Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from domestic sewage and industrial effluents which can significantly alter the air-water CO2 flux rates. In this regard, we quantified the partial... more
Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from domestic sewage and industrial effluents which can significantly alter the air-water CO2 flux rates. In this regard, we quantified the partial pressure of CO2 in the surface water (pCO2(water)), air-water CO2 fluxes, and associated biogeochemical parameters in the Hooghly River, India, flowing through two of the most polluted cities of the country, Kolkata and Howrah, over a complete annual cycle during spring tidal phase (SP) and neap tidal phase (NP). This urbanized part of Hooghly River was always supersaturated with CO2 having an annual mean pCO2(water) and air-water CO2 flux of ~ 3800 μatm and ~ 49 mol C m−2 year−1, respectively. Significant seasonal variability was observed for both pCO2(water) and air-water CO2 flux (pre-monsoon, 3038 ± 539 μatm and 5049 ± 964 μmol m−2 h−1; monsoon, 4609 ± 711 μatm and 7918 ± 1400 μmol m−2 h−1; post-monsoon, 2558 ± 258 μatm and 4048 ± 759 μmol m−2 h−1, respectively). Monthly mean pH and total alkalinity varied from 7.482 to 8.099 and from 2437 to 4136 μmol kg−1, respectively, over the annual cycle. pCO2(water) showed significant positive correlation with turbidity and negative correlation with electrical conductivity and gross primary productivity (GPP). High water discharge could have facilitated high turbidity, especially during the monsoon season, which led to depletion in GPP and enhancement in pCO2(water) which in turn led to very high CO2 effluxes. The CO2 efflux rate in this urbanized riverine stretch was substantially higher than that observed in previous studies carried out in the less urbanized estuarine stretch of Hooghly. This indicates that the presence of highly urbanized and polluted metropolis potentially enhanced the pCO2(water) and CO2 effluxes of this river. Similar observations were made recently in some Asian and Australian urban rivers.
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The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) of the tropical Hooghly estuary is analyzed in this work. In situ observations of water temperature, salinity, dissolved oxygen,... more
The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) of the tropical Hooghly estuary is analyzed in this work. In situ observations of water temperature, salinity, dissolved oxygen, TAlk, and pH were measured in four different stations of the Hooghly estuary. It was measured once every month during 2015–2016, and subsequently, DIC was estimated. A carbon budget was constructed to quantify carbon flows through the freshwater-marine continuum of the Hooghly estuary, and plausible impacts on the adjacent coastal ocean, the northern Bay of Bengal, were examined. The biogeochemical mass balance box model was used to compute the seasonal flow of carbon flux, and subsequently, the annual budgeting of lateral fluxes of TAlk and DIC to the adjacent coastal ocean was carried out. The net annual TAlk and DIC flux from the Hooghly estuary to the adjacent coastal ocean were 4.45 ± 1.90 × 1011 mol and 4.59 ± 1.70 × 1011 mol, respectively. The net annual DIC flux of the Hooghly estuary is about 30 to 60 times higher than surface area integrated air–water CO2 flux, which is an indication of promoting acidification in the adjacent coastal ocean. The present study indicates that the lateral DIC flux has increased substantially in the Hooghly estuary during the last two decades. The increase in inorganic carbon load in the Hooghly estuary due to the enhanced discharge of inorganic and organic matter load in the upper reaches of the estuary led to this increase in lateral DIC flux. The results strongly establish the need of having such regional studies for better understanding the estuarine carbon dynamics, and its role in controlling the adjacent coastal ocean dynamics.
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The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer... more
The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer (MODIS) and advanced very high resolution radiometer (AVHRR). The in situ measurements were done during winter months (December, January and February) of the year 2011–12. Sea surface CO2 fugacity (fCO2), sea surface temperature (SST) and chlorophyll-a were measured in situ to develop an empirical relationship with fCO2 but only the SST showed a significant correlation (r 2 = 0.55, n = 64, p < 0.05). This relationship was used to assess fCO2 (water) and its temporal change in decadal scale from the year 2002–2003 to 2011–2012 of the winter months using remotely sensed SST data. The study area acted as a mild sink for atmospheric CO2 at the mean rate of −28 µmol m−2 h−1 (MODIS derived) to −40 µmol m−2 h−1 (AVHRR derived). An overall winter-to-winter increasing trend of fCO2 was observed in the last decade which is accompanied by a similar decrease in the chlorophyll-a concentrations.
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Mangroves have long been recognized as a potential sink of carbon owing to their high productivity and carbon sequestration potential. The short term CO2 dynamics of mangroves are often put under lenses to examine their potential to... more
Mangroves have long been recognized as a potential sink of carbon owing to their high productivity and carbon sequestration potential. The short term CO2 dynamics of mangroves are often put under lenses to examine their potential to combat the human induced CO2 emission. Mainly three types of CO2 fluxes take place within a mangrove ecosystem namely (i) atmosphere-biosphere CO2 exchange, (ii) soil CO2 efflux and (iii) air-water CO2 flux. In this chapter, we have compiled all types of the CO2 flux data from mangrove ecosystems with special emphasis on the Sundarban, the world’s largest mangrove forest and analyzed the regulating factors of these fluxes. Summarizing all the studies, it can be inferred that the terrestrial compartments of mangroves acts as net sink for CO2, though the soil continually emit CO2 (apart from few exceptions). Almost all the mangrove surrounding waters act as source of CO2, however, the magnitude of air-water CO2 fluxes are much less than the inward fluxes of CO2 towards the canopy, hence the ecosystem as a whole acts as a net sink for CO2. Light conditions, air temperature, salinity, tidal cycle and so forth are mainly found to regulate the atmosphere-biosphere CO2 flux, whereas, soil temperature, moisture and waterlogging are the principal factors regulating the soil CO2fluxes. In case of air-water fluxes, the main governing factors are the variation in salinity, pore-water flushing during ebb tide and wind speed.
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The Indian Sundarban Delta (ISD) situated on the western tide-dominated part of the Ganges–Brahmaputra–Meghna delta, was formed by the sedimentation of the river Ganges and its tributaries. It is crisscrossed by several interlinked... more
The Indian Sundarban Delta (ISD) situated on the western tide-dominated part of the Ganges–Brahmaputra–Meghna delta, was formed by the sedimentation of the river Ganges and its tributaries. It is crisscrossed by several interlinked channels. Most of these rivers which used to nourish the delta have become defunct with the passage of time. To ensure sustainable flow and to enhance the flow-dependent ecosystem services in this region, the identification of the disconnected river reaches and their restoration is required. Keeping these perspectives in mind, this study has been conducted to identify the discontinuities in the flow paths of some major rivers using multispectral satellite imageries in geo-informatics platform. To extract the river network from the Landsat Thematic Mapper (TM) images, the water indexes like Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) have been calculated. These indexes use the differential spectral reflectance of water sensitive near-infrared and shortwave-infrared band with green band to identify the derelict paths. The spectral profiles of near-infrared band across these discontinuous stretches have been compared and validated with field data to map the actual blockages. The study reveals that the rivers Ichhamati, Jamuna, Bidyadhari, Noai, Suti, Kumarjol, Ghagramari, Karati, and Matla have been disconnected from their parent rivers and their courses are frequently interrupted by natural and man-made obstructions. River Adi Ganga is discontinuous in its middle stretches. The decayed river channels have been converted into ponds, agricultural fields, or aquaculture farms and have also been encroached by settlements. Restoration of these decayed channels may revitalize the river network and enhance the benefits of flow-dependent ecosystem services in the ISD.
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Loss of two small estuarine islands, Lohachara and Suparibhanga has been reported earlier from the Indian Sundarban lying adjacent to the northern Bay of Bengal. The present paper reports the loss of another offshore island, New Moore,... more
Loss of two small estuarine islands, Lohachara and Suparibhanga has been reported earlier from the Indian Sundarban lying adjacent to the northern Bay of Bengal. The present paper reports the loss of another offshore island, New Moore, popularly known as Purbasha at the border of India and Bangladesh. The island came into existence after a cyclone in 1970. This study reveals the loss of New Moore Island within the time period of 1985 to 2000 from the analysis of multi-temporal satellite images. The rate of erosion, of two other offshore islands, Jambu Dwip (0.187 sq. km yr.−1) and Maya Dwip (0.508 sq. km yr.−1) situated along the same latitude of New Moore, were also estimated within the same time period. A close relationship was observed between the rate of erosion of small islands and the rate of rising sea level in this region as measured from the tide data at the Sagar Island and other observatories during the study period. The sea surface temperature analysis from the year 1990 to 1998 showed a slight increase (~ 0.8 °C increase), indicating the thermal expansion of the sea surface. Moreover, the sea surface height analyzed during the period 1993–2000 using satellite altimeter data of TOPEX/POSEIDON revealed a steady increase of 1.23 cm yr.−1 sea level acceleration.
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Dataset for the article entitled "Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans"
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The fugacity of CO2 (fCO2 (water)) and air‐water CO2 flux were compared between a river‐dominated anthropogenically disturbed open estuary, the Hugli, and a comparatively pristine mangrove‐dominated semiclosed marine estuary, the Matla,... more
The fugacity of CO2 (fCO2 (water)) and air‐water CO2 flux were compared between a river‐dominated anthropogenically disturbed open estuary, the Hugli, and a comparatively pristine mangrove‐dominated semiclosed marine estuary, the Matla, on the east coast of India. Annual mean salinity of the Hugli Estuary (≈7.1) was much less compared to the Matla Estuary (≈20.0). All the stations of the Hugli Estuary were highly supersaturated with CO2 (annual mean ~ 2200 µatm), whereas the Matla was marginally oversaturated (annual mean ~ 530 µatm). During the postmonsoon season, the outer station of the Matla Estuary was under saturated with respect to CO2 and acted as a sink. The annual mean CO2 emission from the Hugli Estuary (32.4 mol C m−2 yr−1) was 14 times higher than the Matla Estuary (2.3 mol C m−2 yr−1). CO2 efflux rate from the Hugli Estuary has increased drastically in the last decade, which is attributed to increased runoff from the river‐dominated estuary.
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The Sundarbans is currently a subject of serious concern due to the massive coastline erosion that is responsible for reshaping the geomorphological content of the islands. The coastal islands of the Sundarbans have become more... more
The Sundarbans is currently a subject of serious concern due to the massive coastline erosion that is responsible for reshaping the geomorphological content of the islands. The coastal islands of the Sundarbans have become more susceptible to sea-level rise, cyclonic storms, and coastal flooding, which further accelerate the process of coastal erosion. Identification of erosion-prone regions is highly essential for integrated coastal zone management. Till date, no scientific study has been done to relate the coastal erosion accretion process with tidal velocity and current direction in the Indian Sundarbans. In this perspective, the present study identifies the erosion-accretion zones in the Indian Sundarbans using Landsat imageries of 2000 and 2020 using geoinformatics. It investigates the impact of tidal velocity and direction on the erosion accretion processes. MIKE 21 two-dimensional hydrodynamic model was simulated to predict tidal velocities and directions. The study finds that the sea-facing islands of the Indian Sundarbans experience the maximum amount of erosion. A significant shrinking of the land area takes place in the Bulchery, Bhangaduiani, and Dalhousie islands. The rates of erosion of these islands are 485.99 m/year, 487 m/year, and 480.65 m/year, respectively. Places with high velocity are found to be erosion-prone, while the rate of erosion significantly varied with the flow directions. Two islands, Bulchery and Dalhousie, on the south-eastern margin of the delta, suffered maximum erosion over the past decades due to the impact of high-velocity currents from the southeast and southwest, respectively. Alternatively, minor accretions were observed along with the sheltered island precincts where velocities were comparatively low. Such studies on the current drive erosion–accretion processes along the delta margin during sea-level rise appear to be of utmost importance for sustainable coastal protection and management.
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The population structure of Hilsa Shad (Tenualosa ilisha), a choicest table fish, in the estuaries of India, Bangladesh and Myanmar of Bay of Bengal has been studied by different methods and each provided complementary data on population... more
The population structure of Hilsa Shad (Tenualosa ilisha), a choicest table fish, in the estuaries of India, Bangladesh and Myanmar of Bay of Bengal has been studied by different methods and each provided complementary data on population structure. Considering the present scenario of climate change, increasing pollutant load in Indo–Bangladesh estuarine region and its effect on reproduction and maturation of anadromous Hilsa Shad, a thorough and detailed understanding of the life history of Hilsa is a pre requisite criterion. Results of such studies would be important for sustainable management of this highly economic biological resource. The present paper deals with the aspects of life history and population dynamics of Hilsa Shad in Sundarban estuaries. The data collection was done during the period of June 2011 to March 2012 at Frasergunje Fishing Harbour and offshore of northern Bay of Bengal. The length and weight of total 617 Hilsa fish were measured under this study. Monthly ...
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The Sundarban Biosphere Reserve (SBR), India lies in the tide-dominated southern part of deltaic West Bengal and supports 4.43 million strong populations. Freshwater is a scarce resource in the SBR though it is traversed by numerous... more
The Sundarban Biosphere Reserve (SBR), India lies in the tide-dominated southern part of deltaic West Bengal and supports 4.43 million strong populations. Freshwater is a scarce resource in the SBR though it is traversed by numerous creeks and rivulets and receives a huge amount of precipitation during the monsoon months. Scarcity of freshwater above and below the ground during the dry season and high salinity of soil and water make it very difficult for the people of the SBR to secure their livelihood. The present paper assesses these sectoral demand and availability of water in 19 administrative blocks of the SBR. Increasing water demand of the ever-increasing population leads to water deficit in most of the blocks during dry season. In this study, the annual demands of drinking and domestic water in the SBR have been estimated at 8.08 million cubic metres (mcm) and 105.1 mcm, respectively. The water demand for agriculture has been calculated as 2782.83 mcm. It is observed that the SBR gets 2000–2500 mcm annual runoff from its upper catchments, and the habitated region of the SBR generates additional 1800–2000 mcm annual runoff within its territory. Blockwise water availability from different sources has also been estimated. The research reveals the growing population pressure on agriculture with an average man-cropland ratio of 14 person/hectare land. The highest cropping and irrigation intensity has been observed in the northern blocks where shallow groundwater is available for agriculture. On the contrary, the lowest values have been observed in the southern blocks nearer to sea, due to existence of saline water in shallow aquifers. Available water from 70,000 freshwater tanks and around 8000 shallow borewells are not sufficient to meet the agricultural water demand during the Rabi (winter) and summer seasons. Unavailability of freshwater restricts food production, which endangers the food security of 87.5% of the people in the SBR. To ensure food security in the present changing climatic condition, expansion of irrigation network and harnessing of new water sources are essential. This study emphasizes that rooftop rainwater harvesting in this region has potential to supply additional 45 mcm water which can be used to meet the domestic water demand partially. Large-scale rainwater harvesting, rejuvenation and reconnection of disconnected river channels, artificial recharge within shallow aquifers and desalination of shallow groundwater can be some other major policy options to meet the water demand in the SBR in the future.
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ABSTRACT Selective accumulation of heavy metals in mangrove plant parts have been reported earlier; however, varying heavy metal accumulation in the sediments adjacent to different mangrove plant species is rarely reported. We... more
ABSTRACT Selective accumulation of heavy metals in mangrove plant parts have been reported earlier; however, varying heavy metal accumulation in the sediments adjacent to different mangrove plant species is rarely reported. We hypothesized that the pattern of heavy metal accumulation could vary in the adjacent sediments of different mangrove plant species. We compared the heavy metal accumulation (As, Co, Cu, Cd, Cr, Pb, Ni, and Zn) in the mangrove sediments adjacent to Avicennia marina (AM), Bruguiera gymnorrhiza (BG), Rhizophora mucronata (RM), and Excoecaria agallocha (EA) from a mixed mangrove stand within the Indian Sundarbans. Metal concentrations (except Cr) varied significantly among the four mangrove sites. The highest concentrations of As, Cd, and Pb were observed in EA sites, Cu and Zn, in BG sites, followed by Co and Ni, in AM sites. Contamination factor, enrichment ratio, and geo-accumulation indices indicated significant Cd pollution in all the sites; however, the highest magnitudes of these indices were observed in EA sites. These indices showed very high Cu and Zn pollution in BG sites. Pollution load index and potential ecological risk index depicted overall ‘deterioration of sediment quality’ and very high risk in all the sites. Principal component analysis and cluster analysis also showed that metal accumulation was significantly different in the four sites. Overall, the results indicated that the heavy metal type and concentration in mangrove sediments could vary depending on the mangrove plant species thriving in its adjacency. However, characterizing the reasons behind such differential accumulation needs further study.
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Indian Sundarban Biosphere Reserve (SBR) area lies in the south-western part of Ganges Brahmaputra delta and supports 4.43 million population. Though crisscrossed by numerous rivers and bestowed by good amount of rainfall annually,... more
Indian Sundarban Biosphere Reserve (SBR) area lies in the south-western part of Ganges Brahmaputra delta and supports 4.43 million population. Though crisscrossed by numerous rivers and bestowed by good amount of rainfall annually, scarcity of potable water is a major problem in SBR. Most of the rivers in Sundarbans have been disconnected from their sources and don’t receive upstream flows. Shallow ground water in SBR is brackish to saline while fresh groundwater occurs below 300m depth. To achieve the sustainable development goal of providing water for all in the region, assessment of water demand, its availability and accessibility are essential. From the population and its projection, the potable water demand has been estimated as 9.21 mcm and 22.68mcm in the SBR for the years 1991 and 2051 respectively. The available potable water in Sundarbans is not adequate to meet the need of the future population. The people of SBR mostly depend on spot water sources which are not always ea...
The paper discusses the correlation between the Catch per Unit Effort (CPUE) of fishes with the phytoplankton biomass (chlorophyll-a) and nutrients in the West Bengal marine fishing zone (northern Bay of Bengal) during the post-monsoon... more
The paper discusses the correlation between the Catch per Unit Effort (CPUE) of fishes with the phytoplankton biomass (chlorophyll-a) and nutrients in the West Bengal marine fishing zone (northern Bay of Bengal) during the post-monsoon season of 2010-11 and 2011-12. A total of 12 Potential Fishing Zone forecasts were simultaneously validated on board, covering 70 random samplings points wherein the physico-chemical parameters were also measured. A strong positive correlation of the CPUE with phytoplankton biomass was observed. The CPUE also positively correlated with the essential nutrients like dissolved inorganic phosphate (DIP), dissolved inorganic nitrate (DIN) and silicate. Four components were figured out in the principal component analysis out of 11 environmental variables. The first component primarily consisted of salinity, Secchi depth (positive loadings), turbidity and dissolve oxygen (DO) (negative loadings). Increases in component 2 were associated with increases in nut...
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Absorption spectra of chromophoric dissolved organic matter (CDOM) and other physico-chemical components were measured in the coastal water of northern Bay of Bengal (nBoB) lying adjacent to West Bengal coast, India, during October,... more
Absorption spectra of chromophoric dissolved organic matter (CDOM) and other physico-chemical components were measured in the coastal water of northern Bay of Bengal (nBoB) lying adjacent to West Bengal coast, India, during October, 2014-March, 2015. Absorption coefficient [aCDOM(440)] of CDOM exhibited a considerable inverse linear relationship with salinity in the surface waters implying traditional mixing effect of marine and fresh water. A dominant terrestrial CDOM signal influenced by higher fresh water discharge from the river Hugli was seen prior of winter (October, 2014). However, during January, aCDOM(440) value again increased along with a concomitant increase in chlorophyll-a. However, total suspended matter (TSM) showed strong linear positive and consistent relationship with aCDOM(440) throughout the study period, ascertaining terrestrial source of CDOM. Moreover, prior of winter, study site receives more discharge from rivers with corresponding signals of lower slope va...
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Climate change literature mentions that the Indian Sundarban is under accelerating threat of climate change-related impacts. This can be of disastrous consequences as the Sunderban is the world’s largest repository of mangrove and... more
Climate change literature mentions that the Indian Sundarban is under accelerating threat of climate change-related impacts. This can be of disastrous consequences as the Sunderban is the world’s largest repository of mangrove and mangrove-associated flora and fauna with the highest species diversity. It is also home to nearly 4.6 million human population Mousuni island, one of the 54 islands in the Indian Sundarban to have been occupied by settlers of the early nineteenth century, is highly vulnerable due to severe coastal erosion, repeated breach of embankments, cyclones, storm surge, and inundation causing loss of lives, properties and displacement and migration of families. From the perspectives of climate change-related coastal hazards, Composite Vulnerability (VRc) which is a product of physical as well as socioeconomic vulnerability at community level has been computed. The estimated VRc indicates overall vulnerability of each family having its geographical position determined by the GPS. The physical vulnerability characterizes relative vulnerability to physical changes of the island in quantifiable manner, whereas socioeconomic vulnerability illustrates the locally relevant socioeconomic components that further quantify the degree of vulnerability of the island community. Geoinformatics techniques have been employed to integrate both the physical and the socioeconomic components of vulnerability in order to identify and locate the most vulnerable families. This will help in planned adaptation that can be taken up by administrators and policymakers for reducing the risks due to climate change.
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The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer... more
The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer (MODIS) and advanced very high resolution radiometer (AVHRR). The in situ measurements were done during winter months (December, January and February) of the year 2011–12. Sea surface CO2 fugacity (fCO2), sea surface temperature (SST) and chlorophyll-a were measured in situ to develop an empirical relationship with fCO2 but only the SST showed a significant correlation (r 2 = 0.55, n = 64, p < 0.05). This relationship was used to assess fCO2 (water) and its temporal change in decadal scale from the year 2002–2003 to 2011–2012 of the winter months using remotely sensed SST data. The study area acted as a mild sink for atmospheric CO2 at the mean rate of −28 µmol m−2 h−1 (MODIS derived) to −40 µmol m−2 h−1 (AVHRR derived). An overall winter-to-winter increasing trend of fCO2 was observed in the last decade which is accompanied by a similar decrease in the chlorophyll-a concentrations.
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In the present paper population structure of four commercially important fishes were studied, namely Tenualosa ilisha, Pampus argenteus, Scomberomorus guttatus and Osteogeneiosus militaris, in the Sundarban Estuary of the northern Bay of... more
In the present paper population structure of four commercially important fishes were studied, namely Tenualosa ilisha, Pampus argenteus, Scomberomorus guttatus and Osteogeneiosus militaris, in the Sundarban Estuary of the northern Bay of Bengal from June 2011 to March 2012. However, a thorough understanding of life history based on length and weight data of these four fishes (617 T. ilisha, 485 P. argenteus, 351 S. guttatus and 416 O. militaris) would be immensely important. Results of such studies would be important for sustainable management of these highly economic biological resources. The analysis of life history parameters of these four species, such as growth, exploitation, mortality, etc. showed that their stocks in coastal waters off West Bengal were overexploited during the study period as exploitation rate of T. ilisha, P. argenteus, S. guttatus and O. militaris were 0.78, 0.62, 0.75 and 0.54 respectively. Widespread fishing of juvenile and growing fish declined the popul...
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The Sundarban Biosphere Reserve (SBR), India lies in the tide-dominated southern part of deltaic West Bengal and supports 4.43 million strong populations. Freshwater is a scarce resource in the SBR though it is traversed by numerous... more
The Sundarban Biosphere Reserve (SBR), India lies in the tide-dominated southern part of deltaic West Bengal and supports 4.43 million strong populations. Freshwater is a scarce resource in the SBR though it is traversed by numerous creeks and rivulets and receives a huge amount of precipitation during the monsoon months. Scarcity of freshwater above and below the ground during the dry season and high salinity of soil and water make it very difficult for the people of the SBR to secure their livelihood. The present paper assesses these sectoral demand and availability of water in 19 administrative blocks of the SBR. Increasing water demand of the ever-increasing population leads to water deficit in most of the blocks during dry season. In this study, the annual demands of drinking and domestic water in the SBR have been estimated at 8.08 million cubic metres (mcm) and 105.1 mcm, respectively. The water demand for agriculture has been calculated as 2782.83 mcm. It is observed that the SBR gets 2000–2500 mcm annual runoff from its upper catchments, and the habitated region of the SBR generates additional 1800–2000 mcm annual runoff within its territory. Blockwise water availability from different sources has also been estimated. The research reveals the growing population pressure on agriculture with an average man-cropland ratio of 14 person/hectare land. The highest cropping and irrigation intensity has been observed in the northern blocks where shallow groundwater is available for agriculture. On the contrary, the lowest values have been observed in the southern blocks nearer to sea, due to existence of saline water in shallow aquifers. Available water from 70,000 freshwater tanks and around 8000 shallow borewells are not sufficient to meet the agricultural water demand during the Rabi (winter) and summer seasons. Unavailability of freshwater restricts food production, which endangers the food security of 87.5% of the people in the SBR. To ensure food security in the present changing climatic condition, expansion of irrigation network and harnessing of new water sources are essential. This study emphasizes that rooftop rainwater harvesting in this region has potential to supply additional 45 mcm water which can be used to meet the domestic water demand partially. Large-scale rainwater harvesting, rejuvenation and reconnection of disconnected river channels, artificial recharge within shallow aquifers and desalination of shallow groundwater can be some other major policy options to meet the water demand in the SBR in the future.