Environmental Science and Pollution Research, May 24, 2020
Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from do... 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.
Environmental Monitoring and Assessment, Jun 12, 2021
The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic c... 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.
The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of... 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.
Mangroves have long been recognized as a potential sink of carbon owing to their high productivit... 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.
The Indian Sundarban Delta (ISD) situated on the western tide-dominated part of the Ganges–Brahma... 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.
Journal of The Indian Society of Remote Sensing, Feb 6, 2016
Loss of two small estuarine islands, Lohachara and Suparibhanga has been reported earlier from th... 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.
Zenodo (CERN European Organization for Nuclear Research), Mar 2, 2021
Dataset for the article entitled "Low CO2 evasion rate from the mangrove-surrounding waters ... more Dataset for the article entitled "Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans"
The fugacity of CO2 (fCO2 (water)) and air‐water CO2 flux were compared between a river‐dominated... 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.
The Sundarbans is currently a subject of serious concern due to the massive coastline erosion tha... 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.
Environmental Science and Pollution Research, May 24, 2020
Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from do... 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.
Environmental Monitoring and Assessment, Jun 12, 2021
The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic c... 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.
The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of... 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.
Mangroves have long been recognized as a potential sink of carbon owing to their high productivit... 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.
The Indian Sundarban Delta (ISD) situated on the western tide-dominated part of the Ganges–Brahma... 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.
Journal of The Indian Society of Remote Sensing, Feb 6, 2016
Loss of two small estuarine islands, Lohachara and Suparibhanga has been reported earlier from th... 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.
Zenodo (CERN European Organization for Nuclear Research), Mar 2, 2021
Dataset for the article entitled "Low CO2 evasion rate from the mangrove-surrounding waters ... more Dataset for the article entitled "Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans"
The fugacity of CO2 (fCO2 (water)) and air‐water CO2 flux were compared between a river‐dominated... 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.
The Sundarbans is currently a subject of serious concern due to the massive coastline erosion tha... 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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