Stable isotopes as an effective tool for N nutrient source identification in a heavily urbanized and agriculturally intensive tropical lowland basin

© 2020, Springer Nature Switzerland AG. We present the application of dual stable isotope analyses of NO3 (δ15N-NO3 and δ18O-NO3) to provide a comprehensive assessment of the provenance, partitioning, and conversion of nitrate across the Day River Basin (DRB), Vietnam, which is heavily impacted by agriculture and urbanization. Stable isotope compositions of river water δ18O-H2O, in addition to their δ15N-NO3 and δ18O-NO3 signatures, were sampled at 12 locations in the DRB. Sample collection was conducted during three different periods to capture changes in regional weather and agricultural fertilization regimes; April (the dry season and key fertilization period), July (the rainy season and another key fertilization period) and October (the rainy season with no regional fertilization). Ranges of NO3 stable isotopes are − 7.1 to + 9.2‰ and − 3.9 to + 13.2‰ for δ18O and δ15N, respectively. Interpretation of the stable isotope data characterizes 4 main sources of NO3 in the DRB; (1) nitrified urea fertilizer derived from an intensive agricultural irrigation network, (2) soil and groundwater leaching from within the basin (3) manure and sewage inputs (which is more prevalent in downstream river sections) and (4) upstream inflow from the Red River which discharges into the Day River through the Dao River. We applied a mixing model for the DRB consisting of 4 variables, representing these 4 different sources. The partition calculation shows that during the fertilization and rainy period of July, more than 45% of river NO3 is derived from nitrified urea sources. During the other sampling periods (April and October), manure and sewage contribute more than 50% of river NO3 and are derived from the middle portion of the DRB, where the Day River receives domestic wastewater from the Vietnamese capital, Hanoi. Stable isotope data of O and N reveal that nitrification processes are more prevalent in the rainy season than in dry season and that this predominantly takes place in paddy field agricultural zones. In general, data demonstrate that nitrate loss in the DRB is due to denitrification which takes place in polluted stretches of the river and dominates in the dry season. This study highlights that (i) domestic waste should be treated prior to its discharge into the Day River and (ii) the need for better catchment agricultural fertilization practices as large portions of fertilizer currently discharge into the river, which greatly impacts regional water quality

Nitrate pollution in the Red River Delta

The Red River Delta is home to the capital of Vietnam, Hanoi. The large population relies on the catchment for the provision of primary water resources for its industry and agriculture. This critical reserve is rapidly becoming impacted by anthropogenic activities and we demonstrate how nitrate pollution, in particular, is influencing the health of the Red River Delta

Study on total lipid content, lipid class composition of some fire and soft corals collected in Nha Trang, Vietnam

For the first time, the total lipid content and lipid class composition of  the Vietnamese soft corals (Sinularia brassica, Sinularia flexibilis) and fire corals (Millepora dichotoma, Millepora platyphylla) were investigated. The results indicated that the total lipid content of the investigated species was significantly different. Compositions of the lipid classes were analyzed using TLC and image analysis program Sorbfil TLC Videodensitometer DV and the results showed that phospholipids (PL, 10.91–16.02%), monoalkyldiacylglycerols (MADAG, 20.69-39.92%) and hydrocarbon wax (HW, 29.83-37.17%) were the main lipid classes of the total lipid in soft coral species. Meanwhile, PL (24.11-33.23%), TG (14.27–34.92%), ST (10.10–14.50%) and HW (12.08–19.95%) were predominant in fire coral species. ST, TG and FFA contents in soft and fire corals were at low level. DG was only present in the Sinularia flexibilis but not in other studied corals

Identifying the controls on nitrate and metabolic state within the Red River delta (Vietnam) with the use of stable isotopes

In many places around the world, anthropogenic activities have resulted in nitrate (NO3−) pollution and changes in the metabolic state of aquatic ecosystems. Here we combined stable isotope and physico-chemical monitoring to assess the sources of NO3− and the overall metabolic state within the Red River delta, Vietnam. River water stable isotope compositions (δ18O-H2O) ranged between −11.2 and −2.7 ‰, δ18O-NO3− between −7.1 and + 29.7 ‰ and δ15N-NO3− between −3.9 and + 14.0 ‰. We identified the dominant NO3− sources as: 1) soil leachate, 2) domestic waste flushed from urban areas, and 3) NH4+ fertilizers washed from paddy fields. The relative impact of each source depends on geographical location within the delta and the time of year, due to dilution and concentration effects during wet and dry seasons. The primary NO3−source upstream is natural soil leachates, predominantly from tributaries connected to the Red River’s main stream. Within the middle-lower section of Red River delta, urban pollution from manure and septic waste reaches as high as 50 % of the total NO3− load during dry season. NO3− leached from fertilizers is also high at sites in the middle of the delta, related to agricultural activities. Dissolved oxygen isotope (δ18O-O2) values calculated from δ18O-H2O and δ18O-NO3− values indicate that the aquatic metabolism is net autotrophic (oxygen from primary production exceeds consumption by respiration), but high inputs of biodegradable organic matter from untreated domestic waste and high rates of sediment oxygen demand (SOD) and chemical oxygen demand (COD) have resulted in the whole river system becoming undersaturated in oxygen. High NO3− loads and low DO saturation are of critical concern and require mitigation practices to improve water quality for millions of people

Evaluation of awake prone positioning effectiveness in moderate to severe COVID-19

Evidence mainly from high income countries suggests that lying in the prone position may be beneficial in patients with COVID-19 even if they are not receiving invasive ventilation. Studies indicate that increased duration of prone position may be associated with improved outcomes, but achieving this requires additional staff time and resources. Our study aims to support prolonged (≥ 8hours/day) awake prone positioning in patients with moderate to severe COVID-19 disease in Vietnam. We use a specialist team to support prone positioning of patients and wearable devices to assist monitoring vital signs and prone position and an electronic data registry to capture routine clinical data

Water quality and nutrient transfers in the continuum from the upstream red river basin to the Delta (budget and modelling)

L objectif de ce travail est d analyser les contributions du basin amont du Fleuve Rouge au delta et d étudier les transformations et rétentions de matière au sein du delta. Le bilan hydrologique a été établi pour les 2 années 1996 et 2006, le DFR peut exporter annuellement 100 à 140 km3 d eau à la mer. Des bilans agricoles ont été établis pour les 5 sous-bassins, en termes de flux entrant et sortant de matière en suspension et de nutriments, de la production agricole et de consommation. Le bassin amont exporte 160.106 kgN/an vers le delta, le flux de nutriments exporté à l exutoire du delta est seulement de 130.106 kgN/an, ce qui indique un taux de rétention de 43% pour azote. Le flux de phosphore à l exutoire du delta est 32.106 kgP/an, ce qui représente une rétention de 50%. Par contre la rétention de silice est faible, de l ordre de 8% par an. Les valeurs de N-ICEP (-10.2 kgC/km /jour) and the P-ICEP (-19.9 kgC/km /jour) diminuent par rapport à l amont du delta, montrant un effet bénéfique du delta par rapport à l eutrophisation; de plus avec de valeurs qui diminuent à l exutoire du delta au dessous du zéro, les risques d eutrophication des zones côtières seraient limités. L implémentation du modèle Rivertrahler pour le système Nhue Day permet de calculer les variations géographiques et saisonnières du débit, de la qualité de l eau et du fonctionnement écologique du réseau hydrographique. Le modèle a été validé pour ces trois années 2006, 2007 et 2008. Le modèle a enfin été utilisé pour explorer divers scénarios de possibles changements futurs du delta concernant l usage du sol et l agriculture, la population et son régime alimentaire et sa gestion des eaux usées.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceViet-NamFRV

A prospective scenario for the Red River Delta at 2050 horizon

Based on the use of the Seneque/Riverstrahler model, a prospective scenario of water quality has been developed based on expected demographic, land use and agricultural production changes in the Red River delta in northern Vietnam in order to evaluate the resulting changes in water pollution and nutrient loading delivered to the coastal zone at the horizon 2050. The Vietnamese population is predicted to reach 112 million in 2050 with 57% that live in urban area. The amount of wastewater expressed in kg of suspended matter, N and P per inhabitant per day is estimated to decrease by about 10% in 2050 compared with current values. On the other hand, the wastewater discharge should increase twice, i.e. to 200 l/inhabitant/day. Besides, if the productivity of agriculture in the Red River Delta is to be nearly doubled in the future, this would likely result in a N surplus of about 150 kgN/ha/yr on the agricultural soils. Assuming the same leached fraction as currently observed, this would imply a mean leaching rate of 15 kgN/ha/yr, i.e. 3 times the present level. By applying the above scenario to the Red River delta, our simulation shows that nutrient elements such as ammonium, phosphorus and silica seem to remain at the same concentration value. However, the concentration of these last elements will be largely on the dependence of the water volume due to the flood. Indeed, the delta floodplain improves largely the biogeochemical processes involved in the nutrient recycling. Our modelling results highlight that the Red River Delta system is already at its maximum of the nutrient recycling capacity. So an increase of discharge from urban wastewaters and from agricultural intensification will lead immediately and definitely to an increase of the polluted waters in the hydrological system of the Nhue and Day Rivers, in spite of efforts in urban wastewater treatments