The research team, led by Vu Duy Vinh of the Institute of Oceanography in Vietnam together with Sylvain Ouillon of the University of Toulouse and colleagues, examined daily observations from four weather stations representing four very different settings: a coastal site (VT), a lower-delta station (VK), an estuarine location, and an inland urban station (TSH). All four records were compared over the common period 1983 to 2024, giving the analysis a robust forty-year window. The choice of stations was deliberate. In a delta where the coastline, the river network and the urban sprawl of Ho Chi Minh City all lie within a few hundred kilometres, averaging rainfall across the region would blur exactly the contrasts the scientists wanted to expose.

The first thing the records confirm is how sharply seasonal rainfall is in this part of the world. Between 75 and 85 percent of the annual total arrives during the wet season, driven by the monsoon circulation that dominates Southeast Asian climate. The stations also reveal a clear climatological gradient running from the coast inland, with rainfall amounts and behaviour shifting systematically as one moves away from the sea. That gradient matters, because it means the same large-scale climate driver can push different parts of the delta in different directions, and the new study shows that this is precisely what has been happening over the past four decades.

The most dramatic divergence appears between the coastal station and the urban one. At VT, on the coast, annual rainfall has decreased significantly since 1983. Crucially, the decline is not the result of individual storms becoming weaker; instead, it stems primarily from fewer rainfall events during the core of the monsoon season. In other words, the coast is drying not because its downpours have softened but because the rainy days themselves are becoming scarcer when it matters most. Meanwhile, just inland at VK, the lower-delta station shows no significant long-term trend at all, a reminder that even neighbouring environments in a delta can respond to climate forcing in entirely different ways.

The urban station tells the opposite story. At TSH, rainfall has been increasing, but the mechanism is different from what many might expect. The rise is driven by more frequent wet days and higher accumulated rainfall over the season, rather than by stronger peak daily precipitation. This distinction is more than academic. Urban flooding often depends on the intensity of the heaviest bursts of rain, but the total volume of water falling across a season determines how saturated ground and drainage systems become. An urban environment collecting more rain more often, without dramatic single-day extremes, faces a chronic, cumulative kind of water management challenge rather than a purely acute one.

Untangling the role of the El Niño–Southern Oscillation proved to be the study’s most technically demanding task. ENSO, the periodic warming and cooling of the tropical Pacific that reshapes weather patterns worldwide, is known to influence rainfall across Southeast Asia. Yet when the researchers directly correlated standard ENSO indices with the original rainfall measurements, the relationships were weak, with correlation coefficients below 0.2 in absolute value. On the face of it, the mighty Pacific oscillator seemed barely to register in the delta’s rain gauges.

The resolution came from a sophisticated signal-processing technique called Complete Ensemble Empirical Mode Decomposition with Adaptive Noise, or CEEMDAN. Rather than treating a rainfall record as a single undifferentiated series, CEEMDAN breaks it down into components operating on different timescales, separating short-lived fluctuations from interannual rhythms and longer-term trends. When the researchers isolated the component of the rainfall data corresponding to the ENSO frequency band and compared it with ENSO indices, the associations strengthened considerably, reaching correlations of roughly 0.3 to 0.6. The lesson is an important one for climate science: ENSO’s influence was there all along, but it was masked in the raw data by higher-frequency noise and by longer-term variability layered on top of it.

The decomposition also revealed which aspects of rainfall respond most strongly to ENSO. Rainfall frequency, the persistence of wet spells, and accumulated seasonal rainfall all showed the clearest ENSO-related relationships, while peak daily precipitation remained only weakly tied to the oscillator. This pattern fits the physical picture of how ENSO operates in the region: by shifting large-scale circulation and moisture supply over the western Pacific and Southeast Asia, El Niño and La Niña episodes tend to modulate how often and how persistently rain falls over a season, rather than dictating the intensity of any single storm. For forecasters and water managers, that means ENSO state offers a useful, if imperfect, seasonal clue about whether a wet season will be generous or stingy in total volume, even when it says little about the worst individual downpours.

The broader significance of the study lies in what it says about how long-term climate change and natural interannual variability interact. The authors conclude that long-term rainfall change and ENSO variability jointly shape rainfall extremes in the northeastern delta, and that the two forces cannot be cleanly separated in the raw observations. A coastal zone losing monsoon rain days while an inland city gains wet days is not a contradiction; it is evidence that regional responses to global forcing are filtered through local geography, land use and position relative to the sea breeze, the river plume and the urban heat island. Any flood-risk assessment for the delta that treats the region as a single unit risks getting the answer wrong in both directions, underestimating drying pressure on the coast and underestimating accumulating water loads in the city.

For the millions of people who live and farm in the Mekong Delta, the stakes could hardly be higher. The region is already identified as one of the world’s most vulnerable delta systems, with groundwater extraction driving land subsidence and sea-level rise pushing saltwater ever further inland. Rainfall that arrives less reliably on the coast, and more abundantly over expanding urban areas, adds another layer of complexity to an already precarious water balance. The study’s methodological message may prove as influential as its regional findings: by applying CEEMDAN to separate the timescales embedded in climate records, scientists can recover signals that conventional correlation analysis misses. As climate records lengthen and the need for precise, location-specific adaptation planning grows, that approach is likely to find eager users far beyond the Mekong’s embankments.

Subject of Research: ENSO modulation of extreme rainfall and contrasting coastal and urban rainfall trends in the northeastern Mekong Delta, Vietnam

Article Title: ENSO modulation of extreme rainfall and contrasting coastal–urban trends in the northeastern Mekong Delta

Article References: Vinh, V. D., Ouillon, S., Hai, N. M., Minh, P. T., Van Anh, V. T., & Thinh, N. D. (2026). ENSO modulation of extreme rainfall and contrasting coastal–urban trends in the northeastern Mekong Delta. Theoretical and Applied Climatology, 157(10), Article 674. https://doi.org/10.1007/s00704-026-06611-2

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06611-2

Keywords: ENSO, Mekong Delta, extreme rainfall, monsoon, CEEMDAN, coastal rainfall, urban flooding, Vietnam, climate variability, rainfall trends, flood risk, Theoretical and Applied Climatology

The stakes are considerable. Agriculture, forestry, and other land-use sectors account for roughly 22 percent of total global greenhouse gas emissions, and rice cultivation alone releases more than 686 million tonnes of carbon dioxide equivalent each year, according to figures cited from the FAO. Methane is the dominant culprit among paddy emissions, and its global warming potential is 28 times greater than that of carbon dioxide. The problem is particularly acute when rice straw is returned to flooded fields, a practice that builds soil organic carbon but feeds the anaerobic archaea that generate methane as a metabolic byproduct.

The research team, led by Phan Thi Ngoc Nhanh and Nguyen Quoc Khuong, focused on a setting where the challenge is compounded by soil chemistry. Acid sulfate soils, widespread in the Mekong Delta, are characterized by very low pH and high concentrations of toxic aluminum, iron, and manganese. Soil pH values in the sampled fields ranged from 3.82 to 5.30, and aluminum concentrations in some locations exceeded 235 milligrams per kilogram, well above phytotoxic thresholds. These conditions suppress both rice productivity and the activity of most soil microbes, making conventional biological approaches difficult.

Purple nonsulfur bacteria, however, are metabolic generalists. They can grow aerobically, microaerobically, or anaerobically, in light or in darkness, using a wide range of organic substrates including acetate, succinate, and pyruvate. Crucially, that substrate flexibility overlaps with the carbon sources methanogenic archaea depend on, which means the bacteria can compete directly with methane producers for food in flooded soils. Previous work had shown that related strains could reduce methane emissions in saline and heavy-metal-contaminated paddies, but acid sulfate environments remained largely unexplored.

To find suitable candidates, the researchers collected 60 soil and 60 water samples from four representative acid sulfate rice-growing regions: the Plain of Reed and the Depressed of Hau River in Dong Thap and Hau Giang provinces, the Long Xuyen Quadrangle in An Giang, and the Ca Mau Peninsula in Bac Lieu. Samples were taken 30 days after sowing, near rice roots and below the water surface, and composited from 13 points per field. The team then cultured the samples in anaerobic, illuminated tubes and purified the resulting pink, red, and purple colonies until 118 distinct strains were obtained.

Screening was deliberately brutal. Each strain was tested for growth at pH 4.5 and in the presence of iron at 200 milligrams per liter, aluminum at 100 milligrams per liter, and manganese at 1,100 milligrams per liter, concentrations mirroring the worst field conditions. More than 90 percent of the isolates grew well under the acidic conditions, and 100 strains tolerated all three metals. Those survivors were then evaluated for traits valuable to farmers: nitrogen fixation, solubilization of three insoluble phosphate forms, and production of indole-3-acetic acid, a plant growth hormone. Nitrogen fixation rates reached up to 61.9 milligrams of ammonium per liter, phosphate solubilization exceeded 180 milligrams per liter for iron phosphate in the best strains, and hormone production peaked at 14.1 milligrams per liter.

The decisive test came in sealed glass bottles containing fresh acid sulfate soil, ground rice straw, and water, with or without bacterial inoculation. After five days, headspace gas was analyzed by gas chromatography. All 20 top-performing strains reduced methane under both microaerobic light and aerobic dark conditions, but three stood out. Strain WHA-9B achieved reductions of 61.3 percent under light and 75.2 percent in the dark, while WHA-1A reached 68.6 percent in the dark and SPL-4A achieved 45.9 percent under light. Genetic sequencing of the 16S rRNA gene identified WHA-1A and SPL-4A as Rhodobacter sphaeroides and WHA-9B as Blastochloris sulfoviridis.

The mechanism, the authors argue, is substrate competition. When rice straw decomposes anaerobically, it releases acetate, hydrogen, carbon dioxide, and dissolved organic carbon, the preferred fuels of methanogenic archaea. Purple nonsulfur bacteria consume many of the same compounds, diverting carbon into bacterial biomass instead of methane. The bacteria also raise environmental pH during growth, pushing conditions beyond the optimal range of 6.4 to 7.2 for methanogens. Earlier studies support this interpretation: experiments with Rhodopseudomonas palustris found a negative correlation between bacterial cell density and methane emission, and field applications of purple bacteria have cut emissions by the equivalent of roughly three tonnes of carbon dioxide per hectare per season.

The nutrient-supplying traits add a second layer of benefit. By fixing atmospheric nitrogen, the bacteria could reduce dependence on synthetic fertilizers, which themselves stimulate methanogenic activity in flooded soils. By solubilizing the insoluble iron, aluminum, and calcium phosphates that lock up phosphorus in acid sulfate soils, they make a critical nutrient available to rice roots. And by producing indole-3-acetic acid, they promote root development, which improves oxygen transport into the rhizosphere and further suppresses methane production. In principle, a single inoculant could detoxify the soil, feed the plant, and starve the methane producers all at once.

The authors are careful to note the limits of the work. The methane assays were conducted in controlled incubations, and the study did not directly measure changes in methanogen or methanotroph communities, so the proposed mechanisms remain inferential. They recommend follow-up research using quantitative PCR of methanogenic marker genes such as mcrA or high-throughput sequencing to confirm how the bacteria reshape the microbial food web. Even so, the identification of acid- and metal-tolerant strains that combine methane mitigation with plant growth promotion marks a promising step toward biofertilizers tailored to one of the world’s most challenging rice-growing environments, where the dual pressures of food security and climate change meet in the mud.

Subject of Research: Isolation of acid sulfate-tolerant purple nonsulfur bacteria that mitigate methane emissions and supply nutrients in Mekong Delta rice paddies

Article Title: Selection of acid sulfate purple nonsulfur bacteria for mitigating methane emissions from paddy soils in the Mekong Delta, Vietnam

Article References: Nhanh, P. T. N., Nhan, T. C., Bao, M. C., Quang, L. T., Thu, L. T. M., Trong, N. D., Nguyen, T. T. K., Xuan, L. N. T., Xuan, D. T., Phuc, N. T. H., & Khuong, N. Q. (2026). Selection of acid sulfate purple nonsulfur bacteria for mitigating methane emissions from paddy soils in the Mekong Delta, Vietnam. International Microbiology. https://doi.org/10.1007/s10123-026-00883-4

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00883-4

Keywords: purple nonsulfur bacteria, methane emissions, acid sulfate soils, Mekong Delta, rice paddies, greenhouse gases, Rhodobacter sphaeroides, Blastochloris sulfoviridis, nitrogen fixation, phosphate solubilization, biofertilizer, soil microbiology

The three-spot gourami is easy to recognize. Its laterally compressed body carries two distinct black spots along the flanks, adults display faint vertical stripes, and its dorsal fin, shorter than the anal fin, bears both spines and soft rays. Individuals typically reach about ten centimeters in length. The species thrives in ponds, swamps, canals, and floodplains throughout the Mekong River basin, where submerged vegetation offers both shelter and feeding grounds in water temperatures between 24 and 30 degrees Celsius. Beyond its role in local food webs, where it serves as prey for larger carnivores such as the snakehead Channa striata and the striped catfish Pangasianodon hypophthalmus, the gourami is prized in the ornamental fish trade, making its biology relevant to both ecologists and aquaculturists.

To build their dataset, the researchers collected 32 specimens from Tra Su in March 2025 using hand nets with a 2.5 centimeter mesh, preserving the fish in 4 percent formalin before laboratory analysis. In the lab, they recorded total length, standard length, body weight, eye diameter, interorbital distance, body depth, head length, and mouth width, along with fin ray counts for the pectoral, pelvic, dorsal, anal, and caudal fins. The fish sampled ranged from 6.70 to 9.00 centimeters in total length, averaging 7.76 centimeters, and weighed between 4.10 and 10.30 grams with a mean of 6.50 grams. This meticulous measurement campaign provides a baseline against which future populations can be compared, a critical tool in a region where freshwater ecosystems are under mounting pressure.

The meristic counts revealed a remarkably stable anatomical blueprint. Caudal fins carried 14 to 16 rays, with 16 the most frequent. Each pelvic fin consistently bore a single ray, while the pectoral fins consisted of two elongated filaments positioned anterior to the anal fin. Dorsal fins held 5 to 7 spines, most commonly 7, and 6 to 10 soft rays, typically 8 or 9. The anal fin showed a fixed count of 11 spines with 30 to 35 soft rays, most often 32 or 33, and pectoral fins carried 8 to 12 rays, usually 9 or 10. These figures align closely with earlier descriptions from the Mekong Delta and Cambodia, reinforcing the view that the species maintains morphological stability across varied environmental conditions and strengthening the taxonomic foundation for identifying T. trichopterus in the region.

Growth analysis delivered one of the study’s most consequential findings. Using the classic length-weight relationship, in which body weight scales with total length raised to an exponent b, the team estimated a growth coefficient of 2.98 plus or minus 0.16, statistically indistinguishable from 3, the hallmark of isometric growth. In practical terms, the fish gains weight in proportion to its length, reflecting balanced somatic development. The coefficient of determination exceeded 0.93, meaning more than 93 percent of the variation in body weight was explained by length alone. Comparable near-isometric patterns have been reported for the species in the Ogan Ilir peat swamp of South Sumatra, Indonesia, and for other Mekong Delta fishes such as the tank goby Glossogobius giuris, though the exponent is known to shift with environmental conditions.

That flexibility was underscored by aquaculture experiments elsewhere, in which probiotic-supplemented diets containing Bacillus subtilis and B. circulans pushed the growth exponent to 3.28, indicating positive allometric growth, while control groups ranged from 2.41 to 2.93. The Tra Su result, sitting almost exactly at isometry, suggests the wetland provides a stable and adequate natural food supply for the gourami, a positive indicator of habitat quality. The regression equation derived from the study can now serve as a practical tool for estimating biomass, monitoring growth, and managing resources in both wild and cultured populations, reinforcing the ecological case for continued conservation of the Tra Su landscape.

The study’s anatomical detective work focused on the digestive system, where the evidence pointed firmly toward an omnivorous lifestyle. The gourami possesses a terminal, slightly upward-facing mouth with a subtly protruding lower jaw, an arrangement suited to surface feeding. Its jaws are lined with numerous small, conical teeth arranged in continuous rows, an adaptation for grasping and scraping soft-bodied prey rather than tearing flesh. The tongue is elongated, flattened, and studded with a row of small V-shaped spots, a region rich in taste receptors that supports sophisticated orosensory food testing. The gill arches carry thin, elongated, closely spaced rakers, a fine filtration apparatus adapted for capturing plankton, in sharp contrast to the shorter, thicker rakers of sympatric predatory gobies.

Further down the tract, the anatomy tells the same story. A short esophagus leads to a sac-like stomach with thickened walls, followed by an extended, tightly coiled intestine ranging from 9.0 to 26.0 centimeters, averaging 17.04 centimeters, a length adapted to processing a mixed diet of plant and animal material. The relative gut length, the ratio of gut length to total body length, averaged 2.19 plus or minus 0.09, squarely within the 1 to 3 range that defines omnivores. This finding revises earlier classifications that labeled the species carnivorous, and it contrasts instructively with relatives: the congeneric Trichogaster fasciata shows a much higher relative gut length of 5.12, consistent with herbivory, while carnivorous Mekong gobies possess markedly shorter intestines.

Stomach content analysis confirmed the omnivorous verdict and revealed a striking dietary hierarchy. Fish eggs appeared in 45 percent of gut samples and dominated by biovolume at 38.02 percent, followed by zooplankton at 33.99 percent and Chlorophyta green algae at 16.98 percent. Euglenophyta, Cyanophyta, and Bacillariophyta contributed smaller shares between 1.37 and 6.15 percent. A modified Costello diagram, plotting frequency of occurrence against volumetric contribution, identified fish eggs as the primary food resource, with zooplankton and Chlorophyta serving as important supplemental items and the remaining algal groups likely ingested incidentally. The pattern reveals an opportunistic omnivore with a pronounced preference for high-protein prey, consistent with reports from Indian coastal wetlands where the species consumed detritus, algae, zooplankton, and even plastic debris.

The implications ripple outward from Tra Su. Freshwater habitats cover only 0.1 percent of the Earth’s water surface yet harbor roughly 40 percent of known fish species, and freshwater fishes rank as the second most threatened vertebrate group after amphibians, with about 20 percent of species projected to face extinction within the next 25 to 50 years. Tra Su itself presents harsh conditions, with water pH as low as 2.75, dissolved oxygen frequently below 5 milligrams per liter, and elevated ammonium and total iron concentrations, making the gourami’s success there a testament to its adaptability. By documenting stable morphology, isometric growth, and a flexible omnivorous diet, the study establishes the foundational knowledge needed for taxonomic work, ecological monitoring, artificial breeding programs, and sustainable fisheries management. The authors point toward ecological aquaculture as a promising avenue, urging further research into reproductive biology, population genetics, and adaptive capacity under culture conditions, work that could help safeguard both the species and the livelihoods that depend on the Mekong Delta’s vanishing wetlands.

Subject of Research: Morphometrics, growth pattern, and feeding ecology of the three-spot gourami Trichopodus trichopterus in the Tra Su wetlands of the Vietnamese Mekong Delta

Article Title: First report on morphometrics, length–weight relationship, feeding habit, and diet composition of Trichopodus trichopterus from Tra Su, An Giang, Vietnam

Article References: Nguyen, V. Q., Van Ly, V., Vo, L. T. T., Nguyen, H. T. K., & Dinh, Q. M. (2026). First report on morphometrics, length–weight relationship, feeding habit, and diet composition of Trichopodus trichopterus from Tra Su, An Giang, Vietnam. Discover Animals, 3(1), Article 87. https://doi.org/10.1007/s44338-025-00130-6

Image Credits: AI Generated

DOI: 10.1007/s44338-025-00130-6

Keywords: Trichopodus trichopterus, three-spot gourami, Mekong Delta, Tra Su, morphometrics, length-weight relationship, isometric growth, omnivorous diet, fish eggs, zooplankton, freshwater conservation, Vietnam