Saigon River Research Articles

Saigon River Valley: A Navigation, Trade, Mitigation, Invasion, Liberation, and Unification Pathway

The Saigon River is located in southern Vietnam with headwaters starting in southeastern Cambodia. The river flows southeast for about 225 km to the South China Sea. Most readers of Vietnam’s history know about the American-Vietnam War (1965-1973). However, centuries before that time, Vietnam fought with the Chinese, the Khmers, the Chams and the Mongols. The history of Vietnam begins in the Red River Delta, where farmers first cultivated rice. A millenia of struggle against the Chinese then followed. The Saigon River Valley was the pathway used by the North Vietnamese Army (NVA) to get from the Ho Chi Minh Trail in Cambodia to Saigon during the 1968 Tet Offensive. The NVA dug Cu Chi and Iron Triangle soil tunnels near Cu Chi in the Old Alluvium terrace to hide from American Forces and Air Force bombers. In 1962, the Tan Son Nhut Air Force base on the northern edge of Saigon received the first shipments of Agent Blue, the arsenic based herbicide, used to destroy the rice crop. The most dioxin TCDD and arsenic contaminated site in Vietnam was Bien Hoa Air Force base on the Saigon River just 30 km northeast east of Ho Chi Minh City. The adjacent Bien Hoa City has a population of over 800,000. The Port of Ho Chi Minh City is the most significant river port in Vietnam and Southeast Asia. The river is navigable by ships which draft up to 9 m. Vietnam only became a united country in the 19th century. Its independence was soon affected by French colonialism and then the destructive American intervention in the Vietnam War. The Vietnam War Archive no. 2 in Ho Chi Minh City houses residual correspondence between the Republic of Vietnam (RV) President Diem’s administration and US President Kennedy’s administration related to the Khai Huang program (hamlet strategy). In addition, the archive contains some of the tactical herbicide spray records of the RV military for the Mekong Delta. The primary objective this study is to document the role that the Saigon River Valley played, in modern warfare. The Saigon River Valley was used as a navigation, trade, invasion, liberation and unification pathway. The Vietnamese people have survived centuries of stormy, troubled times and their power of character has served them well.

Influence Of Flood Control Facilities On The Water Level In The Downstream Of The River System Sai Gon - Dong Nai

Ho Chi Minh City, Vietnam’s largest city, located on the lower reaches of the Sai Gon-Dong Nai (SG-DN) river system, is facing increasingly severe flooding due to changes in river flow and water levels. This article presents the results of a study to assess the impact of hydraulic structures located in the upper reaches on the water level in the lower reaches of the SG-DN River. As part of a study to assess the impact of upstream reservoirs and flood control structures on the water level in the lower reaches of the SG-DN River, hydrological data of the river network were collected and a hydraulic model was developed based on a digital elevation model (DEM) using the software package Mike 11, Mike 21 and Mike Flood. The water level of the Sai Gon River from the upper reaches to the Thu Dau Mot measuring station directly depends on the Dau Tieng reservoir, and the Tri An reservoir directly affects the water level in the river section from behind the Tri An dam to the Dong Nai section in the Tam An - Long Phuoc area. In the sections of the Sai Gon and Dong Nai rivers, which are less affected by the two overlying reservoirs, it is necessary to develop preventive measures to supply sufficient fresh water to meet the needs of the population and industries. In areas prone to flooding and underflooding as a result of the operation of anti-flood locks, it is also necessary to reconstruct hydraulic structures (raise the elevations of foundations, expand drainage systems, build reservoirs for collecting flood water etc.)

Influence of flood control facilities on water level in downstream of river system Sai Gon -Dong Nai

Ho Chi Minh City, Vietnam's largest city, located on the lower reaches of the Sai Gon-Dong Nai (SG-DN) river system, is facing increasingly severe flooding due to changes in river flow and water levels. This article presents the results of a study to assess the impact of hydraulic structures located in the upper reaches on the water level in the lower reaches of the SG-DN River. As part of a study to assess the impact of upstream reservoirs and flood control structures on the water level in the lower reaches of the SG-DN River, hydrological data of the river network were collected. A hydraulic model was developed based on a digital elevation model (DEM) using the software package Mike 11, Mike 21 and Mike Flood. The water level of the Sai Gon River from the upper reaches to the Thu Dau Mot measuring station depends on the Dau Tieng reservoir, and the Tri An reservoir directly affects the water level in the river section from behind the Tri An dam to the Dong Nai section in the Tam An - Long Phuoc area. In the sections of the Sai Gon and Dong Nai rivers, which are less affected by the two overlying reservoirs, it is necessary to develop preventive measures to supply sufficient fresh water to meet the population's and industries' needs. In areas prone to flooding and underflooding due to the operation of anti-flood locks, it is also necessary to reconstruct hydraulic structures (raise the elevations of foundations, expand drainage systems, build reservoirs for collecting flood water, etc.)

Typical pathogens on plastic debris in downstream of Sai Gon and Dong Nai rivers: an initial observation

Plastic pollution is recently receiving significant attention. In aquatic ecosystem, plastic debris can provide a habitat for microbial communities, including pathogens which might cause ad-verse impacts on aquatic animals and human health. This study, for the first time, investigated densities of typical pathogens of Coliforms and Vibrio spp. associated on plastic samples col-lected in surface water (SW), water column (WC, 5 m below surface water), and sediment (SED) at downstreams of Sai Gon river (Phu My bridge site) and Dong Nai river (Binh Khanh habour site) in the dry season of 2022. The results showed that densities of pathogens associat-ed on SW plastics were significantly higher than densities of pathogens associated on WC and SED plastics. For instance, (i) densities of Coliform on SW plastics (9.7 ± 0.1 × 106 and 180.0 ± 10.0 × 106 CFU/g plastic) were significantly higher than the ones on WC plastics (3.1 ± 0.5 × 106 and 5.5 ± 1.2 × 106 CFU/g plastic), and the ones on SED plastics (1.7 ± 0.3 × 106 and 5.7 ± 0.7 × 106 CFU/g plastic); and similarly (ii) densities of Vibrio spp. on SW plastics (4.2 ± 0.1 × 104 and 1.3 ± 0.2 × 105 CFU/g plastic) were significantly higher than the ones on WC plastics of 0.0 ± 0.0 and 7.7 ± 0.4 × 103 CFU/g plastic, and the ones on SED plastics of 2.0 ± 0.2 × 104 and 4.4 ± 0.0 × 104 CFU/g plastic, in Phu My and Binh Khanh, respectively. Other hand, densi-ties of pathogens on plastic samples colleceted in Phu My were significally lower than in the ones collected in Binh Khanh. These findings proposed that pathogen contamination on the plastic debris in downstream area is likely heavier than in upstream area of Sai Gon and Dong Nai rivers.

Characteristics of Microplastics and Their Affiliated PAHs in Surface Water in Ho Chi Minh City, Vietnam.

Microplastic pollution has become a worldwide concern. However, studies on the distribution of microplastics (MPs) from inland water to the ocean and their affiliated polycyclic aromatic hydrocarbons (PAHs) are still limited in Vietnam. In this study, we investigated the distribution of MPs and PAHs associated with MPs in canals, Saigon River, and Can Gio Sea. MPs were found at all sites, with the highest average abundance of MPs being 104.17 ± 162.44 pieces/m3 in canals, followed by 2.08 ± 2.22 pieces/m3 in the sea, and 0.60 ± 0.38 pieces/m3 in the river. Fragment, fiber, and granule were three common shapes, and each shape was dominant in one sampling area. White was the most common MP color at all sites. A total of 13 polymers and co-polymers were confirmed, and polyethylene, polypropylene, and ethylene-vinyl acetate were the three dominant polymers. The total concentration of MPs-affiliated PAHs ranged from 232.71 to 6448.66, from 30.94 to 8940.99, and from 432.95 to 3267.88 ng/g in Can Gio sea, canals, and Saigon River, respectively. Petrogenic sources were suggested as a major source of PAHs associated with MPs in Can Gio Sea, whereas those found in Saigon River and canals were from both petrogenic and pyrogenic sources.

Rivers running green: water hyacinth invasion monitored from space

Water hyacinth is an aquatic free-floating plant that is highly invasive, to the extent that it is now present in most freshwater bodies in sub-tropical and tropical regions worldwide. Due to the ecological and socio-economic damages these plants can cause, monitoring their spatial coverage and seasonality is key for development of timely and efficient mitigation measures. Hyacinth patches are sufficiently large to be detectable in high-resolution satellite imagery, allowing for monitoring using freely available remote sensing data collected by platforms such as Sentinel-2. In this study, we estimated water hyacinth coverage and seasonal dynamics over three years (2018–2020) for the Saigon river, Vietnam. Using a Naïve Bayes classifier, hyacinth coverage was mapped in Sentinel-2 imagery with an accuracy of 91%. We show that the dry season (December-May) corresponds to highest water hyacinth abundance, with maximum coverage in February. Lower rainfall and relative humidity were found to be highly correlated (r = −0.56 and r = −0.64, respectively) with higher hyacinth cover. We also detected substantial interannual variability: annual means in hyacinth coverage varied by a factor of five between the 2018/2019 and 2020 yearly averages, with peak cover occurring in February 2020. The percentage of Saigon river covered by hyacinths over the entire study area peaked at 14% and reached as much as 24% for the upstream section. This confirms the prevalence of these invasive plants in the region, and the growing threat to river navigability and biodiversity. Our study provides an openly available automated workflow for long-term monitoring of hyacinth coverage, which can be scaled-up and extended to other freshwater systems. As such, it provides a step for building a large-scale monitoring tool of this highly invasive species, which may also be used for designing mitigation and reduction strategies of hyacinth and the pollutants it carries along.

Microplastics pollution in selected rivers from Southeast Asia

Microplastics have been found in all hemispheres of the world. However, studies on microplastics are mainly conducted in Europe, North America, and East Asia. Few studies are reported in the Southeast Asian region, where a large number of plastic waste is disposed of improperly into the water. This study investigated the abundance and characteristics of microplastics in the surface water of the Chao Phraya River (Thailand), Citarum River (Indonesia), and Saigon River (Vietnam). Samples were collected at urban and estuary zones of these rivers. The numbers of microplastics at the urban zones were 80±60, 12±6, and 68±20 items/m3 at the Chao Phraya, Citarum, and Saigon River, respectively. At the estuary zones, the numbers of microplastics were 48±8, 0±0 (0.08±0), and 42±5 items/m3 at the Chao Phraya, Citarum, and Saigon River, respectively. Microplastics with morphologies of fragments and fibres were mainly found in the rivers. Polypropylene and polyethylene particles were the most abundant in all collected samples. Since the selected rivers play important roles in water supply and aquaculture activities, the presence of microplastics in these rivers may negatively impact aquaculture and human health. Potential plastic management strategies to minimize microplastic problems in the selected rivers were also proposed in this study.

Does eutrophication enhance greenhouse gas emissions in urbanized tropical estuaries?

Estuaries are considered as important sources of the global emission of greenhouse gases (GHGs). Urbanized estuaries often experience eutrophication under strong anthropogenic activities. Eutrophication can enhance phytoplankton abundance, leading to carbon dioxide (CO2) consumption in the water column. Only a few studies have evaluated the relationship between GHGs and eutrophication in estuaries. In this study, we assessed the concentrations and fluxes of CO2, methane (CH4) and nitrous oxide (N2O) in combination with a suite of biogeochemical variables in four sampling campaigns over two years in a highly urbanized tropical estuary in Southeast Asia (the Saigon River Estuary, Vietnam). The impact of eutrophication on GHGs was evaluated through several statistical methods and interpreted by biological processes. The average concentrations of CO2, CH4 and N2O at the Saigon River in 2019–2020 were 3174 ± 1725 μgC-CO2 L−1, 5.9 ± 16.8 μgC-CH4 L−1 and 3.0 ± 4.8 μgN-N2O L−1, respectively. Their concentrations were 13–18 times, 52–332 times, and 9–37 times higher than the global mean concentrations of GHGs, respectively. While CO2 concentration had no clear seasonal pattern, N2O and CH4 concentrations significantly differed between the dry and the rainy seasons. The increase in eutrophication status along the dense urban area was linearly correlated with the increase in GHGs concentrations. The presence of both nitrification and denitrification resulted in elevated N2O concentrations in this urban area of the estuary. The high concentration of CO2 was contributed by the high concentration of organic carbon and mineralization process. GHGs fluxes at the Saigon River Estuary were comparable to other urbanized estuaries regardless of climatic condition. Control of eutrophication in urbanized estuaries through the implantation of efficient wastewater treatment facilities will be an effective solution in mitigating the global warming potential caused by estuarine emissions.

ANTIMICROBIALS IN ANIMAL FAECES (CHICKEN, COW AND SWINE) FROM THE BREEDING FARMS IN THE UPSTREAM OF SAI GON RIVER

The widespread use of antimicrobials in husbandry has increased antimicrobial residues in animal faeces. Therefore, the investigation of antimicrobials in animal faeces is essential because they are the main cause of environmental pollution. This study analyzed and assessed samples of chiken, cow and swine faeces for seven antimicrobials, namely trimethoprim (TRI), ormethoprim (ORM), ofloxacin (OFL), norfloxacin (NOR), tetracycline (TET), chlortetracycline (CTE) and tylosin (TLS). Samples were taken from faeces heaps at breeding farms in the upstream of the Sai Gon river. The samples were analyzed in the laboratory by using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine antimicrobials. TRI, with the highest mean concentration, was found in all fecal samples (10,399 - 47,987 mg/kg) while ORM with the lowest average concentration was only detected in chicken fecal samples (542 mg/kg). CTE, with the second high mean concentration, was also found in all fecal samples (1,085 - 12,385 mg/kg), whereas TET was only detected in chicken fecal samples (9,050 mg/kg). OFL with the third average concentration, was aloso found in all fecal samples (1,516 - 9280 mg/kg), while NOR was detected in cow fecal samples at a low mean concentration (2,479 mg/kg). TLS was only found in chicken and cow fecal samples (798 - 5,802 mg/kg). These numbers show a very large amount of consumption of antimicrobials in livestock production. The results from this study are likely to encourage further monitoring of antimicrobials used in livestock production, and promote discussion of existing policies regarding the inclusion of antimicrobials in animal feed rations and veterinary medicines.

Influences of anthropogenic activities on water quality in the Saigon River, Ho Chi Minh City.

Water quality for the surface water along the Saigon River in Ho Chi Minh City was assessed for four groups of water samples collected at the agricultural, industrial, residential, and less impacted areas. A variety of parameters indicating water quality including physicochemical parameters, nutrients, heavy metals, and antibiotic residues were measured for both the rainy and dry seasons, two main tropical seasons in HCM City using the standard methods. The results showed that the river water in the rainy season was detected with significantly higher values of turbidity, BOD5, PO4-P, NH4-N, NO3-N; and lower values of pH, temperature, conductivity, DO, salinity, Cu, Zn, As, Ni, Hg compared to that in the dry season. Sulfamethoxazole and trimethoprim were highly detected in the industrial areas compared to the agricultural and residential areas. Multivariate analyses suggested that the industrial and residential activities were more important contributors to the pollution of the Saigon River than the agricultural activities in HCM City.

Statistical and Hydrological Evaluations of Water Dynamics in the Lower Sai Gon-Dong Nai River, Vietnam

The water levels downstream of the Sai Gon and Dong Nai river in Southern Vietnam have been significantly changed over the last three decades, leading to severe impacts on urban flooding and salinity intrusion and threating the socio-economic development of the region and lives of many local people. In this study, the Mann-Kendall (MK) and trend-free prewhitening (TFPW) tests were applied to detect the water level trends and changepoints based on a water level time series at six gauging stations that were located along the main rivers to the sea over 1980–2019. The results indicated that the water level has rapidly increased by about 0.17 to 1.8 cm/year at most gauge stations surrounding Ho Chi Minh City, strongly relating to urbanization and the dike polder system’s impacts that eliminates the water storage space. In addition, the operation of upstream reservoirs has contributed to water level changes with significant consequences since the high-water level at Tri An station on the Dong Nai river occurs 1000–1500 times compared to 300–500 times before the operation. Although the effects of the flows from the sea are less than the two other factors, the local government should seriously consider water level changes, especially in the coastal regions. Our study contributes empirical evidence to evaluate the water level trends in the planning and development of infrastructure, which is necessary to adapt to future changes in Southern Vietnam’s hydrologic system.

Assessment of water quality changes in Saigon and Dong Nai rivers under the influence of domestic wastewater discharges

The study was conducted to evaluate the impact of domestic wastewater discharges on surface water quality (BOD5 and DO) at pumping stations on Sai Gon – Dong Nai river during the dry season and the wet season using the MIKE 21FM model. The results indicated that the water quality in Dong Nai river is rated better than the Sai Gon River. Specifically, the BOD5 concentration was high, and the DO concentration was low at Hoa Phu station in Sai Gon River. However, the surface water quality at pumping stations on Dong Nai river, namely Hoa An and Binh An was up to standard compared to column A2 for domestic water supply purposes according to QCVN 08- MT:2015/BTNMT. Specifically, the wastewater source from Thu Dau Mot city on the Sai Gon river was about 4 km from Hoa Phu pumping station with a discharge volume of 0,66 m3/s, and another source from Bien Hoa city on the Dong Nai river reached a discharge volume of 2,15 m3/s, which was about 4.7 km and 5.5 km from Hoa An and Binh An intakes, respectively. The outcomes proved that Hoa Phu and Hoa An pumping stations were not affected by the wastewater from these cities. Otherwise, there was markedly degraded water quality at Binh An intake in the dry season, which was unsatisfied with QCVN 08- MT:2015/BTNMT (A2 type).

Using the magnetotelluric method to study the deep structure of the Sai Gon river fault in the vicinity of Ho Chi Minh City

This paper presented the study of the two magnetotelluric profiles crossing the Saigon river fault. The first one was 13.5 km long consisting in 8 stations extending from Cu Chi district, Ho Chi Minh city to Ben Cat district, Binh Duong province, and the second was 11.7 km long including 7 stations in Nhon Trach district, Dong Nai province, Vietnam. The data were recorded in the period range 0.002‒259 s using the GEPARD-4 instrument. Because of the influence of the equatorial electrojet (EEJ) on magnetotelluric soundings in this region, only data in the period range shorter than about 1 s for the analysis were used. The resistivity data of both TE and TM modes were used for inversion using the MT2DinvMatlab software. Firstly, data were inverted down to a depth of 10 km to obtain the main electric features of the region. The results showed that on both profiles, the resistivity cross-sections showed a 3-layer geoelectric structure in which the top low resistivity layer had a thickness of about 2 km, the resistive intermediate layer was about 6‒7 km thick, and the underlying low resistivity layer. On these cross-sections, the Saigon river fault could not be observed. Then data were inverted down to 3 km to obtain more detailed information to determine the location and dip direction of the Saigon river fault. The geoelectric cross-sections of 3 km depth showed that for the Cu Chi‒Ben Cat profile, the Saigon river fault corresponded to the low resistivity region below the stations CB5 and CB6, and for the Nhon Trach profile, the river fault Saigon would be related to the low resistivity region below the stations NT3 and NT4. The obtained results confirmed the existence of the Saigon river fault, with the location and its continuous extension from the Cu Chi‒Ben Cat area, through Thu Duc city to Nhon Trach district of Đồng Nai province.

Anthropogenic fibres in white clams, Meretrix lyrata, cultivated downstream a developing megacity, Ho Chi Minh City, Viet Nam

Anthropogenic fibres are an emerging pollutant worldwide. The Can Gio mangrove area is located downstream of the Saigon River, and is characterised by high level of anthropogenic fibres originating from domestic and industrial textile and apparel manufacturing. In this area, biota is thus subjected to a high potential risk of anthropogenic fibre contamination. This study aims to characterise the accumulation of anthropogenic fibres in different tissues, i.e. gills, digestive systems, and remaining tissues, of white clams (Meretrix lyrata) cultivated in the Can Gio beach sand, during a seven-month sampling period. The results showed an average concentration of 3.6 ± 2.1 fibres individual−1 or 2.7 ± 2.4 fibres g−1 ww. Higher fibre accumulation was observed in remaining tissues than in gills and digestive systems, and no temporal variation was observed in all clam tissues. The intake of fibres by humans consuming clams was estimated to be 324 fibres inhabitant−1 yr−1.

Assessment of sewage sludge management at Thu Dau Mot wastewater treatment enterprise

Binh Duong province has built and put into operation 29 industrial zones and 10 industrial clusters, contributing to the strong socio-economic development and accompanied by environmental concerns, especially management, waste treatment in general and waste from drainage systems and sanitation works in particular. Thu Dau Mot wastewater treatment enterprise was built including works such as: inlet works, ASBR tank, and disinfection house, sludge concentration tank, sludge extractor, house deodorizing, and so on. The quality of water after treatment meets QCVN 14: 2008 / BTNMT standards (column A), contributing to the protection of Saigon river water sources, ensuring the aesthetics and environmental sanitation of Thu Dau Mot city area. The factory was installed ASBR circulating activated sludge treatment technology, limiting odor generation, not affecting the surrounding environment, increasing 30% of design capacity compared to traditional SBR tanks of the same volume, easy to operate, low operating costs and saving power. The most common non-toxic organic compounds include materials of plant and animal origin such as proteins, amino acids, sugars, fats; compounds containing N, P. Toxic organic compounds include compounds of alkyl phenols, chloro-benzenes. Metals such as: Zn, Pb, Cu, Cd, Ni, Cr, Hg, As. Some of these compounds can be toxic to humans and animals. Harmful microorganisms such as pathogenic bacteria, viruses together with parasitic helminthes can increase the potential harm to human, animal and plant health. Inorganic compounds such as silicates, aluminates, and magnesium compounds. After being treated, the sludge will be collected and transported to South Binh Duong Waste Treatment Enterprise to produce construction materials and make compost.

Prevalence of Antibiotic Resistance Genes in the Saigon River Impacted by Anthropogenic Activities

Despite of a high abundance of antibiotics, heavy metals, and organic matters detected in the Saigon River in Ho Chi Minh City, the level and spread of antibiotic resistance genes in this river are poorly understood. In this study, total 10 antibiotic resistance genes (ARGs), including genes conferring resistance to aminoglycosides (aac(6)-Ib-cr), β-lactam antibiotics (blaCTX-M, blaSHV, blaTEM), quinolones (qnrA, qnrB), sulfonamides (sul1, sul2), trimethoprim (dfrA), efflux pump (oqxB), and three genes of genetic elements, including integron classes 1, 2, and 3 (intI1, intI2, intI3), are quantified by qPCR. Water samples were collected from the industrial, agricultural, residential, and less impacted areas for the wet and dry seasons. The results present high occurrence rates for 10 ARGs that were observed in all the sampling sites with the following order: sul1, sul2, dfrA > aac(6)-Ib-cr > blaCTX-M, blaSHV, blaTEM > qnrA, qnrB. Although the levels of ARGs and integrons in the dry season were found about to be about one order of magnitude higher than those in the wet season, the exact mechanisms for this are not fully clear. The correlation analysis presented here suggests that the contamination of organic matter and nutrients from agricultural, industrial, and residential activities likely contributes to the prevalence of ARGs, integrons, total bacterial load, and the potential development and spread of antibiotic resistance in the aquatic environments considered here.

Phytoplankton characterization in a tropical tidal river impacted by a megacity: the case of the Saigon River (Southern Vietnam).

The spatiotemporal variation of phytoplankton and their relationship with environmental variables were analyzed in the Saigon River-a tropical river in Southern Vietnam. Two longitudinal profiles were conducted during dry and rainy season at 18 sampling sites covering more than 60 km long in the river. Besides, a bi-weekly monitoring conducted in the upstream, urban area (Ho Chi Minh City-HCMC), and downstream of Saigon River was organized from December 2016 to November 2017. The major phytoplankton were diatoms (e.g., Cyclotella cf. meneghiniana, Leptocylindrus danicus, Aulacoseira granulata), cyanobacteria (Microcystis spp., Raphidiopsis raciborskii, Pseudanabaena sp.), and euglenoids (Trachelomonas volvocina). Commonly freshwater phytoplankton species and sometimes brackish water species were dominant during the monitoring. Phytoplankton abundances in dry season were much higher than in rainy season (>100 times) which was explained by a shorter riverine water residence time and higher flushing capacity during the dry season. There was a clear separation of phytoplankton abundance between the urban area and the remaining area of Saigon River because of polluted urban emissions of HCMC. Redundancy analysis shows that the environmental variables (TOC, nitrogen, pH, salinity, Mo, Mn) were the driving factors related to the dominance of L. danicus and Cyclotella cf. meneghiniana in the upstream river and urban section of Saigon River. The dominance of cyanobacterium Microcystis spp. in the downstream of Saigon River was related to higher salinity, Mg, Cu concentrations, and lower concentrations of nutrients, Mn, Co, and Mo. The dominance of potentially toxic cyanobacteria in Saigon River possesses health risk to local residents especially upon the increasing temperature context and nutrient loading into the river in the next decades.

A Field Guide for Monitoring Riverine Macroplastic Entrapment in Water Hyacinths

River plastic pollution is an environmental challenge of growing concern. However, there are still many unknowns related to the principal drivers of river plastic transport. Floating aquatic vegetation, such as water hyacinths, have been found to aggregate and carry large amounts of plastic debris in tropical river systems. Monitoring the entrapment of plastics in hyacinths is therefore crucial to answer the relevant scientific and societal questions. Long-term monitoring efforts are yet to be designed and implemented at large scale and various field measuring techniques can be applied. Here, we present a field guide on available methods that can be upscaled in space and time, to characterize macroplastic entrapment within floating vegetation. Five measurement techniques commonly used in plastic and vegetation monitoring were applied to the Saigon river, Vietnam. These included physical sampling, Unmanned Aerial Vehicle imagery, bridge imagery, visual counting, and satellite imagery. We compare these techniques based on their suitability to derive metrics of interest, their relevancy at different spatiotemporal scales and their benefits and drawbacks. This field guide can be used by practitioners and researchers to design future monitoring campaigns and to assess the suitability of each method to investigate specific aspects of macroplastic and floating vegetation interactions.

Plastic Plants: The Role of Water Hyacinths in Plastic Transport in Tropical Rivers

Recent studies suggest that water hyacinths can influence the transport of macroplastics in freshwater ecosystems at tropical latitudes. Forming large patches of several meters at the water surface, water hyacinths can entrain and aggregate large amounts of floating debris, including plastic items. Research on this topic is still novel and few studies have quantified the role of the water hyacinths in plastic transport. In this study, we present the findings of a six-week monitoring campaign, combining the use of visual observations and Unmanned Aerial Vehicle imagery in the Saigon river, Vietnam. For the first time, we provide observational evidence that the majority of macroplastic is transported by water hyacinth patches. Over the study period, these fast-growing and free-floating water plants transported 78% of the macroplastics observed. Additionally, we present insights on the spatial distribution of plastic and hyacinths across the river width, and the different characteristics of entrapped items compared with free-floating ones. With this study, we demonstrate the role of water hyacinths as a river plastic aggregator, which is crucial for improving the understanding of plastic transport, and optimizing future monitoring and collection strategies.

The toxicity of lead to the freshwater microalgae Scenedesmus and the water flea Daphnia carinata

Sai Gon river is the important source for water supply in Ho Chi Minh City. However, its water quality is degrading gradually due to rapid population growth, increasing of urbanization and industrialization. The river is continuously loaded with xenobiotics released by anthropogenic activities. Among pollutants, heavy metals are considered as the most toxic elements to aquatic living organisms and human health. The aim of this study is to assess the sensibility of freshwater microalgae Scenedesmus and water flea Daphnia carinata, two fresh water species from Viet Nam to lead (Pb). After physical and chemical characterization, field water samples from the upstream of Sai Gon River was used as dilution water in toxicity tests. With water flea D. carinata, the EC50 value of 48h immobilization experiment was 121.64 µg/L for Pb. Growth inhibition of the algae cells was determined following exposure for 96 h, and EC50 values of Pb was 14,767.9 µg/L. The results showed that Pb was highly toxic to D. carinata, and harmful to freshwater algae Scenedesmus. Based on the observed high sensitivity with Pb, D. carinata is a potential bioindicator for the assessment of Pb pollution in Sai Gon river. While lead-tolerance algae Scenedesmus calls for further investigation on metal uptake capacity and utilization in Pb contaminated water treatment