Tanguar Research Articles

Phytoplankton flora of Tanguar Haor ecosystem of Bangladesh: Chlorophyta

The qualitative and quantitative aspects of phytoplankton population belonging to the green algae (Chlorophyta) from Watch Tower and Rauar Station of Tanguar Haor, Sunamganj were studied. In the study, a total of 39 species of three Orders under the algal Division Chlorophyta was worked out. Their photomicrographs and individual densities in the pelagic community of phytoplankton over a study year of 2016 and 2017 are discussed. In Volvocales, Volvox carteri Stein, in Chlorococcales, Coelastrum microporum Nägeli and in Zygnematales, Staurastrum paradoxum Meyen represented the highest number of population in the community. Rauar Station was found to contain the lesser number of phytoplankton densities compared to Watch Tower Station.
 J. Biodivers. Conserv. Bioresour. Manag. 2019, 5(2): 101-106

Phytoplankton in relation to water quality of Tanguar Haor ecosystem, Bangladesh: 2. Watch tower station

Phytoplankton biomass in relation to some environmental and nutritional parameters at Watch Tower Station of Tanguar and Rauar Station has been studied. Since the Haor is a Ramsar Site, it is a globally important aquatic ecosystem. In the present investigation, the structure of the phytoplankton and the water quality factors were worked out and the data were compared Rauar Station with having the same ecosystem. Though weaker, a difference among alkalinity, total dissolved solids (TDS), conductivity, dissolved oxygen (DO), Secchi disc transparency, soluble reactive phosphorous (SRP), soluble reactive silicate (SRS), NO3-N, NH4+, chlorophyll-a and phytoplankton population density was found between the Watch Tower and the Rauar Station of Tanguar Haor. The mean values of the aforsaid parameters were found to some extent higher in the Watch Tower Station. The Watch Tower Station was deeper and perennial, where the depth of water varied from 3.0 - 9.5 m annually with a mean of 6.72 m. In the studied station, air and water temperature varied from 22.6 - 30.6 and 22.7 - 30.3°C, respectively. Water transparency ranged from 2.08 - 3.0 m. From December to March the pH remained 8.1-9.7 and alkalinity from 0.73 - 1.35 meq/l. However, from April to September these two parameters ranged from 7.5 - 7.7 and 0.33 - 1.35 meq/l, respectively. Dissolved oxygen (DO) and free CO2 concentration ranged from 2.5 - 6.09 and 0.084 - 0.087 mg/l, respectively. During April to September the Chlorophyll-a value ranged from 5.5 - 7.5 μg/l while the range of SRP was 24.23 - 30.05 μg/l during the same period. At the latter part of the study year i.e., during the dry period (December to March) those two parameters were relatively low in concentration. In April a high concentration of NH4+ (1380 μg/l) was reported from the haor, at other times this parameter ranged from 690 - 820 μg/l. The NO3-N ranged from 0.25 - 0.75 mg/l. High density of phytoplankton population (2690 ind./l) was reported at the time of high concentration of SRP (30.05 μg/l ) of the haor water. The chlorophyll-a value (7.5 μg/l) was also highest at that time. So, it could be said that SRP concentration in Tanguar haor has been playing a vital role in regulating the standing crop of phytoplankton. To find the variation on a spatial scale, the data of the present investigation were compared with another study station of the haor namely, Rauar Station. No significant difference was observed among the concentrations of different parameters. However, a slight increasing trend in the concentrations of DO, alkalinity, SRP, NO3-N, SRS, NH4+ and total phytoplankton density was observed in the Watch Tower Station compared to Rauar Station. Watch Tower Station is also relatively deeper with an improved light climate as it had been revealed by the mean value of the Secchi depth. The water quality of Tanguar Haor has been classified as mesotrophic.
 Dhaka Univ. J. Biol. Sci. 29(1): 9-18, 2020 (January)

Phytoplankton flora of Tanguar haor ecosystem in Bangladesh: Cyanophyta, Pyrrhophyta, Chrysophyta and Euglenophyta

The present paper is dealt with the composition and density of the population of pelagic phytoplankton collected from two studied stations, namely Watch Tower and Rauar Station of Tanguar Haor in Sunamganj District. Plankton belonging to the divisions Cyanophyta, Pyrrhophyta, Chrysophyta and Euglenophyta were studied from bimonthly collected samples during 2017 and 2018. Division Cyanophyta was represented by the occurrence of 17 species followed by Chrysophyta (16 spp.), Euglenophyta (4 spp.) and Phyrrhophyta (2 spp.). The most dominant plankton taxon was Dinobryon sertularia Ehrenberg whose density was 374 ×103 ind/l and 137.5 ×103 ind/l at Watch Tower and Rauar Station, respectively. Euglenoid population was relatively poorer compared to the other groups of phytoplankton. Abundant population of D. sertularia designates the Tanguar Haor ecosystem as moderate in terms of productivity. A total of 39 species recorded from three algal divisions, namely Cyanophyta, Pyrrhophyta, Chrysophyta and Euglenophyta. Tanguar Haor ecosystem was included with mean phytoplankton population of Cyanophyta, Pyrrhophyta, Chrysophyta and Euglenophyta.
 J. Biodivers. Conserv. Bioresour. Manag. 2019, 5(1): 105-112

Phytoplankton in relation to water quality of Tanguar Haor ecosystem, Bangladesh: I. Rauar station

The water quality at Rauar station of Tanguar Haor, Sunamganj was assessed studying phytoplankton and associated environmental variables. The environmental variables were monitored over a period of one year, collecting samples at two months interval between March, 2017 and March, 2018. Air temperature, rainfall, and humidity ranged from 22.6 - 32.1°C, 48 - 76% and 8 - 930 mm, respectively. Air temperature showed a direct relationship with water temperature which varied from 22.4 - 31.0°C during the study period. The water transparency remained relatively constant throughout the year having a mean Secchi depth (Zs) value of 2.48 m. Total dissolved solids (TDS), conductivity, and pH of the water ranged from 51 - 85 mg/l, 60 - 110 μS/cm, and 7.2 - 9.7, respectively. In December, because of a temperature fall, the dissolved oxygen (DO) concentration of the water reached its maximum value of 6.09 mg/l. In the rest of the period, the concentration remained between 2.44 and 4.80 mg/l. The value of alkalinity ranged from 0.43 - 1.35 meq/l. Among the nutrients, soluble reactive phosphorus (SRP), soluble reactive silicate (SRS), and NO3-N ranged from 5.43 - 36.43 μg/l, 4 - 14.58 mg/l, and 0.06 - 0.31 mg/l, respectively. The concentration of NH4+ ranged from 238 - 1230 μg/l. The highest concentrations (905 and 1230 μg/l) occurred between September and December, 2017. This might be attributed to the higher density of migratory birds during that period. The phytoplanktonic biomass expressed as chlorophyll-a (Chl-a) ranged from 1.35 - 8.45 μg/l while its degraded product phaeophytin concentration ranged from 0.08 - 3.5 μg/l. The standing crop of phytoplankton ranged from 397 - 2480 × 103 individuals/l of haor water exhibiting its maximum abundance in September. This parameter showed a highly significant positive correlation with SRP. From the correlation analysis, the degradation of chl-a to phaeophytin was found to be temperature dependent. Considering the different physicochemical and biological water quality data, it could be said that the Tanguar Haor is still free from organic pollution. However, the range of soluble reactive phosphorus data (5.43 - 36.43 μg/l) show that the Haor has been passing a meso-eutrophic state.
 Dhaka Univ. J. Biol. Sci. 28(2): 131-138, 2019 (July)

Wetland resource governance in Bangladesh: An analysis of community-based co-management approach

Wetland resource governance is a critical issue in Bangladesh, where the rural communities depend on natural resources and cause over-exploitation of natural resources. Purposive exploitation of wetland resources in Bangladesh is a result of the top-down approach. In response to centralized resources management system, community-based co-management emerged mainly to ensure the sustainability of natural resources through benefiting the local communities. Based on our study in Tanguar Haor, a unique wetland ecosystem in the northeastern region of Bangladesh, co-management approach can promote greater participation of the local community in resource management but establishing such governance arrangements take time depending on the potential of community organizations. As the study revealed, the Initiative of establishing co-management is still a challenge in Tanguar Haor, where there is a high dependency on resources given the socio-economic conditions. Also, the ineffectiveness of the existing community organization, largely due to a lack of leadership at the local level, is an obstacle to governing this wetland. Therefore, the findings of this study broadly highlight the necessity for strengthening the community organization through a collaborative process. In line with the commitment of government as well as its realization at the community level, the need for responsible, legitimate and effective roles of the community people including leaders has been further urged towards sustainable management of the wetland resources.

ROLE OF STAKEHOLDERS IN PRESERVING BIODIVERSITY IN BANGLADESH: A STUDY ON TANGUAR HAOR

Tanguar Haor, the most diversified ecosystem of Bangladesh is important for surviving around 70,000 people. Tanguar Haor has been declared ecologically critical area for 20 years. This study aims to examine the role of relevant stakeholders in conserving the countries’ second RAMSAR site. This paper also attempted to understand the causes of loss of biodiversity of Tanguar Haor as well as its solution. Mixed methods (qualitative and quantitative) research has employed for this study applying purposive sampling strategy. Study findings reveal that indiscriminate harvesting of mother fishes, use of agrochemicals, deforestation, hunting migratory birds, increasing trace metal, mixing silt soil with water are the major contributor to loss of biodiversity in Tanguar Haor. With the support of the Swedish Development Corporation (SDC) and International Union for Conservation of Nature (IUCN), the government of Bangladesh has conducted a big budgeted project to preserve biodiversity of Tanguar Haor, however there found lack of coordination among peoples’ representatives, government agencies, and IUCN. Hence, the study findings will hopefully contribute to identify the irregularities in performing the role of different stakeholders that will lead taking further initiatives to preserve biodiversity of Tanguar Haor in Bangladesh.

Continuing evolution of highly pathogenic H5N1 viruses in Bangladeshi live poultry markets

ABSTRACT Since November 2008, we have conducted active avian influenza surveillance in Bangladesh. Clades 2.2.2, 2.3.4.2, and 2.3.2.1a of highly pathogenic avian influenza H5N1 viruses have all been identified in Bangladeshi live poultry markets (LPMs), although, since the end of 2014, H5N1 viruses have been exclusively from clade 2.3.2.1a. In June 2015, a new reassortant H5N1 virus (H5N1-R1) from clade 2.3.2.1a was identified, containing haemagglutinin, neuraminidase, and matrix genes of H5N1 viruses circulating in Bangladesh since 2011, plus five other genes of Eurasian-lineage low pathogenic avian influenza A (LPAI) viruses. Here we report the status of circulating avian influenza A viruses in Bangladeshi LPMs from March 2016 to January 2018. Until April 2017, H5N1 viruses exclusively belonged to H5N1-R1 clade 2.3.2.1a. However, in May 2017, we identified another reassortant H5N1 (H5N1-R2), also of clade 2.3.2.1a, wherein the PA gene segment of H5N1-R1 was replaced by that of another Eurasian-lineage LPAI virus related to A/duck/Bangladesh/30828/2016 (H3N8), detected in Bangladeshi LPM in September 2016. Currently, both reassortant H5N1-R1 and H5N1-R2 co-circulate in Bangladeshi LPMs. Furthermore, some LPAI viruses isolated from LPMs during 2016–2017 were closely related to those from ducks in free-range farms and wild birds in Tanguar haor, a wetland region of Bangladesh where ducks have frequent contact with migratory birds. These data support a hypothesis where Tanguar haor-like ecosystems provide a mechanism for movement of LPAI viruses to LPMs where reassortment with poultry viruses occurs adding to the diversity of viruses at this human-animal interface.

Understanding the Changes of the Wetland Ecosystem and Its Impact on the Biodiversity of Tanguar Haor in Sunamganj, Bangladesh

Understanding the Changes of the Wetland Ecosystem and Its Impact on the Biodiversity of Tanguar Haor in Sunamganj, Bangladesh

Status and economic valuation of ecosystem services of Tanguar haor: A wetland of Bangladesh

Tanguar haor wetland is one of the listed Ramsar sites enrich with biodiversity variety and provides several ecosystem services with significant contribution to the national economy of Bangladesh. But these services were decreasing day by day due to natural and anthropogenic activities. The purposes of this study were to identify the utilized ecosystem services by communities, economic values of utilized ecosystem services and the basic reasons for depleting of ecosystem services. Data were collected through baseline survey, checklists, face to face questionnaire survey and focus group discussion (FGD) from 120 residential respondents and 50 tourist respondents by accepting random sampling techniques during November, 2016 to September, 2017. Physiochemical characteristics of the water were determined where the mean temperature and pH were 28.26°C and 7.72 respectively. The highest TDS, EC, DO, NO3 and PO4 values were 1020 (mg L−1), 1460 (μS cm−1), 8.56 (mg L−1), 1.769 (mg L−1) and 0.078 (mg L−1), respectively. Commonly utilized ecosystem services were crops, vegetables, fuel, fresh water, fishes and migratory birds, climate regulation, water purification, natural hazards protection, aesthetic, social relations, recreation & tourism, health benefit, primary production, nutrient cycling, water cycling habitats for species and provision of habitat etc. Market Value Method (MVM) and Contingent Value Method (CVM) were applied to measure the economic value of Tanguar haor wetland services. DPSIR framework and Impact Matrix (IM) were applied for conceptual analysis to identify the effects on ecosystem services. Total economic value of 39 ecosystem services of Tanguar haor was estimated at 174039980 BDT year−1. Mismanagement of biodiversity, over exploitation, sedimentation of haor, climate change, illegal hunting, land use changes and habitat changes were the responsible factors for depleting ecosystem services. The impact factor (4.161) was identified by natural and anthropogenic factors on ecosystem services. There have a vast prospect of the Tanguar haor wetland services for near communities. Finally the research suggested several sustainable management approaches which have the potentiality to protect the services of the wetland.J. Bangladesh Agril. Univ. 16(2): 237-243, August 2018

Livelihood exposure to climatic stresses in the north-eastern floodplains of Bangladesh

In this paper, we seek to better understand the temporal and spatial aspects of climatic stress on local resource production systems and resource-use behaviors by including the perspectives of resource-dependent communities. Field research was conducted over a nine-month period in the remote north-eastern floodplain communities of Bangladesh, considered one of the most climate-vulnerable, least developed and under-studied regions in the country. This area is heavily dominated by wetland ecosystems, and subjected to regular seasonal flood and extreme rainfall events. Beyond these regular stresses, flash-floods and drought are the two most destructive climatic stresses on livelihood sustainability in the area. Data were collected in 12 villages bordering two significant wetlands (Hakaluki haor and Tanguar haor), involving focus group discussions (n = 14), key informant interviews (n = 35) and household surveys (n = 356). Our results show that climatic stresses on rural livelihoods are catalyzed by human-induced environmental degradation and local resource use behaviors, contextual features that include both socio-economic and bio-physical properties. A climatic event appeared as a stress to livelihood sustainability when it happened in an untimely manner (e.g., flooding during resource harvesting periods) and directly affected the production process (e.g., agriculture and fisheries). We also found that human stress perceptions varied with the level of locally-driven innovation and adoption of technologies, which supports the important role of local experience and knowledge in adaptation planning. Further research is needed into how communities in different settings are already organizing to manage perceived climatic stresses, including traditional knowledge systems, local innovation networks and livelihood practices to help better contextualize adaptation policy.

Replication and pathogenic potential of influenza A virus subtypes H3, H7, and H15 from free-range ducks in Bangladesh in mammals

Surveillance of wild aquatic birds and free-range domestic ducks in the Tanguar Haor wetlands in Bangladesh has identified influenza virus subtypes H3N6, H7N1, H7N5, H7N9, and H15N9. Molecular characterization of these viruses indicates their contribution to the genesis of new genotypes of H5N1 influenza viruses from clade 2.3.2.1a that are dominant in poultry markets in Bangladesh as well as to the genesis of the highly pathogenic H5N8 virus currently causing disease outbreaks in domestic poultry in Europe and the Middle East. Therefore, we studied the antigenicity, replication, and pathogenicity of influenza viruses isolated from Tanguar Haor in the DBA/2J mouse model. All viruses replicated in the lung without prior mammalian adaptation, and H7N1 and H7N9 viruses caused 100% and 60% mortality, respectively. H7N5 viruses replicated only in the lungs, whereas H7N1 and H7N9 viruses also replicated in the heart, liver, and brain. Replication and transmission studies in mallard ducks showed that H7N1 and H7N9 viruses replicated in ducks without clinical signs of disease and shed at high titers from the cloaca of infected and contact ducks, which could facilitate virus transmission and spread. Our results indicate that H7 avian influenza viruses from free-range ducks can replicate in mammals, cause severe disease, and be efficiently transmitted to contact ducks. Our study highlights the role of free-range ducks in the spread of influenza viruses to other species in live poultry markets and the potential for these viruses to infect and cause disease in mammals.

How Do Capital Asset Interactions Affect Livelihood Sensitivity to Climatic Stresses? Insights From the Northeastern Floodplains of Bangladesh

This paper offers a novel methodological approach for better understanding how different capital assets can be organized, transformed, and used in different combinations to reduce livelihood sensitivity to climatic stresses – an area that requires greater research attention in the context of adaptation policy. Research was conducted in the northeastern floodplain communities of Bangladesh, regarded as one of the most climate sensitive, resource poor, and highly understudied areas of the country. This wetland-dominated ecosystem is home to diverse resources user groups (e.g., farmer and fisher) who are subjected to regular seasonal flooding, excessive rainfall, drought, and flash floods. Working in 12 adjacent villages of two significant wetlands (Hakaluki haor and Tanguar haor), qualitative and quantitative data were collected through 15 focus groups (n = 15), 35 key informant interviews, and 356 household surveys to better understand how community members adapt in response to their livelihood sensitivity to the climatic stresses. Results indicate that community members organize and transform capital assets in diverse ways to escape climate-induced “poverty traps”. Findings also reveal that interventions from external agencies (e.g., government, non-governmental organizations and market institutions) are an important key to livelihood sustainability for many households.

Genesis of Influenza A(H5N8) Viruses.

Highly pathogenic avian influenza A(H5N8) clade 2.3.4.4 virus emerged in 2016 and spread to Russia, Europe, and Africa. Our analysis of viruses from domestic ducks at Tanguar haor, Bangladesh, showed genetic similarities with other viruses from wild birds in central Asia, suggesting their potential role in the genesis of A(H5N8).

The Impact of Spatial Changes of Wetlands on Bio-Diversity: A Geo-Spatial Study on Tanguar Haor- Ramsar Site, Bangladesh

<p>Bangladesh is the largest delta in the world. Geographical location and seasonal diversity have made this country unique. Tanguar Haor as a Ramsar site is famous throughout the world with a reservoir of aquatic biodiversity. Due to availability of water flow throughout the year it has reached biodiversity compared to other haors in Bangladesh. In every winter, this haor becomes sonorous with the presence of thousands of migratory and resident birds. A lot of aquatic plants are floating and some are submerged. These aquatic plants decompose with seasonal shift and make the soil fertile. Numerous organism with food and shelter provided by these aquatic plants. Various species of amphibians and reptiles can also be seen in this vast haor. It has merged with the life and tradition of local people. Also human habitation has increased around the haor since the middle of the last century. About 12,870 ha water body have lost from 23,230 ha during last 60 years. Per year, 1.17% of water body have been lost in Tanguar Haor from 1955 to 2015. As a result, population of birds and wildlife is decreasing alarmingly due to the disturbance in the natural balance of the wetland ecosystem.</p>

Comparison of the ecosystem services provided by China's Poyang Lake wetland and Bangladesh's Tanguar Haor wetland

Wetlands are the most productive ecosystem on Earth. China's Poyang Lake wetland and Bangladesh's Tanguar Haor wetland are important natural Asian wetlands. In the past 10–15 years, the ecosystem services provided have been greatly affected by human activities and the resulting significant changes in the wetlands. In this paper, we chose food supply and biodiversity as typical ecosystem services provided by these wetlands, and combined field research with surveys to analyze the changes in the characteristics of these ecosystem services in the two wetlands and their driving forces. From 2000 to 2012, we found that: (1) per capita rice production has decreased greatly in both wetlands, while the rice consumption and the level of food security have decreased in the Poyang Lake wetland and increased in the Tanguar Haor wetland. (2) The fish supply has decreased in both wetlands, with a greater decrease in the Tanguar Haor wetland. (3) The biodiversity services have improved in the Poyang Lake wetland but decreased greatly in the Tanguar Haor wetland. These changes have been caused by differences in the combination of land use policies, land use planning, population growth patterns, and economic development.

Land cover change detection using GIS and remote sensing techniques: A spatio-temporal study on Tanguar Haor, Sunamganj, Bangladesh

Tanguar Haor is one of the two listed Ramsar Site of this country which contains a rich amount of biodiversity as well as a highly productive ecosystem. But the valuable landscape undergoes a radical change in its form over the decades. This study uses past and recent satellite data to evaluate the typical landscape change over the decades. Both pre-classification and post classification change detection approach was used to assess the change result from 1980 to 2010. In pre-classification approach CVA, NDVI and NDWI analysis were implemented to assess the change scenario. Maximum likelihood supervised classification technique was performed to create the signature class of significant land cover category (deep water, shallow water, vegetation, and settlement). After ensuring satisfactory accuracy value for each classified image a detail post classification change detection analysis was executed. Image differencing, statistical change detection techniques (transition probability matrix), change dynamics analysis was also operated to evaluate the statistics of past change relative to present. This study illustrated that, about 40% land cover of the total study area has been converted over 30years period. Forested and high land vegetation’s are disappearing rapidly, deep water bodies consist of large lakes are becoming the rare feature of the study area. Widespread development of settlement and dominant shallow water feature are converting the natural wetland a permanent low lying agricultural land.

Impact of Flash Flood on Agriculture Land in Tanguar Haor Basin

Impact of Flash Flood on Agriculture Land in Tanguar Haor Basin

A review of the sustainability of recent watershed management programmes in Bangladesh

AbstractWatershed management has evolved during the 1990s in Bangladesh. However, it has not yet achieved much exposure in the country, even though wetlands play a very significant role in its ecology, economy and stakeholder livelihoods. Several watershed management programmes have been initiated in the country with a co‐management and participatory approach, but in a piecemeal basis. Many wetland problems have arisen as a result. This study reviews watershed management programmes and undertakes a sustainability analysis of three recent initiatives, namely MACH, Nishorgo and Tanguar Haor projects, on the basis of the main watershed exchanges. This analysis indicates these projects are/were less environmentally, but more socially and economically, sustainable. Thus, this study suggests first incorporating the unaccounted environmental sustainability indicators. Moreover, the country's future management programme(s) should incorporate stakeholder livelihood improvements and social empowerment via education and training schemes, by ensuring social inclusiveness that makes the management initiatives locally sustainable.

Status of Fisheries Resources and Water Quality of Tanguar Haor

The study was conducted to observe the status of fisheries resource of Tanguar haor, one of the large wetland in the north eastern part of Bangladesh. For this purpose the whole study was completed in two parts: interviewing with local people and analyzing the water quality. Indiscriminate harvesting of mother fishes, use of agrochemicals, sedimentation on haor basin and habitat destruction were found as major causes of fisheries resources degradation in the study area. Most of the water quality parameters were found good which were within the standard level set by Government of Bangladesh for fisheries. However, EC and TDS were found higher than the recommended level for fish production.DOI: http://dx.doi.org/10.3329/jesnr.v6i1.22048 J. Environ. Sci. & Natural Resources, 6(1): 103-106 2013

The effects of the flood cycle on the diversity and composition of the phytoplankton community of a seasonally flooded Ramsar wetland in Bangladesh

Freshwater wetlands in Bangladesh are strongly influenced by the monsoons and the annual flood cycle has measurable impacts on the abiotic and biotic components of these ecosystems. The northeastern Haor Basin of Bangladesh is particularly rich in seasonally flooded freshwater wetlands that support a wide diversity of flora and fauna. These wetlands are of great importance to the local economy due to the abundance of rich floodplain fisheries. Little is known about the phytoplankton communities of these wetlands that are known to be linked with zooplankton and fish productivity. We investigated the seasonal variation in the diversity and abundance of phytoplankton assemblages in Tanguar Haor, a Ramsar wetland in northeastern Bangladesh during the period of inundation (June–December). A total of 107 genera of phytoplankton representing five classes were recorded. Blooms of Microcystis dominated the phytoplankton community throughout the study period but were particularly acute during the early part of the high water period. Among the Bacillariophyceae, Melosira was the most dominant, reaching bloom proportions early in the high water period. Factor analysis of physicochemical variables separated the flood cycle into four distinct periods: early high water, mid high water, late high water and low water periods. Phase of the flood cycle, nutrient availability, the physicochemical variables combined with the dominance of Microcystis seemed to be important in controlling the abundance, diversity and dynamics of the phytoplankton genera. The abundance of genera of desmids and some Bacillariophyceae is indicative of the relatively unpolluted conditions of Tanguar Haor.