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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 (CO 2) 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 CO 2 , methane (CH 4) and nitrous oxide (N 2 O) 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 CO 2 , CH 4 and N 2 O at the Saigon River in 2019–2020 were 3174 ± 1725 μgC-CO 2 L−1, 5.9 ± 16.8 μgC-CH 4 L−1 and 3.0 ± 4.8 μgN-N 2 O 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 CO 2 concentration had no clear seasonal pattern, N 2 O and CH 4 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 N 2 O concentrations in this urban area of the estuary. The high concentration of CO 2 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. [Display omitted] • Supersaturation of CO 2 , CH 4 , N 2 O are observed in the Saigon River, an urbanized estuary. • Concentrations of N 2 O and CH 4 have significant seasonal differences. • Eutrophication has linear relationships with CO 2 , CH 4 , N 2 O. • Supersaturation of CO 2 is dominant even under the extreme eutrophication state. [ABSTRACT FROM AUTHOR]

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. • Anthropogenic fibres in clams were 3.6 ± 2.1 fibres individual−1 or 2.7 ± 2.4 fibre g−1 ww. • Higher fibre accumulation was observed in the remaining tissues. • Fibre concentrations in all the clam tissues did not vary temporally. • Fibres may accumulate by adherence to remaining tissues. [ABSTRACT FROM AUTHOR]

Anthropogenic fibers, gathering synthetic fibers, artificial fibers and natural fibers are ubiquitous in the natural environment. Tremendous concentrations of anthropogenic fibers were previously measured in the tropical Saigon River (Vietnam), i.e. a river impacted by textile and apparel industries. In the present study, we want to examine the role of contrasted seasonal variation (e.g., dry and rainy seasons), via the rainfall and monthly water discharges, and of water's physico-chemical conditions on the concentrations of anthropogenic fibers in the surface water. The one year and half monthly survey evidenced that concentrations of anthropogenic fibers varied from 22 to 251 items L−1 and their variations were not related to rainfall, water discharge or abiotic factors. However, their color and length distribution varied monthly suggesting variations in sources and sinks. Based on the 2017 survey, we estimated an annual emission of anthropogenic fibers from the river to the downstream coastal zone of 115–164 × 1012 items yr−1. Image 1 • Anthropogenic fibers were monitored during contrasted seasons in a tropical river-estuary. • Anthropogenic fiber's concentrations ranged from 22 to 251 items L−1. • Fiber's concentrations are not influenced by change of TSS, pH, O 2 , conductivity. • No seasonal variation of fiber concentrations were observed. • Anthropogenic fiber's emission from river to sea were estimated 115–164 1012 items yr−1. Anthropogenic fibers in the Saigon River varied from 22 to 251 items L−1 over eighteen months and their variations were not related to rainfall, water discharge or abiotic factors. [ABSTRACT FROM AUTHOR]

The current study was conducted to (1) examine seasonal and spatial distribution of heavy metals and metalloid in sediment from the Saigon River and (2) apportion and quantify their pollution sources. Ninety-six sediment samples were taken in the rainy and dry season on 13 sampling sites, distributed over the lower reaches of the River, to analyze for exchangeable concentration of 11 heavy metals and metalloid (Al, B, Cd, Co, Fe, In, Mn, Ni, Pb, Sr, and Zn), pH, EC, organic carbon content, and particle-size distribution. Generally, the concentration of 11 elements was ranked in the order Mn > Al > Fe > Zn > Sr > In > B > Ni > Co > Pb > Cd. Hierarchical cluster analysis grouped 13 sampling sites into two parts based on the similar concentration of the 11 elements. Three-way analysis of variance showed that the total exchangeable concentration of 11 elements was significantly higher in the rainy season than in the dry season and in the upper part than in the lower part of the river. Principal component analysis/factor analysis and correlation analysis revealed that three pollution sources (PS) may contribute to enriching the 11 examined elements in the sediment. These sources included (PS1) from catchment through water erosion over natural areas, explaining 83%, (PS2) mixed sources from catchment through water erosion over agricultural fields and inside Ho Chi Minh City, accounting for 6%, and (PS3) mixed sources from lowland areas, explaining 7.8% of the total variance of the elements. In brief, the sediment concentration of 11 metals and metalloid varied with season and space and three major pollution sources from river catchment, inside Ho Chi Minh City, and lowland contributively enriched the elements in the sediment of the River. Image 1 • Sediment can serve as a sink/source of heavy metals (HM) for aquatic ecosystems. • 11-HM concentrations in sediment from the Saigon River varied with season and space. • Rainy season had significantly higher concentration of 11 HMs than the dry season. • River catchment, inside Ho Chi Minh City, and lowland were major sources of 11 HMs. [ABSTRACT FROM AUTHOR]