Sundarbans Mangrove Ecosystem Research Articles

Floral scents, specialized metabolites and stress-response activities in Heritiera fomes and Bruguiera gymnorrhiza from Sundarban mangrove ecosystem.

Floral biochemistry and stress physiology is an underexplored aspect of mangroves, which should be investigated as part of preservation and restoration efforts. A thriving true mangrove tree (Bruguiera gymnorrhiza (L.) Lamk.) and a threatened mangrove-associate species (Heritiera fomes Buch. Ham.) were studied in the Sundarban region of India for seasonal variations in floral odours, non-volatile phytochemicals, antioxidant enzyme activities, and surface water chemistry in surrounding habitat. Both species were found to exhibit significant differences in floral volatilomes, protein contents, antioxidant enzyme activities, total flavonoids, and total phenolic contents between spring and autumn blooms. The bird-pollinated flowers of B. gymnorrhiza also showed considerable seasonal differences in floral anthocyanin and proline contents, indicating vulnerability of the post-anthesis open flowers to environmental factors. Contrarily to previous findings, B. gymnorrhiza floral bouquet appeared to be enriched in various classes of volatiles - dominated by sulphurous compounds in bud stage and terpenoids in open stage. Floral anthocyanins, contributing to the striking colouration of the calyx, were found to comprise cyanidin and delphinidin derivatives. Other glycosides of cyanidin and delphinidin were detected in H. fomes flowers, contributing to visual guides to potential food rewards for pollinating insects. Floral tissue in H. fomes was found to be protected by densely overlapping layers of stellate trichomes containing sesquiterpenoids as phytoprotectants. Comparison of the two floral species suggested that H. fomes flowering is optimized to oligohaline (but not freshwater) vernal conditions; whereas B. gymnorrhiza blooms are adapted for biologically enriched (including abundant herbivores and microbial growth), mesohaline forest habitats.

Acidity and oxidative potential of atmospheric aerosols over a remote mangrove ecosystem during the advection of anthropogenic plumes

To investigate the acidity and the water-soluble oxidative potential of PM10, during the continental biomass-burning plume transport, a three-year (2018–2020) winter-time campaign was conducted over a pristine island (21.35°N, 88.32°E) of Sundarban mangrove ecosystem situated at the shore of Bay of Bengal. The average PM10 concentration over Sundarban was found to be 98.3 ± 22.2 μg m−3 for the entire study period with a high fraction of non-sea-salt- SO42− and water-soluble organic carbons (WSOC) that originated from the regional solid fuel burning. The thermodynamic E-AIM(IV) model had estimated that the winter-time aerosols over Sundarban were acidic (pH:2.4 ± 0.6) and mainly governed by non-sea-salt-SO42-. The volume and mass normalized oxidative potential of PM10 was found to be 1.81 ± 0.40 nmol DTT min−1 m−3 and 18.4 ± 6.1 pmol DTT min−1 μg−1 respectively which are surprisingly higher than several urban atmospheres across the world including IGP. The acid-digested water-soluble transition metals (Cu, Mn) show higher influences in the oxidative potential (under high aerosol acidity) compared to the WSOC. The study revealed that the advection of regional solid fuel burning plume and associated non-sea-salt-SO42- is enhancing aerosol acidity and oxidative stress that in turn alters the intrinsic properties of aerosols over such marine ecosystems rich in ecology and bio-geochemistry.

Enzymatic degradation and metabolic pathway of phenanthrene by manglicolous filamentous fungus Trichoderma sp. CNSC-2

Manglicolous filamentous fungi release extracellular lignolytic enzymes that can readily degrade polycyclic aromatic hydrocarbons (PAHs). The present study emphasizes the role of the extracellular enzyme in phenanthrene degradation by the manglicolous fungus Trichoderma sp. CNSC-2 isolated from the Indian Sundarban mangrove ecosystem. The removal efficiency reached 64.05 ± 0.75 % in 50 mg l−1 phenanthrene-amended mineral salt medium at pH 5.6 after 10 days of incubation. Phenanthrene removal was optimized at different pH, nutrient sources, and Cu2+ concentrations. The degradation significantly increased to 67.75 ± 4.32 % at pH 6 (P < 0.0001). The addition of Cu2+ (30 mg l−1) increased the degradation to 78.15 ± 0.36 % (P < 0.0001). The validation experiment confirmed the increase in phenanthrene degradation up to 79.9 ± 1.67 % under optimized conditions. The Lac1 and CytP450 genes encoding for extracellular and intracellular enzymes, respectively, were identified. The GC-MS derived phenanthrene degradation metabolites, i.e., phthalic acid, isobutyl 2-pentyl ester derivative, 1, 2 benzene dicarboxylic acid, butyl 2-methyl propyl ester derivative, TMS derivative of benzoic acid and 3,5 dihydroxy benzoic acid determined two possible metabolic pathways. The laccase enzyme activity was higher in the presence of Phe+Cu2+ (P < 0.0001), indicating the enzyme induction potential of PAH and Cu2+ ions. Purified laccase had a molecular weight of 45 kDa and was highly stable at pH 4–6 and temperature 20–50 °C. The enzyme retained 47 %, 87 %, and 63 % of enzyme activity at 30 mg l−1 concentration of Pb2+, Cd2+, and Hg2+. However, laccase activity was induced by 1.37 folds in the presence of 30 mg l−1 Cu2+ concentration. Thus, the study suggests the potential role of Trichoderma sp. CNSC-2 in phenanthrene degradation.

Multi-dimensional approach for an environmental health assessment of a deltaic mangrove ecosystem, Sundarbans

The largest contiguous tract of tidal halophytic mangroves in Bangladesh is about 10,000 km2. It has a wide range of physiochemical and nutritional qualities, as well as ecological health. To understand the hazardous and heavy metal concentrations, ten heavy metals concentrations were examined in both water and sediment. Indices for pollution and contamination, such as Modified Hazard Quotient (mHQ), Degree of Contamination (Cd), Geo-Accumulation Index (Igeo), Mean Effect Range Median Quotient (M-ERM-Q), Nemerow's Pollution Index (NPI), Heavy Metal Evaluation Index (HEI) give a more accurate diagnostic result for water and sediment in the Sundarbans mangroves. The Water Quality Index (WQI) and Mangrove Quality Index (MQI) are also evaluated for a final statement. The nutrient concentrations average of NO3, PO4, NH3, and SiO2 are found 0.59 ± 0.05, 0.09 ± 0.01, 0.23 ± 0.02 and 1.72 ± 0.17 (mg/L), respectively in water. Pb, Cd, Hg, As, Cr, Mn, Fe, Ni, Cu, and Zn have average concentrations of 19.1 ± 1.62, 1.1 ± 0.11, 0.48 ± 0.04, 1.19 ± 0.11, 83.27 ± 8.3, 35.45 ± 2.95, 282.73 ± 30.82, 33.85 ± 2.95, 6.09 ± 0.54, and 172.18 ± 17.15 (µg/L) in surface water and 19.57 ± 1.25, 0.16 ± 0.005, 0.026 ± 0.0009, 1.48 ± 0.08, 36.38 ± 4.31, 456.66 ± 76.76, 42.36 ± 2.57, 53.81 ± 1.93, 20.67 ± 1.24, and 43.60 ± 6.09 (mg/kg) for sediments. According to the heavy metals analysis indices, we discovered very little contamination. The WQI indicates that the water quality in the Sundarbans Mangroves is generally protected but occasionally deteriorates. The MQI categorizes the Sundarbans as a moderate mangrove, falling into category 3. Despite being controlled the heavy metal pollution is getting worse as the Mongla port's economy grows. A more seasonal and in-depth approach to this topic can be achieved by collecting more samples over a year. The deltaic Sundarbans mangrove ecosystem is currently in moderate to an acceptable condition, with low or non-significant pollution levels and fair water quality, according to this study, except for certain constraints.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Carbon Biogeochemistry of the Estuaries Adjoining the Indian Sundarbans Mangrove Ecosystem: A Review.

The present study reviewed the carbon-biogeochemistry-related observations concerning CO2 and CH4 dynamics in the estuaries adjoining the Indian Sundarbans mangrove ecosystem. The review focused on the partial pressure of CO2 and CH4 [pCO2(water) and pCH4(water)] and air-water CO2 and CH4 fluxes and their physical, biogeochemical, and hydrological drivers. The riverine-freshwater-rich Hooghly estuary has always exhibited higher CO2 emissions than the marine-water-dominated Sundarbans estuaries. The mangrove sediment porewater and recirculated groundwater were rich in pCO2(water) and pCH4(water), enhancing their load in the adjacent estuaries. Freshwater-seawater admixing, photosynthetically active radiation, primary productivity, and porewater/groundwater input were the principal factors that regulated pCO2(water) and pCH4(water) and their fluxes. Higher chlorophyll-a concentrations, indicating higher primary production, led to the furnishing of more organic substrates that underwent anaerobic degradation to produce CH4 in the water column. The northern Bay of Bengal seawater had a high carbonate buffering capacity that reduced the pCO2(water) and water-to-air CO2 fluxes in the Sundarbans estuaries. Several authors traced the degradation of organic matter to DIC, mainly following the denitrification pathway (and pathways between aerobic respiration and carbonate dissolution). Overall, this review collated the significant findings on the carbon biogeochemistry of Sundarbans estuaries and discussed the areas that require attention in the future.

Isolation and Screening of Dye Degrading Lignocellulolytic Bacteria from Sundarban Mangrove Ecosystem, West Bengal, India

The present research work was carried out on isolating lignocellulolytic enzyme-producing natural bacterial isolates of the Sundarban Mangrove ecosystem in West Bengal, India. Multiple bacterial isolations and qualitative as well as quantitative screening of the isolates was conducted by selective media plates and dye decolorization assay. Growth characterization of the top three isolates, namely GD1, GD2, and GD3, was determined in both nutrient broth and selective media. GD1 showed laccase activity in ABTS plate and decolorized congo red, malachite green, and methylene blue by 64.82%, 47.69%, and 33.33%, respectively, which is the inherent property of laccase. Along with the maximum laccase activity (9.72U/L), it also showed a little amount of cellulase (5.8U/ml) and pectinase (0.55U/ml) activity in the enzyme assay. GD2 showed maximum cellulase activity (6.56U/ml) with only 3.3% degradation of congo red and 39.43% degradation of malachite green. Like GD1, GD2 also bears 5.6U/L laccase and 0.12U/ml pectinase enzyme activity. The last isolate, GD3 specialized in pectinase production and having 4.4U/ml enzyme activity, degraded congo red by 66.75% and malachite green by 54.26%.All isolates showed activity between 30° and 37°C, and pH ranges from 4.5 to 7. The outcomes of this research will be useful in the fiber industry like jute or banana, dye industry, pulp-paper industry, and textile industry for waste remediation, recycling, and fiber modification.

A novel coupled framework for detecting hotspots of methane emission from the vulnerable Indian Sundarban mangrove ecosystem using data-driven models

Coastal mangroves have been lost to deforestation for anthropogenic activities such as agriculture over the past two decades. The genesis of methane (CH4), a significant greenhouse gas (GHG) with a high potential for global warming, occurs through these mangrove beds. The mangrove forests in the Indian Sundarban deltaic region were studied for pre-monsoonal and post-monsoonal variations of CH4 emission. Considering the importance of CH4 emission, a process-based spatiotemporal (PBS) and an analytical neural network (ANN) model were proposed and used to estimate the amount of CH4 emission from different land use land cover classes (LULC) of mangroves. The field work was performed in 2020, and gas samples of various LULC were directly collected from the mangrove bed using the enclosed box chamber method. Historical climatic data (1960–1989) were used to predict future climate scenarios and associated CH4 emissions. The analysis and estimation activities were carried out utilizing satellite images from the pre-monsoonal and post-monsoonal seasons of the same year. The study revealed that pre-monsoonal CH4 emission was higher in the south-west and northern parts of the deforested mangrove of the Indian Sundarban. A sensitivity study of the anticipated models was conducted using a variety of environmental input parameters and related main field observations. The measured precision area under curve of receiver operating characteristics was 0.753 for PBS and 0.718 for ANN models, respectively. The temperature factor (Tf) was the most crucial variable for CH4 emissions. Based on the PBS model with coupled model intercomparison project-6 temperature data, a global circulation model was run to predict increasing CH4 emissions up to 2100. The model revealed that the agricultural lands were the prime emitters of CH4 in the Sundarban mangrove ecosystem.

Whole-genome sequencing of biofilm-forming and chromium-resistant mangrove fungus Aspergillus niger BSC-1

Filamentous fungus Aspergillus niger has gained significant industrial and ecological value due to its great potential in enzymatic activities. The present study reports the complete genome sequence of A. niger BSC-1 which was isolated from Indian Sundarban mangrove ecosystem. The study revealed that the genome of A. niger BSC-1 was 35.1 Mbp assembled in 40 scaffolds with 49.2% GC content. A total of 10,709 genes were reported out of which 10,535 genes were predicted for encoding the proteins. BUSCO assessment showed 98.6% of genome completeness indicating high quality genome sequencing. The genome sequencing of A. niger BSC-1 revealed the presence of rodA and exgA genes for initial adhesion to surface and Ags genes for matrix formation, during biofilm growth. OrthoVenn2 analysis revealed that A.niger BSC-1 shared 9552 gene clusters with the reference strain A. niger CBS554.65. Semi-quantitative RT-PCR analysis unveiled the role of Ags1 and P-type ATPase in fungal biofilm formation and chromium (Cr) resistance, respectively. During biofilm growth the expression of Ags1 significantly (P < 0.0001; two-way ANOVA followed by Sidak's multiple comparisons test) increased with respect to planktonic culture revealing the possible involvement of Ags1 in biofilm matrix formation. Expression of P-type ATPase gene was significantly upregulated (P < 0.0001; one-way ANOVA followed by Dunnett's multiple comparisons test) with the increasing chromium concentration in the fungal culture. Besides, several other genes encoding metalloprotease, copper and zinc binding proteins, and NADH-dependent oxidoreductase were also found in the genome of A. niger BSC-1. These proteins are also involved in heavy metal tolerance and nanofabrication indicating that this filamentous fungus A. niger BSC-1 could be potentially utilized for chromium detoxification through biofilm or nanobiremediation.

Batch adsorption and process optimization for sequestration of Cr(VI) from aqueous solution using biofilm forming filamentous fungus Aspergillus niger BSC-1

Chromium (Cr) contamination in an aquatic environment is one of the greatest concerns nowadays. However, biosorption by various microorganisms is proven to be an environmentally sustainable method. The present study investigated fungal biofilm-mediated sorption of hexavalent chromium [Cr(VI)] using manglicolous filamentous fungus Aspergillus niger BSC-1 obtained from the Indian Sundarban mangrove ecosystem. Biosorbents, such as fungal pellet and fungal biofilm, were utilized for Cr(VI) sequestration. The result showed significantly higher removal of Cr(VI) by fungal biofilm (97.81 ± 2.5 %) than the fungal pellet (79.14 ± 2.4 %) (P < 0.05; two-way ANOVA). Batch adsorption study showed that the highest removal efficiency was attained at 40 °C and pH 3 with 3 g/L of fungal biofilm. The adsorption isotherms, kinetics and thermodynamic analysis suggested monolayer, endothermic and chemisorption of Cr(VI) on the fungal biofilm biosorbent. The adsorption process was further optimized using response surface methodology (RSM) - Central Composite Design (CCD), suggesting the quadratic model for Cr adsorption with high significance (P < 0.0001). The 3D surface plots among the three key variables, i.e., pH, temperature and Cr concentration, revealed that maximum sequestration (92.39 %) was achieved at 40 °C, pH 3 and 30 mg/L of Cr(VI) using 3 g/L of fungal biofilm. Regeneration study demonstrated that fungal biofilm retained 87.19 ± 3.23 % of Cr(VI) sorption with no significant reduction in Cr(VI) removal after five successive adsorption-desorption cycles. X-ray photoelectron spectroscopic analysis showed that adsorption, reduction and complexation mechanisms were involved in Cr(VI) detoxification. Furthermore, the fungal biofilm biosorbent efficiently removed approximately 100 % of Cr(VI) from leather effluent within 90 min of reaction time.

COMPARATIVE STUDY OF MUD CRAB (SCYLLA OLIVACEA) PRODUCTION IN THE SUNDARBANS AND IN TRADITIONAL SHRIMP GHERS OF BAGERHAT DISTRICT, BANGLADESH

The comparative study of mud crab (Scylla olivacea) production between Sundarbans Mangrove Ecosystem and traditional shrimp ghers was conducted in three major landing centers namely Gona, Digraj and Vaga in Bagerhat region at monthly interval from January to December 2002. The maximum production of 1247.15 MT was estimated from Sundarbans mangrove swamp areas while 1016.30 MT from traditional shrimp ghers. The production of mud crab from the Sundarbans ecosystem was 10.20% higher and significant at 5% level than the traditional shrimp ghers of Bagerhat region in 2002. There were no significant differences in production at different landing centers, months and seasons. But the production of different grade sizes from the Sundarbans and traditional shrimp ghers in the region showed significant variation (P&lt;0.05). The production from the Sundarbans was found to be consistent round the year, whereas it was seasonal (May to November) for the traditional shrimp ghers. Fishing closure for mud crab inside the Sundarbans should be enforced effectively in order to maintain the supply of mud crab seed for its production from the shrimp ponds throughout the coastal region of Bangladesh.

Salinity reduces site quality and mangrove forest functions. From monitoring to understanding

Mangroves continue to be threatened across their range by a mix of anthropogenic and climate change-related stress. Climate change-induced salinity is likely to alter the structure and functions of highly productive mangrove systems. However, we still lack a comprehensive understanding of how rising salinity affects forest structure and functions because of the limited availability of mangrove field data. Therefore, based on extensive spatiotemporal mangrove data covering a large-scale salinity gradient, collected from the world's largest single tract mangrove ecosystem – the Bangladesh Sundarbans, we, aimed to examine (QI) how rising salinity influences forest structure (e.g., stand density, diversity, leaf area index (LAI), etc.), functions (e.g., carbon stocks, forest growth), nutrients availability, and functional traits (e.g., specific leaf area, wood density). We also wanted to know (QII) how forest functions interact (direct vs. indirect) with biotic (i.e., stand structure, species richness, etc.) and abiotic factors (salinity, nutrients, light availability, etc.). We also asked (QIII) whether the functional variable decreases disproportionately with salinity and applied the power-law (i.e., Y = a Xb) to the salinity and functional variable relationships. In this study, we found that rises in salinity significantly impede forest growth and produce less productive ecosystems dominated by dwarf species while reducing stand structural properties (i.e., tree height, basal area, dominant tree height, LAI), soil carbon (organic and root carbon), and macronutrient availability in the soil (e.g., NH4+, P, and K). Besides, species-specific leaf area (related to resource acquisition) also decreased with salinity, whereas wood density (related to resource conservation) increased. We observed a declining abundance of the salt-intolerant climax species (Heritiera fomes) and dominance of the salt-tolerant species (Excoecaria agallocha, Ceriops decandra) in the high saline areas. In the case of biotic and abiotic factors, salinity and salinity-driven gap fraction (high transmission of light) had a strong negative impact on functional variables, while nutrients and LAI had a positive impact. In addition, the power-law explained the consistent decline of functional variables with salinity. Our study disentangles the negative effects of salinity on site quality in the Sundarbans mangrove ecosystem, and we recognize that nutrient availability and LAI are likely to buffer the less salt-tolerant species to maintain the ability to sequester carbon with sea-level rise. These novel findings advance our understanding of how a single stressor—salinity—can shape mangrove structure, functions, and productivity and offer decision makers a much-needed scientific basis for developing pragmatic ecosystem management and conservation plans in highly stressed coastal ecosystems across the globe.

Significant reduction of carbon stocks and changes of ecosystem service valuation of Indian Sundarban

The Sundarban mangrove or tidal influenced natural ecosystem is extremely productive and providing multiple goods and services to millions of people. In the last few decades, the quality and quantity of mangrove ecosystem are being deteriorated. The main objectives of this current research are (i) to investigate the ecosystem service values (ESVs) using a time series satellite data (1975, 2000 and 2020) and different unit values (ii) to analyze the dynamic pattern of carbon sequestration through InVEST model and (iii) determination of ESVs change hotspots by Getis-Ord Gi* method. Here, mangrove forest has the highest ecosystem service value and highest carbon sinker. The total loss of ESVs was estimated 3310.79 million USD during last 45 years in Sundarban Biosphere Reserve (SBR) due to high natural and anthropogenic adversities. InVEST model also revealed that the total static carbon storage over the study area was 48.87, 46.65 and 43.33 Tg for the year 1975, 2000 and 2020 respectively. Total 6313944 mg/6.31Tg loss of carbon has been observed in the case of mangrove forest during the overall study period (1975–2020). So, illegal human encroachment should be strictly (through law and regulations) restricted within Sundarban mangrove ecosystem for the benefits of people.

Sedimentation of metals in Sundarban mangrove ecosystem: Dominant drivers and environmental risks.

Metal contamination from upstream river water is a threat to coastal and estuarine ecosystem. The present study was undertaken to unveil sedimentation processes and patterns of heavy metal deposition along the salinity gradient of a tropical estuary and its mangrove ecosystem. Sediment columns from three representative sites of differential salinity, anthropogenic interference, and sediment deposition pattern were sampled and analyzed for grain size distribution and metal concentrations as a function of depth. Sediments were dominantly of silty-medium sand texture. A suite of fluvial and alluvial processes, and marine depositional forcing control the sediment deposition and associated heavy metal loading in this estuary. The depth profile revealed a gradual increase in heavy metal accumulation in recent top layer sediments and smaller fractions (silt + clay), irrespective of tidal regimes. Alluvial processes and long tidal retention favor accumulation of heavy metals. Enrichment factor (0.52-15), geo-accumulation index (1.4-5.8), and average pollution load index (PLI = 2.0) indicated moderate to higher heavy metal contamination status of this estuary. This study showed that alluvial processes acted as dominant drivers for the accumulation of metals in sediments, which prevailed over the influence of marine processes. Longer tidal retention of the water column favored more accumulation of heavy metals. Metal accumulation in the sediments entails a potential risk of bioaccumulation and biomagnification through the food web, and may increasingly impact estuarine ecology, economy, and ultimately human health.

Empirical dynamic model deciphers more information on the nutrient (N)—phytoplankton (P)–zooplankton (Z) dynamics of Hooghly-Matla estuary, Sundarban, India

Ecological models are considered as snapshots of ecological processes that are frequently expressed by mathematical equations. Parameters that explain the rate of the processes in the system are included in mathematical equations of the ecological process.The empirical dynamic model (EDM) is an equation-free, non-parametric model that is based on time-series data to recover the dynamic attractor of the system that governs the system dynamics. The model selection is made through the measure of forecast skill and its optimization. The non-linearity of the Sundarban mangrove ecosystem is hard to define by the limited parameters. Thus, the application of EDM in such a super-dynamic system is considered to be a need of current research to understand the complex system dynamics. The cross convergent mapping identifies the causal variables of the system. The EDM showed that the salinity of downstream and nutrient input from mangrove forests determines the nutrient availability; and the water temperature, surface solar irradiance, and salinity are the main drivers behind phytoplankton abundance in the estuary of the Sundarban mangrove ecosystem. The higher values of the forecast skill and lower values of root mean square error (RMSE) ensure better predictability of the non-parametric model over the parametric model.

Dynamics of methane and carbon dioxide emissions in the reclaimed islands of Sundarban mangrove ecosystem, India

AbstractThe loss and deterioration of mangroves would lead to potentially important greenhouse gases (GHG) from the mangrove ecosystem. Seasonal variations of methane (CH4) and carbon dioxide (CO2) fluxes are studied in the Indian part of the Sundarban mangrove ecosystem. Considering the importance of CH4 and CO2 fluxes, a dynamic model is proposed here with CH4 and CO2 as state variables. The data used in the model are collected and analysed from the field over two years. The parameters that are taken from the literature sources are calibrated in the model. Sensitivity analysis is conducted to assess the valuable contribution of various parameters to the dynamics of CH4 and CO2 emissions from the mangrove beds. Model simulation results are appropriately validated with the observed data. Results showed that CH4 and CO2 fluxes were higher during monsoon. Pearson correlation was done to assess the relationships between emissions and all the physical–chemical factors involved in the model. Sensitivity analysis indicated that the temperature sensitivity (Q10) was the system‐sensitive parameter for CH4 and CO2 emissions. The soil moisture and relative light intensity were the sensitive parameters for CH4 and CO2 emissions, respectively. Model showed that the increase in the anthropogenic emissions including emissions from livestock and fossil fuel caused an increase of 2% of CH4 and 3% of CO2 in the system, respectively. The proposed model could be a tool for environmental managers to assess the emission process at different global locations.

Decadal loss of above-ground biomass and subsequent potential CO2 emission from the Sundarbans mangrove ecosystem, India

Mangrove forests harbour some of the highest carbon densities of any ecosystem, yet their decline has resulted in potential carbon dioxide (CO2) emissions. The emission of CO2 due to the loss of above-ground biomass (AGB) of the Sundarbans mangrove ecosystem was calculated using the ArcMap and ERDAS software. Hence, classification of the Satellite images between 1990 and 2020 of the Indian portions of the Sundarbans was done.The total loss of mangrove area in the Indian part of Sundarbans is 138.4 km2 in the last 30 years. Around 57% of the total loss is due to erosion, 22% is converted to fallow lands, and the remainder is transformed into different landforms for human use. The AGB loss has led to the potential CO2 emission of 2028.4 ± 713.7 Gg, which costs $101.42 million in terms of the social cost of carbon (SCC).The stability analysis of the system showed that the fluctuations during the high tidal surges of cyclone ‘Aila’ that struck the coastline of the Bay of Bengal, resulted in the decrease of mangrove covers and acted as a driving force behind the depletion of ‘blue carbon’ of the Sundarbans.

Microbial populations regulate greenhouse gas emissions in Sundarban mangrove ecosystem, India

Mangrove ecosystems are significant sources of greenhouse gases (GHG) that is attributed to microbial activity. However, it is still unknown how the sediment microbial populations affect GHG emissions in mangrove ecosystem. Since little is known about microbial populations of mangroves, the present study was aimed to understand the structure and function of microbial communities in the Indian part of the Sundarban mangrove ecosystem in relation to environmental variables and variation of GHG emissions during three seasons: pre-monsoon (March–June), monsoon (July–October) and post-monsoon (November–February).Seasonal variations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) gas samples were taken from the mangrove bed. Culture methods were used to detect twelve different types of microbes such as heterotrophic (Htp), N2 fixing (Nfix), nitrifying (Ntfn), sulfur oxidizing (Soxd), Gram-negative (GMn), Gram-positive (GMp), spore forming (Sfor), denitrifying (DNtfn), anaerobic (Anrb), phosphate solubilizing (Psol), cellulose degrading (Cdeg) bacteria and actinomycetes (Actm). In the monsoon, populations of the Htp, Anrb, Psol, and Cdeg bacteria were more prevalent, whereas populations of the GMn, GMp, Ntfn, DNtfn bacteria, and Actm bacteria were more prevalent in the post-monsoon. Monsoonal CO2 and CH4 fluxes were larger than pre-monsoon and post-monsoon, resulting in increased microbial soil respiration and breakdown of soil organic carbon. Because of higher denitrification and soil temperature, N2O flux was higher in the pre-monsoon period, followed by monsoon and post-monsoon periods. A univariate statistical correlation was employed to assess the relationships between environmental variables and different microbial populations. An ANN (artificial neural network) model was proposed to evaluate the relevance of microbial population contribution to GHG emissions, and it indicated that the Htp, Anrb, and Dntfn microbial populations were most relevant for CO2, CH4, and N2O emissions. The suggested model would be used to assess the drivers behind GHG emission in the mangroves located at different parts of the world.

Exploring changes in bacterioplankton community structure in response to tannic acid, a major component of mangrove litterfall of Sundarbans mangrove ecosystem: a laboratory mesocosm approach.

Tannic acid is a secondary compound produced by vascular plants and is a major component of mangrove litterfall. Tannic acid is water soluble, leaches out from mangrove litterfall and contributes to DOC and DON pools in adjacent estuaries. About 50% of the litterfall may be degraded and channelized into the marine microbial loop. The influence of tannic acid on bacterioplankton community structure was tested by setting up laboratory-based barrel experiments. Estuarine water from Stn3 of Sundarbans Biological Observatory Time Series(SBOTS) was enriched with tannic acid, and the change in concentration of dissolved nutrients was determined on a daily basis over a span of 15 days. Concentrations of tannic acid, gallic acid and other dissolved nutrients such as nitrate and ortho-phosphate were determined using a UV-Vis spectrophotometer. Tannic acid significantly affected the concentrations of gallic acid and dissolved nitrate in the barrels. Degradation of tannic acid was tracked by a decrease in concentration of tannic acid and generation of gallic acid. The influence of tannic acid on bacterioplankton community structure was analysed on the start (day 0), intermediate (day 3, day 5, day 7 and day 9) and end (day 15) of the experiment. Bacterioplankton community structure was elucidated by sequencing the V3-V4 region of 16S ribosomal RNA on an Illumina MiSeq platform. Proteobacteria was found to be the most dominant bacterial phylum in control and tannic acid-enriched barrels (barrels 1 and 2) on day 0. With the progression of experiment, the abundance of Proteobacteria altered significantly in the control barrel indicating the possible role of this phylum in the breakdown of tannic acid within estuarine mangroves. The abundance of Proteobacteria in the tannic acid-enriched barrels remained high, indicating that members of Proteobacteria may be capable of using tannic acid as a source of carbon and nitrogen. Tannic acid appeared to inhibit most of the other bacterioplankton phyla including Actinobacteria, Acidobacteria and Verrucomicrobia that existed in large abundance in the control barrel on day 15 but were almost absent in the tannic acid-enriched barrels. At class level, Bacteroides was found to be present in highest abundance in the tannic acid-enriched barrels. Tannic acid appeared to strongly influence the abundant bacterioplankton phyla and families as indicated by Pearson's correlation coefficient and non-metric multidimensional scaling ordination plots. Gallic acid is one of the final products of tannic acid degradation. Breakdown of tannic acid could influence the marine nitrogen and carbon cycling by releasing DON and DOC, respectively, into the adjacent estuaries. Information of breakdown and remineralization of components of litterfall such as tannic acid would also be important for calculation of carbon and nitrogen budgets of coastal ecosystems including in mangroves.

Geo-ecological impact assessment of severe cyclonic storm Amphan on Sundarban mangrove forest using geospatial technology

We report the damage caused by Amphan, a category five tropical cyclonic storm, to the ecology and shoreline of the Sundarban mangrove ecosystem, located in India and Bangladesh. In this study, net shoreline movement (NSM) combined with vegetation indices, such as normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), were used to analyze land use and land cover changes and the position of the shoreline in pre- and post-cyclone periods. The results show that the cyclone wreaked havoc in the Sundarban mangrove ecosystem, causing dangerous impacts on vegetation and severe erosion along the shoreline. The impact on the Sundarban mangrove forest, shown by NDVI and EVI values, indicates that the mangrove vegetation suffered degradation and fragmentation. Dense and moderately dense mangrove tree cover area shrank from 77% to 34%, less dense and sparse cover increased from 20% to 63%. More than 68% of shoreline transects registered signs of erosion, with mean shoreline change and erosion rate measurements of −31 m and −48 m, respectively. As a result, agricultural lands and aquaculture ponds suffered inundation, leading to crop damage. A single cyclone episode can damage mangrove cover by knocking down tall trees, killing more salt-sensitive mangrove species such as Sundari, and leads to increased man-animal encounter. We argue that post-cyclone biodiversity loss and ecosystem services loss should be analyzed in tandem and synchrony with human and livestock casualty and economic damage assessment.