Abhra Chanda - Academia.edu (original) (raw)
Papers by Abhra Chanda
The degree of heavy metal contamination was estimated in the river water, sediments and benthic o... more The degree of heavy metal contamination was estimated in the river water, sediments and benthic organisms in the Kolkata metropolitan sewage outfall zone and downstream areas along the Kulti River track. Four heavy metals namely Cr, Pb, Zn and Cd were studied seasonally. The hierarchy of heavy metals in the water samples and sediments was found in the order Zn>Pb>Cr>Cd and Zn>Cr>Pb>Cd respectively in most of the cases. Among the four heavy metals, Pb was found to be beyond the permissible limit recommended by Central Pollution Control Board of India for inland discharge. The extent of contamination by Cd is very prominent in the sediments followed by Pb, which is observed not only in the outfall region but also found persistent in the downstream stations. On the other hand contamination of Zn and Cr was not found to be widespread. Contamination in sediments of the outfall zone was most pronounced during the monsoon, while in the same season it was observed least in case of water samples. The pollution load index study revealed that the overall metal pollution load depleted towards the downstream. Among the two benthic organisms studied, metals were found to be accumulated more in Uca rosea than Boleopthalmus spp. 2012 pp. [153][154][155][156]
The degree of heavy metal (Cr, Pb and Hg) contamination in the paddy fields utilizing the sewage ... more The degree of heavy metal (Cr, Pb and Hg) contamination in the paddy fields utilizing the sewage effluent of Kolkata metropolitan city, near East Kolkata Wetland, India, along with the irrigation water and paddy grains were investigated in 2010 and 2011. The nutrient concentration, pH and electrical conductivity status during the sowing time was also monitored. Though the pH of the irrigation water was found suitable in all instances but the electrical conductivity values were observed to be inappropriate in 4 sites. Hg was found beyond the permissible limit in the water used for irrigation as well as paddy soils of all the study sites. Evaluation of enrichment ratio revealed alarming Hg contamination in two sites out of six sites studied. Enrichment ratio values of Pb were moderately high in four sites exhibiting polluting effect. The geo-accumulation index calculated was found to support similar observations. Cr in water and soil samples was found within the threshold limit, but in the paddy grain it was found beyond the maximum allowable limit. Hg and Pb, however, were found below detection level in all the rice samples. Pollution load index was estimated in all the sites and it varied from 0.860 to 1.827. Virtually no polluting activity was found in the samples obtained from control stations situated far away from the effluent source, where irrigation is primarily done using groundwater.
Journal of Applied Remote Sensing, 2014
Mangroves are active carbon sequesters playing a crucial role in coastal ecosystems. In the prese... more Mangroves are active carbon sequesters playing a crucial role in coastal ecosystems. In the present study, aboveground biomass (AGB) was estimated in a 5-year-old Avicennia marina plantation (approximate area ≈190 ha) of Indian Sundarbans using high-resolution satellite data in order to assess its carbon sequestration potential. The reflectance values of each band of LISS IV satellite data and the vegetation indices, viz., normalized difference vegetation index (NDVI), optimized soil adjusted vegetation index (OSAVI), and transformed difference vegetation index (TDVI), derived from the satellite data, were correlated with the AGB. OSAVI showed the strongest positive linear relationship with the AGB and hence carbon content of the stand. OSAVI was found to predict the AGB to a great extent (r 2 ¼ 0.72) as it is known to nullify the background soil reflectance effect added to vegetation reflectance. The total AGB of the entire plantation was estimated to be 236 metric tons having a carbon stock of 54.9 metric tons, sequestered within a time span of 5 years. Integration of this technique for monitoring and management of young mangrove plantations will give time and cost effective results. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
Environmental Earth Sciences, 2013
Journal of Oceanography, 2013
Your article is protected by copyright and all rights are held exclusively by The Oceanographic S... more Your article is protected by copyright and all rights are held exclusively by The Oceanographic Society of Japan and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Journal of Earth System Science, 2013
The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gr... more The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gradient technique at three distant stations, within the world's largest 27 mangrove ecosystem of Sundarban (Indian part), between April, 2011 and March, 2012. 28 Quadrat analysis revealed that all the three study sites are characterized by a strong 29 heterogeneity in the mangrove vegetation cover. At day time the forest was a sink for CO 2 , 30 but its magnitude varied significantly from -0.39 mg m -2 s -1 to -1.33 mg m -2 s -1 . The station 31 named Jharkhali showed maximum annual fluxes followed by Henry Island and Bonnie 32 Camp. Day time fluxes were higher during March and October, while in August and January 33 the magnitudes were comparatively lower. The seasonal variation followed the same trend in 34 all the sites. The spatial variation of CO 2 flux above the canopy was mainly explained by the 35 canopy density and photosynthesis efficiency of the mangrove species. The CO 2 sink strength 36 of the mangrove cover in the different stations varied in the same way with the CO 2 uptake 37 potential of the species diversity in the respective sites. The relationship between the 38 magnitude of day time CO 2 uptake by the canopy and photosynthetic photon flux was defined 39 by a non-linear exponential curve (R 2 ranging from 0.51 to 0.60). Water vapor fluxes varied 40 between 1.4 mg m -2 s -1 and 69.5 mg m -2 s -1 . There were significant differences in magnitude 41 between day and night time water vapor fluxes, but no spatial variation was observed. 42 Keywords: Carbon dioxide fluxes; water vapor fluxes; photosynthetic photon flux; spatial 44 variation; mangrove forests; Sundarban 45 46 47 48 Recent estimates revealed that the terrestrial gross primary production (GPP) is the largest 62 global CO 2 flux (~123 ± 8 Pg C year -1 ) driving several ecosystem functions (Beer et al. 63 2010). 64 Micrometeorological techniques made continuous monitoring and frequent collection of data 65 possible without disturbing the environment around the plant canopy (Baldocchi et al. 1988). 66 Several endeavours have been undertaken to study the exchange dynamics of greenhouse 67 gases over tropical terrestrial forests but a comparatively lesser attention has been paid on the 68 mangrove forests at the land ocean boundary. Mangroves are one of the most productive and 69 bio-diverse ecosystems developed along estuaries, sea coasts and river mouths in the tropical 70 and subtropical intertidal zones. In general the mangrove ecosystem including the below and 71 above ground compartments act as sinks for CO 2 , but the water column and the sediment are 72 largely found to emit the same (Borges et al. 2003). The present carbon burial rate within the 73 mangrove systems has been assessed to be ≈ 18.4 Tg C yr -1 based on the global mangrove 74 cover of 1,60,000 km 2 (Bouillon et al. 2009). 75 Sundarban is the largest continuous stretch of mangrove forests of the world covering about 76 2.84% of the global mangrove area (15 × 10 4 km 2 ) and having a unique bio-climatic zone in 77 the landocean margin of the Bay of Bengal, out of which 40% lies within India and the rest 78 in the rest in Bangladesh counterpart. In the year 1989, Sundarban Biosphere Reserve was 79 constituted in the Indian Sundarban part, after the core area of the Sundarban Tiger Reserve 80 i.e. Sundarban national park received the recognition of UNESCO World Heritage Site. Few 81 studies were undertaken in the past in selected locations of the Sundarban deltaic system, 82 which revealed dual character of this ecosystem in terms of source and sink for CO 2 . 83 Mukhopadhyay et al. (2000) carried out a short term survey in Jambu Island and observed the 84 environment to be a sink for CO 2 in the pre-monsoon season at a rate of 24 × 10 9 kg C year -1 85 while the same authors conducted another study at Lothian Island which reflected the source 86 character with an emission rate of 1.51×10 6 mg day -1 (Mukhopadhyay et al. 2001). Long term 87 annual studies conducted later at the Lothian Island also confirmed a source character for 88 CO 2 as reported by Mukhopadhyay et al. (2002), while at the same Lothian Island and 89 Sajnekhali, Ganguly et al. (2008) observed a mean net influx of -48.3 g m -2 day -1 and total 90 sink strength of 206 Gg day -1 was estimated for the entire reserve forest area (4264 km 2 ). All 91 the observations made so far tried to illustrate the holistic scenario of the ecosystem based on 92 the results obtained from the particular study sites, but no prior attempts have been taken to 93 discuss the spatial variability of the CO 2 exchange within the same time frame in such a 94 complex and heterogeneous gigantic mangrove ecosystem. The structure and functioning of 95 mangrove forests are influenced by several physico-chemical and bio-geographical factors 96 like soil type, availability of water table, vapor pressure deficit, photosynthetic photon flux 97 which again vary over different spatial and temporal scales (Duke et al. 1998). Apart from 98 these factors, species diversity along with the species specific carbon uptake potential, which 99 determines the sink strength of a forest cover and canopy density also plays a crucial role 100 behind the spatial variation of fluxes. 101 The present study aims to investigate the nature and magnitude of the atmosphere-102 biosphere CO 2 and H 2 O fluxes above the forest canopy at three selected locations situated at 103 the northern, middle and southern part of the Indian Sundarbans. Micrometeorological 104 techniques were implemented to carry out the investigation throughout a complete annual 105 cycle. The study also strives to find out the relationship between the micrometeorological 106 variables and the gas exchange, along with the effect of species composition, if any.
Environmental Monitoring and Assessment, 2012
A comprehensive attempt has been made to evaluate the diurnal and spatial pattern of CO2 exchange... more A comprehensive attempt has been made to evaluate the diurnal and spatial pattern of CO2 exchange between the atmosphere and water along the estuarine track of Indian Sundarbans during the two summer months, April and May, 2011. Rigorous field observations were carried out which included the hourly measurements of total alkalinity, pH, fugacity of CO2 in ambient air and water surface, dissolved oxygen, and chlorophyll a. The estuarine water was found rich in total alkalinity and was oversaturated with CO2 throughout the diurnal cycle in the two stations situated at the inner and middle estuary, respectively, whereas an entirely reverse situation was observed in the outer fringes. The fugacity of CO2 in water ranged from 152 to 657 μatm during the study period. The percentage of over-saturation in inner and middle estuary varied from 103 to 168 and 103 to 176 %, respectively, whereas the degree of under-saturation in the outer estuary lied between 40 and 99 %. Chlorophyll a concentrations were found higher in the outer estuary (12.3 ± 2.2 mg m(-3)) compared to the middle (6.4 ± 0.6 mg m(-3)) and inner parts (1.6 ± 0.2 mg m(-3)), followed by a similar decreasing pattern in nutrient availability from the outer to inner estuary. The sampling stations situated at the inner and middle estuary acted as a net source of 29.69 and 23.62 mg CO2 m(-2) day(-1), respectively, whereas the outer station behaved as a net sink of -33.37 mg CO2 m(-2) day(-1). The study of primary production and community respiration further supports the heterotrophic nature of the estuary in the inner region while the outer periphery was marked by dominant autotrophic character. These contrasting results are in parity with the source characters of many inner estuaries and sinking characters of the outer estuaries situated at the distal continental shelf areas.
The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gr... more The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gradient technique at three distant stations, within the world's largest 27 mangrove ecosystem of Sundarban (Indian part), between April, 2011 and March, 2012. 28 Quadrat analysis revealed that all the three study sites are characterized by a strong 29 heterogeneity in the mangrove vegetation cover. At day time the forest was a sink for CO 2 , 30 but its magnitude varied significantly from -0.39 mg m -2 s -1 to -1.33 mg m -2 s -1 . The station 31 named Jharkhali showed maximum annual fluxes followed by Henry Island and Bonnie 32 Camp. Day time fluxes were higher during March and October, while in August and January 33 the magnitudes were comparatively lower. The seasonal variation followed the same trend in 34 all the sites. The spatial variation of CO 2 flux above the canopy was mainly explained by the 35 canopy density and photosynthesis efficiency of the mangrove species. The CO 2 sink strength 36 of the mangrove cover in the different stations varied in the same way with the CO 2 uptake 37 potential of the species diversity in the respective sites. The relationship between the 38 magnitude of day time CO 2 uptake by the canopy and photosynthetic photon flux was defined 39 by a non-linear exponential curve (R 2 ranging from 0.51 to 0.60). Water vapor fluxes varied 40 between 1.4 mg m -2 s -1 and 69.5 mg m -2 s -1 . There were significant differences in magnitude 41 between day and night time water vapor fluxes, but no spatial variation was observed. 42 Keywords: Carbon dioxide fluxes; water vapor fluxes; photosynthetic photon flux; spatial 44 variation; mangrove forests; Sundarban 45 46 47 48 Recent estimates revealed that the terrestrial gross primary production (GPP) is the largest 62 global CO 2 flux (~123 ± 8 Pg C year -1 ) driving several ecosystem functions (Beer et al. 63 2010). 64 Micrometeorological techniques made continuous monitoring and frequent collection of data 65 possible without disturbing the environment around the plant canopy (Baldocchi et al. 1988). 66 Several endeavours have been undertaken to study the exchange dynamics of greenhouse 67 gases over tropical terrestrial forests but a comparatively lesser attention has been paid on the 68 mangrove forests at the land ocean boundary. Mangroves are one of the most productive and 69 bio-diverse ecosystems developed along estuaries, sea coasts and river mouths in the tropical 70 and subtropical intertidal zones. In general the mangrove ecosystem including the below and 71 above ground compartments act as sinks for CO 2 , but the water column and the sediment are 72 largely found to emit the same (Borges et al. 2003). The present carbon burial rate within the 73 mangrove systems has been assessed to be ≈ 18.4 Tg C yr -1 based on the global mangrove 74 cover of 1,60,000 km 2 (Bouillon et al. 2009). 75 Sundarban is the largest continuous stretch of mangrove forests of the world covering about 76 2.84% of the global mangrove area (15 × 10 4 km 2 ) and having a unique bio-climatic zone in 77 the landocean margin of the Bay of Bengal, out of which 40% lies within India and the rest 78 in the rest in Bangladesh counterpart. In the year 1989, Sundarban Biosphere Reserve was 79 constituted in the Indian Sundarban part, after the core area of the Sundarban Tiger Reserve 80 i.e. Sundarban national park received the recognition of UNESCO World Heritage Site. Few 81 studies were undertaken in the past in selected locations of the Sundarban deltaic system, 82 which revealed dual character of this ecosystem in terms of source and sink for CO 2 . 83 Mukhopadhyay et al. (2000) carried out a short term survey in Jambu Island and observed the 84 environment to be a sink for CO 2 in the pre-monsoon season at a rate of 24 × 10 9 kg C year -1 85 while the same authors conducted another study at Lothian Island which reflected the source 86 character with an emission rate of 1.51×10 6 mg day -1 (Mukhopadhyay et al. 2001). Long term 87 annual studies conducted later at the Lothian Island also confirmed a source character for 88 CO 2 as reported by Mukhopadhyay et al. (2002), while at the same Lothian Island and 89 Sajnekhali, Ganguly et al. (2008) observed a mean net influx of -48.3 g m -2 day -1 and total 90 sink strength of 206 Gg day -1 was estimated for the entire reserve forest area (4264 km 2 ). All 91 the observations made so far tried to illustrate the holistic scenario of the ecosystem based on 92 the results obtained from the particular study sites, but no prior attempts have been taken to 93 discuss the spatial variability of the CO 2 exchange within the same time frame in such a 94 complex and heterogeneous gigantic mangrove ecosystem. The structure and functioning of 95 mangrove forests are influenced by several physico-chemical and bio-geographical factors 96 like soil type, availability of water table, vapor pressure deficit, photosynthetic photon flux 97 which again vary over different spatial and temporal scales (Duke et al. 1998). Apart from 98 these factors, species diversity along with the species specific carbon uptake potential, which 99 determines the sink strength of a forest cover and canopy density also plays a crucial role 100 behind the spatial variation of fluxes. 101 The present study aims to investigate the nature and magnitude of the atmosphere-102 biosphere CO 2 and H 2 O fluxes above the forest canopy at three selected locations situated at 103 the northern, middle and southern part of the Indian Sundarbans. Micrometeorological 104 techniques were implemented to carry out the investigation throughout a complete annual 105 cycle. The study also strives to find out the relationship between the micrometeorological 106 variables and the gas exchange, along with the effect of species composition, if any.
The degree of heavy metal contamination was estimated in the river water, sediments and benthic o... more The degree of heavy metal contamination was estimated in the river water, sediments and benthic organisms in the Kolkata metropolitan sewage outfall zone and downstream areas along the Kulti River track. Four heavy metals namely Cr, Pb, Zn and Cd were studied seasonally. The hierarchy of heavy metals in the water samples and sediments was found in the order Zn>Pb>Cr>Cd and Zn>Cr>Pb>Cd respectively in most of the cases. Among the four heavy metals, Pb was found to be beyond the permissible limit recommended by Central Pollution Control Board of India for inland discharge. The extent of contamination by Cd is very prominent in the sediments followed by Pb, which is observed not only in the outfall region but also found persistent in the downstream stations. On the other hand contamination of Zn and Cr was not found to be widespread. Contamination in sediments of the outfall zone was most pronounced during the monsoon, while in the same season it was observed least in case of water samples. The pollution load index study revealed that the overall metal pollution load depleted towards the downstream. Among the two benthic organisms studied, metals were found to be accumulated more in Uca rosea than Boleopthalmus spp. 2012 pp. [153][154][155][156]
The degree of heavy metal (Cr, Pb and Hg) contamination in the paddy fields utilizing the sewage ... more The degree of heavy metal (Cr, Pb and Hg) contamination in the paddy fields utilizing the sewage effluent of Kolkata metropolitan city, near East Kolkata Wetland, India, along with the irrigation water and paddy grains were investigated in 2010 and 2011. The nutrient concentration, pH and electrical conductivity status during the sowing time was also monitored. Though the pH of the irrigation water was found suitable in all instances but the electrical conductivity values were observed to be inappropriate in 4 sites. Hg was found beyond the permissible limit in the water used for irrigation as well as paddy soils of all the study sites. Evaluation of enrichment ratio revealed alarming Hg contamination in two sites out of six sites studied. Enrichment ratio values of Pb were moderately high in four sites exhibiting polluting effect. The geo-accumulation index calculated was found to support similar observations. Cr in water and soil samples was found within the threshold limit, but in the paddy grain it was found beyond the maximum allowable limit. Hg and Pb, however, were found below detection level in all the rice samples. Pollution load index was estimated in all the sites and it varied from 0.860 to 1.827. Virtually no polluting activity was found in the samples obtained from control stations situated far away from the effluent source, where irrigation is primarily done using groundwater.
Journal of Applied Remote Sensing, 2014
Mangroves are active carbon sequesters playing a crucial role in coastal ecosystems. In the prese... more Mangroves are active carbon sequesters playing a crucial role in coastal ecosystems. In the present study, aboveground biomass (AGB) was estimated in a 5-year-old Avicennia marina plantation (approximate area ≈190 ha) of Indian Sundarbans using high-resolution satellite data in order to assess its carbon sequestration potential. The reflectance values of each band of LISS IV satellite data and the vegetation indices, viz., normalized difference vegetation index (NDVI), optimized soil adjusted vegetation index (OSAVI), and transformed difference vegetation index (TDVI), derived from the satellite data, were correlated with the AGB. OSAVI showed the strongest positive linear relationship with the AGB and hence carbon content of the stand. OSAVI was found to predict the AGB to a great extent (r 2 ¼ 0.72) as it is known to nullify the background soil reflectance effect added to vegetation reflectance. The total AGB of the entire plantation was estimated to be 236 metric tons having a carbon stock of 54.9 metric tons, sequestered within a time span of 5 years. Integration of this technique for monitoring and management of young mangrove plantations will give time and cost effective results. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
Environmental Earth Sciences, 2013
Journal of Oceanography, 2013
Your article is protected by copyright and all rights are held exclusively by The Oceanographic S... more Your article is protected by copyright and all rights are held exclusively by The Oceanographic Society of Japan and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Journal of Earth System Science, 2013
The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gr... more The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gradient technique at three distant stations, within the world's largest 27 mangrove ecosystem of Sundarban (Indian part), between April, 2011 and March, 2012. 28 Quadrat analysis revealed that all the three study sites are characterized by a strong 29 heterogeneity in the mangrove vegetation cover. At day time the forest was a sink for CO 2 , 30 but its magnitude varied significantly from -0.39 mg m -2 s -1 to -1.33 mg m -2 s -1 . The station 31 named Jharkhali showed maximum annual fluxes followed by Henry Island and Bonnie 32 Camp. Day time fluxes were higher during March and October, while in August and January 33 the magnitudes were comparatively lower. The seasonal variation followed the same trend in 34 all the sites. The spatial variation of CO 2 flux above the canopy was mainly explained by the 35 canopy density and photosynthesis efficiency of the mangrove species. The CO 2 sink strength 36 of the mangrove cover in the different stations varied in the same way with the CO 2 uptake 37 potential of the species diversity in the respective sites. The relationship between the 38 magnitude of day time CO 2 uptake by the canopy and photosynthetic photon flux was defined 39 by a non-linear exponential curve (R 2 ranging from 0.51 to 0.60). Water vapor fluxes varied 40 between 1.4 mg m -2 s -1 and 69.5 mg m -2 s -1 . There were significant differences in magnitude 41 between day and night time water vapor fluxes, but no spatial variation was observed. 42 Keywords: Carbon dioxide fluxes; water vapor fluxes; photosynthetic photon flux; spatial 44 variation; mangrove forests; Sundarban 45 46 47 48 Recent estimates revealed that the terrestrial gross primary production (GPP) is the largest 62 global CO 2 flux (~123 ± 8 Pg C year -1 ) driving several ecosystem functions (Beer et al. 63 2010). 64 Micrometeorological techniques made continuous monitoring and frequent collection of data 65 possible without disturbing the environment around the plant canopy (Baldocchi et al. 1988). 66 Several endeavours have been undertaken to study the exchange dynamics of greenhouse 67 gases over tropical terrestrial forests but a comparatively lesser attention has been paid on the 68 mangrove forests at the land ocean boundary. Mangroves are one of the most productive and 69 bio-diverse ecosystems developed along estuaries, sea coasts and river mouths in the tropical 70 and subtropical intertidal zones. In general the mangrove ecosystem including the below and 71 above ground compartments act as sinks for CO 2 , but the water column and the sediment are 72 largely found to emit the same (Borges et al. 2003). The present carbon burial rate within the 73 mangrove systems has been assessed to be ≈ 18.4 Tg C yr -1 based on the global mangrove 74 cover of 1,60,000 km 2 (Bouillon et al. 2009). 75 Sundarban is the largest continuous stretch of mangrove forests of the world covering about 76 2.84% of the global mangrove area (15 × 10 4 km 2 ) and having a unique bio-climatic zone in 77 the landocean margin of the Bay of Bengal, out of which 40% lies within India and the rest 78 in the rest in Bangladesh counterpart. In the year 1989, Sundarban Biosphere Reserve was 79 constituted in the Indian Sundarban part, after the core area of the Sundarban Tiger Reserve 80 i.e. Sundarban national park received the recognition of UNESCO World Heritage Site. Few 81 studies were undertaken in the past in selected locations of the Sundarban deltaic system, 82 which revealed dual character of this ecosystem in terms of source and sink for CO 2 . 83 Mukhopadhyay et al. (2000) carried out a short term survey in Jambu Island and observed the 84 environment to be a sink for CO 2 in the pre-monsoon season at a rate of 24 × 10 9 kg C year -1 85 while the same authors conducted another study at Lothian Island which reflected the source 86 character with an emission rate of 1.51×10 6 mg day -1 (Mukhopadhyay et al. 2001). Long term 87 annual studies conducted later at the Lothian Island also confirmed a source character for 88 CO 2 as reported by Mukhopadhyay et al. (2002), while at the same Lothian Island and 89 Sajnekhali, Ganguly et al. (2008) observed a mean net influx of -48.3 g m -2 day -1 and total 90 sink strength of 206 Gg day -1 was estimated for the entire reserve forest area (4264 km 2 ). All 91 the observations made so far tried to illustrate the holistic scenario of the ecosystem based on 92 the results obtained from the particular study sites, but no prior attempts have been taken to 93 discuss the spatial variability of the CO 2 exchange within the same time frame in such a 94 complex and heterogeneous gigantic mangrove ecosystem. The structure and functioning of 95 mangrove forests are influenced by several physico-chemical and bio-geographical factors 96 like soil type, availability of water table, vapor pressure deficit, photosynthetic photon flux 97 which again vary over different spatial and temporal scales (Duke et al. 1998). Apart from 98 these factors, species diversity along with the species specific carbon uptake potential, which 99 determines the sink strength of a forest cover and canopy density also plays a crucial role 100 behind the spatial variation of fluxes. 101 The present study aims to investigate the nature and magnitude of the atmosphere-102 biosphere CO 2 and H 2 O fluxes above the forest canopy at three selected locations situated at 103 the northern, middle and southern part of the Indian Sundarbans. Micrometeorological 104 techniques were implemented to carry out the investigation throughout a complete annual 105 cycle. The study also strives to find out the relationship between the micrometeorological 106 variables and the gas exchange, along with the effect of species composition, if any.
Environmental Monitoring and Assessment, 2012
A comprehensive attempt has been made to evaluate the diurnal and spatial pattern of CO2 exchange... more A comprehensive attempt has been made to evaluate the diurnal and spatial pattern of CO2 exchange between the atmosphere and water along the estuarine track of Indian Sundarbans during the two summer months, April and May, 2011. Rigorous field observations were carried out which included the hourly measurements of total alkalinity, pH, fugacity of CO2 in ambient air and water surface, dissolved oxygen, and chlorophyll a. The estuarine water was found rich in total alkalinity and was oversaturated with CO2 throughout the diurnal cycle in the two stations situated at the inner and middle estuary, respectively, whereas an entirely reverse situation was observed in the outer fringes. The fugacity of CO2 in water ranged from 152 to 657 μatm during the study period. The percentage of over-saturation in inner and middle estuary varied from 103 to 168 and 103 to 176 %, respectively, whereas the degree of under-saturation in the outer estuary lied between 40 and 99 %. Chlorophyll a concentrations were found higher in the outer estuary (12.3 ± 2.2 mg m(-3)) compared to the middle (6.4 ± 0.6 mg m(-3)) and inner parts (1.6 ± 0.2 mg m(-3)), followed by a similar decreasing pattern in nutrient availability from the outer to inner estuary. The sampling stations situated at the inner and middle estuary acted as a net source of 29.69 and 23.62 mg CO2 m(-2) day(-1), respectively, whereas the outer station behaved as a net sink of -33.37 mg CO2 m(-2) day(-1). The study of primary production and community respiration further supports the heterotrophic nature of the estuary in the inner region while the outer periphery was marked by dominant autotrophic character. These contrasting results are in parity with the source characters of many inner estuaries and sinking characters of the outer estuaries situated at the distal continental shelf areas.
The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gr... more The above canopy carbon dioxide and water vapor fluxes were measured by 26 micrometeorological gradient technique at three distant stations, within the world's largest 27 mangrove ecosystem of Sundarban (Indian part), between April, 2011 and March, 2012. 28 Quadrat analysis revealed that all the three study sites are characterized by a strong 29 heterogeneity in the mangrove vegetation cover. At day time the forest was a sink for CO 2 , 30 but its magnitude varied significantly from -0.39 mg m -2 s -1 to -1.33 mg m -2 s -1 . The station 31 named Jharkhali showed maximum annual fluxes followed by Henry Island and Bonnie 32 Camp. Day time fluxes were higher during March and October, while in August and January 33 the magnitudes were comparatively lower. The seasonal variation followed the same trend in 34 all the sites. The spatial variation of CO 2 flux above the canopy was mainly explained by the 35 canopy density and photosynthesis efficiency of the mangrove species. The CO 2 sink strength 36 of the mangrove cover in the different stations varied in the same way with the CO 2 uptake 37 potential of the species diversity in the respective sites. The relationship between the 38 magnitude of day time CO 2 uptake by the canopy and photosynthetic photon flux was defined 39 by a non-linear exponential curve (R 2 ranging from 0.51 to 0.60). Water vapor fluxes varied 40 between 1.4 mg m -2 s -1 and 69.5 mg m -2 s -1 . There were significant differences in magnitude 41 between day and night time water vapor fluxes, but no spatial variation was observed. 42 Keywords: Carbon dioxide fluxes; water vapor fluxes; photosynthetic photon flux; spatial 44 variation; mangrove forests; Sundarban 45 46 47 48 Recent estimates revealed that the terrestrial gross primary production (GPP) is the largest 62 global CO 2 flux (~123 ± 8 Pg C year -1 ) driving several ecosystem functions (Beer et al. 63 2010). 64 Micrometeorological techniques made continuous monitoring and frequent collection of data 65 possible without disturbing the environment around the plant canopy (Baldocchi et al. 1988). 66 Several endeavours have been undertaken to study the exchange dynamics of greenhouse 67 gases over tropical terrestrial forests but a comparatively lesser attention has been paid on the 68 mangrove forests at the land ocean boundary. Mangroves are one of the most productive and 69 bio-diverse ecosystems developed along estuaries, sea coasts and river mouths in the tropical 70 and subtropical intertidal zones. In general the mangrove ecosystem including the below and 71 above ground compartments act as sinks for CO 2 , but the water column and the sediment are 72 largely found to emit the same (Borges et al. 2003). The present carbon burial rate within the 73 mangrove systems has been assessed to be ≈ 18.4 Tg C yr -1 based on the global mangrove 74 cover of 1,60,000 km 2 (Bouillon et al. 2009). 75 Sundarban is the largest continuous stretch of mangrove forests of the world covering about 76 2.84% of the global mangrove area (15 × 10 4 km 2 ) and having a unique bio-climatic zone in 77 the landocean margin of the Bay of Bengal, out of which 40% lies within India and the rest 78 in the rest in Bangladesh counterpart. In the year 1989, Sundarban Biosphere Reserve was 79 constituted in the Indian Sundarban part, after the core area of the Sundarban Tiger Reserve 80 i.e. Sundarban national park received the recognition of UNESCO World Heritage Site. Few 81 studies were undertaken in the past in selected locations of the Sundarban deltaic system, 82 which revealed dual character of this ecosystem in terms of source and sink for CO 2 . 83 Mukhopadhyay et al. (2000) carried out a short term survey in Jambu Island and observed the 84 environment to be a sink for CO 2 in the pre-monsoon season at a rate of 24 × 10 9 kg C year -1 85 while the same authors conducted another study at Lothian Island which reflected the source 86 character with an emission rate of 1.51×10 6 mg day -1 (Mukhopadhyay et al. 2001). Long term 87 annual studies conducted later at the Lothian Island also confirmed a source character for 88 CO 2 as reported by Mukhopadhyay et al. (2002), while at the same Lothian Island and 89 Sajnekhali, Ganguly et al. (2008) observed a mean net influx of -48.3 g m -2 day -1 and total 90 sink strength of 206 Gg day -1 was estimated for the entire reserve forest area (4264 km 2 ). All 91 the observations made so far tried to illustrate the holistic scenario of the ecosystem based on 92 the results obtained from the particular study sites, but no prior attempts have been taken to 93 discuss the spatial variability of the CO 2 exchange within the same time frame in such a 94 complex and heterogeneous gigantic mangrove ecosystem. The structure and functioning of 95 mangrove forests are influenced by several physico-chemical and bio-geographical factors 96 like soil type, availability of water table, vapor pressure deficit, photosynthetic photon flux 97 which again vary over different spatial and temporal scales (Duke et al. 1998). Apart from 98 these factors, species diversity along with the species specific carbon uptake potential, which 99 determines the sink strength of a forest cover and canopy density also plays a crucial role 100 behind the spatial variation of fluxes. 101 The present study aims to investigate the nature and magnitude of the atmosphere-102 biosphere CO 2 and H 2 O fluxes above the forest canopy at three selected locations situated at 103 the northern, middle and southern part of the Indian Sundarbans. Micrometeorological 104 techniques were implemented to carry out the investigation throughout a complete annual 105 cycle. The study also strives to find out the relationship between the micrometeorological 106 variables and the gas exchange, along with the effect of species composition, if any.