Impacts of a saline water control project on aquaculture livelihoods in the Vietnamese Mekong Delta

PurposeDrought and salinity intrusion aggravated by climate change threaten agricultural livelihoods in Viet Nan's Mekong Delta. In response, authorities have built water management infrastructure for irrigation and salinity protection. This study assessed the impact of one such project, the Ba Lai dam in Ben Tre province, on the livelihoods of aquaculture farmers.Design/methodology/approachThis study uses the Sustainable Livelihoods Framework to assess the impact of the Ba Lai dam on the livelihood capitals of 18 farming households in four communes, located both upstream and downstream of the dam.FindingsThe authors find that, apart from some positive effects, the dam has also brought negative environmental consequences, such as increased water pollution. The authors also find that farmers have responded to the changes by adapting their livelihood practices.Research limitations/implicationsThe samples were relatively small, encompassing four communes in Ben Tre province. On the other hand, this case study is instructive to the many ongoing infrastructure projects in the Vietnamese Mekong Delta.Social implicationsThe project have caused an increase in water-related social conflict.Originality/valueThe case of the Ba Lai dam provides a cautionary example for infrastructure-based water management plans, both in Viet Nam and more broadly. The study suggests the need to strengthen community participation and prioritize impacts of farmers' capital assets when constructing water management infrastructure for climate change adaptation.

Removal of Arsenic in Groundwater Using Fe(III) Oxyhydroxide Coated Sand: A Case Study in Mekong Delta, Vietnam

Because of its threat to the quality of freshwater resources and human health, arsenic (As) pollution is important to scientific communities and policymakers around the world. The Mekong Delta, Vietnam, is one hotspot of As pollution. Its risk assessment of different environmental components has been well documented; however, very few studies focus on As removal techniques. Considering this information gap, this study aimed to investigate the performance of an innovative and low-cost treatment system using Fe(III)-oxyhydroxide (FeOOH) coated sand to remove As(III) from aqueous solution. Batch and column experiments were conducted at a laboratory scale in order to study removal kinetics and efficiency. Experimental results indicated that the adsorption isotherm of As(III) on FeOOH coated sand using Langmuir and Freundlich models have high regression factors of 0.987 and 0.991, respectively. The batch adsorption experiment revealed that contact time was approximately 8 h for rough saturation (kinetic test). The concentration of As(III) in effluents at flow rates of 0.6 L/h, 0.9 L/h, and 1.8 L/h ranged from 1.1 µg/L to 1.7 µg/L. Results from this study indicated that FeOOH coated sand columns were effective in removing As(III) from water, with a removal efficiency of 99.1%. Ultimately, FeOOH coated sand filtration could be a potential treatment system to reduce As(III) in the domestic water supply in remote areas of the Vietnamese Mekong Delta.

Spatiotemporal variations in length-weight relationship, growth pattern and condition factor of Periophthalmus variabilis Eggert, 1935 in Vietnamese Mekong Delta

Length-weight relationship (LWR), growth pattern and condition factor (CF) play a vital role in fish resource evaluation and management but data on this is limited for Periophthalmus variabilis. This is an amphibious fish that lives in the mudflats of the mangrove forests in the Western Pacific regions, including the Vietnamese Mekong Delta (VMD). This paper contributes to the understanding of the LWR, growth pattern and CF of P. variabilis. Fish specimens were collected by hand at four sites in the VMD from April 2020 to March 2021. The analysis of 495 individual fish (259 females and 236 males) showed that fish weight could be estimated from a given fish length due to high determination values (r2 = 0.70 − 0.97). Dusky-gilled mudskippers of the VMD exhibited positive allometry, as indicated by their larger than 3 b value (b = 3.094 ± 0.045, p = 0.04). However, the growth pattern of the mudskipper between the sex and maturation stage (immature versus mature) showed isometry. These fish displayed positive allometry in the dry season (b = 3.138 ± 0.065) (>3, p = 0.04) but isometry in the wet season (b = 3.058 ± 0.061) (≈3, p = 0.34). Fish growth ranged from isometry to positive allometry and varied by site (b = 2.850 ± 0.103–3.370 ± 0.114) and month (b = 2.668 ± 0.184–3.588 ± 0.299) based on the b value. The CF of P. variabilis was not affected by sex (p = 0.29), body size (p = 0.64) or season (p = 0.43), but was affected by site (p = 0.01) and month (p = 0.01). The CF of this species (1.05 ± 0.02) was higher than 1 (p < 0.001), indicating that the fish adapted well to their habitat.

Sedimentation strategies provide effective but limited mitigation of relative sea-level rise in the Mekong delta

The Mekong delta is experiencing rapid environmental change due to anthropogenic activities causing accelerated subsidence, sea-level rise and sediment starvation. Consequentially, the delta is rapidly losing elevation relative to sea level. Designating specific areas for sedimentation is a suggested strategy to encourage elevation-building with nature in deltas. We combined projections of extraction-induced subsidence, natural compaction and global sea-level rise with new projections of fluvial sediment delivery to evaluate the potential effectiveness of sedimentation strategies in the Mekong delta to 2050. Our results reveal that with current rates of subsidence and sediment starvation, fluvial sediments alone can only preserve elevation locally, even under optimistic assumptions, and organic sedimentation could potentially assume a larger role. While sedimentation strategies alone have limited effectiveness in the present context, combined with enhanced organic matter retention and interventions reducing anthropogenic-accelerated subsidence, they can considerably delay future relative sea-level rise, buying the delta crucial time to adapt.

Role of wind, mesoscale dynamics and coastal circulation in the interannual variability of South Vietnam Upwelling, South China Sea. Answers from a high resolution ocean model

The South Vietnam Upwelling (SVU) develops in the South China Sea off the Vietnamese coast under the influence of southwest monsoon winds. A very high resolution configuration (1 km at the coast) of the SYMPHONIE model was developed over the western coastal region of the South China Sea. A simulation was performed over the period 2009–2018 to study the functioning, variability and influence of oceanic circulation and hydrology in the coastal region, in particular of the SVU. The realism of the simulation in terms of representation of ocean dynamics and water masses, from daily to interannual and coastal to regional scales, is assessed here in detail by comparison with available satellite data and 4 sets of in-situ observations. The interannual variability of the SVU is examined for its 4 main development areas: the southern (SCU) and northern (NCU) coasts, the offshore area (OFU), and the Sunda Shelf area off the Mekong Delta (MKU). For the SCU and OFU, our results confirm the driving role of the summer mean wind and the summer circulation over the offshore area in the interannual variability of the upwelling intensity. They moreover reveal the impact of the spatial and temporal organization of mesoscale ocean structures and high frequency atmospheric forcing. For the NCU, the upwelling interannual variability does not seem to be related to regional scale forcing and dynamics, but is mainly determined by coastal mesoscale structures and circulation: similar summer wind conditions can be associated with very contrasting NCU intensities, and vice versa, depending on the circulation in the NCU area. Finally, our study reveals that upwelling also develops off the Mekong Delta, with an interannual variability mostly determined by the summer wind and the wind-driven circulation over the SVU region.

Decomposition of rice straw residues and the emission of CO2, CH4 under paddy rice and crop rotation in the Vietnamese Mekong Delta region – A microcosm study

This study investigated the influence of soil undergoing different crop rotations on the CH₄, CO₂ emissions, and decomposition of rice straw. The studied soil undergoing crop rotation systems were rice-rice-rice (SR) and baby corn-rice-mungbean (SB). Two main microcosm set-ups: anaerobic (SR-AN, SB-AN) and aerobic (SR-AE, SB-AE) conditions. Litter bags containing rice stems were inserted into the soil and recollected at different time points for chemical analysing and the gas sampling was collected to measure the CO₂ and CH₄ emissions. The results indicated that the total carbon (TC) decreased around 30%, and the TC removal in anaerobic was significantly higher than in aerobic conditions. The residue cellulose content varied in a range from 68.2% to 78.6%, while the hemicellulose content varied from 57.4% to 69.3% at day 50 after incorporation. There were no significant differences in the total nitrogen removal, cellulose, hemicellulose, and lignin contents among the microcosm set-ups. CO₂ emission increased in all the microcosm set-ups with the treatments without rice straw (CTSR, CTSB) in both aerobic and anaerobic conditions. CH₄ release in the SR-AN treatments did not differ significantly compared with the SB-AN treatments. This study confirmed that the decomposition of rice straw residues is faster in the anaerobic paddy soil condition compared to the aerobic crop rotation condition.