Sundarbans Mangrove Ecosystem Research Articles

Multi-cluster analysis of Crabs and Ichthyofaunal Diversity in relation to habitat distribution at Tropical Mangrove ecosystem of the Indian Sundarbans

Mangroves have enormous ecological significance and socio-economic importance as promising hub for tropical marine and estuarine biotope. Therefore, mangroves are considered one of the world’s richest resources of biological and genetic diversity. Although, crabs and fishes significantly occur among the other macrofauna of the Sundarbans mangrove ecosystem, supportive information on resource and diversity of mangrove’s macrofauna are insufficient due to their non judicious exploitation in unscientific ways. Concerning that, the present survey based experimental research find out the localized endemic composition and bio-distribution of crabs and estuarine fish species which are prevalent in the tropical Sundarbans mangrove systems. A special drive has also been taken to characterize the variation of such species in course of spatial and environmental changing scenario. The consequences of this research concluded a total 115 numbers of crab species and 312 numbers of brackish and marine water fish species were available at Sundarbans. Which are identified, categorically assessed showing their predominant positions in the localized mangrove-associated estuary of 17 different specified clusters or survey areas. Apart from that, the Multivariate Cluster Analysis was performed on the available fish and crab diversity, up to the Family and Species level following their present conservation status.

Anthropogenic influence shapes the distribution of antibiotic resistant bacteria (ARB) in the sediment of Sundarban estuary in India

The abundance and dissemination of antibiotic resistance genes as emerging environmental contaminants have become a significant and growing threat to human and environmental health. Traditionally, investigations of antibiotic resistance have been confined to a subset of clinically relevant antibiotic-resistant bacterial pathogens. During the last decade it became evident that the environmental microbiota possesses an enormous number and diversity of antibiotic resistance genes, some of which are very similar to the genes circulating in pathogenic microbiota. Recent studies demonstrate that aquatic ecosystems are potential reservoirs of antibiotic-resistant bacteria (ARBs) and antibiotic resistance genes (ARGs). Therefore, these aquatic ecosystems serve as potential sources for their transmission of ARGs to human pathogens. An assessment of such risks requires a better understanding of the level and variability of the natural resistance background and the extent of the anthropogenic impact. We have analyzed eight sediment samples from Sundarban mangrove ecosystem in India, collected at sampling stations with different histories of anthropogenic influences, and analyzed the relative abundance of the blaTEM gene using quantitative real-time PCR. The blaTEM gene abundance strongly correlated with the respective anthropogenic influences (polyaromatic hydrocarbon, heavy metals etc.) of the sampling stations. Besides, 18 multidrug-resistant (ampicillin, kanamycin, vancomycin, and tetracycline resistant) bacterial strains (ARBs) were isolated and characterized. Moreover, the effect of different antibiotics on the biofilm forming ability of the isolates was evaluated quantitatively under a variety of experimental regimes. This is the first report of preservation and possible dissemination of ARGs in the mangrove ecosystem.

Draft Genome Sequence of Bioactive Strain Streptomyces sp. SMS_SU21, Isolated from Soil Sediment of the Sundarbans Mangrove Ecosystem.

Streptomyces sp. SMS_SU21 possesses strong antimicrobial activity and antioxidant potential. This strain was isolated from the Sundarbans mangrove ecosystem, and its draft genome comprises 7,449,420 bp with 6,680 open reading frames. Genome analysis of strain SMS_SU21 provides insight into its secondary metabolite arsenal and reveals the gene clusters putatively responsible for its bioactive potential.

Toxicity of Pyrethroids to Grapsid Crab (Pseudograpsus sp.) Collected from the Sundarbans Mangrove Ecosystem, Bangladesh

Toxicity of Pyrethroids to Grapsid Crab (Pseudograpsus sp.) Collected from the Sundarbans Mangrove Ecosystem, Bangladesh

Microbial assay of N2 fixation rate, a simple alternate for acetylene reduction assay

Nitrogen is an essential element for living creatures in every ecosystem but nitrogen cannot be absorbed by the plant itself directly from the atmosphere, so for nitrogen, plant depends on both free living and symbiotic microbes present in the soil. Nitrogen fixation potentiality of the soil thus reveals its fertility with respect to nitrogen. Researchers developed and modified techniques for measuring nitrogen fixation rate of the soil and acetylene reduction assay (ARA) technique became the most popular till now. At the same time this technique has few limitations especially for the researchers from third world country due to lack of special infrastructure in the laboratory and the most required instrument for this technique, gas chromatograph machine, is very expensive. Any alternation of this technique is deserved highly for the researchers from the developing countries. The present work/method explained a new approach for determination of nitrogen fixation rate and this new method was named as “Microbial bio-assay”. In this technique nitrogen fixers were cultured in specific medium and condition and after required time of interval the amount of nitrogen fixed by them were calculated. Exploration of soil of the Sundarban mangrove ecosystem was performed regarding the microbial N2 fixing capacity of that particular ecosystem.•The nitrogen fixation rate measured by acetylene reduction assay (ARA) was 1.13 times lower than the N2 fixation rate measured by microbial bio-assay.•Microbial bio-assay can be used as an alternate of ARA method to measure N2 fixation rate. The rates of N2 fixation measured by both two methods were positively correlated with the population of N2 fixing bacteria present in the soil of that particular ecosystem (R2?=?0.85, p?<?0.005, n?=?85 for microbial bio-assay and R2?=?0.78, p?<?0.005, n?=?85 for ARA).

Trace metal distribution, assessment and enrichment in the surface sediments of Sundarban mangrove ecosystem in India and Bangladesh

Comparative study of trace metals distribution in the surface sediment of Sundarban mangrove ecosystem in India and Bangladesh is one of the primary baseline study done so far. Trace metal distribution assessment covering lower salinity zone to higher salinity zone was done along Matla River (tidal river) in Indian side and freshwater zone to higher salinity zone along Passur River in Bangladesh side of Sundarban; representing anthropogenic influenced area, agricultural area, tourist site and pristine area. Trace metals distribution in the surface sediments of Sundarban mangrove ecosystem shows relatively higher value of trace metals, Co, Cr, Cu, Fe, Ni, Pb and Zn in Indian part when compared to Bangladesh. Enrichment factor shows the highest enrichment of Pb in both parts of Sundarban mangroves. Co, Cr, Cu, Pb and Zn show EF>1 indicates sediment contamination from anthropogenic activities. Cr, Ni and Pb were found to have moderate accumulation in geoaccumulation index with Fe showing high accumulation. Normalized data of trace metals shows 87.5% from Indian site and 80% of Bangladesh site as outlier, indicating anthropogenic influence. Out of total sampling site 50% of Indian and 40% of Bangladesh site show trace metal values enriched more than predicted value of trace metals indicating Indian part have more polluted sites than Bangladesh side of Sundarban, which is also confirmed by enrichment factor, I-geo and normalization values in both the sides.

An updated species checklist for free-living marine nematodes from the world’s largest mangrove ecosystem, Sundarbans

The present study provides an updated species checklist for free-living marine nematode species from the world’s largest contiguous mangrove ecosystem, the Sundarbans (India and Bangladesh). The species checklist includes information available from Sundarbans from the 1950s to the present (2016), using the most recent taxonomic classification of nematodes. The species list contains 179 species in 84 genera and 29 families. Four families, Xyalidae (22 species), Linhomoeidae (18 species), Desmodoridae (16 species) and Chromadoridae (15 species) were most speciose. The genera Halalaimus (9 species), Sabatieria and Daptonema (8 species each) were most species rich; 50 genera were represented by just a single species. Six species are new distributional records for Indian waters. The species checklist is the most extensive list of free-living marine nematodes from the Sundarbans mangrove ecosystem to date and provides a framework for studying biogeography of free-living marine nematodes from mangrove ecosystems globally.

Mangrove Methane Biogeochemistry in the Indian Sundarbans: A Proposed Budget

Biogeochemical cycling of CH4 was investigated at Lothian Island, one of the relatively pristine islands of Indian Sundarbans and its adjacent Saptamukhi estuary, during June 2010 to December 2012. Intertidal mangrove sediments were highly anoxic and rich in organic carbon. Mean rates of methanogenesis were 3547 and 48.88 µmol m-3 wet sediment d-1, for intertidal (up to 25 cm depth) and sub-tidal sediments (first 5 cm depth), respectively. CH4 in pore-water was 53.4 times more supersaturated than in adjacent estuarine waters. This resulted in significant CH4 efflux from sediments to estuarine waters - via advective and diffusive transport. About 8.2% of the total CH4 produced in intertidal mangrove sediments was transported to the adjacent estuary through advective flux, which was 20 times higher than diffusive CH4 flux. Mean CH4 concentrations in estuarine surface and sub-surface waters were 69.9 and 56.1 nM, respectively, with a dissolved CH4 oxidation rate in estuarine surface waters of 20.5 nmol L-1 d-1. An estimated 0.09 Gg yr-1 of CH4 is released from estuaries of Sundarbans to the regional atmosphere. The mean CH4 mixing ratio over the forest atmosphere was 2 ppmv. On annual basis, only 2.75% of total supplied CH4 to the forest atmosphere was transported to the upper atmosphere via biosphere-atmosphere exchange. Mean CH4 photo-oxidation rate over the forest atmosphere was 3.25 x 10-9 mg cm-3 d-1. Using new and and previously published data we present for the first time, a CH4 budget for Sundarbans mangrove ecosystem which in part, revealed the existence of anaerobic CH4 oxidation in the mangrove sediment column.

Sources and dynamics of sedimentary organic matter in Sundarban mangrove estuary from Indo-Gangetic delta

IntroductionMangrove forests are highly productive ecosystems distributed along the tropical coast line. Nutrient biogeochemistry of mangroves are primarly driven by both allochthonous and autochthonous sources. Characterization of organic matter in coastal ecosystems enables to understand the biogeochemical transformation of organic matter and its influence on ecosystem productivity in response to various changing environmental conditions. Therefore, the elemental and stable carbon and nitrogen levels were employed to understand the organic matter (OM) dynamics in the Sundarban mangrove ecosystem (India-Bangladesh).ResultsDifferences in stable isotope values indicate that variable sources influence the OM dynamics in Sundarban sediments. The progressive enrichment in δ 13C levels along the land-coastal continuum indicates that the terrestrial and marine inputs are dominant at the landward and seaward ends, respectively. The CuO oxidation-derived lignin phenol monomers describe significant levels of total lignin are preserved in Sundarban mangrove sediments during diagenesis. The phenol monomer ratios are lower than the plant litter explaining that aromatic ring cleavage is the dominant mechanism for the lignin degradation. Furthermore, the Ad/Al ratios were higher than the plant litter explaining the oxidation of propyl side chain of vascular OM influencing the carbon cycling in Sundarban sediments. Largely, the Ad/Al ratios describe the vascular OM degradation is through the oxidation of propyl side chain.ConclusionsThe regional variability in land-use regulates the spatial variability in C, N, OC/TN ratio, δ 13C and δ 15N between the Indian and the Bangladesh Sundarban mangroves and indicates that in the upstream terrestrial organic matter and/or mangrove plant litter contribute significant amount of organic matter, whereas the marine POC influences the organic matter dynamics in downstream. The three end-member mixing model applying terrestrial plant litter, seston, and marine POC as end-members explains the relative contribution of OM from various sources, and marine inputs were dominant in Sundarban sediments.

Soil Urease Activity of Sundarban Mangrove Ecosystem, India

Vertical occurrence of soil urease activity along with ammonia content from three distinct regions viz. Deep forest region (No tidal action and wave attack occurs as it is furthest from river shore and it contains maximum content of organic carbon and minimum soil salinity and silicate concentration. In this zone plenty of pneumatophores, below ground root and dense vegetation are found), Rooted region (It is situated in between Deep forest region and Un-rooted region. This region contains only pneumatophores but it is devoid of long roots and vegetations. It faces wave attack and tidal action less than that of Un-rooted region) and Un-rooted region (It is closest to river shore and faces maximum wave attack and tidal action; it contains minimum organic carbon but maximum soil salinity and silicate concentration. This zone is totally devoid of any roots, pneumatophores and vegetations) of Sundarban mangrove forest ecosystem, India revealed an interesting explanation. Soil urease activity showed a decreasing pattern with increase in depth from the deep forest region of the Sundarban forest ecosystem. Soil urease activity was found to be more sensitive to soil temperature and pH rather than soil salinity. This ensured that soil urease along with the microbes present in the Sundarban forest ecosystem are more tolerant to fluctuation in salinity than that of temperature. Soil ammonia concentration was found to be directly governed by the soil urease activity [The regression equation is Ammonia in soil = -1.64 + 0.0402 Urease Activity (R-Sq = 62.9%, P < 0.001, n = 41)].

Projected changes in area of the Sundarban mangrove forest in Bangladesh due to SLR by 2100.

The Sundarbans mangrove ecosystem, located in India and Bangladesh, is recognized as a global priority for biodiversity conservation and is an important provider of ecosystem services such as numerous goods and protection against storm surges. With global mean sea-level rise projected as up to 0.98 m or greater by 2100 relative to the baseline period (1985–2005), the Sundarbans – mean elevation presently approximately 2 m above mean sea-level – is under threat from inundation and subsequent wetland loss; however the magnitude of loss remains unclear. We used remote and field measurements, geographic information systems and simulation modelling to investigate the potential effects of three sea-level rise scenarios on the Sundarbans within coastal Bangladesh. We illustrate how the Sea Level Affecting Marshes Model (SLAMM) is able to reproduce the observed area losses for the period 2000–2010. Using this calibrated model and assuming that mean sea-level is a better proxy than the SLAMM assumed mean lower low water for Mangrove area delineation, the estimated mangrove area net losses (relative to year 2000) are 81–178 km2, 111–376 km2 and 583–1393 km2 for relative sea-level rise scenarios to 2100 of 0.46 m, 0.75 m and 1.48 m, respectively and net subsidence of ±2.5 mm/year. These area losses are very small (<10 % of present day area) and significantly smaller than previous research has suggested. Our simulations also suggest that erosion rather than inundation may remain the dominant loss driver to 2100 under certain scenarios of sea-level rise and net subsidence. Only under the highest scenarios does inundation due to sea-level rise become the dominant loss process.

High Cadmium Contamination at the Gateway to Sundarban Ecosystem Driven by Kolkata Metropolitan Sewage in India

Cr, Pb, Zn, Cd, Ni, Cu, Co and Fe content in the surface sediments was studied at three sites along a 20 km stretch on the Bidyadhari River (situated at the gateway to Indian Sundarban mangrove ecosystem) starting from the sewage outfall zone of the Kolkata metropolis (northern limit of Sundarban) during the dry (March) and wet (August) seasons in the year 2011. The concentration levels of the heavy metals (mg kg -1 ) were in the following order: Fe (30399 ± 3679) > Cr (68.16 ± 39.28) > Zn (61.33 ± 10.47) > Ni (32.50 ± 4.79) > Cu (27.67 ± 6.59) > Pb (19.69 ± 5.20) > Co (15.23 ± 4.39) > Cd (1.70 ± 0.63). Computation of pollution load index comprising all the heavy metals was found higher during the wet season, mainly due to the enhanced surface run-off led by monsoonal rain. Concentrations of Cr and Co were found higher than the world average in a few cases (especially during wet season); however, computation of pollution indices like contamination factors, enrichment ratio and geoaccumulation index exhibited extremely high Cd contamination in all the sites and during both seasons.

Distribution, enrichment, and potential toxicity of trace metals in the surface sediments of Sundarban mangrove ecosystem, Bangladesh: a baseline study before Sundarban oil spill of December, 2014.

The distribution, enrichment, and ecotoxicity potential of Bangladesh part of Sundarban mangrove was investigated for eight trace metals (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) using sediment quality assessment indices. The average concentration of trace metals in the sediments exceeded the crustal abundance suggesting sources other than natural in origin. Additionally, the trace metals profile may be a reflection of socio-economic development in the vicinity of Sundarban which further attributes trace metals abundance to the anthropogenic inputs. A total of eleven surficial sediment samples were collected along a vertical transect along the freshwater-saline water gradient. The sediment samples were digested using EPA 3051 method and were analyzed on ICP-MS. Geo-accumulation index suggests moderately polluted sediment quality with respect to Ni and As and background concentrations for Al, Fe, Mn, Cu, Zn, Pb, Co, As, and Cd. Contamination factor analysis suggested low contamination by Zn, Cr, Co, and Cd, moderate by Fe, Mn, Cu, and Pb while Ni and As show considerable and high contamination, respectively. Enrichment factors for Ni, Pb, and As suggests high contamination from either biota or anthropogenic inputs besides natural enrichment. As per the three sediment quality guidelines, Fe, Mn, Cu, Ni, Co, and As would be more of a concern with respect to ecotoxicological risk in the Sundarban mangroves. The correlation between various physiochemical variables and trace metals suggested significant role of fine grained particles (clay) in trace metal distribution whereas owing to low organic carbon content in the region the organic complexation may not be playing significant role in trace metal distribution in the Sundarban mangroves.

Trace element accumulation and trophic relationships in aquatic organisms of the Sundarbans mangrove ecosystem (Bangladesh)

The Sundarbans forest is the largest and one of the most diverse and productive mangrove ecosystems in the world. Located at the northern shoreline of the Bay of Bengal in the Indian Ocean and straddling India and Bangladesh, the mangrove forest is the result of three primary river systems that originate further north and northwest. During recent decades, the Sundarbans have been subject to increasing pollution by trace elements caused by the progressive industrialization and urbanization of the basins of these three rivers. As a consequence, animals and plants dwelling downstream in the mangroves are exposed to these pollutants in varying degrees, and may potentially affect human health when consumed.The aim of the present study was to analyse the concentrations of seven trace elements (Zn, Cu, Cr, Hg, Pb, Cd and As) in 14 different animal and plant species collected in the Sundarbans in Bangladesh to study their transfer through the food web and to determine whether their levels in edible species are acceptable for human consumption. δ15N values were used as a proxy of the trophic level.A decrease in Zn, Cu, Pb and Cd levels was observed with increasing trophic position. Trace element concentrations measured in all organisms were, in general, lower than the concentrations obtained in other field studies conducted in the same region. When examined with respect to accepted international standards, the concentrations observed in fish and crustaceans were generally found to be safe for human consumption. However, the levels of Zn in Scylla serrata and Cr and Cd in Harpadon nehereus exceeded the proposed health advisory levels and may be of concern for human health.

Antimicrobial activities of actinomycetes isolated from unexplored regions of Sundarbans mangrove ecosystem.

BackgroundNew broad spectrum antimicrobial agents are urgently needed to combat frequently emerging multi drug resistant pathogens. Actinomycetes, the most talented group of microorganisms isolated from unexplored regions of the world may be the ultimate solution to this problem. Thus the aim of this study was to isolate several bioactive actinomycetes strains capable of producing antimicrobial secondary metabolite from Sundarbans, the only mangrove tiger land of the world.ResultsFifty four actinomycetes were isolated and analyzed for antimicrobial activity against fifteen test organisms including three phytopathogens. Nine morphologically distinct and biologically active isolates were subjected to polyphasic identification study.16 s rDNA sequencing indicated eight isolates to reveal maximum similarity to the genus streptomyces, whereas one isolate presented only 93.57 % similarity with Streptomyces albogriseolus NRRL B-1305T. Seventy-one carbon sources and twenty-three chemical sources utilization assay revealed their metabolic relatedness. Among these nine isolates three specific strains were found to have notably higher degree of antimicrobial potential effective in a broader range including phyto-pathogenic fungus. Finally the strain SMS_SU21, which showed antimicrobial activity with MIC value of 0.05 mg ml−1 and antioxidant activity with IC50 value of 0.242 ± 0.33 mg ml−1 was detected to be the most potential one. True prospective of this strain was evaluated utilizing GC-MS and the bioactive compound responsible for antimicrobial activity was purified.ConclusionRare bioactive actinomycetes were isolated from unexplored heritage site. Antimicrobial compound has also been identified and purified which is active against a broad range of pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0495-4) contains supplementary material, which is available to authorized users.

Economic Assessment for Harvesting Artisanal Giant Freshwater Prawn from the Sundarban Mangrove Ecosystem in Bangladesh

Harvesting Giant Freshwater Prawn, Golda (Macrobrachium rosenbergii de Man 1879) in the Sundarnbans mangrove forest plays an important role in the economy of the country as well as the livelihood of local community. The study focused the economic assessment of small-scale artisanal Golda fishery. Overall the Hookline gear showed the best performance in terms of economic return. However, it was found to withstand a shock from 20% decrease in market prices or 30% fall in catch rate in terms of Return on investment, payback period and Benefit-cost ratio. Operating cost and fixed cost for Hookline fishery was the lowest and Khathijal was the highest. No significant variation (P<0.05) observed in the mean catch rate per trip boat-1 among the gears studied. Total revenue earned after completion a trip varied considerably between BDT 1,307 to 1,562. Yearly, total net revenue reached at the maximum by Hookline (BDT 38,506), followed by Chandijal (BDT 38,377) and the minimum by Khalpata (BDT 33,885). The findings of this study are supposed to be helpful for policy makers in improving the current status of Golda fishery and relevant human livelihood as well as conserving the Sundarbans Mangrove Ecosystem.

Vertical Profile of Phosphatase Activity in the Sundarban Mangrove Forest, North East Coast of Bay of Bengal, India

Impact of phosphate solubilizing bacteria along with soil phosphatase activity on phosphorous cycle was found to be quiet interesting in the Sundarban mangrove ecosystem. Soil phosphatase activity showed a decreasing pattern with increase in depth [soil phosphatase activity (μg pnp produced g−1 dry wt of soil) = 906.85 – 5.6316 Depth (cm)] from the deep forest region of the Sundarban forest ecosystem. Soil salinity showed a very little effect on soil phosphatase activity whereas soil temperature and pH was found to show significant impact on the soil phosphatase activity. This ensured that the microbes associated with phosphate mineralization present in the Sundarban forest ecosystem are more tolerant to fluctuation in salinity than that of temperature and pH. A direct correlation was perceptible between the number of phosphate solubilizing bacteria and phosphatase activity in the soil during the study period from 2007 to 2012. Soil phosphate concentration was found to be directly governed by the soil phosphatase activity [The regression equation is: avg PO4−3-P (μg g−1 dry wt of soil) = 0.0311 + 0.000606 soil phosphatase activity (μg pnp produced g−1 dry wt of soil); R2 = 63.2%, p < 0.001, n = 62].

Eddy covariance based methane flux in Sundarbans mangroves, India

We report the initial results of the methane flux measured using eddy covariance method during summer months from the world’s largest mangrove ecosystem, Sundarbans of India. Mangrove ecosystems are known sources for methane (CH4) having very high global warming potential. In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans (India). The tower is equipped with eddy covariance flux tower instruments to continuously measure methane fluxes besides the mass and energy fluxes. This paper presents the preliminary results of methane flux variations during summer months (i.e., April and May 2012) in Sundarbans mangrove ecosystem. The mean concentrations of CH4 emission over the study period was 1682 ± 956 ppb. The measured CH4 fluxes computed from eddy covariance technique showed that the study area acts as a net source for CH4 with daily mean flux of 150.22 ± 248.87 mg m−2 day−1. The methane emission as well as its flux showed very high variability diurnally. Though the environmental conditions controlling methane emission is not yet fully understood, an attempt has been made in the present study to analyse the relationships of methane efflux with tidal activity. This present study is part of Indian Space Research Organisation–Geosphere Biosphere Program (ISRO–GBP) initiative under ‘National Carbon Project’.

Biogeochemical cycle of nitrogen in a tropical mangrove ecosystem, east coast of India

Like many coastal systems, nitrogen is the critical limiting factor for mangrove net production. This study used a box model approach to assess the nitrogen budget in the Sundarban mangrove ecosystem, which acts as a sink for atmospheric nitrogen in terms of NOx, NH3, N2, and water column dissolved inorganic nitrogen. The coupling of biosphere and atmosphere in terms of atmospheric NOx and NH3 uptake showed that uptake of ammonia (130×106molyr−1) was about six fold as large as that of NOx, (22×106molyr−1). The nitrogen stored by the processes such as plant uptake of NOx, NH3 from the atmosphere, nitrogen fixation (5×109molyr−1), and sediment water exchange (8×106molyr−1) was about two times as large as that of recycled nitrogen from litter (3×109molyr−1), and could account 74% of the nitrogen required for mangrove net production. Most of the nitrogen was conserved in the living biomass (living biomass: 118×103molha−1 versus soil: 3×103molha−1). The loss of nitrogen was 23% of the total amount that was conserved from the external sources in the Sundarban mangrove system. Thus, the coastal ecosystem like Sundarban mangroves could retain only 0.2% (8×106mol) of the annual river flux of nitrogen to the coastal waters and nitrogen is generally conserved within the system.

Analysis of Relationship between Salinity and Top-Dying Diseases of Sundri Trees in Sundarbans, Bangladesh

At the advent of British rule in 1765, the Sundarbans forests were double their present size (Seidensticker, and Hai, 1983; Khan, 1997). Sundarbans mangroves in Asia including Bangladesh, India, and East Africa previously contained a much fuller range of species (Seidensticker, and Hai, 1983; Khan, 1997). In the Southeast Asian region, species diversity of mangroves was previously much higher (Ellison, 1998, 2000). Although, a particular class of men made a profession of collection of wood, fish, Golpata, Goran, natural beauty, oil, honey, and wax in Sundarbans (Awal, 2007), but it is facing tremendous problems (Awal, 207, 2009, 2014). But, it is now under serious threatened through human destruction, and by ecological pollution (Awal, 2007). The cause of this dieback is still not well understood unknown. The present work has investigated one of the possible factors that might be causing this top-dying, namely the concentrations of various chemical elements present in the sediments, particularly Salinity (Na), Exchangeable K, heavy metals, though other chemical parameters such as the pH, salinity, moisture content of the sediment and nutrient status were also assessed. (Awal, 2007). Na has no relationship with the amount of top-dying of Sundri trees in Sundarbans. However, a serious killer disease (top dying) of H. fomes in Sundarbans is affecting millions of the trees (Awal, 2007). The loss of H. fomes will have a major impact on the Sundarbans mangrove ecosystem, as well as lead to economic losses. A questionnaire survey was conducted among different groups of people inside and outside of Sundarbans to explore local perceptions as to the possible causes of top dying. This confirmed the increase in top-dying prevalence (Awal, 2007). Most of the elements including Salinity of soil and water studied had no significant correlation with the top dying of Heritiera fomes. However, Sn, Exchangeable K, and soil pH were significantly related, and three elements, namely Pb, Zn, Ni, were also close to significance. Sn concentration is negatively associated with top dying. Soil pH varied significantly in the different plots. Exchangeable K was positively associated with the tree diameter whether the top dying was severe or mild.