Sundarbans Research Articles

Successive Cyclones Attacked the World’s Largest Mangrove Forest Located in the Bay of Bengal under Pandemic

Despite the global focus on the COVID-19 pandemic, the promise of impact to tropical coastlines and stochasticity of destruction caused by tropical cyclones remains unaltered, forcing human societies to adapt to new unadaptable scenarios. Super Cyclone Amphan’s landfall—the third cyclone of the season within the world’s largest mangrove forest—brought a new uncertainty to this undeveloped region of South Asia. How do vulnerable people deal with multiple disasters that limit necessary humanitarian response while still maintaining the natural environmental integrity of a system harboring critical wildlife populations and protecting people from further disaster? We explored this reality for the Sundarbans region using a remote sensing technique and found that the western part of Sundarbans mangroves was severely damaged by Amphan, suggesting that rapid remote sensing techniques can help direct resources, and recognize the eventuality that response will be a best effort for now. If 2020 is a window, multiple disaster management scenarios may become more common in the future. Yet, society’s obligation for maintaining environmental integrity remains unchanged.

Previous Shoreline Dynamics Determine Future Susceptibility to Cyclone Impact in the Sundarban Mangrove Forest

Extreme weather events are a cause of mangrove forest loss and degradation globally. Almost half of the world’s mangroves are found in the tropical cyclone belt, and forests often experience disturbance in structure, functioning and ecosystem service provision. Understanding the factors that increase the vulnerability of mangroves to such disturbances is a challenge. Using a novel remote sensing analysis combining water class change with vegetation classification, we showed that mangrove loss across multiple cyclone events is influenced by previous erosion history, suggesting that the prior state of the coastline affects susceptibility to future disturbance events. During Cyclone Amphan in May 2020, more than 1,200 km2 of mangroves were damaged and 40.6 km2 of shoreline was lost. Cyclone Amphan caused the most damage out of three recent cyclones, with the most mangrove loss (18.8%) experienced along shorelines that were eroding over the past 35 years. This can be explained by the long-term effect of erosion on the overall intertidal morphology of the shoreline. Landscape-scale mangrove management, particularly of sediment budgets is essential to switch previously eroding mangroves to a state where they can withstand cumulative storm impacts.

Distribution and Dynamics of Radiatively Active Gas (RAG) Emissions From Major Estuaries of the Sundarbans Mangrove, India

The world’s largest mangroves ecosystem, the Sundarbans, being highly productive and a place for extensive organic matter cycling, is considered to be the hotspot for biogeochemical studies in the tropical estuarine environment. Hence, the spatial and temporal dynamics of the biogenic gases (CO2, CH4, and N2O), also known as radiatively active gases, were measured in mangrove-dominated estuaries of the system. In addition to spatial and seasonal observation, three full tidal cycles were observed at one site. Results showed that the air/water gas saturations were widely distributed and highly variable along the stretch. The gas saturations showed varying responses to salinity and tidal fluctuations. This indicated that localized biogeochemical processes may be more influential than simple mixing and dilution processes in controlling the variability of these gases. The surface waters were always supersaturated with CH4 (Up to 13,133%) relative to the atmosphere. However, N2O ranged from 8 to 1,286% and CO2 from 30 to 2075%. N2O fluxes were ∼4.8 times higher in the pre-monsoon than the post-monsoon. CH4 fluxes were ∼3.6 times higher in the pre-monsoon than both the monsoon and the post-monsoon. CO2 fluxes were ∼10 times higher in the monsoon than both the pre-monsoon and the post-monsoon. The seasonality in the gas saturation could be linked more to the availability of substrates than physicochemical parameters. Overall, air/water CH4 fluxes varied maximally (0.4–18.4 μmol m−2 d−1), followed by CO2 fluxes (−0.6–10.9 mmol m−2 d−1), and N2O fluxes varied the least of all (−0.6–5.4 μmol m−2 d−1). Interestingly, CH4 and N2O fluxes were positively correlated to each other (p < 0.05), suggesting organic matter decomposition as the key factor in the production of these two gases. Finally, these water–air CO2, CH4, and N2O flux estimates show that the estuaries are a modest source of CH4 but fluctuate between sources and sinks for CO2 and N2O gases.

Is co-management a double-edged sword in the protected areas of Sundarbans mangrove?

The overall objective of the study was to examine the pros and cons of the participatory approach adopted in natural resource management in the ecologically protected areas of the Sundarbans mangrove of Bangladesh. A comparative study was done between the people who are involved and non-involved in this approach. Empirical data was collected through personal interviews with a structured questionnaire. The Gini coefficient was measured first and then embedded with the Lorenz curve to draw a line between perfect equality and inequality vis-a-vis. The study revealed that the co-management built awareness in favor of biodiversity conservation and the efficient use of natural resources. Contradictorily, a segment of different hierarchical committees was involved in destructive activities like poisoning the wetlands for fishing. Therefore, a mixed outcome was found. The findings will help the policymakers in identifying the pitfalls and bottlenecks rooted in co-management. Hence, the study recommends revising the approach to ensure the community’s active participation on an equal basis and take action against them who degrade those resources. Exploring profitable alternative income-generating activities is warranted to narrow down the dependency on the Sundarbans mangrove’s natural resources. In order to address the tragedy of the commons, the study advocates for the unity of all knowledge ranging from science to humanistic scholarship for sound policymaking.

Unique characteristics of ecosystem CO2 exchange in Sundarban mangrove forest and their relationship with environmental factors

Sundarban mangroves, known to be the largest single block of tidal halophytic mangrove forest globally, covers a significant portion of the world's mangroves and contributes substantially to the global mangrove carbon budget. Nevertheless, there is still a lack of long-term continuous monitoring of CO2 fluxes over this crucial ecosystem and their dynamics in response to climatic variations. This study presents the carbon balance and seasonal dynamics of this oldest and undisturbed mangrove ecosystem using quasi-continuous eddy covariance measurements from April 2012 to March 2016. These tidal forests are found to be net C sink with a mean net primary production (NEP) of 276 g C m−2 yr−1 (±35; ±1 Standard deviation amongst the four years). The NEP is partitioned into gross primary production (GPP) and ecosystem respiration indicate gross sequestration of 1581 (±152) g C m−2 yr−1 with a respiratory loss of 1305 (±184) g C m−2 yr−1. We have observed that inter- and intra-annual variations in CO2 fluxes are primarily controlled by environmental factors such as temperature, vapour pressure deficit (VPD), rainfall and photosynthetic active radiation. At the study site, the photosynthetic activity and light use efficiency decreased with an increase in temperature and VPD. Though minimal seasonal fluctuations in CO2 fluxes were observed, a strong linkage has been observed between C fluxes and satellite-derived enhanced vegetation index (MODIS EVI) during the study period. Further, the carbon assimilation rates were found to be higher under diffused sky than normal conditions due to the increased photosynthetic activity by penetration of diffused radiation within the mangrove canopies. Additionally, ecosystem productivity during the study period was higher during the wet periods than dry periods. Our findings show that ecosystem productivity rates are strongly related to temperature, vapour pressure deficit, rainfall, and radiation, implying that global warming could have a significant impact on these environmental factors and other underlying parameters (such as salinity, tidal inundation patterns etc.) and potentially reduce the C sequestration potential of these tropical mangroves of India.

Tourists’ willingness to pay for restoration of Sundarbans Mangrove forest ecosystems: a contingent valuation modeling study

Tourists’ willingness to pay for restoration of Sundarbans Mangrove forest ecosystems: a contingent valuation modeling study

Flowering and Fruiting Behavior, Seed Germination, and Survival Status of Heritiera fomes Buch-Ham and Excoecaria agallocha L. Species in the Sundarban Mangrove Forest of Bangladesh

Flowering and Fruiting Behavior, Seed Germination, and Survival Status of Heritiera fomes Buch-Ham and Excoecaria agallocha L. Species in the Sundarban Mangrove Forest of Bangladesh

Trophic Transfer of Microplastics in the Aquatic Ecosystem of Sundarbans Mangrove Forest, Bangladesh

Trophic Transfer of Microplastics in the Aquatic Ecosystem of Sundarbans Mangrove Forest, Bangladesh

Pesticidal Activity of Sundarban Mangrove Plant Extracts against Sitophilus Pests and Identification of Active Constituents Using LC-MS.

Plants act as a rich source of novel natural pesticides. In the backdrop of the recent revival of interest in developing plant-based insecticides, this study was carried out to investigate the pesticidal activity of Sundarban mangrove plants. A total of nine different plant parts from five plants, namely, Aegiceras corniculatum, Excoecaria agallocha, Heritiera fomes, Xylocarpus moluccensis, and Xylocarpus granatum, were extracted with methanol and tested for insecticidal activity against two common stored product pests Sitophilus oryzae and Sitophilus zeamais using direct contact feeding deterrent wafer disc method. Three bark extracts from A. corniculatum, E. agallocha, and H. fomes showed potent and statistically significant insecticidal activity against both S. oryzae and S. zeamais pests (80–100% mortality). All the active bark extracts were further fractionated using C-18 solid-phase extraction (SPE) columns and tested for their insecticidal activity against S. oryzae pest to identify the active fraction. Only the SPE4 fraction (100% MeOH) from all the three active plants showed the activity against S. oryzae pest with a lethal concentration 50% (LC50) value of 0.5, 1.0, and 1.5 mg/disc for A. corniculatum, E. agallocha, and H. fomes, respectively. The active fraction of A. corniculatum was further profiled for identification of active compounds using LC-ESI-MS and identified (along with some unknown peaks) two previously reported compounds at m/z 625.17630 (isorhamnetin 3-O-rutinoside) and 422.25346 (paspaline) as major constituents. Insecticidal activities of these plants are reported in this study for the first time and would be useful in promoting research aiming for the development of new biopesticides from mangrove plants.

RESPONDENT ANALYSIS IN CONTEXT TO IMPACT OF CLIMATE CHANGE ON THE REGULATING SERVICES OF MANGROVE VEGETATION

The mangrove ecosystem in the lower Gangetic delta is noted for providing several regulatory services. The major regulatory services include erosion, natural disaster, Phytoremediation, carbon sequestration, siltation, and sea-level rise. Here, we have attempted to develop a mechanism of assessing and ranking the magnitude of regulatory services offered by Sundarban mangroves based on stakeholder’s views on the subject. The respondents were categorized into five major classes namely policy level worker, researcher, fisherman, agriculturist, and local inhabitant. About 295 respondents belonging to these 5 categories were asked about the types of regulatory services and their respective magnitude by ranking the services between 1 and 6. Finally, based on data generated, three separate Combined Mangrove Regulating Service Scale (CMRSS) were assessed for three sectors (western, central, and eastern) of Indian Sundarbans. The basic root for such assessment is contrasting variations between these three sectors based on geographical features, salinity, and biodiversity. The present approach of analysis can be a road map to identify and empirically score the regulatory services of mangroves.

English

The Sundarban Reserve Forest (SRF) of Bangladesh provides tourism services to local and international visitors. Indeed, tourism is one of the major ecosystem services that this biodiversity-rich mangrove forest provides. Through a convenient sampling technique, 421 tourist respondents were interviewed to assess their willingness to pay for the tourism services of the Sundarban, using the Zonal Travel Cost Method (ZTCM). The estimated annual economic contribution of tourism in the Sundarban mangroves to the Bangladesh economy is USD 53 million. The findings of this study showed that facilities for watching wildlife and walking inside the forest can increase the number of tourists in the SRF. The findings also show that the availability of information like forest maps, wildlife precautionary signs, and danger zones would increase the number of tourists as well. Thus, the government of Bangladesh should consider increasing visitor entry fees to fund improvements and to enhance the ecotourism potential of the Sundarban mangroves.

Seedling Diversity Considerably Changes Near Localities in Three Salinity Zones of Sundarbans Mangrove Forest, Bangladesh

The status of natural seedlings near localities in the Sundarbans Mangrove Forest was assessed through a stratified random sampling method to observe seedling composition and diversity, importance value index, family importance value, and species evenness. A total of 63 sample plots of 3,990 m2 area were surveyed in three natural and anthropogenic influenced salinity zones of Sundarbans. A total of 16,166 seedlings of 15 species under 12 families were found. Family Euphorbiaceae showed the highest (59.59%) family relative density and Rhizophoraceae presented the highest (20%) family relative diversity Index (FRDI). The maximum family importance value (FIV) showed by Euphorbiaceae (66.26) and the maximum importance value index (IVI) of species has been observed in Excoecaria agallocha (114.74). Excoecaria agallocha showed the highest relative density (59.6%) and relative abundance (39.87%) where the highest relative frequency (15.27%) was observed by Heritiera fomes. The mean stem density and species diversity index in the whole survey area was 2701 stem ha-1 and 0.0009 correspondingly. The Shannon-Wienner's diversity index was 1.52 where the maximum Shannon-Wienner's diversity index was 2.708. The Simpson's diversity index and Dominance of Simpson index were 0.38 and 0.62 with Simpson's reciprocal index 2.632. The Species evenness index, Menhinick’s, and Margalef's indices were 0.561, 0.118, and 1.445 respectively. The Species diversity index of the three salinity zones were 0.0017, 0.0029, and 0.0035 respectively. The Shannon-Wienner's diversity index of Low Salinity Zone (LSZ), Moderate Salinity Zone (MSZ), and Strong Salinity Zone (SSZ) were 0.887, 1.369, and 1.845 correspondingly where LSZ (0.632) showed the highest Simpson's diversity index follow ed by MSZ (0.394) and SSZ (0.21). The Species evenness index for LSZ, MSZ, and SSZ were 0.346, 0.505, and 0.742 where Menhinick’s Index were 0.148, 0.210, and 0.207 respectively. The analysis showed poor diversity indices and the area was dominated by few species with few families. The status is also reduced with increasing salinity.

The Decadal Response of Vegetation in the Sundarbans Mangrove Forest to the Climate Variabilities: Observing from the Space

The Decadal Response of Vegetation in the Sundarbans Mangrove Forest to the Climate Variabilities: Observing from the Space

Detection and Prediction of Sundarban Reserve Forest using the CA-Markov Chain Model and Remote Sensing Data

Detection and Prediction of Sundarban Reserve Forest using the CA-Markov Chain Model and Remote Sensing Data

Ecological and human health risk evaluation using pollution indices: A case study of the largest mangrove ecosystem of Bangladesh

Wetlands such as mangroves are major centres of biodiversity and the production of ecosystem services from which society gathers goods and benefits. However, these attributes rely on a high environmental quality. That quality is recorded by quantitative indicators which are essential for environmental management. As such, three different salinity domains (Kachikhali, Katka, and Dublarchar) in the Sundarban Mangrove Forest, a world heritage site, were sampled in 2019 and 2020 to determine the heavy metal contamination levels and estimate the probable ecological and human health risks. The study revealed that with the exception of the changed dissolved oxygen (DO) concentration (4.5 to 6.05 mg/L), there was no significant difference between the two years in eight water quality parameters. Heavy metal concentrations followed the sequence in sediment as (mg/kg): Fe (31500) > Mn (281) > Sr (208) > Zn=Cu (77) > Co (6) > Pb (2) and in water as (μg/L): Fe (33.5) > Sr (0.6) > Cu (0.3) > Zn (0.22) > Pb (0.15) > Mn=Co (0.05). Sediment was moderately contaminated by copper as indicated by the degree of contamination (Cd=3.6 to 5.42) and the geo-accumulation index (Igeo=0.07 to 0.33). The human health hazard index (HI) values were 261, 20.6 and 20.6 for children, adult male and adult female, respectively, in Mn due to the inhalation process, indicating elevated health risk. Children can be at high risk due to manganese contamination by skin contact where HI = 2.18 ×10. In contrast, all the Hazard Quotient (HQ) and HI values for other metals were deemed to be safe (<1). This study gives both a comparison for less-contaminated sites and a model for similarly contaminated sites.

Twoblotch ponyfish Nuchequula blochii (Valenciennes, 1835) in the Sundarban Reserve Forest habitat of Bangladesh: Second record and establishment probability

AbstractClimate changes and anthropogenic activities have paved the way for the dislocation of native species into areas located far away from their natural habitats. To this end, the Bay of Bengal and its adjacent coast have experienced the invasion of many alien species coming from different oceans, seas and bays around the world. Recently, a single specimen of the Twoblotch ponyfish (Nuchequula blochii) was captured. It had a total length of 69 mm and bodyweight 0.98 g. The specimen was caught at a depth of 18 m in the world's largest mangrove habitat, Sundarban, with a soft sandy bottom. Because the species N. blochii was previously recorded for the first time in the water area of Bangladesh, the single captured species above was considered as the ‘second record.’ There are several potential factors responsible for the introduction of this species in the Bay of the Bengal coast, one being the similar habitat conditions available to them. Because this species was previously reported from the water area of Bangladesh and is still appearing now, there is a possibility that it may become established in the water area of Bangladesh.

Anti-Bacterial, Anti-Diarrheal, and Cytotoxic Activities of Edible Fruits in the Sundarbans Mangrove Forest of Bangladesh.

This study evaluated anti-bacterial, anti-diarrheal, and cytotoxic activities of ten edible fruits (Aegiceras corniculatum, Avicennia officinalis, Bruguiera gymnorrhiza, Ceriops decandra, Heritiera fomes, Nypa fruticans, Phoenix paludosa, Sarcolobus globosus, Sonneratia caseolaris, and Xylocarpus mekongensis) in the Sundarbans mangrove forest of Bangladesh. Highest antibacterial activity was shown for ethanol:methanol (1:1) extracts of S. caseolaris (2 mg/disc), which demonstrated inhibition zones of 16.7, 17.0, 14.7, 15.7, and 15.7 mm against Escherichia coli, Klebsiella sp., Shigella boydii, Shigella sonnei, and Staphylococcus aureus, respectively. In mice with castor oil-induced diarrhea, S. caseolaris extract (250 mg/kg body weight) showed the highest inhibition (87.7%) and delayed the onset time (273 min) of diarrheal episodes, followed by A. corniculatum extract (inhibition, 83.6%; delayed onset time, 187.4 min). S. caseolaris and A. corniculatum fruit powders were successively fractionated into n-hexane, diethyl ether, chloroform, ethanol, and methanol. Antidiarrheal activity significantly increased with increasing polarity of these fractions. In brine shrimp lethality assay, S. globosus extract demonstrated the highest cytotoxicity (59.2 μg/mL), followed by H. fomes (74.1 μg/mL) and C. decandra (116.7 μg/mL); however, lowest cytotoxicity was shown for A. corniculatum, A. officinalis, and S. caseolaris extracts. Mice treated with A. corniculatum extract did not experience any acute toxicity. These results demonstrate that S. caseolaris and A. corniculatum fruits have potential to treat diarrhea and may act as useful nutraceuticals.

Analysis of erosion–accretion dynamics of major rivers of world’s largest mangrove forest using geospatial techniques

Geomorphological dynamics is the dominating process behind the Sundarbans mangrove forest development. Here, satellite images can illuminate Sundarbans’ erosion–accretion​ dynamics to improve our understanding of better river management. Previous morphological studies were on mangrove vegetation loss or gain and shoreline changes detection. Nevertheless, those studies did not provide channel/river specific erosion and accretion dynamics for the Sundarbans in Bangladesh. In this study, we analyzed historical Landsat satellite images from 1980 to 2019 for six major rivers, namely Passur, Shibsa, Arpangasia, Baleshwar, Malancha, and Shella of the Sundarbans in Bangladesh, which carry freshwater from upstream and supply them into all the tributaries of Sundarbans. Image analysis shows a remarkable erosion rate in all the major rivers. The erosion rates were significantly higher for Passur (2139 ha, 55 ha/yr), Baleshwar (2122 ha, 54 ha/yr), and Shibsa (1809, 46.5 ha/yr) rivers compared to the other three rivers (Arpangasia-995 ha, 26 ha/yr; Malancha-774 ha, 20 ha/yr; Shella-332 ha, 8.5 ha/yr). The spatial pattern of lateral erosion was not uniform for all major rivers. The southern parts of all the rivers were prone to severe erosion compared to the central and northern parts. Reduced freshwater flow has less effect on the lateral erosion of major rivers of the Sundarbans. Besides, NDVI analysis shows that vegetation density has declined tremendously over the last 40 years (highest NDVI value in 1980 and 2019 was 0.87 and 0.44 respectively) along the major river banks as well as in whole Sundarbans which in turn reduces soil binding capacity. Hence, our work suggests that mangrove restoration with careful consideration of biophysical characteristics in the degraded site will aid better resistance against strong wave action.

Carbon Stock of Different Parts of Major Plant Species of Three Ecological Zones of Bangladesh Sundarbans

The biomass and carbon sequestration by different parts namely leaf, stem and roots of major dominant plant species of different quadrats established in three ecological zones of Bangladesh Sundarban Mangrove Forests (SMF) were determined. A visit was done during 28 March to 1 April 2016 covering the oligohaline, mesohaline and polyhaline zones of SMF. Plant parts (stem, branch and leaf) of major plant species were collected from 16 quadrats of different locations. The major plant species were selected on the basis of abundance (number). Aboveground biomass (AGB) was estimated as the product of tree volume and wood density. Below ground biomass (BGB) were estimated from the 20% of above ground stem biomass. Carbon stock and CO2 sequestration were estimated from the dry weight of AGB and BGB. A total of 20 species in 16 different quadrats in three ecological zones and overall SMF was recorded. Among 20 species 10 dominant tree species were considered on the basis of abundance (number) for the estimation of AGB, BGB and CO2 sequestration. Species wise mean AGB (ton/ha) of 10 dominant mangrove trees are in order Heritiera fomes (186.423) &gt; Excoecaria agallocha (28.752) &gt; Avicennia officinalis (24.082) &gt; Ceriops decandra (5.021) &gt; Cynometra ramiflora (1.403) &gt; Tamarix dioica (0.592) &gt; Xylocarpus moluccensis (0.500) &gt; Bruguiera gymnorrhiza (0.307) &gt; Aegiceras corniculata (0.241) &gt; Aglaia cuculata (0.038).Species wise mean BGB (ton/ha) of 10 dominant mangrove trees are in order H. fomes (34.99) &gt; E. agallocha (4.94) &gt; A. officinalis (4.79) &gt; C. decandra (0.704) &gt; X. moluccensis (0.47) &gt; C. ramiflora (0.15) &gt; B. gymnorrhiza (0.018) &gt; A. corniculata (0.015) &gt; T. dioica (0.008) &gt;A. cuculata (0.004). The total CO2 sequestered (above ground and below ground) in overall SMF (considered land area 4143 km2) was 192.869 megaton.&#x0D; Bangladesh J. Bot. 50(2): 373-385, 2021 (June)

Assessing Good Governance in Protected Areas (PA) Co-management: A Case Study of the Sundarbans Mangrove Forests of Bangladesh

ABSTRACT Co-management has been adopted in the Sundarbans of Bangladesh since 2008 toward biodiversity conservation and livelihood improvement of local communities. However, we have limited research on how good governance was maintained and practiced in co-managed mangrove protected areas (PA). Drawing on a case study, this research assessed stakeholders’ perception on good governance in PA co-management in the Sundarbans of Bangladesh. We adopted a ‘good governance framework’ consisting of six governance principles (stakeholders’ participation, transparency, responsiveness, legitimacy, fairness and organizational capacity) and deployed both qualitative (11 key-informants’ interviews and 4 focus group discussions) and quantitative methods (135 structured interviews) for data collection. Median, frequencies (percent), contingency table chi-square tests were performed for quantitative data. About 30–35% of the respondents perceived neutral in their responses to good governance principles (stakeholders’ participation, transparency, responsiveness, legitimacy, fairness and organizational capacity) indicating moderate level of governance in PA co-management in the Sundarbans. This study has demonstrated a wider implementation gap between the ambitious intent enshrined in the new policy framework and actual rollout of PA governance on the ground. These results would be useful to policy-makers, development agencies and PA managers in formulating and implementing effective policies for PA co-management in Bangladesh and elsewhere.