientific background for assessing further impacts of flooding on agricultural land in Hoa Vang District, Da Nang City.      

THE AGGRADED - ERODED DEVELOPMENT OF THAIBINH - NAMDINH SHORELINE FROM LATE HOLOCENE TO PRESENT IN RELATION TO EVOLUTION OF DELTAIC LOBES AND HISTORYOF SO RIVER Trần Nghi (1), Trần Thị Thanh Nhàn (1), Trần Ngọc Diễn (2), Đinh Xuân Thành (1), Trần Thị Dung (1), Nguyễn Thị Phương Thảo (1) Trần Xuân Trường3, Đỗ Mạnh Tuân3, Doãn Đình Lâm (4)  (1) VNU University of Science (2) Marine Geology and Mineral Resources Division – General department of Geoloy and minerals of VietNam (3) Hanoi university of natural resources and environment (4) Geology of Institue, Vietnam academy of science and technology   The aggraded-eroded development of Thaibinh - Namdinh shoreline from late Holocene to present have occured in deferent situation concerning the evolution of deltaic bobes and history of So River. The shoreline of Balat River mouth is stronglly aggrading, in contrary, the Haihau shoreline have eroded to create serious damage for the people living in coastal area. In Quaternary Geological maps of 1/200000 and 1/50000 scale, cariried out by Hoang Ngoc Ky (1973-1975) and Vu Nhat Thang (1991-1994). The research on lithofacies analysis and sequence stratigraphy was interested by Tran Nghi and Doan Dinh Lam (1991-2014). Vu Cao Minh et al (2006) described in detail based on data of “the geological description of a place” about the change process of Red River mouth from Halan (Nam Dinh) to Balat (Thai Binh) since XIX century.  The evidents of aggraded- eroded shoreline mentioned above have observed by a lot of authors, however nobody has explained what reason is it? This paper should be contributing to clarify the question of why’s the Haihau shoreline rapidly transformed from the aggradation (before 1960) to erosion (since 1960)? These proccess was related to three main evidences: (1) The evolution of deltaic lobes associated with paleoshorelines; (2) The flood in 1787 moved the Red River channel from Nam Dinh to Thai Binh area; (3) The construction of the dam So River in 1960. The process of moving the paleoshorelines and extending from the mainland to the sea remained the remarcable sign of 8 successive deltaic lobes that combined each other in fan form of paleo - shorelines 2500 y. BP, 1000 years. Bp, 500 years. BP and modern shoreline. Before 1787 main Red River channel flowed into the sea through Hai Hau area and then poured into Halan mouth. During that time the distributary flowing though Thai Binh area and pouring into Balat mouth was too small.  However, in 1787 the great flood narrowed the Red River and becoming the So River, in the same time, the main Red River channel transformed from Nam Dinh to Thai Binh area. From 1787 to 1960 Hai Hau shoreline was continuouslly aggradated with velocity of 30m/y. Since the construction of dam So River in 1960 up to now Hai Hau shoreline have eroded for 19.5m/y. Therefore, the cause of erosion in Hai Hau shore line was due to the construction of dam So River in 1960. The simple and effective solution of interpreting on erosion of Hai Hau shoreline is to break the dam So River for returning the natural law of sedimentary balance.

Abstract

This paper presents the results of the benefit of biogas solution in wastewater treatment system and the application of mathematical statistical methods to evaluate the benefits of this method for pig groups in concentrated pig farms in Hanoi, Bac Giang, Hoa Binh, Nghe An and Ha Tinh. The results of 8 pig farms in those localities idicate the potential revenue benefits from the sale of greenhouse gas emissions credits, save money for electricity and reduce environmental protection fee for the waste water from each group of pigs at different stages of growth (pregnant sows, sows, piglets and porkers). The average annual value of pregnant sows is 146.611 ± 37.718 VND, 126.424±68.920 VND for sows, 155.405 ±64.414 VND for piglets and 122.680 ±61.217 VND for porkers (confident interval is 68.2%). The initial results of this study show that the statistical method was applied effectively to solve environmental problems, and also provide useful information to propose solutions to improve the efficiency of the biogas system inmanagement of waste and biogas use to reduce greenhouse gas emissions and save energy.

The coastal area of Thanh Hoa province has a large proportion of sandy soil and is suffering negative impacts from climate change that affect crop productivity. The aim of this study is to investigate the use of biochar to improve the soil fertility and productivity of drought-tolerant sweet potatoes. The effect of biochar contents on the productivity of three sweet potatoes VC 04-24, KL C3, and VC 68-2 in the coastal sandy soil area of Thanh Hoa province was examined. The results indicated that the yield of sweet potatoes was the highest when applying five tons of biochar per hectare, equivalent to using 10 tons of manure. With the same biochar content, the productivity and other factors related to the product quality of these sweet potatoes such as the number of tubers per plant and the average mass of tuber were the highest. In detail, the estimated commercial productivity of VC 04-24, KL C3, and VC 68-2 were 25.46, 24.92, and 21.76 ton/ha, respectively. With the least significant difference at the probability of 0.05% (LSD0.05), the VC 04-24 and KL C3 showed high productivity. The economic efficiency of the sweet potatoes-growing model at Hai An commune, Tinh Gia district, Thanh Hoa province showed that the productivity of the model was 24 tons/ha, higher than the actual productivity of the control model (20.2 ton/ha). The productivity and the economic efficiency of the model were 18.8% and 31.38% higher than those of the control model, respectively. In addition, the test results showed that using 5-6 ton/hectare of biochar can improve the physical and chemical properties of soils.