Dibyendu Rakshit | University of Calcutta (original) (raw)

Papers by Dibyendu Rakshit

The study presents the first preliminary report on the community composition, abundance, biomass ... more The study presents the first preliminary report on the community composition, abundance, biomass and production rate of the ciliated tintinnids in the coastal waters of Sundarban mangrove wetland, formed at the confluence of the Ganges River Estuary, India. Total 32 species under 5 agglomerated (29 species) and 3 non agglomerated (3 species) genera have been identified from six sites of different hydrodynamic conditions. In general, Tintinnopsis (22 species) dominates the community structure followed by Leprotintinnus (2 species), Tintinnidium (2 species), Stenosemella (2 sp), Codonellopsis (1 sp), Amphorellopsis (1 sp), Metacylis (1 sp) and Favella (1 sp). Pronounced seasonal variations were noticed in environmental parameters and abundance, biomass, production rates of tintinnids: Being the highest during pre monsoon followed by post monsoon and monsoon. Water temperature, Chl a and salinity were found to regulate the seasonal tintinnid variations as revealed by stepwise multiple ...

th May, 2009. The Aila incident not only caused stupendous changes in the physicochemical charact... more th May, 2009. The Aila incident not only caused stupendous changes in the physicochemical characteristics of the water but also left direct impact on the mesozooplankton biomass. A sharp increment in water turbidity, chemical oxygen demand (COD), phytopigment chlorophyll b (chl b) and micronutrients (nitrate, phosphate and silicate) were noticed during post-Aila period with a corresponding decrease of water transparency and phytopigments chl a and chl c. Reduction of zooplankton biomass, density and species diversity was also pronounced during post-Aila period. An absolute dominance of two copepod species of diverse feeding guilds, namely, Bestiolina similis (herbivore) and Oithona brevicornis (carnivore) was the most interesting feature observed during post-Aila period. The meroplanktons such as nauplius, zoea and ichthyoplanktons which constituted the most dominant forms (~31 % of total mesozooplankton) during pre-Aila period, were completely absent in post-Aila stage.

World Academy of Science, Engineering and Technology, International Journal of Bioengineering and Life Sciences, 2016

Deterioration of water quality due to high turbidity (11.87±1.13 NTU) and biochemical oxygen dema... more Deterioration of water quality due to high turbidity (11.87±1.13 NTU) and biochemical oxygen demand (1.66±0.38 mg l) coupled with low chlorophyll (chl a) (0.94±0.15 mgm) during immersion has been recorded. Decreasing trend of numerical density for loricate ciliate tintinnid (microzooplankton) [post-immersion (224±52 cells l) > pre-immersion (144±36 cells l) > immersion (85±30 cells l)] and phytoplankton [post-immersion (2745±912 cells l) > pre-immersion (2337±441 cells l) > immersion (1660±334 cells l)] was evident.

Environmental Geochemistry and Health, 2019

Journal of the Marine Biological Association of India, 2016

Regional Studies in Marine Science, 2017

Marine Pollution Bulletin, 2017

CLEAN – Soil, Air, Water, 2016

The study first investigated the spatial distribution, diversity, and biomass of the planktonic c... more The study first investigated the spatial distribution, diversity, and biomass of the planktonic choreotrich ciliate tintinnids inhabiting the biosphere reserve, the core region of Indian Sundarban mangrove wetland. A total of 21 species (eight genera and six families) were recorded including agglomerated and non‐agglomerated or hyaline forms from these intricate estuarine network systems. Maximum mean abundance (2747 ± 111 individuals L−1) and species diversity (H′ = 2.32) of tintinnid ciliate were recorded at the sampling site located towards the Bay of Bengal whereas lower abundance (666 ± 56 individuals L−1) and diversity (H′ = 1.55) were encountered towards inner part of the estuary. Tintinnopsis represented the most dominant agglutinated genus comprising of Tintinnopsis beroidea, Tintinnopsis fimbriata, Tintinnopsis cylindrica, Tintinnopsis tocantinensis, and Tintinnopsis radix, accounting ∼52% of total tintinnid community. The agglomerated forms Amphorellopsis tetragona, Eutin...

Environmental Materials and Waste, 2016

The environmental, social, and economic problems associated with acid mine drainage (AMD) from ab... more The environmental, social, and economic problems associated with acid mine drainage (AMD) from abandoned mine sites are globally significant. As a consequence of mining exploration of metallic mineral deposits, large quantities of sulfides are exposed to weathering processes (oxygen, water, and bacteria) that generate acidic environments and promote metal(loid) solubilization, forming so-called AMD. The pollution caused by AMD can be minimized by adopting suitable strategies and approaches to mitigate AMD or prevent its generation and migration. The current work was undertaken for an in-depth account of the generalized features of AMD and in-depth case studies of the impact of AMD in the northern part of Portugal. The first part was prepared to highlight basic features dealing with (the) origin of AMD; (2) the characteristics of AMD; (3) factors controlling the formation of AMD; (4) the environmental impact of AMD; (5) resource recovery from AMD; and (6) prevention, mitigation, and treatment of AMD. The second part accentuates in-depth case studies of mine drainage water collected bimonthly from abandoned mines situated in northern Portugal over 1 year. In the mines that were studied are acidic waters with low pH and significant concentrations of SO4, and metal(loid)s (As, Fe, Mn, Zn, Cu, Pb, Cd, and Ni), whereas in superficial natural stream waters outside the mines, the pH is close to neutral, with low conductivity and lower metal concentrations. Stream waters inside the mines have an intermediate composition between AMD and natural stream waters outside the mines. The environmental impact of the quality of the superficial waters is marked only in the closest surroundings of the pollution source (1 to 2 km). Several coherent and integrated processes contribute to this situation, such as (1) dilution by other groundwater and surface waters that flow toward stream waters; (2) precipitation or co-precipitation of metallic cations by hydroxides and sulfates; and (3) adsorption of metallic cations by organic and inorganic sediments and aquatic plants. Hydrochemical processes and the environmental impact in the study sites are important issues necessitating potential resource recovery from AMD (eg, iron or other metals) and appropriate strategies and approaches to mitigate AMD and pollution prevention.

Marine Pollution Bulletin, 2015

The study first illustrates a comprehensive account of large-scale changes in water quality chara... more The study first illustrates a comprehensive account of large-scale changes in water quality characteristics and plankton community structure due to occurrence of Annual Gangasagar Festival (AGF) at Sagar Island, western part of Indian Sundarban megadelta for 3-year duration (2012-2014; n=36). About 1 million pilgrims across India converge to take their holy bath at the confluence of Hooghly estuary and Bay of Bengal during January each year. This mass scale bathing results negative impact on water quality due to high turbidity (14.02 ± 2.34 NTU) coupled with low chlorophyll a (1.02 ± 0.21 mg m(-3)) and dissolved oxygen (3.94 ± 1.1 mg l(-1)). A marked decrease in abundance (from 4140 to 2997 cells l(-1)) and diversity (H'=2.72-1.33) of phytoplankton and microzooplankton tintinnids (from 450 to 328 ind l(-1); H'=4.31-2.21) was recorded. The festival acts as multiple stressors modifying natural functions of the delta. Sound and sustainable management strategies are to be adopted to maintain the protection-usage equilibrium.

Regional Studies in Marine Science, 2016

Marine Pollution Bulletin, 2014

Marine Pollution Bulletin, 2014

Marine Pollution Bulletin, 2012

Journal of Cleaner Production, 2015

Environmental Monitoring and Assessment, 2014

The study is the first documentation of seasonal variations in species composition, abundance and... more The study is the first documentation of seasonal variations in species composition, abundance and diversity of tintinnid (Ciliata: Protozoa), in relation to water quality parameters along the stretch of the Hooghly (Ganges) River Estuary (HRE), eastern coastal part of India. A total of 26 species (22 agglomerated and 4 non-agglomerated) belonging to 8 genera has been identified from 8 study sites where Tintinnopsis (17 species) represented the most dominant genera, contributing up to 65 % of total tintinnid community followed by Tintinnidium (2 species), Leprotintinnus (2 species) and Dadayiella, Favella, Metacylis, Eutintinnus and Helicostomella (each with solitary species). The maximum (1,666 ind. l(-1)) and minimum (62 ind. l(-1)) abundance of tintinnids was recorded during post-monsoon and monsoon, respectively. A distinct seasonal dynamics in terms of biomass (0.005-2.465 μg C l(-1)) and daily production rate (0.04-3.13 μg C l(-1) day(-1)) was also noticed, accounting highest value during pre-monsoon. Chlorophyll a and nitrate were found to be potential causative factors for the seasonal variations of tintinnids as revealed by a stepwise multiple regression model. The result of ANOVA showed a significant variation between species abundance and months (F = 2.36, P ≤ 0.05). k-dominance curves were plotted to determine the comparison of tintinnid dominance between the investigated stations. Based on a principal component analysis (PCA), three main groups were delineated with tintinnid ciliates and environmental parameters. The changes in lorica morphology in terms of temperature and salinity, recorded for three dominant species, provided information on the ecological characteristics of the species assemblage in this estuarine system.

Environmental Monitoring and Assessment, 2012

The study presents the first preliminary report on the community composition, abundance, biomass ... more The study presents the first preliminary report on the community composition, abundance, biomass and production rate of the ciliated tintinnids in the coastal waters of Sundarban mangrove wetland, formed at the confluence of the Ganges River Estuary, India. Total 32 species under 5 agglomerated (29 species) and 3 non agglomerated (3 species) genera have been identified from six sites of different hydrodynamic conditions. In general, Tintinnopsis (22 species) dominates the community structure followed by Leprotintinnus (2 species), Tintinnidium (2 species), Stenosemella (2 sp), Codonellopsis (1 sp), Amphorellopsis (1 sp), Metacylis (1 sp) and Favella (1 sp). Pronounced seasonal variations were noticed in environmental parameters and abundance, biomass, production rates of tintinnids: Being the highest during pre monsoon followed by post monsoon and monsoon. Water temperature, Chl a and salinity were found to regulate the seasonal tintinnid variations as revealed by stepwise multiple ...

th May, 2009. The Aila incident not only caused stupendous changes in the physicochemical charact... more th May, 2009. The Aila incident not only caused stupendous changes in the physicochemical characteristics of the water but also left direct impact on the mesozooplankton biomass. A sharp increment in water turbidity, chemical oxygen demand (COD), phytopigment chlorophyll b (chl b) and micronutrients (nitrate, phosphate and silicate) were noticed during post-Aila period with a corresponding decrease of water transparency and phytopigments chl a and chl c. Reduction of zooplankton biomass, density and species diversity was also pronounced during post-Aila period. An absolute dominance of two copepod species of diverse feeding guilds, namely, Bestiolina similis (herbivore) and Oithona brevicornis (carnivore) was the most interesting feature observed during post-Aila period. The meroplanktons such as nauplius, zoea and ichthyoplanktons which constituted the most dominant forms (~31 % of total mesozooplankton) during pre-Aila period, were completely absent in post-Aila stage.

World Academy of Science, Engineering and Technology, International Journal of Bioengineering and Life Sciences, 2016

Deterioration of water quality due to high turbidity (11.87±1.13 NTU) and biochemical oxygen dema... more Deterioration of water quality due to high turbidity (11.87±1.13 NTU) and biochemical oxygen demand (1.66±0.38 mg l) coupled with low chlorophyll (chl a) (0.94±0.15 mgm) during immersion has been recorded. Decreasing trend of numerical density for loricate ciliate tintinnid (microzooplankton) [post-immersion (224±52 cells l) > pre-immersion (144±36 cells l) > immersion (85±30 cells l)] and phytoplankton [post-immersion (2745±912 cells l) > pre-immersion (2337±441 cells l) > immersion (1660±334 cells l)] was evident.

Environmental Geochemistry and Health, 2019

Journal of the Marine Biological Association of India, 2016

Regional Studies in Marine Science, 2017

Marine Pollution Bulletin, 2017

CLEAN – Soil, Air, Water, 2016

The study first investigated the spatial distribution, diversity, and biomass of the planktonic c... more The study first investigated the spatial distribution, diversity, and biomass of the planktonic choreotrich ciliate tintinnids inhabiting the biosphere reserve, the core region of Indian Sundarban mangrove wetland. A total of 21 species (eight genera and six families) were recorded including agglomerated and non‐agglomerated or hyaline forms from these intricate estuarine network systems. Maximum mean abundance (2747 ± 111 individuals L−1) and species diversity (H′ = 2.32) of tintinnid ciliate were recorded at the sampling site located towards the Bay of Bengal whereas lower abundance (666 ± 56 individuals L−1) and diversity (H′ = 1.55) were encountered towards inner part of the estuary. Tintinnopsis represented the most dominant agglutinated genus comprising of Tintinnopsis beroidea, Tintinnopsis fimbriata, Tintinnopsis cylindrica, Tintinnopsis tocantinensis, and Tintinnopsis radix, accounting ∼52% of total tintinnid community. The agglomerated forms Amphorellopsis tetragona, Eutin...

Environmental Materials and Waste, 2016

The environmental, social, and economic problems associated with acid mine drainage (AMD) from ab... more The environmental, social, and economic problems associated with acid mine drainage (AMD) from abandoned mine sites are globally significant. As a consequence of mining exploration of metallic mineral deposits, large quantities of sulfides are exposed to weathering processes (oxygen, water, and bacteria) that generate acidic environments and promote metal(loid) solubilization, forming so-called AMD. The pollution caused by AMD can be minimized by adopting suitable strategies and approaches to mitigate AMD or prevent its generation and migration. The current work was undertaken for an in-depth account of the generalized features of AMD and in-depth case studies of the impact of AMD in the northern part of Portugal. The first part was prepared to highlight basic features dealing with (the) origin of AMD; (2) the characteristics of AMD; (3) factors controlling the formation of AMD; (4) the environmental impact of AMD; (5) resource recovery from AMD; and (6) prevention, mitigation, and treatment of AMD. The second part accentuates in-depth case studies of mine drainage water collected bimonthly from abandoned mines situated in northern Portugal over 1 year. In the mines that were studied are acidic waters with low pH and significant concentrations of SO4, and metal(loid)s (As, Fe, Mn, Zn, Cu, Pb, Cd, and Ni), whereas in superficial natural stream waters outside the mines, the pH is close to neutral, with low conductivity and lower metal concentrations. Stream waters inside the mines have an intermediate composition between AMD and natural stream waters outside the mines. The environmental impact of the quality of the superficial waters is marked only in the closest surroundings of the pollution source (1 to 2 km). Several coherent and integrated processes contribute to this situation, such as (1) dilution by other groundwater and surface waters that flow toward stream waters; (2) precipitation or co-precipitation of metallic cations by hydroxides and sulfates; and (3) adsorption of metallic cations by organic and inorganic sediments and aquatic plants. Hydrochemical processes and the environmental impact in the study sites are important issues necessitating potential resource recovery from AMD (eg, iron or other metals) and appropriate strategies and approaches to mitigate AMD and pollution prevention.

Marine Pollution Bulletin, 2015

The study first illustrates a comprehensive account of large-scale changes in water quality chara... more The study first illustrates a comprehensive account of large-scale changes in water quality characteristics and plankton community structure due to occurrence of Annual Gangasagar Festival (AGF) at Sagar Island, western part of Indian Sundarban megadelta for 3-year duration (2012-2014; n=36). About 1 million pilgrims across India converge to take their holy bath at the confluence of Hooghly estuary and Bay of Bengal during January each year. This mass scale bathing results negative impact on water quality due to high turbidity (14.02 ± 2.34 NTU) coupled with low chlorophyll a (1.02 ± 0.21 mg m(-3)) and dissolved oxygen (3.94 ± 1.1 mg l(-1)). A marked decrease in abundance (from 4140 to 2997 cells l(-1)) and diversity (H'=2.72-1.33) of phytoplankton and microzooplankton tintinnids (from 450 to 328 ind l(-1); H'=4.31-2.21) was recorded. The festival acts as multiple stressors modifying natural functions of the delta. Sound and sustainable management strategies are to be adopted to maintain the protection-usage equilibrium.

Regional Studies in Marine Science, 2016

Marine Pollution Bulletin, 2014

Marine Pollution Bulletin, 2014

Marine Pollution Bulletin, 2012

Journal of Cleaner Production, 2015

Environmental Monitoring and Assessment, 2014

The study is the first documentation of seasonal variations in species composition, abundance and... more The study is the first documentation of seasonal variations in species composition, abundance and diversity of tintinnid (Ciliata: Protozoa), in relation to water quality parameters along the stretch of the Hooghly (Ganges) River Estuary (HRE), eastern coastal part of India. A total of 26 species (22 agglomerated and 4 non-agglomerated) belonging to 8 genera has been identified from 8 study sites where Tintinnopsis (17 species) represented the most dominant genera, contributing up to 65 % of total tintinnid community followed by Tintinnidium (2 species), Leprotintinnus (2 species) and Dadayiella, Favella, Metacylis, Eutintinnus and Helicostomella (each with solitary species). The maximum (1,666 ind. l(-1)) and minimum (62 ind. l(-1)) abundance of tintinnids was recorded during post-monsoon and monsoon, respectively. A distinct seasonal dynamics in terms of biomass (0.005-2.465 μg C l(-1)) and daily production rate (0.04-3.13 μg C l(-1) day(-1)) was also noticed, accounting highest value during pre-monsoon. Chlorophyll a and nitrate were found to be potential causative factors for the seasonal variations of tintinnids as revealed by a stepwise multiple regression model. The result of ANOVA showed a significant variation between species abundance and months (F = 2.36, P ≤ 0.05). k-dominance curves were plotted to determine the comparison of tintinnid dominance between the investigated stations. Based on a principal component analysis (PCA), three main groups were delineated with tintinnid ciliates and environmental parameters. The changes in lorica morphology in terms of temperature and salinity, recorded for three dominant species, provided information on the ecological characteristics of the species assemblage in this estuarine system.

Environmental Monitoring and Assessment, 2012