Pond Ecosystems of the Indian Sundarbans

Ponds are small lentic bodies that are abundant throughout the world. In the rural setup of many Asian countries, especially in the deltaic regions (where adjacent waters are mostly saline), ponds serve as an essential source of fresh water. The Sundarbans is renowned for being the largest mangrove forest on Earth. India and Bangladesh share this unique ecoregion. The Indian part shelters a thickly populated marginalized section of people, who exclusively rely on this forest to meet their livelihood demands. The mangroves and other land use classes of the Indian Sundarbans have received ample attention in the past. However, the millions of ponds in this setup did not receive the adequate scientific focus, which it deserves. The present book is perhaps the first attempt to furnish a holistic overview of the biogeochemical status and socio-economic importance of these ponds. Given proper management, these ponds can play a crucial role in provisioning food resources for the local inhabitants, and thus, can serve to achieve a few of the United Nations Sustainable Development Goals (SDG 2—Zero hunger; SDG 6—Clean water and sanitation). At present, these ponds remain neglected with no proper attempt of nurturing the potential ecosystem services that these aquatic ecosystems can offer. This chapter detailed the nitty–gritty of the ponds of Indian Sundarbans from all possible viewpoints and provides a foundation for the entire book.

The Indian part of Sundarbans hosts a population of more than 4.4 million people and the land-use-land-cover dynamics of this region has witnessed significant changes in the recent past due to multifarious anthropogenic interventions. Though several pieces of research characterized the land-use-land-cover dynamics of this region, exclusive focus on the ponds of this region is yet to receive any such attention. We selected four administrative blocks of the Sundarban Biosphere Reserve (SBR), namely Sagar, Patharpratima, Gosaba, and Hingalganj, and analyzed the present scenario of the ponds along with their size classes and spatial distribution. The present analysis indicated that Sagar, Patharpratima, Gosaba, and Hingalganj comprise around 9000, 20,500, 11,500, and 7700 ponds. On the whole, the number of ponds varied proportionally with the total area of the blocks; however, the total surface area covered by the ponds did not show any significant relationship with the total number of ponds in each of the blocks. Most of the ponds belonged to the size class having an area between 100 m² and 200 m². Spatially, the majority of the ponds were situated within 500 m from the river boundary, plausibly indicating the abundance of aquaculture ponds near the river boundary. Besides, a gross scenario of the spatial distribution of the lentic water bodies and their ratio with the other prominent land-use classes were analyzed in this chapter. However, differentiation in terms of the type of ponds, like the household ponds, community ponds, and aquaculture ponds should be carried out in the future to develop a more comprehensive understanding of both spatial as well temporal dynamics of these crucial lentic ecosystems.

Though agriculture continues to be the predominant livelihood option for the millions residing within the Indian Sundarban Biosphere Reserve (SBR), inland fishing has lately emerged as a promising and viable option to alleviate the financial status of the grossly impoverished population of this region. Ponds and rearing of fishes in those ponds are integral components of the daily life of the people of Sundarbans. However, fishes are grown in most of the household ponds for self-consumption, and extensively without much investment. Aquaculture operations, on the other hand, require substantial scientific intervention to commercialize the fish yield and get a handsome return against the time and labor input. The present chapter collated the knowledge acquired so far in this domain, from the perspective of SBR. The fish diversity and the aquaculture management practices are detailed in a nutshell. The salient features and the typical characteristics of the ponds of the SBR are also discussed. This chapter also identifies the basic threats and challenges that the aquaculture farms of this region are facing at present. Overall, this chapter gives a brief overview of the inland fish farming practice and the attitude of the local inhabitants towards this promising sector of earning revenues.

In the present study, chlorophyll-a and nutrients were studied in the pond water collected from three brackish water ponds of Namkhana, Indian Sundarbans. Within these three ponds, one pond is treated with iron fertilizer and another one is with mangrove litter. The third pond acted as a control pond. The maximum value of chlorophyll concentration in the iron fertilized pond indicates the higher concentration of phytoplankton due to iron enhancement. Moreover, low nutrient concentrations accorded with the maximum chl-a concentration in the iron-fertilized pond. This observation indicated that the nutrients were used by phytoplankton during the higher rate of photosynthesis in the presence of higher iron value. The present study can be used to enhance the fish production of aquaculture ponds of Indian Sundarbans as well as link up with the future adaptation policies related to increasing the income of the vulnerable communities of Indian Sundarban.

Lentic ecosystems though encompass a much smaller area compared to the lotic water bodies of the world, are found to emit substantial quantities of greenhouse gases like CO₂, towards the atmosphere. The Sundarbans Biosphere Reserve (SBR) of India, besides being the abode of the world’s largest mangrove forest, shelters almost 4.4 million people with a substantially high population density. The CO₂ dynamics from several compartments of this biosphere reserve is studied in the recent past; however, the ponds are yet to receive any attention as such. The present chapter reports the variability of the partial pressure of CO₂ in water [pCO₂(water)] and the air–water CO₂ flux from four different types of ponds situated within the SBR. One of these selected ponds is abandoned, and not used for any human purpose and another pond is well-maintained and not at all used for any human purpose. The rest of the two ponds are typical homestead ponds with varying degrees of anthropogenic disturbances. The results indicated that all four ponds acted as a source of CO₂ towards the atmosphere; however, the rate of emission varied across the ponds. The most well-maintained least anthropogenically disturbed pond emitted CO₂ at the lowest rate, whereas the dilapidated and abandoned pond, which exist in a hypereutrophic state emitted the most. The other two ponds showed an intermediate range of fluxes. Biological processes played a dominant role over physical processes in governing the CO₂ fluxes. Water temperature showed a strong, positive, and statistically significant relationship with pCO₂(water). Thus, given the ongoing climate-change-induced rise in temperature can effectively enhance the emission rate of these ponds.

Small aquatic ecosystems like ponds and lakes have been found to emit a significant amount of CH₄ towards the atmosphere and their role is worth inclusion in delineating the global CH₄ budget. The Sundarbans Biosphere Reserve (SBR) of India, besides being the abode of the world’s largest mangrove forest, shelters almost 4.4 million people with a substantially high population density. The CH₄ dynamics from several compartments of this biosphere reserve is studied in the recent past; however, the ponds are yet to receive any attention as such. The present chapter reports the variability of the partial pressure of CH₄ in water [pCH₄(water)] and the subsequent air–water CH₄ fluxes from four different types of ponds situated within the SBR. One of these selected ponds is abandoned, and not used for any human purpose and another pond is well-maintained and not at all used for any human purpose. The rest of the two ponds are typical homestead ponds with varying degrees of anthropogenic disturbances. The results indicated that all four ponds acted as a source of CH₄ towards the atmosphere; however, the rate of emission varied across the ponds. The most well-maintained least anthropogenically disturbed pond emitted CH₄ at the lowest rate, whereas the dilapidated and abandoned pond, emitted the most. The other two ponds showed an intermediate range of fluxes. Water temperature showed a strong, positive, and statistically significant relationship with pCH₄(water). The results indicate that the ongoing climate-change-induced rise in temperature can effectively enhance the CH₄ emission rate from these ponds. However, the dissolved oxygen levels exhibited a significant negative relationship with pCH₄(water), which indicates that if autotrophic conditions can be maintained through proper pond management practices, methanotrophy can negate the dominance of methanogens to a large extent.

The aquaculture ponds have been recognized as significant sources of greenhouse gases like CO₂ and CH₄ as a substantial amount of organic matter remains unspent during fish culture, which eventually mineralizes into inorganic form and escapes the water bodies as CO₂ or the methanogens act upon these organic substrates to form CH₄. The Indian Sundarban Biosphere Reserve shelters a population as high as 4.4 million people, and in the recent past, a trend in livelihood switch from traditional agriculture to aquaculture has been noticed and reported by many eminent researchers. However, endeavors of characterizing the rate of greenhouse gas emissions and their regulators in these ponds are yet to be reported. The present chapter takes this opportunity to monitor and report the variability in the partial pressure of CO₂ and CH₄ in water [pCO₂(water) and pCH₄(water), respectively] and the air–water CO₂ and CH₄ flux from two aquaculture ponds situated in the north and south of the Indian Sundarbans that culture Penaeus monodon (tiger prawn). Both of the ponds emitted CO₂ and CH₄ of varying magnitudes throughout the year. However, the pond in the north which utilized the adjacent estuarine water full of anthropogenic load emitted more CO₂ and CH₄ compared to the one situated down south, which had higher dominance of seawater. A significant positive relationship of pCO₂(water) and pCH₄(water) with water temperature warrants that in the future the ongoing climate change would lead to an increase in the emission rates. Enhanced lime treatment was found to increase the pH levels which favored reducing pCO₂(water). An oxygen-rich environment was found to dampen both the CO₂ and CH₄ fluxes, which indicates that if the autotrophic potential of these ponds could be increased, a reduction in CO₂ and CH₄ fluxes is possible.

The State of West Bengal has an uncountable number of ponds and occupies 7.45% of the total water resources of India. Apart from small ponds, the State also has large ponds, known as Dighi and Beel. These large ponds serve as rainwater reservoirs, which find extensive use during the post-monsoon and the summer seasons. In Sundarbans, since there are no large ponds or natural lakes, the small ponds are crucial for domestic agriculture and allied activities. These water bodies are the only source of surface water in the Sundarbans. The demand for fresh water is increasing day by day due to the population growth in the region. Freshwater storage is the primary ecosystem service of the ponds because these water bodies provide substantial provisioning and Supporting services and very few cultural and regulating services. Due to changes in the agricultural activity in Sundarbans, the provisioning services (irrigation, fish farming, and domestic purposes) are declining day by day. Low awareness of ecosystem services and extreme weather events are the main reasons for the decrease in the social benefits from these ponds. So to protect the only source of freshwater ecosystem services, it is high time to assess the value of the services. Apart from ecosystem services evaluation, various stakeholders (fisher, agricultural farmer, and pond user) engagement is essential to know the importance of different ecosystem services.

Ponds are intrinsic to deltaic life as they are important for both household-level activities and supporting livelihoods. Based on field observations from areas of the Gosaba Community Development Block (Indian Sundarbans), this chapter presents descriptions of the different kinds of ponds. These descriptions illustrate the form of these different kinds of ponds. Following this descriptive section, the chapter uses qualitative data to document the varied uses of these ponds by different people, applying a gender lens and emphasising their socio-cultural and economic importance. It also explores changes over time, showing how the form and uses are embedded within wider social and economic change, and what might be expected in the future.

Heavy metals in varying quantities exist in the earth’s surface as well as natural aquatic bodies. However, beyond a certain threshold concentration, all these heavy metals pose toxicity to a multitude of life forms that come in contact with these metals or ingest substantial quantities through food. The Sundarbans mangrove ecosystem lies at a critical junction between the pristine mangroves in the south and the urbanized setup in the north. This ecosystem receives substantial industrial effluents and signatures of heavy metal accumulation have been observed in the estuarine water column, sediments, floras, and faunas. However, the lentic aquatic systems like that of ponds, which are integral to the daily life of the millions that reside in this zone, have received the least attention. This study was aimed to develop a preliminary idea on certain selected heavy metal accumulation levels in the brackish water ponds of Indian Sundarbans. Concentrations of Cd, Pb, Zn, and Fe were detected in two such ponds of the Indian Sundarbans mangrove ecosystem at two different locations namely Canning (north) and Frazergaunge (south). The observations indicate that immediate anthropogenic activities are increasing the heavy metal levels in the north of the Sundarbans ecosystem. Whereas, the Hooghly River Estuary, which has been carrying a substantial load of heavy metals for a long time has led to significant heavy metal accumulation in the brackish water ponds situated down south through tidal activities.

A microcosm study has been done to explain the disparities of nutrient variability vis-à-vis the partial pressure of carbon dioxide (CO₂) in water [pCO₂(water)] of brackish water pond of Frazergaunge, Namkhana block, Indian Sundarbans. The present study showed that there are a relationship between the decrease in pCO₂(water) and nutrient removal from the brackish water pond system. Although there are exceptions. The present study revealed that the brackish water pond of Indian Sundarbans acted as an important source of CO₂ during monsoon and pre-monsoon season although having a substantial amount of chlorophyll-a in the pond water to make the pond an autotrophic ecosystem. The present research showed that if the optimum photosynthesis can be continued in a shallow aquaculture pond, it can act as a sink of CO₂. During the post-monsoon season (water column pH is high) the ecosystem acted as a CO₂ sink. The present experiment suggests that the controlled lime treatment could be useful to reverse the character of this shallow aquaculture pond.