The present study aimed to investigate the occurrence and distribution of microcystin-(MC) and geosmin-producing cyanobacteria in the Tri An Reservoir, a drinking-water supply in Southern Vietnam. The MC concentration was measured using high-performance liquid chromatography (HPLC). Geosmin production was screened using headspace solid-phase microextraction (HPME) and gas chromatography/mass spectrometry (GC/ MS). The ability of cyanobacteria to produce MC and geosmin was determined by the presence of two molecular markers: mcyA and geoA, respectively. A maximum MC concentration of 207.6 ± 14.2 μg g –1 dry weight (DW) was detected from an isolated Microcystis aeruginosa (Kützing) (strains TAMA1), and the maximum geosmin concentration of 114.2 ± 6.1 ng g –1 wet weight (WW) was detected from an isolated Dolichospermum circinale (Rabenhorst) (strains TADC4); MC and geosmin were also observed in water-bloom samples, with the highest concentrations being 463.6 ± 34.7 μg g –1 DW and 148.5 ± 9.8 ng g –1 WW, respectively. These results represent the first molecular evidence of the co-occurrence of MC- and geosmin-producing cyanobacteria in a drinking-water-supply reservoir in Vietnam. Given the success of the molecular techniques and chemical analysis used, we propose that multiplex polymerase chain reaction assays, HPLC, and HPME GC/MS can be reliable tools for investigating MC and geosmin in water-bloom and cyanobacterial samples. Further, we propose that they can be used to create early-warning systems for harmful secondary metabolites produced by cyanobacteria in drinking-water supplies.

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In recent decades, mangroves have been seriously devastated by shrimp farming development in the Vietnamese Mekong Delta. As a result, integrated mangrove-shrimp farming has emerged as a potential solution to culture shrimps and protect mangroves. The present study aims to understand whether mangrove-to-pond cover ratios influence shrimp yields in an integrated mangrove-shrimp farming system. Five integrated mangrove-shrimp ponds in the Tam Giang Commune, Nam Can District, Ca Mau Province (Southern Vietnam) were chosen for this study. The study estimated that the mangrove-to-pond cover ratios ranged from 42.00 % to 72.50 %. The total shrimp yield per year (kg.ha-1 yr-1 ) was generally high, ranging from 76.62 to 249.09 (including 37.93 to 108.64 for the black tiger shrimp (Penaeus monodon Fabricius, 1798), and 38.69 to 140.45 for other shrimps, namely Penaeus indicus Milne Edwards, 1837, Penaeus merguiensis de Man, 1888, Metapenaeus ensis (De Haan, 1844), and Metapenaeus lysianassa (de Man, 1888)). Moreover, a strong positive correlation between the mangrove-to-pond cover ratios and the shrimp yields were observed (r > 0.71, P < 0.05). In conclusion the mangrove-to-pond cover ratios have a direct impact on the total shrimp yield. The mangrove-to-pond cover ratios should be 50 % to enhance shrimp yields in this system.

Water can make a substantial contribution to human life for drinking as well as purposes related to human life and human nature.  Because of increasing demand for water, there is a need for dam construction in preparation for agricultural purposes, drinking, industry and also flood control, power generation, etc. Simultaneously, they have had a considerable impact on the environment. A large range of potential impacts and hazards linked to the exploitation of dams and reservoirs, such as: (i) Major change in flow regime, thermal regime, physico-chemical cycles, (ii) reduction or loss of biological diversity, particular in aquatic species, (iii) greenhouse gas emissions, (iv) increases in the number of infectious disease and accumulation of heavy metals in food web...Therefore, there are various potential health risks of the environment and residents. However, whilst dam effects are very well documented elsewhere in the world, little or no information about negative effects of dams on the environment is available from Vietnam. Consequently, this paper provides a brief review of the environmental impact of dam constructions and after that, we will investigate some strategies to deal with the effects for Vietnam. By the way, we give some insight into ​​the first studies on the impacts of dams on the environment, which focuses on aquatic species was also noted in paper.

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Macrofauna communities in Ba Lai estuary, Ben Tre province were investigated in three transects from the river mouth to the dam construction, in the order from the right, middle to the left bank. The community characteristics such as the composition, density, biodiversity, and the distribution pattern were recorded and analyzed. The results showed that the macrofauna communities in the marine section part of Ba Lai river consisted of 76 species belonging to 3 phyla: Mollusca, Arthropoda, and Annelida. In this study, it was notable that a high economic value of Ben Tre Clam (Meretrix lyrata) presented in the Ba Lai estuary with a density of 3160 ind /m2 on the right bank. The highest density was recorded in the mid transect of the river, followed by the right and the left (2907 +/- 4298, 1813 +/- 2056; 1730 +/- 1590 ind /m2, respectively). The biodiversity of macrofauna communities was measured by the species richness, Shannon – Wiener index, and Pielou's evenness. Diversity indices illustrated that the middle bank had the highest biodiversity. However, the statistical analysis results showed that the density and biodiversity indices in these transects were not significantly different. The main reason might be due to Ba Lai dam impact, which has been accreting alluvial, causing these locations gradually being similar in the environmental conditions. The distribution pattern of benthic macrofauna communities in this study should be considered as a typical distribution of benthos in rivers affected by dams. Macrofauna communities which gave rapid responses to environmental changes should be used as a bioindicator.

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