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The non-treated wastewater from residential areas contains high concentrations of ammonium-nitrogen (NH4+-N). When discharged into the drainage water system, it deteriorates the water quality in urban rivers. This study used two types of materials to form eco-bags, using activated zeolite bead (AZB) and alkaline pretreated straw (APS), in geotextile bags for easy recovery and reuse. The AZB and APS provided the breeding habitat for the microorganisms that promoted biofilm formation on their surface. The immobilization of engineered denitrification microorganisms facilitated the removal of NH4+-N from the urban river water. The NH4+-N removal in the AZB and APS bags were in the range of 64–73%, and 56–61%, respectively, while the chemical oxygen demand (COD) removal in the AZB and APS bags ranged from 33–36%, and 30–31%, respectively. In addition, as evident from DNA and microbial community analysis, the microorganisms demonstrated a greater proclivity to grow and proliferate on the surface of AZB and APS and improved the water quality of urban rivers. HIGHLIGHTS Activated zeolite bead (AZB) and alkaline pretreated straw (APS) were used for the immobilization of microorganism.; Eco-bags prepared using AZB and APS in geotextile bags facilitated easy recovery and reuse.; Engineered denitrification bacteria were used to improve the NH4+-N removal capacity.; Microorganism diversity was investigated to substantiate the water quality improvement ability of AZB and APS.

Ca Mau and Kien Giang, the two provinces of the Mekong Delta bordering the Gulf of Thailand, are facing major environmental challenges affecting the agriculture and aquaculture sectors upon which many livelihoods in this region depend on. This study maps the suitability of these two provinces for paddy rice cultivation and shrimp farming according to soil characteristics and current and future environmental conditions for variables found to significantly influence the yield of those two sectors, i.e., the level of saltwater intrusion, water availability for rainfed agriculture, and the length of the growing period. Future environmental conditions were simulated using the MIKE 11 hydrodynamic model forced by four hydrodynamic scenarios, each one representing different extents of saltwater intrusion during both the dry and rainy seasons, while also considering the availability of water resources for rainfed agriculture. The suitability zoning was performed using a GIS-based analytic hierarchy process (AHP) approach, resulting in the categorisation of the land according to four suitability levels for each sector. The analysis reveals that paddy rice cultivation will become more suitable to Kien Giang province while shrimp farming will be more suitable to Ca Mau province if the simulated future environmental conditions materialise. A suitability analysis is essential for optimal utilisation of the land. The approach presented in this study will inform the regional economic development master plan and provide guidance to other delta regions experiencing severe environmental changes and wishing to consider potential future climatic and sea level changes, and their associated impacts, in their land use planning.

The sediment regime of the Red River system has changed since dams and reservoirs were implemented, with implications for river processes downstream. We analyzed data for the daily discharge (Q) and suspended particulate matter (SPM) concentrations collected from 1958–2021 at the Son Tay hydrological gauging station, the outlet of the Red River system and entry to the delta. The results showed that the annual sediment load transported by the Red River system decreased significantly, by about 90.4%, over the 64-year study period. From 1958 to 1971, when there were no dams or reservoirs in place, the annual water discharges and sediment loads in the river system were about 115,592×106 m3/yr and 115×106 ton/yr, respectively. From 1971 to 2016, a series of dam-reservoir systems were gradually implemented (Thac Ba (1971), Hoa Binh (1988), Tuyen Quang (2008), Son La (2010), Ban Chat (2013), Huoi Quang (2015), and Lai Chau (2016)). By 2016, the annual sediment load and water discharges in the Red River system had decreased significantly, and were 9×106 ton/yr and 88,709×106 m3/yr, respectively. The data show that the discharge and sediment loads increased slightly from 2016–2021, perhaps reflecting the combined effects of human activities, such as land-use change, deforestation, and population increases. Climate may also have played a role in these increases, with changes in air temperature and increases in rainfall triggering severe soil erosion and large discharges of sediment into the Red River system.

The abundance of heat-trapping asphalt and concrete, smog, and heat emitted from buildings and vehicles is one of the major reasons for the prevailing high temperature, air and noise pollution in c...

Island tourism development is frequently associated with increased use of natural resources for constructing facilities that serve tourism activities. The existing island tourism tools have had limited success in ensuring sustainable island tourism development. Our knowledge of water capacity and monitoring of the algae dominated marine environment need to be expanded to ensure the sustainability. The paper uses data from Phu Quoc Island, Kien Giang, Vietnam to address these two above issues. The objective was gained through a combination of literature review, semi-structured interviews, and ecological sampling of marine algal species. The sustainability of tourism development in Phu Quoc is at risk due to inadequate focus on water resource management, poor wastewater treatment, and poor law enforcement. Inadequate water supply facilities cause water shortages, especially in the peak season, which resulted in uncontrolled groundwater extraction. Poor wastewater treatment and poor law enforcement create water quality problems in outflows causing degradation. Determination of water capacity should be prioritized and legally required as a compulsory element of sustainable island tourism development, and should guide the number of visitors and the types of tourism allowed at each site. Marine algal species should be accepted as a crucial indicator of the marine environment where algal species are dominant.

The paper aims to critically review the current management of mangrove forests allocated to local communities for protecting and using mangrove forests for livelihoods in the Mekong Delta of Vietna...

This study aims to investigate the diversity of mangrove species and their soil erosion mitigation performance in Hung Hoa Mangrove Forest, Vinh City, Vietnam. Under high rainfall climatic condition, the mangrove plants were found to reduce soil erosion due to storm runoff during dry season. The soil organic matter in the covered and uncovered part by species of the mangrove forest was 141.1 ± 37.6 g/kg and 95.2 ± 19.2 g/kg, respectively. The percentage of clay and silt in the mangrove forest, covered and uncovered by mangrove species were found to be 55.7 ± 2.4% and 45.5 ± 2.2%, respectively. The increase in distance from 10,045 to 14,378 m was correlated to the decrease in soil salinity from 5.9 ± 0.8 to 3.8 ± 0.5 ppt (r2 = 0.546; P

Melaleuca forests significantly contribute to economic development through silviculture and play an important role in carbon sequestration and supply of oxygen. Currently, Melaleuca seedlings are planted on bunds in inundated areas or on trenches in elevated areas. Little is known of what planting methods and growth stage of Melaleuca trees are best for developing new forest areas and sequestering highest levels of carbon. We selected U Minh Ha National Park in search for answers to the questions. We established 12 standard plots (10m x 10m) in the park where Melaleuca trees at two ages (10 years of age and 15 years of age) were planted on bunds and trenches. We employed Anova analysis, SPSS software and numerical analysis for analyzing and evaluating carbon sequestration by Melaleuca trees. We found that planting method significantly contributes to developing new forest areas in terms of tree volume, biomass, and carbon sequestration. Bund-based planting proves to be more cost-effective in developing new forest areas and carbon sequestration than trench-based planting. Trees at the age of 10 planted on bunds has been the most effective category for sequestering carbon. Our methodology in examining the relationship proves to be a feasible reference to new forest development and payment for forest service scheme in the Mekong Delta region or elsewhere in the broader region.

Mangrove-dominated muddy coasts have been allocated for developing livelihood models, particularly in developing countries. Uncontrolled allocation causes the mangrove forests to be vulnerable and even severely eroded. Restoration of vulnerable and eroded coastal areas has been merely conservation-driven, leaving livelihood-oriented mangrove forests unprotected. As a consequence, mangrove-dominated muddy coasts have not been well-protected. How livelihood-oriented mangrove forests are configured towards protecting coasts and protecting local livelihoods remains a challenge. This study employed a critical review for addressing this matter. The results reveal that there is limited practical knowledge of configuring livelihood-oriented models for protecting the coasts. The configuration process reported in this study is merely based on technical recommendations in South East Asia to date. The recommended configuration commences with the first stage of voluntarily designating a certain percentage of allocated forests on the seaward side to protect coasts, relocating livelihood models in the gaps among current stands of mangrove forests landward. Abandoned ponds are ecologically restored using sediment trapping structures for providing suitable substrate for promoting regrowth of local mangrove species as the second stage, followed by designation of an appropriate percentage as mangrove belts on the seaward side. The two-step configuration is highly likely to be replicable and applicable nationally and regionally due to full consideration of different political, sociocultural, and environmental characteristics in Vietnam and Indonesia.

Offshore breakwaters can be effective in reducing the energy of incident waves through dissipation, refraction or reflection. Breakwaters are increasingly constructed to stabilize eroded muddy coasts, particularly in developing countries. Accumulation of fine-grained sediment and wave attenuation are two attributes of a stable muddy coast. Effective interventions in stabilizing eroded muddy coasts include two important elements: accumulation of fine-grained sediment and wave reduction. The efficacy of offshore breakwaters in stabilizing eroded muddy coasts is, however, not yet adequately understood. A crucial question needing attention is whether accumulation of fine-grained sediment and wave attenuation should be used in evaluating the efficacy of these offshore breakwaters in stabilizing eroded muddy coasts. To address this issue, a pile-rock offshore breakwater in Huong Mai, Tieu Dua of Ca Mau, Vietnam was selected as an appropriate example in this regard. Accumulation of fine-grained sediment and wave attenuation were tested as means to investigate the efficacy of the Huong Mai structure in stabilizing the eroded muddy coast. The study was undertaken using field-based measurements and semi-structured interviews in three stages between October 2016 and December 2020. We found that this structure has had limited efficacy in stabilizing the eroded muddy coast. The structure was effective in dissipating the energy of incident waves, but we found no evidence of fine-grained sediment accumulation due to an inappropriate structural design. There was also no monitoring system in place, leading to difficulties in evaluating its efficacy in terms of wave attenuation and accumulation of fine-grained sediment. The gaps between the shoreline and the structure have not been adequately explained, resulting in substantial challenges in replicating the structure elsewhere. The Huong Mai structure should be strengthened using supplementary measures and granulometric tests in order to improve the efficacy in stabilizing eroded muddy coasts. The methods in this study provide new insights in this regard.

Ecological engineering (EE) was employed for developing strategies for stabilizing eroded muddy coasts (EMCs). However, there was a limited analysis of these EE strategies with respect to design, performance, and lessons learned. This study employed a critical review for addressing the limitations. There were four EE models designed with different restoration interventions for stabilizing EMCs. The models using active interventions have not been cost-effective in controlling erosion because the interventions failed to achieve their goals or were costly and unnecessary. Of the two passive intervention models, the one with structures constructed from onshore proved to be more cost-effective in terms of construction costs, the survival rate of transplanted seedlings, and levels of sea mud accumulation. Interventions with adequate consideration of the muddy coastal ecological processes and the ecological reasoning for the positioning of these interventions play a crucial role in stabilizing EMCs. A passive restoration model using gradually expanded interventions should be promoted in order to ensure sustainable management of EMCs in the future.