Meghna River Research Articles

32 years of changes in river paths and coastal landscape in Bangladesh, Bengal Basin

AbstractThis study examines the geomorphological changes and environmental impacts on the coastline and the evolution of major river systems in Bangladesh over the past 32 years using remote sensing and GIS analyses. The central coastal area, characterized by fine sediments, has experienced significant land erosion due to the dynamics of the Meghna Estuary and its depositional patterns. In contrast, the southwestern Sundarbans Forest coast has remained relatively stable, aided by mangrove root stabilization despite anthropogenic threats. Channel migration analysis revealed the Brahmaputra River’s persistent braided configuration, while its tributaries, Teesta and Dharla, increased meandering nature due to reduced water availability and human interventions. The Ganges-Padma system displayed a shift towards a more sinuous channel pattern driven by reduced water discharge due to the Farakka Barrage construction in the upstream and a minor decrease in precipitation. The Upper Meghna River maintained moderate sinuosity with stable anastomosed patterns, whereas the lower Meghna River’s convergence with the Jamuna and Padma Rivers increased its susceptibility to erosion. These findings highlight the interplay of natural processes and human activities in shaping the coastal and fluvial landscapes of Bangladesh and the Bengal Basin, emphasizing the need for sustainable land-use practices and adaptive management strategies to mitigate future risks associated with sea-level rise and river course changes.

Combining Local Ecological Knowledge (LEK) and Conventional Scientific Knowledge (CSK) for Exploring Nursery Grounds and Spawning Biology of Yellowtail Catfish Pangasius pangasius in the Meghna River Estuary, Bangladesh

ABSTRACTThe yellowtail catfish (Pangasius pangasius) population in Bangladesh is facing imminent threats that led to endangered status. We used conventional scientific knowledge (CSK) and local ecological knowledge (LEK) of fishers (n = 155) to identify nursery grounds and spawning seasons of yellowtail catfish in the Meghna river estuary. Nineteen nursery grounds were pinpointed using fishers' LEK (confluence/influent zone, current, depth, catch data, and turbidity) and later validated by CPUE data. The peak spawning season was identified in July–September based on GSI (gonadosomatic index) and LEK (58.06% of fishers identified the spawning season). Fecundity (810,980 ± 455,679) and condition factor (0.94–1.52) were quantified with CSK. Using CSK and LEK to delineate nursery grounds and spawning season underscores the value of LEK as a tool for fish population management that deserves policy recommendation and wider application.

Study of Hepatosomatic Index, Gonadosomatic Index and Fecundity of Tengra Fish (Mystus gulio)

The tengra fish (Mystus gulio) is an important commercial species found in the coastal regions of West Bengal, India and Bangladesh. M. gulio is an important species within its ecosystem and has significance in local fisheries. Its adaptability to both freshwater and brackish environments makes it a resilient species. This study investigated the hepatosomatic index (HSI), gonadosomatic index (GSI), and fecundity of M. gulio to better understand its reproductive biology. Specimens were collected monthly from the Meghna River estuary between February and June 2023. The GSI was found to be highest in August (9.95±0.15%), indicating the peak spawning season. The HSI showed an inverse relationship with GSI, being lowest in March. Fecundity ranged from 88,495 to 264,104 eggs, with a mean of 171,581±17,855. Fecundity was positively correlated with total length, body weight, and gonad weight. Statistical analysis revealed significant differences in GSI and HSI between sexes and age groups (virgin vs 1+ year). Regression models showed that fecundity was highly dependent on gonad weight (r2=0.809) compared to length (r2=0.047) and weight (r2=0.216). M. gulio is an important brackish water fish with good taste and nutritional value. While it is optimally exploited from the East Coast of India, its culture potential is being explored through polyculture experiments and research on seed production and farming techniques. These findings provide valuable insights into the reproductive dynamics of M. gulio and can inform management strategies for sustainable fisheries. However, further research is needed to fully understand the reproductive biology of this catfish across its range to inform sustainable management strategies.

Tracing fluorescent dissolved organic matter (fDOM) characteristics and water quality parameters: Insights from an urban industrial river to marine zone.

This study aims to identify continuous water quality changes and identify fluorescence properties from urban rivers to marine zones. Various types of natural and anthropogenic sources derived dissolved organic matter (DOM) have been identified in this study. These include soil-derived DOM, plant remnants, and soluble particles produced when organic material partially decomposes and is released by microorganisms, such as bacteria, algae, and plants. DOM was characterized using a three-dimensional excitation-emission matrix (3DEEM), parallel factor analysis (PARAFAC), and water quality parameters from the Buriganga River, Dhaka to Patenga Seaport, Chittagong, along with the Shitalakshya River, a small portion of the Padma River, and the Meghna River. To better understand the data analysis, the study area was divided into three central regions: urban industrial rivers, industrial estuarine rivers, and marine zones. In the urban industrial river, 3DEEM and PARAFAC identified five fluorophores (peaks: A, C, M, T, and Tuv) with five components: detergent-like, fulvic-like, tryptophan or protein-like, fulvic-like (C-type), and protein-like, which might originate from the industrial activities and sewage pollution. In the industrial estuarine river zone, three fluorophores have been identified (peaks: A, C, Tuv) with two known components, namely, fulvic acid (A-type) and fulvic acid (C-type), with an unknown photoproduct at Ex/Em = 295/368 (peak Tuv). Components in the industrial river zone may originate from terrestrial sources, indicating vegetation along the river. In the marine zone, four fluorophores have been identified (peaks: Tuv, A, T, C) with two components, that is, protein- or tryptophan-like and humic acid-like from coral origin. The intensities of both fulvic-like and protein-like substances were high in urban industrial river water owing to industrial activity and sewage pollution. SUVA254 suggests high aromaticity in all three regions, whereas the optical properties suggest that terrestrial and microbial components are present in the urban industrial and estuarine rivers. This further indicates that urban industrial river water quality is highly polluted. The lowest degradation potential index (DPI) in the marine zone might result from the presence of the highest number of dissolved solids in the water, and the highest DPI of industrial estuarine rivers explains the comparatively high presence of terrestrial-derived humic (A)- and humic (C)-like components in the ratio to the unknown photoproduct of mid-wavelength. PRACTITIONER POINTS: This study's uniqueness is a 220-km cruise from an urban river to a coastal seaport to analyze fluorescence properties. The study found that most water parameters were within the DoE standards, except for DO, which was consistently low. 3DEEM-PARAFAC identified five fluorophores linked to detergent, fulvic, and protein-like substances from sewage and industrial sources. Our study concludes that microbial and terrestrial sources dominate dissolved organic matter in urban, estuarine, and marine regions.

On the compilation of the bathymetric data of the bay of Bengal domain in the nodal points of triangular mesh to be compatible for the implementation of finite element method

This study focuses on the compilation of bathymetric data for the Bay of Bengal domain, specifically for the area between 15°N to 23°N latitudes and 85°E to 95°E longitudes, to ensure compatibility with the Finite Element Method (FEM). A high-resolution color map of the region was generated using ArcGIS software, which served as the basis for discretizing the domain into a triangular mesh. Bathymetric data for the Bay of Bengal, including the Meghna River, was then compiled using a combination of recent data from the Bangladesh Inland Water Transport Authority (BIWTA) and generated data, which were interpolated using a two-way cubic spline interpolation method. The Modified Inverse Distance Weighted Interpolation (MIDWI) method was employed to map this bathymetric data to the nodal points of the triangular mesh, ensuring accurate representation of the seafloor’s varying depths. This work is essential for developing a reliable storm surge prediction model for the Bay of Bengal using FEM, as it provides the necessary geometric and bathymetric details required for precise numerical modeling.

Hotspots of Dissolved Arsenic Generated from Buried Silt Layers along Fluctuating Rivers.

Previous studies along the banks of the tidal Meghna River of the Ganges-Brahmaputra-Meghna Delta demonstrated the active sequestration of dissolved arsenic (As) on newly formed iron oxide minerals (Fe(III)-oxides) within riverbank sands. The sand with high solid-phase As (>500 mg/kg) was located within the intertidal zone where robust mixing occurs with oxygen-rich river water. Here we present new evidence that upwelling groundwater through a buried silt layer generates the dissolved products of reductive dissolution of Fe(III)-oxides, including As, while mobilization of DOC by upwelling groundwater prevents their reconstitution in the intertidal zone by lowering the redox state. A three end-member conservative mixing model demonstrated mixing between riverbank groundwater above the silt layer, upwelling groundwater through the silt layer, and river water. An electrochemical mass balance model confirmed that Fe(III)-oxides were the primary electron acceptor driving the oxidation of DOC sourced from sediment organic carbon in the silt. Thus, the presence of an intercalating silt layer in the riverbanks of tidal rivers can represent a biogeochemical hotspot of As release while preventing its retention in the hyporheic zone.

FORMATION AND EVOLUTION OF SANDBARS IN THE PADMA RIVER, BANGLADESH

Sandbars are natural formations in river channels, typically composed of sand and other sedimentary particles, created by river flow and erosion-deposition The shapes, sizes, and types of these sandbars exhibit diversity depending on factors such as river flow, sediment composition, hydrological conditions, and erosion-deposition processes. These sandbars are an integral part of the river ecosystem and influence the water flow patterns, navigation routes, aquatic habitats and even provide shelter to humans and habitats. In the context of Bangladesh, there is a considerable size of population that dwell in these sandbars. The process of sandbar formation and recession is quite dynamic, and its complexity is further accentuated within the confluence zones. The Ganges, the Brahmaputra, and the Meghna River systems together form the largest delta (GBM Delta) in the world which is characterized by numerous interlaced rivers, canals, and streams. These river systems contain numerous sandbars which contribute to its complex river morphology. These sandbars are home to many people, animals, and wildlife. However, the dynamic nature of sandbars, high monsoon discharge, flooding and erratic erosion-deposition patterns make the sandbar formation and recession process quite unpredictable and puts the lives of people living on it in danger. This paper aims to study the morphological changes in sandbars, the erosion-deposition patterns within these river systems causing the sandbar formations, compare the sandbar formations in the two confluence zones of the Padma River, determine the changes in water-sandbar surface area ratio, visualize the evolution of sandbars, and quantify the movements of sandbars. The study revealed that over the past two decades (1990-2010), the main channel of the river was dominated by sandbar area. In contrast, in the past 7 years (2016-2022), the average surface area of water within the main channel of the Padma River was approximately 73,387 ha while the sandbars covered an area of around 51,274 ha, highlighting the recent dominance of water in the main channel. Conversely, in a similar time frame (2016-2022), at the two confluence zones of the Padma River, the average surface area of sandbar was greater than that of water within a 30km radial distance from each confluence node. At the upstream confluence (Padma-Jamuna-Ganges), the average surface area of sandbars was approximately 40150 ha while water covered an area of around 28531 ha. Similarly, at the downstream confluence (Padma-Meghna), sandbars covered an area of 43696 ha on an average while water covered an area of around 40889 ha. This showed that sandbars have been rapidly accumulating at the two confluence zones. It is also observed that the sandbars are very dynamic as both lateral and longitudinal migrations are observed. It is however evident that the littoral sandbars are more stable compared to the medial sandbars and therefore more suitable for habitation. From visual inspection it is evident that the bankline of the medial sandbar (Amirabad) shifts more rapidly compared to the littoral sandbar (Harirampur within the period from 2016 to 2022. Additionally, the coefficient of variation of area for the littoral sandbar and the medial sandbar are approximately 2.11% and 5.37% respectively. This indicates that the area of the littoral sandbar is more stable over the years compared to the medial sandbar as it has a lower coefficient of variation and therefore is less active. Over the years, the confluence nodes on either side of the Padma River have constantly shifted due to rapid sandbar accumulation. Between 1990 and 2022, the maximum shifting of the upstream and downstream confluences reached approximately 7500 meters and 18000 meters respectively, both in the southeast direction.

Prediction of Dynamics of Riverbank Erosion: A Tale of the Riverine Town Chandpur Sadar

River channel migration often occurs inside the floodplain areas of the river. The structural changes occurring in rivers within floodplain zones serve as a significant ecological signal of their tremendous impact on both ecological and human survival. The aim of the research is to assess the spatial and temporal fluctuations of the Meghna River's bankline from 1990 to 2020 (for 30 years), and to predict the future bankline position. The Landsat imageries from USGS were used for this study. The bankline was extracted from satellite imageries (Landsat) using Modified Normalized Difference Water Index (MNDWI) indices. The variations in bankline dynamics were assessed through the application of Net Shoreline Movement (NSM) and End Point Rate (EPR) analyses using the Digital Shoreline Analysis System (DSAS). Predictive modeling was conducted utilizing the Modified EPR Model, with validation performed via the Root Mean Square Error (RMSE) technique. Adjustment of errors was achieved by employing error coefficients tailored to each individual transect. Over the past three decades, the cumulative river erosion in Chandpur Sadar amounted to 18.03 square kilometers, with the highest Net Shoreline Movement (NSM) recorded at −1979.62 m during the study period. The forecasted maximum Net Shoreline Movement (NSM) is anticipated to be −495.79 m, signifying that the transect is associated with erosion, resulting in landward movement. Conversely, the minimum NSM is projected to be −1.01 m. The most significant movement is expected to occur in Puran Bazar, while the least movement is foreseen in Bakharpur. On average, the NSM across all transects is predicted to be −76.25 m. This study presents a cost-effective approach for evaluating the changes in river erosion over time. This technique may be valuable for policymakers in developing effective plans to reduce the negative impacts of erosion-related risks.

Body shape divergence of paradise thread fish (Polynemus paradiseus) collected from different coastal habitats of southern Bangladesh: A multivariate approach for population discrimination

The paradise thread fish (Polynemus paradiseus) is a commercially and ecologically important euryhaline fish that primarily lives in diversified coastal and estuarine habitats. A comprehensive understanding of the divergence in body shape and discrimination in population parameters related to habitats is crucial for fisheries management and conservation endeavours. To test whether significant morphological differences exist between P. paradiseus populations inhabiting different coastal environments, a total of 366 individuals (198 male and 168 female) were collected from five distant places over three zones- Cox's Bazar (Bakkhali River) and Chattogram (Karnaphuli River) in the southeast coastal regions, Noakhali (lower Meghna River) in the southcentral zone, and Khulna (Shibsa River) and Borguna (Bishkhali River) in the southwest zones adjacent to the Bay of Bengal, Bangladesh in November 2022. The truss networking and geometric morphometric analysis (GMA) indicated variations in body shape among P. paradiseus individuals induced by sexual dimorphism. Wireframe graphs demonstrated that female individuals had wider dorsal-abdominal parts than males. Using the truss networking dataset for five coastal habitats, multivariate analyses revealed two overlapping clusters: southwest (Borguna and Khulna) populations in one cluster, while central (Noakhali) and southeast (Chattogram and Cox's Bazar) populations form separate clusters. The GMA also illustrated that the Khulna-Borguna population was located near the opposite end of the Chattogram-Cox's Bazar population axis, and the Noakhali populations were somewhat in the middle, with a high degree of overlap. Wireframe graphs displayed a significant body shape variations among populations, mainly in the snout shape, the width of the dorsal-abdominal part, the tail shape, and the head shape. The Discriminant Function Analysis revealed that there were pronounced variations in body shape between two populations located in distant regions, while there were minimum variations between two populations located close to each other. This study underscores the effectiveness of landmark-based truss networking and geometric morphometrics in discerning morphological variations across different habitats. These variations likely hold adaptive significance and are critical for informed population management and conservation strategies in the population structure of euryhaline P. paradisus.

Exploring the Rich Diverse: Freshwater Fish Diversity and Bionomics in the Sundarbans, India

The Sundarban is a mangrove area in the deltaformed by the confluence of the gangas brahmaputra and meghna river in the Bay of Bengal. The hooghly river in india state of West Bengal to the baleswar river in bangladesh. It comprises closed and open mangrove forests agriculturally used land, mudflats and barren lands. It is intersected by multiple tidal streams and channels. Four protected area in the Sundarbans are enlisted as UNESCO WORLD HERITAGE SITES, Sundarbans national park,Sundarban west, east and south wildlife santuaries. The bengali name Sundarban is beautiful forest. It may have benn derived from the word sundari, the local name of the mangrove sp Heritiera fomes. There many biodiversity like 453 faunal wildlife, including 290 birds,120 fish, 42 mammal, 35 reptiles and 8 amphibians. The goal of this review paper is discussing about freshwater fish diversity and its bionomics in Sundarban delta. Also about the a brief description of study area (Sundarban) encompassing definition of a mangrove ecosystem, importance of mangrove ecosystem, area and distribution of Sundarban; Indian Sundarban – area, location, fisheries related activities; importance of studying fish diversity. And try to generate a data base on some of the life history parameters and their conservation status and atlast study threats associated with fish diversity measures for sustainable fishery.

Modeling the Impact of Climate Change on Streamflow in the Meghna River Basin: An Analysis Using SWAT and CMIP6 Scenarios

This study assesses future climate change impacts on the hydrologic response of the Upper Meghna River Basin (UMRB), a major river system in Bangladesh. Separate SWAT (Soil and Water Assessment Tool) hydrologic models were developed for the three major sub-basins of the UMRB, i.e., Barak, Meghalaya, and Tripura, considering their unique geographical, hydrological, and land-use characteristics. To evaluate the efficiency of multi-site modeling in providing better model performance, the SWAT models were calibrated at both single and multiple locations. Those models were then simulated to estimate future flows using climate projection data from thirteen CMIP6 General Circulation Models (GCMs) under moderate and extreme emission scenarios, SSP2-4.5, and SSP5-8.5. The results revealed that the annual maximum flow will keep increasing gradually with time. The outlets of the Meghalaya sub-basin will experience a more significant rise in future flow in the upcoming decades compared to the Barak and Tripura sub-basins. Results showed that dry season flows with increases of up to 31–50% would be less affected compared to the wet periods, which could experience increases of up to 47–66%) across the sub-basins by the end of the 21st century under extreme emission projections. Besides an increasing trend in the mean flow, future flows at several outlets also exhibited an escalation in the intensity and frequency of extreme flood events.

Neotectonism and reactivation of tectonic elements in eastern part of Shillong Plateau, India: constraints from morpho-tectonic analyses

ABSTRACT The Shillong Plateau is the only elevated topography in the Himalayan foreland bounded and crisscrossed by several prominent faults and shear zones. The plateau is situated in a complex tectonic compressional set up, owing to which the fault systems both at the periphery and within tend to be neotectonically active. Due to the elevation difference of the plateau with the Brahmaputra and Meghna River valleys flanking it, coupled with the impervious lithologies present, an intricate network of drainage system has developed in the plateau. In this paper, morphometric and structural analyses of four selected drainage basins from the east-central part of Shillong Plateau have been carried out to comprehend the effects of neotectonic reactivation of fault systems and associated basin tilting which in turn controls the development of drainage pattern. This has led to the understanding of the effects of the ever-evolving fluvial landforms on the anthroposphere in this part of Indian sub-continent, where the agrarian-economy is completely dependent on the intricate fluvial systems.

Assessment of spawning and nursery habitats of hilsa in the Tetulia and Meghna river estuaries

The Meghna River estuary (MRE) and Tetulia River estuary (TRE) are tropical estuaries on the middle coast of Bangladesh. Hilsa shad (Tenualosa ilisha), is one of the most important anadromous fish (ascending rivers from the sea for breeding), migrates into the Meghna and Tetulia River estuarine systems from the Bay of Bengal. This study assessed the spawning and nursery habitats of hilsa in the Tetulia and Meghna River estuaries by examining the environmental parameters of both estuarine ecosystems. Water samples were collected from nineteen selected sampling sites along and across the estuaries from January to December 2021 covering both the dry and wet seasons. Salinity, dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) concentration varied significantly (p < 0.05) between the MRE and TRE during the dry season. In contrast, no significant variation (p > 0.05) was observed in the salinity, DIN and DIP between the MRE and TRE during the wet season. In addition, no significant variation (p > 0.05) was observed in chlorophyll-a concentration between the MRE and TRE during the dry and wet seasons. The salinity tolerance range is an important driver for the spawning (salinity <0.1 psu) and nursery (salinity <0~2 psu) habitat of hilsa. This study explored that the TRE is suitable for spawning and nursery habitat (salinity <0.09 psu) for hilsa all year round because the TRE acts as a freshwater ecosystem (salinity <0.1 psu) annually. Therefore, the government should focus on protecting and conserving juvenile hilsa (jatka) and brood hilsa in the TRE year round. Ann. Bangladesh Agric. (2023) 27 (1): 57-69

Variation of Satellite-Based Suspended Sediment Concentration in the Ganges–Brahmaputra Estuary from 1990 to 2020

The Ganges–Brahmaputra estuary, located in the northern Bay of Bengal, is situated within the largest delta in the world. This river basin features a complex river system, a dense population, and significant variation in watershed vegetation cover. Human activities have significantly impacted the concentration of total suspended matter (TSM) in the estuary and the ecological environment of the adjacent bay. In this study, we utilised the Landsat series of satellite remote sensing data from 1990 to 2020 for TSM retrieval. We applied an atmospheric correction algorithm based on the general purpose exact Rayleigh scattering look-up-table (LUT) and the shortwave-infrared (SWIR) bands extrapolation to Landsat L1 products to obtain high-precision remote sensing reflectance. In conjunction with the normalised difference vegetation index (NDVI), precipitation, and discharge data, we analysed the variation and influencing mechanisms of TSM in the Ganges–Brahmaputra estuary and its surrounding areas. We revealed notable seasonal variation in TSM in the estuary, with higher concentrations during the wet season (May–October) compared to the dry season (the rest of the year). Over the period from 1990 to 2020, the NDVI in the watershed exhibited a significant upward trend. The outer estuarine regions of the Hooghly River and Meghna River displayed significant decreases in TSM, whereas the Baleswar River, which flows through mangrove areas, showed no significant trend in TSM. The declining trend in TSM was mainly attributed to land-use changes and anthropogenic activities, including the construction of embankments, dams, and mangrove conservation efforts, rather than to runoff and precipitation. Surface sediment concentration and chlorophyll in the northern Bay of Bengal exhibited slight increases, which means the limited influence of terrestrial inputs on long-term change in surface sediment concentration and chlorophyll in the northern Bay of Bengal. This study emphasises the impact of human activities on the river–estuary–coast continuum and sheds light on future sustainable management.

Assessment of fishing gears, crafts, and socio-economic status of the Hilsa (Tenualosa ilisha) fishers’ community near the Meghna River, Bangladesh

An evaluation was conducted to assess the current state of fishing gears, crafts, and socio-economic aspects among the Hilsa (Tenualosa ilisha Hamilton, 1822) fishers communities residing along the Meghna River region in Gazaria and Munshiganj Sadar Upazila, located in the district of Munshiganj, Bangladesh. About 150 fishers were interviewed using pre-tested questionnaires from selected areas from July 2019 to June 2020, and the data that was obtained was analysed using appropriate statistical tools. The methods employed for Hilsa fishing included the use of drift gill nets (known as Ilish jal, Fash jal, and Poa jal) and seine nets (referred to as Jagat ber jal), while the crafts utilised were Chandi boat and Donga. Most fishers were 31-40 years old (53.33%) in Ismanirchar and (46.67%) in Kalirchar village. Many fishers were Hindus (80%) in Ismanirchar and Muslims (96%) in Kalirchar. Regarding educational level, 69.33% and 70.67% of fishers in Ismanirchar and Kalirchar can only sign, respectively. Semi-earthen toilets were the primary type of sanitary facilities found in the area. Approximately half of the fishers residing in the two villages owned land ranging from 0 to 15 decimals. A significant portion, around 80%, relied on loans from non-governmental organisations (NGOs), while the remaining fishers obtained financial assistance from their neighbours. Hilsa fishing was found to be the main occupation in the study area. The fishers' income increased from September to November and March to May. The primary issues identified included extortion from local criminal groups, insufficient access to credit, absence of proper storage facilities, ongoing conflicts between professional and non-professional fishers, as well as tensions between Muslim and Hindu fishers. To improve their socio-economic situation and ensure sustainable livelihoods, fishers require more institutional support, better organisation, enhanced technical assistance, and increased access to credit.

Diverse sedimentary organic matter within the river-aquifer interface drives arsenic mobility along the Meghna River Corridor in Bangladesh

In alluvial aquifers with near-neutral pH and high dissolved arsenic (As) concentrations, the presence and character of sedimentary organic matter (SOM) regulates As mobility by serving as an energetically variable source of electrons for redox reactions or forming As–Fe-OM complexes. Near tidally and seasonally fluctuating rivers, the hyporheic zone (HZ), which embodies the mixing zone between oxic river water and anoxic shallow groundwater, may precipitate (or dissolve) iron (Fe)-oxides which sequester (or mobilize) As. To understand what is driving the mobilization of As within a shallow aquifer and riverbank sands adjacent to the tidally fluctuating Meghna River, we characterized the chemical reactivity of SOM from the sands, and a silt and clay layer, underlying the HZ and aquifer, respectively. Dissolved As (50–500 μg/L) and Fe (1–40 mg/L) concentrations increase with depth within the shallow aquifer. Similar vertical As and Fe concentration gradients were observed within the riverbank sands where concentrations of the products of reductive dissolution of Fe-oxides increase with proximity to the silt layer. Compared to all other sediments, the SOM in the clay aquitard contains older, more recalcitrant, terrestrially-derived material with high proportions of aromatic carboxylate functional groups. The shallow silt layer contains fresher SOM with higher proportions of amides and more labile polysaccharide moieties. The SOM in both the riverbank and aquifer is terrestrially-derived and humic-like. The labile SOM from the silt layer drives the microbially mediated reductive dissolution of As-bearing Fe-oxides in the HZ. In contrast, the carboxylate-rich SOM from the clay aquitard maintains dissolved As concentrations at the base of the aquifer by complexing with soluble As and Fe. This highlights that SOM-rich fine (silt or clay) layers in the Bengal basin drive As and Fe mobility, however, the specific processes mobilizing As and Fe depend on the lability of the SOM.

Preferred food items of Juvenile hilsa (Tenualosa ilisha) of the Meghna river estuary in Moju Chowdhury Hat, Lakshmipur

Preferred food items of Juvenile hilsa (Tenualosa ilisha) of the Meghna river estuary in Moju Chowdhury Hat, Lakshmipur

Fishermen's community livelihood and socio-economic constraints in coastal areas: An exploratory analysis

The growing interest in alternative employment amongst Bangladeshi fishermen indicates a shift from river fishing. However, a greater willingness is required to encourage river-based fishing, hindered by factors like fish level reduction, water pollution, natural disasters, unfair market prices, and market control by brokers. This challenges fishermen's families, struggling amidst rising prices of essential commodities. The current study aims to evaluate the socio-economic constraints and livelihood of fishermen in the Karnaphuli, Jalkhadar, and Meghna River two Upazila from August 2022 to May 2023. River challenges have reduced fishermen's income, necessitating aid in income, fish sales, market prices, syndicate issues, and natural calamities. Data from these selected river locations were collected through surveys and interviews. We collected 100 respondents' data. Bangladesh has a total number of fishermen of 1,733,328 in 64 districts. amongst them, 97 % are male fishermen, and 3 % of females are connected with fishermen's lives. Of these respondents, 34 % were female, and 66 % the male of the total. Even 66 % of the total respondents had nuclear family status. This study uses Cronbach's Alpha acceptable reliability α=0.95 and findings that fishermen's income is falling daily. In this coastal region, fishermen are considering changing their profession due to various barriers. Hindrances to accessing fish markets include restrictions, inadequate social amenities, and health and education challenges. However, fishermen propose solutions, urging NGOs and governments to establish educational, medical, and social facilities in coastal and rural areas. They emphasize that government support for the economy and the enforcement of fish legislation are vital for enhancing income levels.

Microplastics in Different Tissues of a Commonly Consumed Fish, Scomberomorus guttatus, from a Large Subtropical Estuary: Accumulation, Characterization, and Contamination Assessment.

Microplastics (MPs) ingestion by fish signifies a worldwide threat to human health but limited research has examined their existence within the consumable portions (muscle) of fish. Thus, this study was undertaken to unveil the prevalence, characterization, and contamination extent of MPs across various body tissues, including the muscle of the king mackerel (S. guttatus) from the lower Meghna estuary in Bangladesh-a pioneering investigation in this region. In our analysis, we identified a total of 487 MPs, with an average abundance of 48.7 ± 20.3 MPs/individual. These MPs were distributed across different tissues, with respective concentrations of 0.84 ± 0.45 items/g in the digestive tract, 2.56 ± 0.73 items/g in the gills, and 0.3 ± 1.72 items/g in the muscle tissue. The observed variations among these tissue types were statistically significant (p < 0.05). Moreover, a significant positive correlation indicated that fish with higher weight had higher MPs in their gills and DT (digestive tract). The majority were <0.5 mm in size (97.74%) and exhibited a fiber-like shape (97.74%), with a notable prevalence of transparent (25.87%) and a pink coloration (27.92%). Remarkably, the majority of MPs were discovered within the size range of <0.5-1 mm (100%), particularly in the muscle tissue, signifying a substantial transfer of MPs into the human diet. Besides, we discovered only three polymer types of microplastics which could be attributed to the extensive use of food packaging, plastic containers, wrapping plastics, residential garbage, and plastic pipes that end up in the aquatic environment via river discharges. The contamination factor (CF) values of fish muscle (5.75) and the digestive tract (5.50) indicated that these fish organs were considerably contaminated (3 < CF < 6) with MPs. The pollution index of MPs (PLI > 1) indicated a high contamination level for MPs pollution of S. guttatus in the lower Meghna River estuary.

Redox trapping of arsenic in hyporheic zones modified by silicate weathering beneath floodplains

Groundwater containing high concentrations of dissolved arsenic (As) and iron (Fe(II)) discharges to rivers across the Ganges-Brahmaputra-Meghna delta. Observed Fe(III)-oxyhydroxide (FeOOH)–As deposits lining the riverbanks of the Meghna River may have been created by bidirectional mixing in the hyporheic zone (HZ) from ocean tides. This process has been named the Natural Reactive Barrier (NRB). Sedimentary organic carbon (SOC) is deposited annually on floodplains. Floodwaters that infiltrate through this layer may chemically transform the groundwater prior to discharging through the HZ in ways that influence the capture and retention of As in the NRB. The goal of this study is to understand how the interaction of these two scales of river-groundwater mixing influence the fate of As trapped within an NRB. Monitoring wells were installed to 1–17 m depth, up to 100 m distance from the river's edge during the dry season on the East (Site 1) and West (Site 2) sides of the river. They were sampled during the dry season (January) under gaining river conditions. The physical properties and elemental composition of the sediment was described by hand observation and hand-held X-Ray Fluorescence (XRF), respectively. Mixing with river water was quantified using the sum of charge of major cations (TC). Site 1 has a sloping bank that is only partially inundated during the wet season. The aquifer is composed of homogeneous sand. Site 2 is flat and therefore fully inundated in the wet season. The aquifer is composed of sand with thin (1–20 cm thick) clay layers. Both sites generate the dissolved products of FeOOH-reduction coupled to organic carbon oxidation, and silicate weathering beneath the floodplain. These products are dissolved Fe, As, silica, bicarbonate, calcium and phosphate. This chemistry is conducive to the formation of crystalline iron oxide minerals such as goethite which may co-precipitate with As, trapping it long-term.