Nutrient ratios and the complex structure of phytoplankton communities in a highly turbid estuary of Southeast Asia

Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system.     

Study of the Climate Change Impacts on Water Quality in the Upstream Portion of the Cau River Basin,Vietnam

This paper presents simulations of climate change impacts on water quality in the upstream portion of the Cau River Basin in the North of Vietnam. The integrated modeling system GIBSI was used to simulate hydrological processes, pollutant and sediment wash-off in the river basin, and pollutant transport and transformation in the river network. Three projections for climate change based on emission scenarios B1, B2, and A2 of IPCC Special Report on Emission Scenarios (SRES) were considered. By assuming that the input pollution sources and watershed configuration were constant, based on 2008 data, water quality in the river network was simulated up to the terminal year 2050. For each climate change scenario, patterns of precipitation in wet and dry year were considered. The change in annual and monthly trends for dissolved oxygen (DO), biochemical oxygen demand (BOD), and ammonium ions (NH4+) load and concentration for different portions of the watershed have been analyzed. The results of these simulations show that climate change has more impact on changing the seasonal water quality parameters than on altering the average annual load of the pollutants. The percent change and change pattern in water quality parameters are different for wet and dry year, and the changes in wet year are smaller than those in dry year.     

Spatial Variations in Fish Abundance in the Mekong Delta

Russian Journal of Ecology - For the first time, the density of fish population has been quantitatively assessed in the Mekong River delta in the territory of the Socialist Republic of Vietnam. The...     

Human ecological effects of tropical storms in the coastal area of Ky Anh (Ha Tinh,Vietnam)

Vietnam is prone to tropical storms. Climate change effects contribute to sea level rise, floods, progression of the low water line and coastal erosion. This paper inventories the perception of local people, assesses and values main aspects of the livelihood damage caused by the tropical storms of the period 2008–2013 in three coastal communes of the Ky Anh District of the Ha Tinh Province in Central Vietnam. The communes were selected because the location of their coastal line is perpendicular to the storm itself, which made them prone to damage. The effects of increasingly extreme weather conditions on three communities in an area most affected by storms and floods on the local residents and their responses to these changing environmental conditions are analyzed and assessed. The results of questionnaires completed by randomly selected local inhabitants of these communes show that storms and related hazards such as flood, sea level rise and heavy rain are perceived as the most impacting climate change intensified phenomena on agriculture and aquaculture, livestock, household property and income. Opinions and measured data provided by the commune and district authorities allow estimating the total direct cost of the tropical storm at 1.56 million $US (The used conversion rate VND/$US is 21,730 when the research was conducted in 2014) during the period 2008–2013. The long-term costs of adaptation and social impact measures will be significantly higher. Details of the monetary figures allow identifying the physical and natural capital of the area as being most affected by the storm. Trend and cost analysis show that the total financial support for hazard prevention and management during 2014–2019 is estimated at 1.19 up to 1.32 million $US. Local stakeholders indicate that climate change adaptation should not be limited to technical measures such as strengthening dikes, but also should target planting protection forests and mangroves and land use planning. Financial support for the relocation policy, stakeholder involvement and integrating climate change adaptation in both the socioeconomic development master plan and local land use planning are also of importance.     

Impact of metal stress on the production of secondary metabolites in <Emphasis Type="Italic">Pteris vittata</Emphasis> L. and associated rhizosphere bacterial communities

Plants adapt to metal stress by modifying their metabolism including the production of secondary metabolites in plant tissues. Such changes may impact the diversity and functions of plant associated microbial communities. Our study aimed to evaluate the influence of metals on the secondary metabolism of plants and the indirect impact on rhizosphere bacterial communities. We then compared the secondary metabolites of the hyperaccumulator Pteris vittata L. collected from a contaminated mining site to a non-contaminated site in Vietnam and identified the discriminant metabolites. Our data showed a significant increase in chlorogenic acid derivatives and A-type procyanidin in plant roots at the contaminated site. We hypothesized that the intensive production of these compounds could be part of the antioxidant defense mechanism in response to metals. In parallel, the structure and diversity of bulk soil and rhizosphere communities was studied using high-throughput sequencing. The results showed strong differences in bacterial composition, characterized by the dominance of Proteobacteria and Nitrospira in the contaminated bulk soil, and the enrichment of some potential human pathogens, i.e., Acinetobacter, Mycobacterium, and Cupriavidus in P. vittata’s rhizosphere at the mining site. Overall, metal pollution modified the production of P. vittata secondary metabolites and altered the diversity and structure of bacterial communities. Further investigations are needed to understand whether the plant recruits specific bacteria to adapt to metal stress.     

Combined effects of deltamethrin, temperature and salinity on oxidative stress biomarkers and acetylcholinesterase activity in the black tiger shrimp (Penaeus monodon)

This study aimed to investigate the interactions of two abiotic factors (temperature and salinity) and deltamethrin (pyrethroid pesticide) exposure on some oxidative stress biomarkers as well as on acetylcholinesterase activity (AChE) in hepatopancreas, gills and muscle of black tiger shrimp (Penaeus monodon). A combination of three temperatures (24, 29 and 34 °C), two salinities (15 and 25 ppt), and the absence or presence of 0.1 μg L⁻¹ deltamethrin was applied on shrimp during 4 d under laboratory conditions. Lipid peroxidation level (LPO) and glutathione S-transferase activity (GST) were not affected by combined effect of temperature, salinity and deltamethrin in any of the studied tissues. Deltamethrin impaired other tested oxidative stress biomarkers, i.e. total glutathione (tGSH), catalase (CAT), glutathione peroxidase (GPx). tGSH level significantly increased in hepatopancreas due to deltamethrin exposure mainly at 34 °C, while pesticide effects on tGSH and CAT activity in gills were influenced by both temperature and salinity. In addition, GPx activity in hepatopancreas decreased after deltamethrin treatment mainly at 24 °C. Finally, AChE in muscle was strongly inhibited by deltamethrin at all tested temperatures and salinities. These novel findings demonstrate that interactions between abiotic factors and a commonly used pesticide exposure should be taken into account when analyzing some widespread biomarkers in black tiger shrimp.     

Exposure assessment of lead to workers and children in the battery recycling craft village,Dong Mai,Vietnam

Human exposure to lead (Pb) due to uncontrolled Pb-acid battery recycling has been an environmental health issue in newly developed industrial regions. We conducted a human monitoring survey in Dong Mai, a battery recycling village in Vietnam, to assess exposure status to Pb. Lead level was measured in hair, blood and urine samples of residents in Dong Mai and two reference sites during 4 years spanning 2007–2011. In Dong Mai, Pb levels in three matrixes were significantly higher than those in reference sites. Blood Pb levels of all adults and children exceeded 10 μg/dL, the Centers for Disease Control and Prevention definition of an elevated blood Pb level. Clear increase of urinary δ-aminolevulinic acid (ALA) level with increasing blood Pb level indicated disruption of heme synthesis. One adult exceeded 100 μg/dL of blood Pb, where encephalopathy is of concern. The blood Pb levels achieved various toxic effect threshold values, and elevated blood Pb was not limited to recycling workers, but was also in children and women of reproductive age. Serious pollution status of Dong Mai village suggests an importance of further monitoring surveys in various developing Asian countries.     

Photochemical Smog Modeling for Assessment of Potential Impacts of Different Management Strategies on Air Quality of the Bangkok Metropolitan Region,Thailand

Abstract

A photochemical smog model system, the Variable-Grid Urban Airshed Model/Systems Applications International Mesoscale Model (UAM-V/SAIMM), was used to investigate photochemical pollution in the Bangkok Metropolitan Region (BMR). The model system was first applied to simulate a historical photochemical smog episode of two days (January 13-14, 1997) using the 1997 anthropogenic emission database available at the Pollution Control Department and an estimated biogenic emission. The output 1-hr ozone (O₃) for BMR, however, did not meet the U.S. Environmental Protection Agency suggested performance criteria. The simulated minimum and maximum O₃ values in the domain were much higher than the observations. Multiple model runs with different precursor emission reduction scenarios showed that the best model performance with the simulated 1-hr O₃ meeting all the criteria was obtained when the volatile organic compound (VOC) and oxides of nitrogen (NO_x) emission from mobile source reduced by 50% and carbon monoxide by 20% from the original database. Various combinations of anthropogenic and biogenic emissions in Bangkok and surrounding provinces were simulated to assess the contribution of different sources to O₃ pollution in the city. O₃ formation in Bangkok was found to be more VOC-sensitive than NO_x-sensitive. To attain the Thailand ambient air quality standard for 1-hr O₃ of 100 ppb, VOC emission in BMR should be reduced by 50-60%. Management strategies considered in the scenario study consist of Stage I, Stage II vapor control, replacement of two-stroke by four-stroke motorcycles, 100% compressed natural gas bus, 100% natural gas-fired power plants, and replacement of methyltertiarybutylether by ethanol as an additive for gasoline.     

Residual congener pattern of dioxins in human breast milk in southern Vietnam

This study evaluated residual congener patterns of dioxin/furan (=PCDD/DF) related to tactical herbicides aerially sprayed over the regions of southern Vietnam through Operation Ranch Hand. The study focused on Cam Chinh (CC) commune, Quang Tri province (an area sprayed with tactical herbicides), and the Cam Phuc (CP) commune, Ha Tinh province (a non-sprayed area). Breast milk samples for analysis were collected in September 2002 and July 2003 from lactating primiparous and multiparous mothers born after the war (<31 years old). We found the levels of each congener in the CC commune were higher than in the CP commune, and determined specificity in the PCDD/DF congener pattern in CC commune samples by cluster analysis. The congener pattern is characterized by higher (the hexa-, the hepta-, and the octa-) chlorinated PCDD/DFs; this appears to be the same profile as that presented by pentachlorophenol (PCP), rather than 2,4,5-trichlorophenoxy acid (2,4,5-T) contaminated with 2,3,7,8-TCDD. A GC/MS study in the 1970s detected the chlorophenols 2,4-di and 2,4,6-trichlorophenol in some Agent Orange samples, which contained, like PCP, a wide variety of PCDD/DF congeners. In this context, it may be expected that certain tactical herbicides contaminated with various chlorophenol impurities, have a unique congener pattern when compared with pure 2,4,5-T formulations.     

Activated carbon/Fe(3)O(4) nanoparticle composite: fabrication, methyl orange removal and regeneration by hydrogen peroxide

In the water treatment field, activated carbons (ACs) have wide applications in adsorptions. However, the applications are limited by difficulties encountered in separation and regeneration processes. Here, activated carbon/Fe₃O₄ nanoparticle composites, which combine the adsorption features of powdered activated carbon (PAC) with the magnetic and excellent catalytic properties of Fe₃O₄ nanoparticles, were fabricated by a modified impregnation method using HNO₃ as the carbon modifying agent. The obtained composites were characterized by X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption isotherms and vibrating sample magnetometer. Their performance for methyl orange (MO) removal by adsorption was evaluated. The regeneration of the composite and PAC-HNO₃ (powdered activated carbon modified by HNO₃) adsorbed MO by hydrogen peroxide was investigated. The composites had a high specific surface area and porosity and a superparamagnetic property that shows they can be manipulated by an external magnetic field. Adsorption experiments showed that the MO sorption process on the composites followed pseudo-second order kinetic model and the adsorption isotherm date could be simulated with both the Freundlich and Langmuir models. The regeneration indicated that the presence of the Fe₃O₄ nanoparticles is important for a achieving high regeneration efficiency by hydrogen peroxide.