Significant Seasonal Variation Research Articles

Microbiological water quality assessment of swimming pools and jacuzzis in Northern Greece: a retrospective study.

Swimming pools and jacuzzis can pose significant public health risks as potential sources of infections. The present study aimed to evaluate the prevalence and concentration of microbiological indicators in recreational water facilities in Thessaloniki, Northern Greece, focusing on their hygiene status before and after the COVID-19 pandemic. Between January 2018 and December 2022, 1114 water samples were analyzed by the regional Water Hygiene Laboratory at Aristotle University of Thessaloniki, using standardized ISO methods. Jacuzzis exhibited the highest microbial contamination, particularly for Pseudomonas aeruginosa (19.7%), while indoor adult pools showed the lowest. Overall, P. aeruginosa was found in 12.4% of samples, with the highest concentrations in jacuzzis (median: 30 CFU/100 ml). Significant seasonal variations were identified in the prevalence of total microbial flora (p < 0.001) and total coliforms (p = 0.03), as well as in the concentration of residual chlorine (p = 0.023). During the COVID-19 pandemic, microbial prevalence decreased across facilities. We concluded a strong compliance with Greek and international microbiological standards. The decline in microbial prevalence overtime likely reflects the impact of the strict hygiene measures implemented during the pandemic. These findings highlight the importance of maintaining rigorous hygiene practices to protect public health.

Remote Sensing Estimation of CDOM for Songhua River of China: Distributions and Implications

Rivers are crucial pathways for transporting organic carbon from land to ocean, playing a vital role in the global carbon cycle. Dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) are major components of dissolved organic matter and have significant impacts on maintaining the stability of river ecosystems and driving the global carbon cycle. In this study, the in situ samples of aCDOM(355) and DOC collected along the main stream of the Songhua River were matched with Sentinel-2 imagery. Multiple linear regression and five machine learning models were used to analyze the data. Among these models, XGBoost demonstrated a superior, highly stable performance on the validation set (R2 = 0.85, RMSE = 0.71 m−1). The multiple linear regression results revealed a strong correlation between CDOM and DOC (R2 = 0.73), indicating that CDOM can be used to indirectly estimate DOC concentrations. Significant seasonal variations in the CDOM distribution in the Songhua River were observed: aCDOM(355) in spring (6.23 m−1) was higher than that in summer (5.3 m−1) and autumn (4.74 m−1). The aCDOM(355) values in major urban areas along the Songhua River were generally higher than those in non-urban areas. Using the predicted DOC values and annual flow data at the sites, the annual DOC flux in Harbin was calculated to be approximately 0.2275 Tg C/Yr. Additionally, the spatial variation in annual CDOM was influenced by both natural changes in the watershed and human activities. These findings are pivotal for a deeper understanding of the role of river systems in the global carbon cycle.

Investigation of the Origin of Elevated Amounts of Iron and Manganese in a Dam Reservoir

On the outskirts of the Pinios dam reservoir (Ilia Regional Unit, Greece), a water treatment plant serves the water supply needs of the surrounding municipalities, in which high concentrations of Fe and Mn, before treatment, have been observed. The main purpose of this research was to investigate the mechanism of increased iron (Fe) and manganese (Mn) levels in the reservoir of the Pinios dam, which impacts its water treatment plant operation. A wide range of hydrochemical and sedimentological analyses were conducted over a hydrological year, focusing on the spatial and temporal distribution of Fe and Mn in both water and sediment samples across the established research monitoring stations. Sediment samples from the reservoir’s bottom revealed predominantly fine-grained material, rich in total organic carbon, with elevated Mn and Fe oxide levels. Significant seasonal variations in Fe and Mn levels were also discovered, with higher Mn levels observed in the anoxic bottom waters of the reservoir during the dry season, attributed to the reduced conditions favoring Mn oxide dissolution over Fe. Conversely, during the wet season, a homogenization of metal concentrations throughout the water column was observed due to increased oxygenation and freshwater inflow. These outcomes were confirmed by the hydrochemical analysis, indicating that the redox conditions, pH, and temperature, as well as the presence of organic matter, significantly influence the mobility and bioavailability of these metals in the reservoir. The findings of this study clarify that the high concentration of Fe and Mn can be linked to the mineral composition of the upstream Neogene and flysch formations in the study area. As these formations are affected by geological weathering, they tend to enrich the streams, through soil erosion and runoff processes, with metals like Fe and Mn, which are eventually transported into the dam reservoir. This study highlights the critical influence of lithological, sedimentological, and hydrological factors on the redox conditions and seasonal stratification that govern the behavior of Fe and Mn concentrations and mobility in dam reservoirs. These findings are critical for informing water resource management practices and dam infrastructure operators and developing effective environmental conservation strategies in similar cases.

Properties of Biofilm Prokaryotic and Eukaryotic Communities in a Representative Hypereutrophic Urban River

ABSTRACT Biofilms play an important role in nutrient and food web dynamics of shallow aquatic ecosystems. Multiple prokaryotic and eukaryotic microorganisms within biofilms interact with each other to shape the community structure and their functional attributes. However, there is no clear understanding of varied patterns of biofilm prokaryotic versus eukaryotic microbial abundances, diversities and communities, which limit our understanding of how biofilm communities and functions in hypereutrophic urban river ecosystems are changing. To elucidate the properties of biofilm communities and controls on biofilm communities in a hypereutrophic urban river, we conducted a one‐year study to investigate the seasonal and water‐depth variations on the abundance/biomass, diversity and structure of biofilm prokaryotic and eukaryotic communities. The structure and dynamics of biofilm prokaryotic and eukaryotic communities were determined by high‐throughput sequencing based on the 16S and 18S rRNA gene. Sequencing revealed that Proteobacteria, Bacteroidota and Cyanobacteria were the three dominant phyla in biofilm prokaryotic communities, and Rotifera, Chlorophyta, Annelida and Bacillariophyta were the four dominant phyla in biofilm eukaryotic communities. Biofilm bacterial abundance depended mainly on the water temperature, whereas biofilm algal biomass correlated with rotifer grazing and light levels. Prokaryotic communities had higher species richness and diversity than eukaryotic communities. Species richness and diversity displayed significant seasonal variations with minima for prokaryotic communities in winter and eukaryotic communities in summer, which were linked to water temperature and rotifer grazing, respectively. Variations in biofilm prokaryotic and eukaryotic community composition were mainly related to ammonia concentration and water temperature, respectively. The co‐occurrence network analysis suggested that rotifer grazing could considerably decrease the complexity of the biofilm network in summer, and the algal groups, especially for Chlorophyta and Bacillariophyta, were the key to the formation of stable biofilm networks. There were significant differences in seasonal and water‐depth heterogeneity of biofilm prokaryotic and eukaryotic community composition. Our findings indicate that variations in water temperature, light level, rotifer grazing and nutrients (especially ammonia) appreciably contribute to changes in the abundance, diversity and composition of biofilm prokaryotic versus eukaryotic communities in the hypereutrophic urban river. These findings increase our understanding of biofilm community characteristics in hypereutrophic urban rivers and provide insights for water pollution remediation strategies.

Litter decomposition and nutrient dynamics in a subtropical ecosystem: A comparison of natural and plantation forests (Duabanga grandiflora) in Nagaland, North-East India

Forest litter decomposition is vital for nutrient cycling and carbon turnover. To investigate their decomposition rate, we conducted a litter bag experiment in plantation forests (PF) and natural forests (NF) in a subtropical ecosystem. Our findings showed significant seasonal variation in litter mass loss (p < 0.0001) between the two sites, indicating seasonality as the main driver of decomposition. The decay rate constant (k) expressed in day⁻¹, reflecting the fraction of litter mass lost per day due to decomposition, reveals that NF has higher k value of 0.007 day⁻¹ than PF at 0.005 day⁻¹ , indicating faster decomposition in NF. This constant is essential for predicting litter breakdown duration, highlighting decomposition dynamics between sites, suggesting that even minimal distances between forest types can affect organic matter breakdown. In both sites, litter mass loss varied significantly from the initial to the final year (p < 0.001), with peak rates during the monsoon, followed by pre-monsoon and dry periods. Mixed litter in NF experienced a 99.94 % loss after 730 days, while PF, saw 97.80 % loss. Carbon, lignin, nitrogen, and potassium concentrations were higher during the monsoon and pre-monsoon seasons at both sites. Except for phosphorus in PF, all soil parameters positively correlated with mass loss, along with litter parameters C, N, P, K, and lignin (p < 0.001). Litter decomposition was higher in NF than PF, with significant seasonal effects (p < 0.0001), highlighting seasonality over litter mixture effects. Understanding climate variability and species diversity is essential for sustainable forest management amid ongoing anthropogenic land-use changes.

Effects of Mesoscale Eddies on Southern Ocean Biogeochemistry.

The Southern Ocean is rich in highly dynamic mesoscale eddies and substantially modulates global biogeochemical cycles. However, the overall surface and subsurface effects of eddies on the Southern Ocean biogeochemistry have not been quantified observationally at a large scale. Here, we co-locate eddies, identified in the Meta3.2DT satellite altimeter-based product, with biogeochemical Argo floats to determine the effects of eddies on the dissolved inorganic carbon (DIC), nitrate, and dissolved oxygen concentrations in the upper 1,500m of the ice-free Southern Ocean, as well as the eddy effects on the carbon fluxes in this region. DIC and nitrate concentrations are lower in anticyclonic eddies (AEs) and increased in cyclonic eddies (CEs), while dissolved oxygen anomalies switch signs above (CEs: positive, AEs: negative) and below the mixed layer (CEs: negative, AEs: positive). We attribute these anomalies primarily to eddy pumping (isopycnal heave), as well as eddy trapping for oxygen. Maximum anomalies in all tracers occur at greater depths in the subduction zone north of the Antarctic Circumpolar Current (ACC) compared to the upwelling region in the ACC, reflecting differences in background vertical structures. Eddy effects on air-sea exchange have significant seasonal variability, with additional outgassing in CEs in fall (physical process) and additional oceanic uptake in AEs and CEs in spring (biological and physical process). Integrated over the Southern Ocean, AEs contribute 0.01 Pg C (7 ) to the Southern Ocean carbon uptake, and CEs offset this by 0.01 Pg C (2 ). These findings underscore the importance of considering eddy impacts in observing networks and climate models.

Daily Light Integral Maps for Agriculture Lighting Design in Spain

The Daily Light Integral (DLI) is a key metric to optimise plant cultivation, influence photosynthesis, morphology, yield, and nutritional quality. Our study focuses on (i) the creation of the spatiotemporal DLI map for a representative Mediterranean country, Spain, (ii) the presentation of the improved semi-automatic DLI mapping workflow, (iii) the challenge of the comparability of different DLI value scalings in global (continent) and local context (country). DLI maps provide essential insights into the spatial and temporal distribution of natural and artificial light, critical for optimizing agricultural practices and enhancing crop yields. Spain's diverse topography and climate create significant regional and seasonal variations in DLI values. Using data from SunTracker Technologies and global weather stations, we developed detailed DLI maps at 30-meter resolution. These maps reveal high DLI values in coastal and southern regions, especially in summer, and lower values in northern and interior regions during winter. Our findings emphasize the importance of tailored lighting strategies in agriculture, suggesting higher scaling (from 5 to 2 mol·m−2·d−1) resolution for European contexts. This research underpins the development of smart agricultural systems that both quantitatively and qualitatively regulate lighting conditions (supplementary light and shading management) to maximize crop productivity and sustainability. Integrating DLI maps with IoT and AI technologies offers predictive insights for precision agriculture, highlighting the need for advanced training to leverage these tools effectively.

Prey availability and diet composition of the Grey plover (Pluvialis squatarola) during migration on the South-Western Black Sea coast, Bulgaria

Migratory waders use stopover sites to refuel for the next stages of their migration, relying on seasonally abundant prey. Migration success depends on food quality and availability at these key sites. We studied the diet composition and preferences of the Grey Plover (Pluvialis squatarola) at its migration stopover at Pomorie Lake on the South-Western Black Sea coast, Bulgaria through DNA metabarcoding of faeces collected in autumn 2020 and spring 2021. Prey availability samples were also collected from the surf zone and the supralittoral sandy shore habitats in the study area.Grey Plover had a broad diet spectrum, with 332 prey taxa in total identified by metabarcoding. Both terrestrial and marine taxa were found, suggesting that the birds use multiple coastal habitats for foraging. Terrestrial arthropods, particularly insects, predominated in the Grey Plover diet; mytilid bivalves were the most represented marine taxon. The birds had a generalist feeding strategy, with diverse prey items eaten in small quantities. Most Grey Plovers fed on insects (Diptera, Lepidoptera, Hymenoptera), but some individuals showed specialisation for other taxa (mussels, spiders, polychaetes). The most abundant potential prey in the environment were not the most frequently consumed, but it is possible the prey sampling failed to capture the whole spectrum of available prey due to methodological limitations.We found no significant seasonal variation in Grey Plover diet composition, but the proportions of some prey taxa in the diet changed slightly, probably reflecting seasonal differences in their abundance and activity in coastal habitats.Our results contribute to the knowledge of Grey Plover diet, prey choice and habitat use in a little-studied region, and could help design effective conservation measures to preserve habitat quality at stopover sites for this wader and others with similar ecology.

Arcobacter species isolated from human stool samples, animal products, ready-to-eat salad mixes, and ambient water: prevalence, antimicrobial susceptibility, and virulence gene profiles

IntroductionArcobacter species are emerging foodborne pathogens increasingly associated with human illness worldwide. They are commonly found in the gastrointestinal tracts of animals and are frequently isolated from various food sources, including raw meat, poultry, and seafood. The aim of this study is to investigate the antimicrobial resistance patterns of Arcobacter spp. isolated from human stool samples, animal products, ready-to-eat salad mixes, and ambient water, assess the presence of resistance genes, and explore their potential implications for public health.MethodsIn this study, a total of 683 samples were collected from the Shahrekord area over a 12-month period. Samples were obtained from human stool, chicken meat, raw cow milk, RTE salad mixes, and environmental water sources. Two different methods were used to detect Arcobacter, depending on the sample type: bacteriological isolation and identification, and molecular identification. After identification, antimicrobial susceptibility testing was conducted. Polymerase chain reaction (PCR) was used to identify ten putative Arcobacter virulence and resistance genes.FindingsThe results revealed that Arcobacter spp. were present in 26.06% (178 out of 683) of the tested samples, with varying isolation rates across different sample types. A. butzleri being the most commonly isolated species across all sample types, while A. cryaerophilus was restricted to RTE salads, surface waters, and chicken meat. Notably, A. skirrowii was only isolated from chicken meat and environmental water. The differences of Arcobacter spp. in prevalence between the sample types were statistically significant (p < 0.05), and no significant seasonal variation was found across the sampling periods (p > 0.05). PCR analysis for ten putative virulence genes indicated that the cadF gene was present in all Arcobacter isolates. Similarly, 83.33% of the tested strains harbored the ciaB gene, while other genes were less frequently detected. Regarding resistance genes, tet(O) (7.69%) was the most identified gene, followed by blaOXA-61 (4.37%).ConclusionIn conclusion, this study highlights the alarming prevalence of antimicrobial resistance in Arcobacter spp. Monitoring Arcobacter spp. resistance can be achieved through surveillance, risk assessments, antibiotic stewardship in agriculture, public education, research collaborations, rapid diagnostics, and harmonized policies, all aimed at reducing contamination and safeguarding public health effectively.

Seasonal Patterns in Eosinophilic Esophagitis-Related Emergency Department Visits: A National Database Analysis.

This study investigates seasonal variations in eosinophilic esophagitis (EoE)-related emergency department (ED) visits among adults. We analyzed the National Emergency Department Sample (2016-2021), identifying adult EoE patients using ICD-10 codes. Generalized additive models assessed seasonal patterns. Among 18,791 EoE-related ED visits, a significant seasonal variation was observed, peaking in summer and nadiring in winter. This pattern was consistent across all U.S. regions. Seasonal dietary habits and social behaviors likely contribute to EoE exacerbations. Healthcare providers should emphasize management strategies during high-risk periods, particularly summer months and weekends.

Regional and seasonal drivers of metals and PAHs concentrations in road dust and their health implications in the Czech Republic

While car exhaust emissions in the EU are clearly decreasing, the future of non-exhaust emissions looks more pessimistic. The relative importance of the latter is thus expected to increase in terms of air quality and human health. The aim of the study was to assess regional and seasonal differences in the chemical composition of road dust across the Czech Republic and the health impact of its resuspension, with special respect to polycyclic aromatic hydrocarbons and metals. The road dust samples across all regions and seasons were collected. Based on subsequent laboratory and statistical processing, the spatiotemporal distribution of elements and PAHs was evaluated. Next, the contribution of road dust resuspension to air concentrations was estimated and related health impacts were assessed. A significant regional and seasonal variations in PAHs and metals were discovered. Air quality, leading to atmospheric deposition, was the most important factor contributing to these variations. In contrast, road traffic intensity played only a minor role in influencing the concentrations of metals and PAHs in road dust. Exposure to the PM10 fraction of road dust led to an increase in premature mortality, postneonatal infant mortality, and the prevalence, occurrence, and incidence of bronchitis by several percent. It also significantly raises the annual rate of emergency respiratory hospitalizations and the number of days per year using bronchodilators. Exposure to PAHs and heavy metals in road dust causes cancer incidence on the order of a few cases per 10 million people. Air quality protection measures that lead to a decrease in atmospheric deposition rates are required for the effective reduction of health risks associated with particle resuspension by traffic.

Growth and Grazing Mortality of Microbial Plankton in a Shallow Temperate Coastal Lagoon (Ria Formosa, SW Iberia)

Microzooplankton grazing is widely recognized as an important process of heterotrophic prokaryote and phytoplankton biomass removal. However, few studies have specifically addressed microbial mortality in the Ria Formosa coastal lagoon. This study aimed to assess the growth and mortality of heterotrophic prokaryotes and phytoplankton in this ecosystem using the dilution technique. The results revealed significant seasonal variations in the growth and grazing rates of both heterotrophic prokaryotes and phytoplankton, with mean grazing rates slightly exceeding the mean potential instantaneous growth rates. This indicates that microzooplankton consume a substantial proportion of both microbial groups in the lagoon. For specific phytoplankton taxa, the wide range of observed grazing rates suggests grazer selectivity, highlighting the need for future research to examine the dynamics of each phytoplankton group more closely.

Influence of Tropical Cyclones and Cold Waves on the Eastern Guangdong Coastal Hydrodynamics: Processes and Mechanisms

Influence of Tropical Cyclones and Cold Waves on the Eastern Guangdong Coastal Hydrodynamics: Processes and Mechanisms

Seasonal dynamics of trace metal concentrations and hydrological parameters in the Balu River, Bangladesh

&lt;p&gt;This study investigates the seasonal dynamics of trace metal concentrations and hydrological parameters in the Balu River, Bangladesh, to inform sustainable water management practices and support efforts to meet environmental standards. Water level, discharge, rainfall, and groundwater data were collected from February to August 2019, alongside sediment samples analyzed for Zn, Pb, Cu, Cr, and Cd concentrations. Statistical analyses, including correlation studies, time series modeling, and Kolmogorov-Smirnov tests, revealed significant seasonal variations. Water levels and discharge rates increased dramatically during the wet season, with upstream levels rising by 862.68% and downstream by 752.92%. Trace metal concentrations showed diverse responses: Cd increased by 554.52%, Zn by 11.86%, while Pb, Cu, and Cr decreased by 44.15%, 5.16%, and 32.72% respectively. Strong correlations were observed between certain metals, particularly in wet periods, with notable relationships between Cr-Cu (&lt;em&gt;r&lt;/em&gt; = 0.870) and Zn-Cr (&lt;em&gt;r&lt;/em&gt; = 0.742). The integrated analysis of hydrological parameters and metal concentrations, using Gower coefficient and partial correlation analyses, suggests complex interactions between seasonal changes and pollutant dynamics. These findings highlight the need for season-specific water management strategies and more frequent monitoring to better understand and mitigate the environmental impacts of trace metal pollution in the Balu River system. The study contributes valuable insights into the interplay between hydrological conditions and trace metal behavior, essential for developing effective pollution control measures and achieving sustainable river management in Bangladesh.&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;

High Inter-Specific Diversity and Seasonality of Trunk Radial Growth in Trees Along an Afrotropical Elevational Gradient.

Understanding mechanisms driving tropical tree growth is essential for comprehending carbon sequestration and predicting the future of tropical forests amid rapid deforestation. We conducted a natural experiment in Mount Cameroon to identify climatic factors limiting diurnal and seasonal growth in dominant tree species across a 2200-m elevation gradient, from lowland rainforests to montane mist forests with distinct wet and dry seasons. Using high-precision automatic dendrometers, we recorded radial growth rates of 28 tropical tree species from 2015 to 2018, correlating them with rainfall (11 100-2500 mm) and temperatures (23-14°C) across elevations. Significant growth limitations were suggested at both extremes of water availability. Tree growth peaked during the dry and prewet seasons at humid lower elevations and during wet seasons at drier higher elevations. Growth rates increased with soil moisture at higher elevations and peaked at medium soil moisture at lower elevations. Trees grew fastest at lower temperatures relative to their elevation-specific means, with growth limited by high daytime temperatures and promoted by nighttime temperatures. Our results revealed significant interspecific diurnal and seasonal growth variations hindered by both water scarcity and excess in West African rainforests, essential for forecasting and modelling carbon sinks.

Multidimensional analysis of NDVI dynamics in response to climate and land use/land cover change in Northwest Algeria

Abstract Climate change has emerged as a major concern at both regional and global scales in recent decades. Northwestern Algeria is particularly vulnerable as a semi-arid zone, where changes in climate and land cover (LC) will have a significant impact on vegetation in the long term. This study analyses, through a multidimensional approach, the influence of climate change and LC on vegetation dynamics. Hierarchical partitioning (HP) analysis was conducted to determine the most influential climatic variables (precipitation, temperature) on the dynamics of NDVI. The results show that the annual NDVI shows a fluctuating spatial trend between decrease and increase in different regions. Trends in seasonal NDVI are spatially varied and less uniform. Variations in precipitation are stable, while temperatures show clear and consistent significant increases across the region, with a general tendency to increase (p&lt;0.01) in spring and summer. In mountainous areas, NDVI shows an increasing trend both annually and seasonally. The correlation (r²) between NDVI, temperature and precipitation (0.75–1.0) over the different seasons reveals significant seasonal and regional variability. LC transition patterns also influence spatio-temporal trends in vegetation cover. They reveal that the rate of change of NDVI varies between LC types and regions, with resilience in forests and grasslands. These variations have significant implications for vegetation dynamics, as observed by NDVI.

Seasonal resin production in Pinus pinaster Ait. plantations: Dendrometric and meteorological influences

The relationship between dendrometric and meteorological parameters and resin production in Pinus pinaster plantations was studied using data from 90 trees collected between June and October. Resin production was measured every 15 days over a five-month period to explore how environmental factors influence resin production rates. The correlation between diameter at breast height (DBH) ranging from 20 cm to 49 cm and total and average resin production was examined, with the goal to optimize resin harvesting practices and to understand the ecological significance of resin in these plantations. The bi-monthly resin production was tested using the open wound tapping method over a five-month period beginning in June. Through regression models, significant seasonal variability in resin production was observed. Specifically, higher resin yields were recorded in June (354 g) and lower yields in October (53.5 g). The impact of DBH, tree height, basal area, and volume on resin yield were also assessed. Descriptive statistics, correlation, and regression analyses elucidated the relationships between tree metrics, meteorological factors, and resin production. This study contributes new insights into how tree characteristics influence resin production and how this relationship is modulated by seasonal changes. Such findings can inform sustainable forest management practices and improve resin harvesting methods.

Ebullition mediated transport dominates methane emission from open water area of the floating national park in Indo Burma hotspot.

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH4 emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH4 emissions and understand the factors influencing CH4 ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH4 flux ranged from 220.24 to 1889.35mgm-2 d-1, while the overall CH4 fluxes varied widely ranging from 345.81 to 2240.56mgm-2 d-1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO2 comprising 8.82% of the total sediment gas in the wetland. This suggests that CH4 emission through ebullition plays an important role in transporting biogenic CH4 to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH4 emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH4 production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH4 ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research.

Seasonal variation and fundamental characteristics of baroclinic tides in the Arabian Gulf

In the Arabian Gulf, baroclinic tides significantly impact physical and biological phenomena, shaping the region’s marine ecosystem. This study provides the first high-resolution investigation of the baroclinic tides using the three-dimensional, nonhydrostatic MIT general circulation model (MITgcm). The simulation outputs were validated against data from Oregon State University’s Tidal Inversion Software (OTIS), tidal stations, and mooring observations, showing high agreement and confirming the model’s accuracy. We further examined the characteristics of baroclinic and barotropic tides, identifying four key regions with high-intensity baroclinic tides based on energy budget analysis: 1) the narrow Strait of Hormuz; 2) the strait’s entrance along the trough, including the islands Farur, Siri, Abumusa, and Greater Tunb; 3) the central axial trough area with sea-bottom ridges; and 4) the northern area following a secondary ridge. Most baroclinic tides dissipate quickly due to interactions with complex bottom topography and do not propagate far from their sources. Significant seasonal variation shows that in winter, only the Strait of Hormuz and the area around the four islands showed significant baroclinic tidal energy, likely due to well-mixed upper layer seawater that hinders thermocline disturbances. The strong correlation between the simulation results and satellite images of internal waves suggests that intense baroclinic tides generate internal solitary waves in the Gulf.

Climatic oscillation based 3-dimensional drought risk assessment over India

Drought risk assessment is essential for the efficient design of water resource infrastructures and agricultural planning. Conventional drought studies define droughts either in a spatial or temporal framework without considering the simultaneous temporal and spatial progression of droughts. Spatiotemporal drought (SPD), a dynamic and complex phenomenon, has been relatively understudied due to the challenges in developing algorithms for their identification. In this study, we use a 3-dimensional drought identification framework to identify the SPD events across India. Further, as large-scale ocean-atmospheric phenomena namely El Niño Southern Oscillation (ENSO) and Equatorial Indian Ocean Oscillation (EQUINOO) play an important role in modulating the occurrence of droughts in India, we investigated the influence of these climatic oscillations on SPD characteristics across different climatic regions of India. Further, ENSO-based drought risk assessment using drought characteristics and the synergy between univariate and multivariate drought risks are also evaluated. Results show that 1) there are significant seasonal and spatial variations in occurrences and magnitude of SPD characteristics for the different climate phases. SPDs during the ENSO positive (El Niño) and the EQUINOO negative phases have higher severity, especially over the monsoon core region. In northwest India, the median drought severity during El Niño events is over three times higher than La Niña events. Across most of India, a major portion of SPD event onset occurs during the monsoon seasons, however in the north-western and south-eastern regions an equal portion of drought onset occurs during the pre-monsoon and post-monsoon season, respectively. 2) Further, the ENSO-based drought risk assessment reveals that severe and longer-duration SPD events are associated with El Niño phases, making ENSO a crucial factor in drought frequency analysis. 3) The synergy between the univariate and multivariate drought risks conditioned on ENSO reveal that overall drought risks are linked to the magnitude of individual drought characteristics which have a strong association with ENSO phases. Thus, design criteria for drought resilient infrastructure should be based on the dominant drought characteristics influenced by ENSO phases for effective drought risk assessment. Overall, the study underscores the significant impact of ENSO on SPDs in India and the importance of incorporating ENSO information in drought frequency analysis for reliable risk assessments.