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Abstract Understanding heavy metals in rivers is crucial, as their presence and distribution impact water quality, ecosystem health, and human well-being. This study examined the presence and levels of nine heavy metals (Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn) in 16 surface water samples along the Chao Phraya River, identifying Fe, Mn, Zn, and Cr as predominant metals. Although average concentrations in both rainy and dry seasons generally adhered to WHO guidelines, Mn exceeded these limits yet remained within Thailand’s acceptable standards. Seasonal variations were observed in the Chao Phraya River, and Spearman’s correlation coefficient analysis established significant associations between season and concentrations of heavy metals. The water quality index (WQI) demonstrated varied water quality statuses at each sampling point along the Chao Phraya River, indicating poor conditions during the rainy season, further deteriorating to very poor conditions in the dry season. The hazard potential index (HPI) was employed to assess heavy metal contamination, revealing that during the dry season in the estuary area, the HPI value exceeded the critical threshold index, indicating the presence of heavy metal pollution in the water and unsuitable for consumption. Using the species sensitivity distribution model, an ecological risk assessment ranked the heavy metals’ HC5 values as Pb > Zn > Cr > Cu > Hg > Cd > Ni, identifying nickel as the most detrimental and lead as the least toxic. Despite Cr and Zn showing a moderate risk, and Cu and Ni posing a high risk to aquatic organisms, the main contributors to ecological risk were identified as Cu, Ni, and Zn, suggesting a significant potential ecological risk in the Chao Phraya River’s surface water. The results of this study provide fundamental insights that can direct future actions in preventing and managing heavy metal pollution in the river ecosystem.

Southeast Asia (SEA) faces significant environmental challenges due to rapid population growth and economic activity. Rivers in the region are major sources of plastic waste in oceans. Concerns about their contribution have grown, but knowledge of microplastics in the area is still limited. This article compares microplastic levels in sediment and water from urban zones of three major rivers in SEA: Chao Phraya River (Thailand), Saigon River (Vietnam), and Citarum River (Indonesia). The study reveals that in all three rivers, microplastics were found, with the highest concentrations in Chao Phraya’s water (80 ± 60 items/m3) and Saigon’s sediment (9167 ± 4559 items/kg). The variations in microplastic sizes and concentrations among these rivers may be attributed to environmental factors and the exposure duration of plastic to the environment. Since these rivers are important water supply sources, rigorous land-use regulations and raising public awareness are crucial to mitigate plastic and microplastic pollution. [ABSTRACT FROM AUTHOR]

Understanding heavy metals in rivers is crucial, as their presence and distribution impact water quality, ecosystem health, and human well-being. This study examined the presence and levels of nine heavy metals (Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn) in 16 surface water samples along the Chao Phraya River, identifying Fe, Mn, Zn, and Cr as predominant metals. Although average concentrations in both rainy and dry seasons generally adhered to WHO guidelines, Mn exceeded these limits yet remained within Thailand's acceptable standards. Seasonal variations were observed in the Chao Phraya River, and Spearman's correlation coefficient analysis established significant associations between season and concentrations of heavy metals. The water quality index (WQI) demonstrated varied water quality statuses at each sampling point along the Chao Phraya River, indicating poor conditions during the rainy season, further deteriorating to very poor conditions in the dry season. The hazard potential index (HPI) was employed to assess heavy metal contamination, revealing that during the dry season in the estuary area, the HPI value exceeded the critical threshold index, indicating the presence of heavy metal pollution in the water and unsuitable for consumption. Using the species sensitivity distribution model, an ecological risk assessment ranked the heavy metals' HC5 values as Pb > Zn > Cr > Cu > Hg > Cd > Ni, identifying nickel as the most detrimental and lead as the least toxic. Despite Cr and Zn showing a moderate risk, and Cu and Ni posing a high risk to aquatic organisms, the main contributors to ecological risk were identified as Cu, Ni, and Zn, suggesting a significant potential ecological risk in the Chao Phraya River's surface water. The results of this study provide fundamental insights that can direct future actions in preventing and managing heavy metal pollution in the river ecosystem. [ABSTRACT FROM AUTHOR]

Length-weight relationship (LWR) was used as a tool to assess the status of fish stocks, through condition factor, in major rivers in Thailand. Fifty-one fish species from each river, i.e., The examined for LWR using 11 years of monitoring data (2010–2020) for Bang Pakong and 14 years of monitoring data (2007–2020) for Chao Phraya, which comprised 57,871 samples. The parameters for LWR and condition factor were examined by species and by body shape, i.e., ovate, oblong, elongate or eel-like. The coefficient of determination (r²) of all log-transformed LWRs was greater than 0.90. Parameter b of LWR ranged between 2.06 and 3.46 (median = 3.00) for fishes from the Chao Phraya River and between 1.72 and 3.68 (median = 2.76) for fishes from the Bang Pakong River. The overall condition factor, which implies the well-being that indicates the health or fattening of the fishes in a stock, ranged between 0.93 and 1.09. There was no significant difference in the overall well-being (P = 0.279) between the two rivers. Fishes with oblong and elongate shapes in the Chao Phraya River showed higher median values of parameter b of LWR than those from the Bang Pakong River. However, there was no significant difference (P > 0.05) in the well-being of the fish stocks between the two rivers when pooled by shape. The findings are fundamental information for fish stock assessment in the two rivers, which greatly support the small-scale fisheries in Thailand. [ABSTRACT FROM AUTHOR]

Microplastic (MP) debris is now a global concern. The Chao Phraya is the largest river in Thailand and transports MPs from terrestrial areas to the ocean. MP debris in its water and sediment were measured in March 2021, September 2021, and March 2022 in five provinces along the watercourse. Hydrological data were also collected to estimate the MP riverine flux between provinces. Size, shape, color, and types of MP polymers were observed, with sedimentation data collected for MP content. Results showed that MPs were found at all sample stations, with average abundance in all province water samples ranging from 0.54 ± 0.05 to 1.07 ± 0.28 pieces/L, while in sediment sample, numbers ranged from 183.84 ± 38.76 to 546.18 ± 86.84 pieces/kg dry weight throughout all seasons. Overall contamination and accumulation were similar between provinces but significantly different between seasons. Sizes of MPs in water varied between seasons with MPs in sediment mostly 330–5,000 μm (Kruskal–Wallis, P < 0.05). Sedimentation of MPs was different between seasons (Kruskal–Wallis, P < 0.05). The highest MP flux values discharged from Samut Prakan Province to the inner Gulf of Thailand were 1.83 × 105 and 1.60 × 105 million items/day in September 2021 and March 2022, respectively. HIGHLIGHTS Highest microplastic (MP) riverine flux discharged into the sea was recorded as 183,000 million items/day.; Fiber MPs were abundant in both water and sediment samples, with fragment MPs significantly higher in sediment samples than in water samples.; Significant seasonal variations were found in water and sediment samples.; Water discharge and current velocity play important roles in MP contamination in riverine ecosystems.;

Microplastic (MP) debris is now a global concern. The Chao Phraya is the largest river in Thailand and transports MPs from terrestrial areas to the ocean. MP debris in its water and sediment were measured in March 2021, September 2021, and March 2022 in five provinces along the watercourse. Hydrological data were also collected to estimate the MP riverine flux between provinces. Size, shape, color, and types of MP polymers were observed, with sedimentation data collected for MP content. Results showed that MPs were found at all sample stations, with average abundance in all province water samples ranging from 0.54 ± 0.05 to 1.07 ± 0.28 pieces/L, while in sediment sample, numbers ranged from 183.84 ± 38.76 to 546.18 ± 86.84 pieces/kg dry weight throughout all seasons. Overall contamination and accumulation were similar between provinces but significantly different between seasons. Sizes of MPs in water varied between seasons with MPs in sediment mostly 330-5,000 μm (Kruskal-Wallis, P < 0.05). Sedimentation of MPs was different between seasons (Kruskal-Wallis, P < 0.05). The highest MP flux values discharged from Samut Prakan Province to the inner Gulf of Thailand were 1.83 x 105 and 1.60 x 105 million items/day in September 2021 and March 2022, respectively. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) in estuaries are sources of plastic debris that enter the marine environment. However, there is limited information on the seasonal effect on the accumulation of MPs in the estuaries of Thailand. The abundance and spatial distribution of MPs in the dry and wet seasons were investigated in the Chao Phraya River estuary, and possible emission sources were traced. Dominant factors affecting the distribution patterns of MPs have also been reported. All collected water samples contained MPs, with a mean abundance of 4.0 ± 2.8 × 105 particles/km2 in the wet season and 5.2 ± 3.3 × 105 particles/km2 in the dry season. Fragments were mostly observed, with polypropylene and polyethylene being the dominant polymers. The findings also showed that accumulation of MPs was directly influenced by the river discharge rate into the estuary. Further, the spatial distribution of MPs was closely related to seasonal variations in sea surface currents. Microplastic pollution status with seasonal variations and possible emission sources could provide important information to the government and local environmental organizations for MP pollution prevention and future MP studies in estuarine environments. [ABSTRACT FROM AUTHOR]

Sea water receding from the Gulf of Thailand causes salinity diffusion in the Chao Phraya River, Thailand, and the amount of northern water is reduced in the dry season. It has an impact on people, particularly the generation of tap water. The Samlae raw water pumping station is the major pumping station. The Ban Krachaeng subdistrict is located in Mueang district, Pathum Thani province, and is affected by saltwater intrusion, which causes the salinity level to exceed the recommended threshold. In order for the Metropolitan Waterworks Authority (MWA)'s water supply system to achieve the standard, the salinity index at the Samlae raw water pumping station is controlled to not exceed the surveillance threshold of 0.25 g/l in this research. A barrage dam consists of a number of large gates that can be opened or closed to control the amount of fresh water passing through. There is a Chao Phraya barrage dam which is across the Chao Phraya River at Chai Nat, the northern part of the focused area. The objective of this research is to demonstrate a onedimensional steady-state salinity measurement model in a river with a barrage dam. Irrigation is done in rivers with dams using the shooting method to estimate the solution. The results obtained from simulating simulated salinity measurements from Phra-Nakhon Tai Power Plant Station to Samlae Station demonstrated that the shooting method can be used to accurately estimate the solution. Freshwater flow velocity and salinity dissolving efficiency were discovered to be the most important elements controlling salinity levels. The suggested salinity control approach may help to regulate the salinity level until it reaches a normal level. [ABSTRACT FROM AUTHOR]

Turbidity is a standard water quality parameter that indicates its optical property in scattering light along the column containing suspended particles. The satellite imagery information of Sentinel-2 and the Chao Phraya River turbidity data from December 2016 to February 2021 was applied to develop a mathematical equation for turbidity determination. This practical and straightforward approach eliminates some constraints of traditional laboratory analysis, which is labour-intensive and time-consuming in monitoring the entire river. Four studied steps were implemented: data pre-processing, correlating analysis of numerical turbidity and satellite image reflectance, developing the mathematic equations for turbidity estimation, and its validation of use. Four different bands (B2, B3, B4, and B8) and three selection methods were investigated; single-band, combination band, and ratio band. The obtained results depicted that the reflectance of B4 in the single-band process promoted the highest correlation with turbidity compared to the others. The reflectance in visible wavelengths increased when the turbidity of river water increased, particularly B4. The mathematical power equation was a more suitable function for evaluating turbidity than linear regression, quadratic, and exponential functions. A similar concentration was obtained for measured and estimated turbidity in the validation. This finding demonstrated the potential application of remotely sensed data to estimate river water turbidity with high capability and accuracy that adequately supports spatial data continuity acquisition.

The 2011 flood on the Chao Phraya River in Thailand caused enormous damage. The damage was greatest to the industrial sector, accounting for more than 70% of the estimated economic damage, and the resulting disruption of the supply chains of global companies has spread not only throughout Thailand but to other countries around the world. In order to reduce such damage, it is necessary to prepare a flood manual that makes use of past flood experiences or a business continuity planning (BCP) that assumes floods. In addition, business continuity management (BCM) is needed to establish and enhance BCP. Thus, it is essential to obtain flood information on the scale of an industrial park. Therefore, in this study, to provide detailed flood information as above, in addition to a flood inundation analysis model for the Chao Phraya River Basin, a detailed model on the scale of an industrial park was developed. Specifically, we developed a 40 m mesh industrial park-scale model based on survey data using a local aerial laser and the local river channel shape. Furthermore, using the flood discharge and river discharge output obtained from a 1 km mesh model of the Chao Phraya River Basin as inputs for the industrial park scale model for the surrounding boundary conditions, we obtained a more precise inundation analysis. As a result, the flood risk information obtained from the above analysis model can be useful for BCP/BCM. In addition, detailed flood risk information such as road inundation conditions can be obtained at any location, which could be useful in creating evacuation plans for employees. [ABSTRACT FROM AUTHOR]

Turbidity is a standard water quality parameter that indicates its optical property in scattering light along the column containing suspended particles. The satellite imagery information of Sentinel-2 and the Chao Phraya River turbidity data from December 2016 to February 2021 was applied to develop a mathematical equation for turbidity determination. This practical and straightforward approach eliminates some constraints of traditional laboratory analysis, which is labourintensive and time-consuming in monitoring the entire river. Four studied steps were implemented: data pre-processing, correlating analysis of numerical turbidity and satellite image reflectance, developing the mathematic equations for turbidity estimation, and its validation of use. Four different bands (B2, B3, B4, and B8) and three selection methods were investigated; single-band, combination band, and ratio band. The obtained results depicted that the reflectance of B4 in the single-band process promoted the highest correlation with turbidity compared to the others. The reflectance in visible wavelengths increased when the turbidity of river water increased, particularly B4. The mathematical power equation was a more suitable function for evaluating turbidity than linear regression, quadratic, and exponential functions. A similar concentration was obtained for measured and estimated turbidity in the validation. This finding demonstrated the potential application of remotely sensed data to estimate river water turbidity with high capability and accuracy that adequately supports spatial data continuity acquisition. [ABSTRACT FROM AUTHOR]

Quality of water resources is crucial to several activities in human life and life under water. Water resource quality is a complex dynamic system depending on various attributes with nonlinear and non-equilibrium conditions. In this study, we aim to utilize a deep learning (DL) model based on multi-layer feed-forward artificial neural network with back-propagation algorithm and supervised data for water quality prediction. The DL model predicts the water quality from database information that collected by the Pollution Control Department (PCD), Thailand. The following water quality attributes from 2007-2019 were analyzed: biological oxygen demand (BOD), dissolved oxygen (DO), fecal coliform bacteria (FCB), total coliform bacteria (TCB), ammonia-nitrogen (NH3-N), and spatial-temporal data for the Chao Phraya River in Thailand. The results indicated that the DL model had a coefficient of determination (R2) of 0.90, with a mean square error (MSE) of 0.20 and a predicted accuracy of 88.96%. The evaluation DL model result was more precise in predicting values in the unsuitable and poor water quality classes, with 100% of the dataset being in those classes. The DL model was able to process the data at circa 18,000 rows per second. These results supported the possibility of using the DL model as a tool to predict the quality of water resources. [ABSTRACT FROM AUTHOR]

The Chao Phraya River Basin (CPRB) of Thailand faces flooding almost every year. The severest flood occurred in the CPRB in 2011 with the highest property damage costs (46.5 billion USD) and the highest casualty (813 deaths). The objectives of this study were thus to (1) determine flood risk indices and categorize them into four risk zones (low, moderate, high, and very high) across 994 sub-districts in the CPRB during the six rainy months (May–October); and (2) propose specific measures for flood risk management for each of the categorized risk zones. The flood risk indices were assessed as the product of two hazard variables (flood levels and monthly cumulative precipitation) and the vulnerability variable (land uses). The findings revealed spatiotemporal variations in flood risk. Spatially, the sub-districts deemed to be in the high or very high flood risk zone were mainly located close to the Chao Phraya River (CPR), where the flood levels reached 1.1 – 4 m in depth; whereas the sub-districts detected in the low or moderate flood risk zone were located further away from the CPR. Temporally, more sub-districts were detected in the high or very high risk zone in September when heavy rainfalls were observed. Specific measures are proposed herein to manage flood risk regarding the categorized zones during three periods. The preventive and mitigation measures should be prepared before flooding; emergency responses should be practically implemented during flooding; and the recovery after flooding should cover both infrastructural and environmental damage and mental/physical illnesses amongst the affected people. Intensive measures are recommended for the sub-districts located in both the high and very high risk zones. These measures may be properly loosened for the sub-districts located in the low and moderate risk zones.

The food habits of three non-native cichlid fishes, Mayan cichlid (Mayaheros urophthalmus), Mozambique tilapia (Oreochromis mossambicus) and Nile tilapia (O. niloticus), in the lowermost Chao Phraya River basin, Thailand, was examined by stomach contents analysis. The index of preponderance, an index of the importance of prey items, was calculated from two relative metrics of prey quantity: percent frequency and percent volume. The index of niche breadth and the overlap coefficient were calculated to compare the breadth of food habits among the size classes and species groups. The M. urophthalmus mainly preyed on fish scales, detritus and aquatic invertebrates (molluscs and crustaceans). The O. mossambicus and O. niloticus fed mostly on detritus. The diets of the latter two species overlapped almost completely; however, green filamentous algae mixed with detritus was observed in the diet of the O. niloticus only. The observation that fish scales were a predominant food source in the stomach of M. urophthalmus (high importance value 45.48%) was specific to this study area.

Thailand is one of the largest contributors to plastic waste in the oceans. Since mismanaged plastic waste can enter the ocean via inland waterways, microplastic contamination in freshwater used for tap water production has been raised as a potential issue. This study was conducted to determine the abundance and characteristics of microplastics in freshwater and treated tap water in Bangkok. Freshwater and treated water were collected from the eastern and western water supply systems in the dry and wet seasons. The source waters of the eastern and western water supply systems are the Chao Phraya River and Maeklong River, respectively. Approximately 0.40–2.40 particles/L microplastics was determined in the freshwater samples. No significant differences in microplastic abundance with respect to water supply system or season were found. Approximately 82.1% of the total microplastics found in the freshwater were smaller than 300 µm in size. The percentage contribution of various microplastic size ranges decreased with increasing size. The majority of microplastics found in freshwater were fragments (90.2%), colorless (64.3%), and made of polyethylene polymer (45.1%). Only the eastern water supply system was capable of removing microplastic particles (27.7%) from freshwater. The identification of microplastics larger than 100 µm in size in the treated tap water indicated potential contamination from microplastics in the treatment system, particularly after the sand filtration unit. The major characteristics of the microplastics found in treated tap water were similar to those found in freshwater, with 85.6% fragments, 85.1% colorless, and 47.9% made of polyethylene polymer. [ABSTRACT FROM AUTHOR]

Thailand's low-lying capital city Bangkok is a dense metropolis, one of Asia's rapidly growing 'megacities', and home to over 10 million residents. Bangkok's location on the sinking Chao Phraya Delta means it has a high susceptibility to river flooding. However, the possible contribution of marine incursion to river flooding is not as widely recognised and needs further consideration. We therefore re-examine the historically documented floods in AD 1785 and 1983. Available evidence suggests that the superposition of different flood behaviours was important during both events. Attention is drawn to the evidence for, and contributory roles played by, astronomical spring tides, meteorological tides, storm waves and possibly storm surge. These marine effects can exacerbate river floods caused by seasonal peak flows in the tidal lower Chao Phraya River during the early north-east monsoon. For future management of flood risk, it is therefore necessary to recognise that Bangkok has a compound flood-risk profile that includes both hydrometeorological and marine influences. The significance of marine influences on Bangkok's flood risk is likely to increase in future with continuing eustatic sea-level rise and subsidence of the Chao Phraya Delta. [ABSTRACT FROM AUTHOR]

Using high-resolution elevation data (2 m x 2 m), obtained during a 2012 aerial Lidar survey as part of the Chao Phraya River basin flood management project in Thailand, we assessed the impact of sea level rise due to climate change on the Bangkok metropolitan area. The area below the current median tide of 1.11 m was estimated to be 2,520 km², with a vulnerable population of 3.9 million, equivalent to 23% of the total population of the Bangkok metropolitan area. In the worst-case scenario of Representative Concentration Pathway (RCP) 8.5 (sea level rise of +1.10 m), the affected area would extend to 6,140 km², increasing the estimated vulnerable population by 86% to 7.2 million. With a sea level rise of less than +1.10 m, the affected area would extend from the Chao Phraya River mouth to Suphan Buri, which is about 80 km inland; however, the density of the vulnerable population would increase. The results of this study suggest that sea level rise adaptation measures, such as migration and settlement, must be developed as soon as possible. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are distributed globally, including in aquatic environments. While a large number of studies on MPs in marine environments have been performed, few studies are available in freshwater environments. Therefore, the distribution of MPs in surface water and sediment from the Chao Phraya River at Tha Prachan, a high population density area of Bangkok, was investigated. Water samples were collected by a manta trawl with a net mesh size of 300 m. Sediment samples were collected by a Van Veen grab sampler. The total number and concentration of MPs in the water samples were found to be 104 particles/m3 and 805.20 mg/m3, respectively. The dominant MPs were fragments, 0.5 to 1.0 mm in size, for the water samples. In the sediment, MPs were detected only in a size range of 0.053 to 0.5 mm with a total number and concentration of 2,290 particles/kg and 650 mg/kg, respectively. The presence of different types of MPs was confirmed by Fourier-transform infrared spectroscopy with a dominant abundance of polypropylene, polyethylene, and polystyrene. In brief, this study suggests that high levels of MPs occur not only in the water but also in the sediment of the Chao Phraya River at Tha Prachan area. [ABSTRACT FROM AUTHOR]

The purpose of this research was to develop a numerical model of one-dimensional advection-diffusion equation for estimating salinity level in Lower Chao Phraya River, Thailand. The main numerical technique was MacCormack finite-difference scheme with initial and boundary conditions approximated by cubic spline interpolation. The estimates matched satisfactorily with actual measurement data from several salinity monitoring stations along the river. The final model was first used by Thailand's Metropolitan Waterworks Authority for planning salinity control in 2018. [ABSTRACT FROM AUTHOR]

The food habits of three non-native cichlid fishes, Mayan cichlid (Mayaheros urophthalmus), Mozambique tilapia (Oreochromis mossambicus) and Nile tilapia (O. niloticus), in the lowermost Chao Phraya River basin, Thailand, was examined by stomach contents analysis. The index of preponderance, an index of the importance of prey items, was calculated from two relative metrics of prey quantity: percent frequency and percent volume. The index of niche breadth and the overlap coefficient were calculated to compare the breadth of food habits among the size classes and species groups. The M. urophthalmus mainly preyed on fish scales, detritus and aquatic invertebrates (molluscs and crustaceans). The O. mossambicus and O. niloticus fed mostly on detritus. The diets of the latter two species overlapped almost completely; however, green filamentous algae mixed with detritus was observed in the diet of the O. niloticus only. The observation that fish scales were a predominant food source in the stomach of M. urophthalmus (high importance value 45.48%) was specific to this study area. [ABSTRACT FROM AUTHOR]

As the top country for plastic production and consumption, Thailand generated more than 3 million tonnes of plastic waste in 2016. As a result of improper management, 0.15 to 0.41 million tonnes of plastic waste entered annually in the aquatic environment in Thailand. In recent years, a small size of plastic waste in term of microplastics (MPs) became a significant concern due to their persistence, ubiquity and potential to play as vectors for transfer organic pollutants to human and biota. This study reports the concentration of MPs of the Chao Phraya River at Pa Mok District – a huge agricultural area of Ang Thong Province. MPs were sampled on the river by a manta trawl with the mesh size of 300 microns. The samples were treated by hydrogen peroxide with the iron (II) sulfate as a catalyst to remove organic components and inspected under a microscope with different size ranges. The total number of MPs were found to be 41.77 particles/m3. The presence of different types of MPs was confirmed by FTIR spectroscopy, with a predominant abundance of polypropylene, polyamide 6, and polyethylene. Potential origins of these type of polymers are from plastic nets of aquatic farms and plastic films from mulching employed for cultivation. [ABSTRACT FROM AUTHOR]

Background: Free-living Naegleria fowleri and Acanthamoeba spp. amoebae are causative agent of lethal brain infection in human. Due to high fatal rate of the patients, a survey of these pathogenic amoebae should be done for prevention and control in public health. Objective: To investigate the presence and prevalence of N. fowleri and pathogenic Acanthamoeba spp. in the Chao Phraya River and canals located close to Siriraj Hospital (Bangkok, Thailand). Materials and Methods: One hundred eighty-nine freshwater samples collected from 21 sites were investigated between January and April 2017. Sample sediments were incubated at 37°C (regular temperature) and 42°C (tolerant temperature) for five to seven days. All samples were identified by morphologic characteristics and polymerase chain reaction. Results: The samples from eight sites (Bangkoknoi District Office, Taling Chan Floating Market, Wang Lang, Wat Amarinthararam, Wat Khruawan, Wat Pho Riang, Wat Rakhang, Wat Taling Chan) yielded 38% (72/189) Naegleria spp. at 37°C, and 19% (36/189) Naegleria spp. at 42°C by morphological identification. The thermotolerant Naegleria spp. samples (9.5%, 18/189) from Wang Lang and Wat Rakhang were identified as N. fowleri. Forty-five of 189 (23.8%) water samples taken from the Taling Chan Floating Market, Wang Lang, Wat Khruawan, Wat Pho Riang, Wat Taling Chan collection sites were positive for pathogenic Acanthamoeba spp. Conclusion: Our findings suggested that fresh water from the Wang Lang, Wat Rakhang were contaminated with N. fowleri, whereas Taling Chan Floating Market, Wat Khruawan, Wat Pho Riang or Wat Taling Chan were with pathogenic Acanthamoeba spp. Interestingly, we found N. fowleri and pathogenic Acanthamoeba spp. from Wang Lang site. [ABSTRACT FROM AUTHOR]

The present study conducted a field survey of water quality along the Chao Phraya River during the past three years. The main objective was to better understand the spatial–temporal variations in water quality in relation to season and channel morphology. It assessed the water quality in terms of chemical parameters, bacteria, and phytoplankton. The results revealed a duality of seasonal effect for nutrients. The rainy season degraded the water quality by increasing the nutrient concentration in the waterway in the beginning, but cleaned it up by dilution in the end. However, this duality did not apply to Escherichia coli (E. coli), for which the highest level occurred during the second half of the rainy season and a sag curve variation pattern was displayed along the mainstream. Another duality found by this study is that there was no statistically significant difference in water quality in terms of chemical parameters between a river bend and the straight channel shortcutting the bend, but significant differences in the level of E. coli and the phytoplankton community structure were observed between the two. Of particular note, the present study revealed a coexistence of a saproxenous species (algae found in clean water) with a harmful species in the bend river reach.

A sustainable strategy for conjunctive water management must include information on the temporal and spatial availability of this natural resource. Because of water shortages in the dry seasons, farmers on the Upper Plain of the Chao Phraya River basin, Thailand, are increasingly using groundwater to meet their irrigation needs. To evaluate the possibilities of conjunctive water management in the area, the spatial-temporal changes in the water table of the Younger Terrace Aquifer were investigated. First, a regional geomorphological map based on field surveys, remote sensing and previous environmental studies was developed. Then, the well data were analyzed in relation to rainfall, streamflow, yield and pumpage, and the data were interpolated using geostatistical techniques. The results were analyzed via integrated zoning based on color theory as applied to multivariate visualization. The analysis results indicate areas that would be more suitable for groundwater extraction in a conjunctive management framework with regard to the natural hydrogeological processes and the effects of human interaction. The kriging results were compared with the geomorphological map, and the geomorphological areas exhibit distinct hydrogeological patterns. The western fans exhibit the best potential for the expansion of conjunctive use, whereas the borders of the northern fans exhibit the lowest potential. [ABSTRACT FROM AUTHOR]

A devastating flood disaster occurred in Thailand in 2011. In case of such large-scale flooding, it is important to predict the dynamics of inundation on a near real-time basis for safe evacuation. To predict widespread inundation, where both rainfall-runoff from surrounding mountains and rainfall on floodplains contribute to the event, this paper applied a rainfall-runoff-inundation ( RRI) model to the entire Chao Phraya River basin (160 000 km2). Near real-time simulation was conducted for emergency responses with globally available dataset including satellite-based topography ( HydroSHEDS derived from SRTM) and rainfall ( TRMM 3 B42RT) during the disaster. Post-flood simulation was also carried out with more local information. The RRI model was found capable of representing the peak inundation extent with an acceptable accuracy and correctly predicting a 1-month lasting inundation in the lower part of the basin. On the other hand, the prediction overestimated the river discharge by 40% and the inundation water level by 2 m mainly due to the neglect of the evapotranspiration effect. The post-flood simulation improved its accuracy by up to 10% for river discharges and 1 m for peak inundation water levels, but it did not lead to better agreement of flood extents with those based on the remote sensing. Further study is recommended to improve accuracy for modelling of spatial extent of flooding. Furthermore, sensitivity analysis with different input suggested what information should be prioritised for emergency response-type flood simulations. [ABSTRACT FROM AUTHOR]

This paper revisits the 2011 Great Flood in central Thailand to answer one of the hotly debated questions at the time " Could the operation decisions of the flood control structures substantially mitigate the flood impacts in the downstream areas?". Using a numerical modeling approach, we develop a hypothesis such that the two upstream dam reservoirs: Bhumibol and Sirikit had more accurately forecasted the typhoon-triggered abnormal rainfall volumes and released more water earlier to save the storage capacity via 17 different scenarios or alternative operation schemes. We subsequently quantify the potential improvements, or reduced flood impacts in the downstream catchments, solely by changing the operation schemes of these two dam reservoirs, with all other conditions remaining unchanged. We observed that changing the operation schemes could have reduced only the flood depth while offering very limited improvements in terms of inundated areas for the lower Chao Phraya River Basin. Among 17 scenarios simulated, the inundated areas could have been reduced at most by 3.68%. This result justifies the limited role of these mega structures in the upstream during the disaster on one hand, while pointing to the necessity of handling local rainfall differently on the other. The paper expands the discussion into how the government of Thailand has drawn the lessons from the 2011 flood to better prepare themselves against the lurking flood risk in 2021, also triggered by tropical cyclones. The highlighted initiatives, both technical and institutional, could have provided important references for the large river catchment managers in Southeast Asia and with implications of our method beyond the present application region. [ABSTRACT FROM AUTHOR]

Blastocystis is a common zoonotic enteric protozoan that has been classified into 17 distinct subtypes (STs). A cross-sectional study was conducted to determine the prevalence and subtype distributions of Blastocystis in villagers living along the Chao Phraya River, Ayutthaya Province, Thailand, and to assess the risk of zoonotic infection. In total, 220 stool samples were collected, and DNA was extracted. PCR and sequencing were performed with primers targeting the small-subunit ribosomal RNA (SSU rRNA) genes. Blastocystis was present in 5.9% (13/220) of samples, and ST3 (5.0%; 11/220) was the predominant subtype, followed by ST2 (0.45%; 1/220) and ST6 (0.45%; 1/220). Phylogenetic trees were constructed with the maximum-likelihood method based on the Hasegawa-Kishino-Yano + G + I model, neighbor-joining, and maximum parsimony methods. The percentage of bootstrapped trees in which the associated taxa clustered together was relatively high. All the sequences of the Blastocystis-positive samples (KU051524-KU051536) were closely related to those from animals (pig, cattle, and chicken), indicating a zoonotic risk. Therefore, the villagers require proper health education, especially regarding the prevention of parasitic infection, to improve their personal hygiene and community health. Further studies are required to investigate the Blastocystis STs in the animals living in these villages. [ABSTRACT FROM AUTHOR]

The aims of this research are to investigate the hydrodynamics in the downstream part of a tidal river and to rapidly estimate the discharge in the case of the lower Chao Phraya River, Thailand. During flood tide, the depth of the maximum velocity shifts toward the river bottom, whereas during ebb tide, the maximum velocity is located near the water surface. The discharge can be estimated from the area and the mean velocity, which is obtained from the entropy parameter and measurement of maximum velocity. When the entropic linear relationship is assumed to be constant for a station, the estimated discharge is lower than the measured value at flood tide, and in contrast, the estimated discharge is somewhat higher than the measured value at ebb tide. To get a highly reliable value of discharge estimation, the variation in location of maximum velocity with flood and ebb tides must be considered, especially where the location of measurement has a strong influence from tides. [ABSTRACT FROM AUTHOR]

This study examines the recent quantitative characteristics of dry season water allocation in the Chao Phraya River basin, Thailand. Previous studies have focused on inequitable allocation, where the highest priority is given to the domestic water sector and uneven irrigation water variability exists among projects in the delta. This study uses a statistical test and panel data analysis to confirm that the characteristics highlighted in previous studies remain accurate, and it discusses the source of these characteristics in order to understand the issues in water allocation in the Chao Phraya River delta. [ABSTRACT FROM PUBLISHER]

Forty-eight sediment samples collected in the Upper Gulf of Thailand (UGOT) and its nearby rivers including the Mae Klong, Tha Chin, Chao Phraya, and Bang Pakong were analyzed for grain size, heavy metals (Cu, Pb, Zn, Cr, and Cd), and clay minerals. The results reveal that fine-grained sediments with Mz < 30 μm concentrate in the northern coastal area and coarse-grained fractions increase in a seaward direction. The grain size of the sediments mainly controls heavy metal concentrations. The concentrations of Cu, Pb, Zn, and Cr are higher in the northern part of UGOT, with ranges above 20, 23, 45, and 50 mg kg −1 , than in other sampling areas. Meanwhile, Cd content is greater than 120 μg kg −1 in sediments near the Bang Pakong River mouth and area between the Tha Chin and Mae Klong rivers mouth. The concentrations of heavy metals are higher than background data, and statistical analysis of geo-accumulation index indicates that the study area is either unpolluted to moderately polluted or moderately polluted by heavy metals. Our results also verify that illite is the dominant clay mineral, followed by kaolinite, chlorite, and smectite in terms of semi-quantitative content. Smectite/kaolinite can be used as an indicator to trace the riverine sediment in the study area, which present a counterclockwise dispersion pattern of sediment from the Chao Phraya River. [ABSTRACT FROM AUTHOR]

Several studies have shown the change of future river flow projection in the Chao Phraya River basin; however, these researches focused on the natural river flow. In this study, to obtain a realistic river flow projection for the Chao Phraya River basin, bias corrected GCM outputs were given to a regional distributed hydrological model including dam operation and flood inundation components. The projected river flow data was analyzed to assess the change of drought and flood risk. The GCM outputs used were precipitation and evapotranspiration projected by MRI-AGCM3.2S, which is a 20 km spatial resolution general circulation model developed by the Meteorological Research Institute, Japan Meteorological Agency. The results obtained from the projected river flow at the Nakhon Sawan station are as follows: 1) mean monthly discharge tends to increase in both the near-future and far-future projection periods for all months; 2) low-flow exceeding 99% of a mean daily flow duration curve for the near-future and far-future periods tends to decrease; and 3) a flood frequency analysis using the annual maximum daily flow series indicates that the flood risk in the near-future and far-future projection periods becomes higher. [ABSTRACT FROM AUTHOR]

Persistent organic pollutants (POPs) are organic substances that have characteristics of persistence in the environment; transboundary movement, or the ability to travel long distances through air and water; toxicity; and bioaccumulation in living things. Perfluorooctane sulfonate (PFOS), a toxic chemical that never breaks down, was added to the Stockholm Convention on POPs and was listed in the Annex B restrictions with many exemptions to continue using PFOS. This study focused on the occurrence of PFOS in the water system of Bangkok, Thailand, including the Chao Phraya and Bang Pakong Rivers, tap water in industrial zones and residential areas, drinking water, and industrial wastewater. Seasonal effect of PFOS between dry season and wet season was also observed for more than 3 years. Solid phase extraction (SPE) coupled with HPLC-ESI-MS/MS was used for the analysis of these compounds. PFOS was detected in most water samples. The average concentration of PFOS in the Chao Phraya River (urban area) was , whereas lower concentrations were detected in the Bang Pakong River (suburban area), residential tap water, and bottled drinking water, with averages of 0.7, 0.4, and , respectively. Higher concentrations (an average of ) were found in industrial tap water, whose sources were from surface water near the industrial zones. Much higher concentrations were detected in industrial wastewater, with the maximum of . These results indicated that industrial wastewater was one of the major sources of PFOS contamination in the water system of the city of Bangkok. This study provided data on the spatial occurrence, its seasonal effect, and distribution of PFOS in the water environment of Bangkok and surrounding areas, which need continuous attention to this emerging contaminant. [ABSTRACT FROM AUTHOR]

Abstract: In order to elucidate the sources of metals in urbanized areas, heavy metal contents and Pb isotope ratios were determined in the Chao Phraya River sediments. The sediment samples were leached using 1% HNO3 and metal concentrations (Cd, Cu, Cr, Pb, and Zn) and Pb isotopic ratios (208Pb/206Pb and 207Pb/206Pb) in the solutions were analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The highest ranking of potential pollutant evaluations of Cd, Cu, Cr, Pb, and Zn contents was found from samples that were located near to the center of Bangkok. Pb isotope ratios (208Pb/206Pb: 2.075–2.113 and 207Pb/206Pb: 0.834–0.868) in the Chao Phraya River sediments near to the center of Bangkok agreed well to those in the Bangkok road side dust and pond sediments suggesting that river sediments may be contributed from road-side dust and pond sediments. Moreover, Pb isotope ratios confirmed that the polluted sediments were contributed as Pb products of fly ashes (municipal waste combustors) in Bangkok (208Pb/206Pb: 2.100–2.120 and 207Pb/206Pb: 0.867–0.870). [Copyright &y& Elsevier]

The Chao Phraya River basin, the largest basin in Thailand, is located in the centre of the northern part of the country. This basin has two large-scale reservoirs: the Bhumibol Reservoir on the Ping River and the Sirikit Reservoir on the Nan River. A comparison of the annual and monthly flow regimes downstream from the reservoirs before and after reservoir development showed a constant increase in low flow and a drastic decrease in high flow. The spectrum of the daily discharge was analysed using the fast Fourier transform on data collected in the area of Nakhon Sawan and immediately downstream from the Bhumibol Reservoir after the reservoir was constructed. The flow at Nakhon Sawan had a periodic characteristic of 7 days. The water released from the Bhumibol Reservoir at hydrological station P.12 also had a periodic characteristic of 7 days. Reservoir operations have a significant impact on the hydrological cycles. The effect of human activities is evident in the spectrum analysis of recorded historical discharge data. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Untreated or partially treated waste water discharge from industrial and domestic sources entering the Upper Gulf of Thailand have been reported to increase cadmium concentration in bottom sediment. This study was directed at providing a better understanding of cadmium transformation in the sediment from the area. Sediment samples collected from Chao Phraya River mouth (CPY), Bang Pakong River mouth (BPK) and Klong Dan estuary (KD) located in the Upper Gulf of Thailand were analyzed for cadmium concentration in various sediment particle size fractions. Using laboratory microcosms, cadmium release from sediment as affected by salinity and sediment redox condition was studied. A higher concentration of cadmium (0.2-0.6 μ g/g dry weight) was measured in finer sediment particle size fractions (< 0.075 mm) as compared to courser fractions at all sampling stations. Cadmium release from the sediment to water was influenced by both salinity and redox condition. Sediment was spiked with 10 ppm cadmium which is the cadmium level in sediment adopted by the Australia and New Zealand sediment quality guidelines which can cause adverse environmental impacts. Experiments conducted showed soluble cadmium concentration at sediment oxidation reduction conditions representative of bottom sediment were at levels that can adversely impact aquatic organisms, according to the PCADMIUM water quality guideline. In Thailand, there is no sediment quality guideline. Based on these experiments, 10 ppm of cadmium in sediment was recommended as a regulatory guidelines for allowable levels of cadmium in sediment in the study area. [ABSTRACT FROM AUTHOR]

As part of a research programme designed to examine the effect of cadmium on various biochemical responses in fish, a preliminary survey was carried out of cadmium concentrations in water and sediments sampled at 26 sites within the Chao Phraya River system in the Bangkok area of Thailand. Compared with values in the literature, the results of total cadmium analysis of both river water and sediments gave no indication of extreme pollution with cadmium, although two sites were identified with substantially higher than average sediment cadmium concentrations. More detailed sampling at these sites, over several months, compared with nearby `pristine' sites, confirmed their elevated cadmium status. The forms of cadmium present in the sediments at these sites, as determined by sequential fractionation, also provided evidence for the presence of contamination. However, considerable temporal variations in water and sediment cadmium concentrations were observed at individual sites, most probably related to seasonal high water levels and sediment flushing. [ABSTRACT FROM AUTHOR]

• Over 50-years of discharge and sediment data were assessed for 211 stations in the CPR. • For the first time, sub-basin scale sediment yields (42 stations) are reported. • Spatial distribution of sediment yield is analyzed using lithology, climate and human impacts. • Sediment yields were high, but the majority were trapped in dams and floodplains. • This study will be an important reference for future researches in the CPR. In this paper, we provide a holistic view of the hydro-sedimentological regimes of the Chao Phraya River (CPR) Basin, the fifth largest basin in Southeast Asia. Our analysis of daily discharge and sediment data from 42 major gauge stations showed high seasonal variation in the suspended sediment discharge (Qs), with the maximum discharge occurring in October on an inter-annual average. At Nakhon Sawan, the river discharges 304x104 tons of sediment every year, 60% of which is transported in the peak flooding months (September to November). The peak sediment discharge in October is dramatically attenuated at a station 150 km downstream from Nakhon Sawan, mainly due to discharge diversion to irrigation canals, distributaries, and branches, as well as seasonal flooding over the Central Plain. Sediment yield (SY) calculated at major stations showed spatial variability across the basin, generally decreasing in a downstream direction (i.e. as drainage area increases) (R2 = 0.55). Some stations in the upper basin's watersheds showed SY as high as >700 tons/km2/yr, which is comparable to upstream catchments of other large rivers with high sediment production. Two significant sediment sinks were identified in this study: the Bhumibol and Sirikit dams (each on Ping and Nan Rivers) – which trap ~236 × 104 tons of sediment each year (~90% trapping rate) – as well as the floodplain of the CPR which stores 176 × 104 tons annually along the 150 km downstream reach from Nakhon Sawan (~60% of Qs at Nakhon Sawan). By extrapolating the floodplain sediment budget, we estimate that around 300 × 104 tons/yr of suspended sediment can be stored downstream of Nakhon Sawan (to the Gulf); comparable to the total annual storage of the two mega dams upstream. Although these dams have been previously reported to cause substantial sediment starvation in the CPR Delta, this study is the first to recognize the important role of lowland storage on the CPR's basin's sediment discharge to the Gulf of Thailand, and how it contributes a similar degree of threat to the shrinking delta. [ABSTRACT FROM AUTHOR]

Microplastics have received special attention due to their potential risks to environments. However, data on microplastics in estuaries of the Southeast Asian region is still insufficient. This study investigated the abundance and characteristics of microplastics in the sediment and surface water of the Chao Phraya River Estuary, Thailand. Concentrations of heavy metals extracted from microplastics were also reported. The abundance of microplastics in surface water and sediment was 48 ± 8 items/m3 and 39 ± 14 items/kg, respectively. Microplastics with small sizes of 0.05–0.3 mm were predominant in all collected samples. Polypropylene and polyethylene particles were the most abundant in the surface water and sediment, respectively. Toxic metals (Cr, Cu, Ni, Pb, Cd, and Zn) were found in microplastics from surface water samples. Since Chao Phraya River Estuary is an important aquaculture zone in Thailand, the presence of microplastics in this area may severely impact on aquaculture and human health. Unlabelled Image • MPs were detected in all water and sediment samples collected from CPRE. • The highest abundance of MPs was found at bank 2 of the estuary with 63 items/m3. • The variability of MPs on the Chao Phraya Estuary cross-section is not significant. • Small MPs (0.5–0.3 mm) with fragment shapes and types of PP, PE were predominant. • Ni, Cd, Pb, Cu, Zn, and Cr were detected in MPs collected from the surface water. [ABSTRACT FROM AUTHOR]

While a large number of studies on microplastics (MPs) in the western hemisphere have been performed, few studies are available in the eastern hemisphere, especially in Southeast Asia. In this study, the abundance of MPs in water and sediment samples from the Chao Phraya River at the Tha Pra Chan area, Thailand, was investigated. Water samples were collected by a manta trawl, and sediment samples were collected by a Van Veen grab sampler. The average number and concentration of MPs in water samples were 80 ± 65 items/m³ and 53.3 ± 58.4 mg/m³, respectively. The average number and concentration of MPs in sediment samples were 91 ± 13 items/kg and 4.9 ± 3.4 mg/kg, respectively. The main morphologies of MPs were fragments and fibers, mostly white. Polypropylene (PP) was the dominant polymer type found in both water and sediment. Moreover, the content of heavy metals (Cr, Cu, Ni, and Pb) on MPs was extracted by aqua regia solution and analyzed by ICP-OES. Results show high concentrations of Pb and Cu adsorbed on MPs in the study area. In brief, this study suggests that there are high levels of MPs in the water and sediments of the Chao Phraya River at the Tha Pra Chan area. Image 1 • MPs were found in water and sediment of Chao Phraya River at Tha Pra Chan. • MPs in water were detected at 80 ± 65 items/m³ and 53.3 ± 58.4 mg/m³. • MPs in sediment were detected at 91 ± 13 items/kg and 4.9 ± 3.4 mg/kg. • Most MPs were PP, PE and PS with the dominant size of 0.05–0.5 mm. • Heavy metals were found with high concentration of Pb and Cu adsorbed on MPs. [ABSTRACT FROM AUTHOR]