Keywords

1 Introduction

The Ramsar classification of wetland types include 42 types of wetlands, which belong to one of the three broad categories: inland wetlands (e.g., rivers, lakes, creeks), marine/coastal wetlands (e.g., shallow marine waters, estuaries, coral reefs), and human-made wetlands (aquaculture ponds and permanently or temporarily inundated agricultural lands such as rice paddies, salt pans, reservoirs, gravel pits, sewage farms, and canals). There is also a range of other wetland classifications used for different purposes, based on hydro-geomorphology and/or vegetation characteristics, such as:

  • Marine (coastal wetlands, including coastal lagoons, rocky shores, and coral reefs)

  • Estuarine (including deltas, tidal marshes, and mangrove swamps)

  • Lacustrine (wetlands associated with lakes)

  • Riverine (rivers and wetlands along rivers and streams)

  • Palustrine (marshes, swamps, and bogs)

1.1 Importance and Role of Wetlands

Rice, the staple food of about 50% of global population and consumed at the rate of one-fifth of the total global calorie intake, is grown in wetlands. Wetlands, among the most productive and biodiversity-rich areas, filter pollutants and sequester carbon, whereas rivers transport water and nutrients from the catchment downstream. Lakes serve as sediment and carbon sinks (Fischlin et al. 2007). In addition, food (fish and aquatic plants), medicine, and building materials are available from wetlands because of the rich living aquatic resources. Living aquatic resources, as common property natural resources (Nishat 1993), from wetlands play an essential role in people’s livelihood in rural areas in many parts of the world including Bangladesh. The most significant of these are fishes, prawns, crabs, molluscs, and clams that have all or part of their life cycle within a wetland system. Fresh and saltwater fishes are the main source of protein for about 3 billion people globally (at least 20% of their animal protein intake) and an important source of essential vitamins and omega-3-polyunsaturated fatty acids (Kibria et al. 2010). In addition, fish generates a fishing industry that provides 80% of income and employment in developing countries. In countries like Bangladesh, Myanmar, Thailand, Cambodia, and Vietnam, where rice paddies are predominant, rice consumption reaches up to 70%. From wetlands such as mangroves, fuelwood, salt (produced by evaporating seawater), animal fodder, traditional medicines (e.g., from mangrove bark), fibers for textiles, and dyes and tannins are extensively sourced. Various studies also reveal that such wetlands have tremendous potentials for integrated concurrent rice-fish culture and fish nursery operations (Haroon et al. 1992; Haroon and Pittman 1997).

Production cycles in wetlands are closely linked with seasonal changes in temperature and precipitation and therefore are affected by seasonal climate variability or long-term climate changes. Climate change will have significant impacts on wetland ecology, biodiversity, and livelihoods of people connected with it. Wetlands in a natural state are crucial for humans mainly because of their capacity for storing large quantities of freshwater, mitigating the impact of floods and droughts for a whole area and for their enormous biological productivity that can be harvested in the forms of fish, wood, reed, etc. Some wetland types like peat swamps are inaccessible and unproductive. Wetlands, in general, provide the following ecosystem goods and services.

  • Goods: wetland nonfood products, freshwater, food for humans, genetic materials, biomass production, biodiversity, support for food chains, storage of floodwater, and production of logs, fuelwoods, peat, fodder, etc.

  • Cultural services: recreation and tourism, natural heritage values, scientific and educational, and spiritual and inspirational

  • Regulating services: groundwater recharge, shoreline stabilization and reduction of erosion, sediment trapping, nutrient retention/removal, habitat for wildlife, hazard reduction (flood control, storm protection), maintenance of hydrological regimes, water transport, pollution control and detoxification, microclimate stabilization (IWRB 1992), climate regulation, and carbon source and sinks

2 Wetlands of Bangladesh

Wetlands of Bangladesh encompass a wide variety of dynamic ecosystems, viz., mangrove forest (about 577,100 ha), natural lakes, man-made reservoir (Kaptai Lake), freshwater marshes, estuaries, and seasonal inundated floodplains and paddy fields. The freshwater marshes include 114,161 ha of saucer-shaped natural depressions locally called as beels/haors, about 5,488 ha of oxbow lakes locally called as baors, and 371,309 ha of fishponds and dighi (large ponds). The total area of wetlands, both inland freshwater and tidal saltwater wetlands, in Bangladesh, comes to about 50% of the land surface of the country (Table 17.1 and Fig. 17.1). Considering the major rivers (700 rivers), their tributaries and streams, the major wetlands in Bangladesh constitute the fluvial or floodplains, viz., Sundarbans mangroves (140,000 ha), Kaptai Lake (68,800 ha), Chalan beel (36,800 ha), Hakaluki haor (20,400 ha), Chakaria mangroves (20,000 ha), the Naaf river estuary (16,000 ha), Arial beel (14,400 ha), Hail haor (3,643 ha), Tanguar haor (2,802 ha), St. Martin’s Coral Island and reef (800 ha), Kawadighi haor (414 ha), Dekhar haor (325 ha), Erail beel (320 ha), Dubriar beel/haor (150 ha), Meda beel (122 ha), Aila beel (106 ha), Ramsagar dighi (102 ha), Atadanga haor (102 ha), Kuri beel (73 ha), Bogakine Lake (60 ha), Baikka beel, Gopalganj-Khulna beel, Beel bhatia, Atrai basin, lower Punarbhaba floodplains, and Surma-Kushiara floodplains (Islam 2010). These wetlands form a unique mosaic of habitats, extremely rich in biodiversity. Wetlands are critically important in Bangladesh for water resources (rivers, haors), human settlements, biodiversity, agriculture/land resources, navigation and communication, and ecotourism. These wetlands have a wide range of ecological, sociocultural, economic, and commercial importance and values in Bangladesh.

Table 17.1 Wetlands of Bangladesh based on their land types as well as hydrological and ecological functions
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Fig. 17.1
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The major wetlands in Bangladesh (Islam 2010); the Ecologically Critical Areas (ECAs)/Ramsar wetlands are 3, Tanguar haor (Ramsar); 9, Hakaluki haor (ECA); 19–21, Sundarbans (west, south, and east (Ramsar and UNESCO World Heritage Site)); and 26, St. Martin’s Coral Island (ECA)

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2.1 Inland Freshwater Wetlands

Floodplains, beels (low-lying depressions in the floodplain), haors, and baors (oxbow lakes) represent the inland freshwater wetlands. Some important wetlands of the country are Chalan beel, lower Atrai basin, lower Punarbhaba floodplain, Gopalganj-Khulna beels, Arial beel, Akhaura terrace, Tanguar haor, and Hakaluki haor (Fig. 17.1) and Baikka beel of Surma-Kushiyara floodplain. Due to overexploitation of its natural resources and considering its critical conditions, the Government of Bangladesh declared Tanguar haor as an Ecologically Critical Area (ECA) in 1999. In 2000, the Tanguar haor was declared a Ramsar site of international importance. Hakaluki haor, with an area of 181.15 km2, is one of the large marsh wetland systems of northeastern Bangladesh. It is spread over Barolekha, Kulaura, and Juri Upazila (subdistrict) of Moulvibazar district and Golapganj, Fenchuganj Upazila of Sylhet district. Ramsagar dighi (102 ha) is a man-made lake situated about 8 km south of the Dinajpur town. It was created by Raja Ram Nath in the mid-1750s. The lake is about 1,079 m wide from north to south and 192.6 m long from east to west. The Kaptai Lake (68,800 ha) is a man-made lake that was formed due to the Kaptai dam for hydroelectricity generation in the late 1960s in Rangamati, Chittagong.

Haors

The haors are bowl-shaped natural depressions comprising of many individual beels formed during the monsoon, while the beels are low-lying depressions of the haor system retaining water even during the dry months of the year. The haor system is a complex of both lacustrine (lake) and palustrine (marsh) wetlands depending on the hydraulic behavior in different seasons. There are altogether 411 haors spread over 8,000 km2 in the districts of Sunamganj, Sylhet, Moulvibazar, Habiganj, Netrokona, and Kishoreganj (Table 17.2 and Fig. 17.1). To protect the crops in the haor areas, the erstwhile landlords with the participation of the locals constructed dwarf dykes and appurtenant structures for early flood protection and irrigation. Since 1966, Bangladesh Water Development Board (BWDB), adopting “ a better technology, has executed 46 Flood Control Drainage and Irrigation (FCDI) projects in the Sunamganj, Sylhet, Moulvibazar, Habiganj, Netrokona, and Kishoreganj districts. A total of about 0.29 million ha cultivable land has been made free from flash floods by implementing about 2,000 km submersible embankment and ancillary structures [note: the main objectives of the FCDI are (a) to protect from crop losses, loss of life, and property damage due to floods and (b) to improve the physical environment to allow farmers to adopt improved agricultural practices and greater security for crop production].

Table 17.2 Major haors of Bangladesh
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Oxbows

Oxbow lakes are loops of meanders cut-off at times from rivers and gradually plugged with sediment. Locally, these are also known as baor, jheel, and commonly as jalmohal. Oxbows are quite common in Jessore, Faridpur, and Kushtia districts. Oxbows support a large variety of aquatic flora and fauna. During the monsoon season, oxbow lakes act as local water reservoirs and help to control the local flood level. In some areas, these lakes serve as valuable sources of irrigation during the dry season.

Floodplains

Floodplain areas are the most hazard-prone areas of Bangladesh (Fig. 17.2). Elevation of the tidal floodplains from sea level is less than 1–3 m on the main rivers and estuarine floodplains. The floodplains of Bangladesh can be divided into four main regions: (i) the northwest region (in Dinajpur, Rangpur, Bogra, Rajshahi, and Pabna) between the Ganges and the Brahmaputra; (ii) the central region in Tangail, Dhaka, Comilla, and Noakhali, east of the Brahmaputra, Padma, and Lower Meghna; (iii) the main delta west of the Ganges-Padma and south to the coastal zone, in Kushtia, Jessore, Faridpur, Khulna, Barisal, and Patuakhali; and (iv) the northeast wetland regions of Sylhet, Sunamganj, Kishoreganj, Netrokona, and parts of Mymensingh.

Fig. 17.2
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A flooded haor wetland – during the lean season, most of the area of a haor may be dry (Photo courtesy: Md. Wahiduzzaman Sarker)

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Ponds, Dighis

The man-made wetlands including ponds, dighis (about 147,000 ha), and lakes are distributed all over the country. These are predominantly used for bathing, washing, livestock, and fish culture and in some cases for drinking water.

2.1.1 Biodiversity of Inland Wetlands

The flora and fauna reported from the wetlands in Bangladesh are presented in Table 17.3a–f.

Table 17.3 Selected flora and fauna from the wetlands of Bangladesh
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Vegetation

Among the estimated 5,000 species of flowering plants and 1,500 of vertebrates of the country, up to 300 plant species and 400 vertebrate species are dependent on wetlands for all or part of their life. Flora of inland wetlands varies from place to place; but the major species are Barringtonia acutangula, Pongamia pinnata, Rosa clinophylla, Eichhornia crassipes, Utricularia spp., Hydrilla verticillata, Myriophyllum spicatum, Ceratophyllum demersum, Elodea sp., Potamogeton sp., Ipomea aquatica, Colocasia esculenta, Monochoria vaginalis, Sagittaria sagittifolia, Cyperus papyrus, Typha sp., Scirpus sp., Salvinia sp., Pistia stratiotes, Lemna minor, Wolffia arrhiza, Azolla pinnata, Spirodela polyrhiza, Nymphaea nouchali and N. stellata, Nymphoides sp., Nelumbo nucifera, Euryale ferox, Phragmites karka, P. communis, Chara sp., Najas sp., Vetiveria zizanioides, Alternanthera philoxeroides, Enhydra fluctuans, Aponogeton sp., Hygrophila auriculata, Trapa bispinosa and T. maxitnowizii, Ottelia alismoides, and Asparagus racemosus. However, many of these have now become scarce because of overexploitation (see Table 17.3a for common names and conservation status of plants).

Many submergent and floating hydrophytes are used as leafy vegetables. Rootstocks of Aponogeton sp., Nymphaea spp., Nymphoides sp., T. bispinosa, and T. maxitnowizii and seeds of E. ferox are relished by the rural people. Wild species of rice jhora dhan (Oryza rufipogon) of inland wetlands are used as a substitute for cultivated rice. In some wetlands of central (Faridpur, Gopalganj, Muksudpur, Kashiani and Kotalipara, Jessore), southern (Jhalokathi, Pirojpur, Sharupkathi, Najirpur, Banaripara, and Ujirpur), and northeastern areas (Kishoreganj, Netrokona, Brahmanbaria, Sunamganj) of Bangladesh, floating garden made on heaps of decomposed water hyacinth (E. crassipes), locally called baira/daap (Haq et al. 2002), a century-old practice to grow vegetables in flood-prone areas (see below), is evident.

Farming on floating beds (locally known as baira, geto, bed, or daap), soil-less agriculture or hydroponics (Fig. 17.3), is an indigenous practice in the southwestern part of Bangladesh (Haq et al. 2002). This practice is now receiving renewed interest as a potential solution for farmers whose lands have been waterlogged and for landless people. This farming technique uses masses of rotting water hyacinths (E. crassipes) that choke the waterways, and it offers opportunities for the participation of men as well as women. Such agriculture/gardens can be an adaptation to adverse environmental conditions from waterlogging or prolonged flooding (Fig. 17.3). Here plants derive their nutrients not from soil but from water (UNEP 2012; Kibria et al. 2013). The approach employs beds of rotten vegetation, which acts as compost for crop growth. These beds are able to float on the surface of the water, creating areas of land suitable for agriculture within waterlogged regions. Mostly vegetables such as sweet gourd, pumpkin, brinjal, green chili, red and green amaranth, and beans are grown during the flood season. In winter when the water recedes, the farmers use the land to crop winter vegetables such as potato, tomato, radish, carrot, turnip, cabbage, cauliflower, and other crops such as onions and garlic depending on the local situation. Harvesting water hyacinth allows clearing the invasive weed, with the beneficial side effect of reducing breeding grounds for mosquitoes and improving conditions for open water fishing. This practice of floating agriculture also helps to supplement the income of local communities and contributes to poverty alleviation, greater food security by increasing the land output, and supporting capacity for poor and landless people. As both men and women can carry out floating agriculture, it also leads to improvements in gender equity. However, there is a possibility of transfer of pollutants such as trace/heavy metals accumulated in water hyacinth as compost to crops and vegetables grown on them (Kibria et al. 2016).

Fig. 17.3
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Farming on floating beds, baira/daap (Photo courtesy: A. W. R. Hassan, FAO, Bangladesh)

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Fish

The inland capture fishery is based on the vast freshwater fish resources with around 260 species of finfishes (most of them native) and 25 shellfishes. Economically important fishes include Labeo rohita, L. gonius, L. calbasu, L. nandina, L. angra, Catla catla, Cirrhinus cirrhosus, C. reba, Tor tor, T. putitora, Wallago attu, Pangasius pangasius, Aorichthys/Sperata aor, A. seenghala, Bagarius bagarius, Rita rita, Clarias batrachus, Heteropneustes fossilis, Ompok bimaculatus, O. pabo, Mystus tengara, M. cavasius, M. vittatus, Lepidocephalichthys guntea, Anabas testudineus, Notopterus notopterus, N. chitala, Rhinomugil corsula, Botia dario, Pseudeutropius atherinoides, Puntius sarana, P. ticto, P. sophore, Puntius sp., Chela laubuca, Colisa fasciata, Ctenops nobilis, Nandus nandus, Ambassis ranga, A. nama, Macrognathus aculeatus, M. armatus, M. pancalus , Gudusia chapra, Glossogobius giuris, Channa gachua, C. punctatus, C. striatus, C. marulius, Xenentodon cancila, Amblypharyngodon mola, Osteobrama cotio, Danio rerio, D. devario, Esomus danricus, and Salmostoma laubuca (Siddiqui et al. 2007a). These once common species are now threatened due to various anthropogenic interventions including pollution, climate change, and water diversion (see Table 17.3b for common names of fishes and their conservation status).

Prawns

Among the freshwater prawns, Macrobrachium rosenbergii, M. malcolmsonii, M. rude, M. lamarrei, and Palemon styleferus are important and common.

2.1.2 Case Study: Hakaluki Haor

Hakaluki haor (see Fig. 17.1 for Its Location) is a marsh wetland located in northeastern part of Bangladesh. It is the country’s largest inland freshwater wetland. From the wetland, 558 species of animal species have been recorded that includes 417 species of birds. Of 417 avifaunal species, 26 are threatened, two are vulnerable, 10 are endangered, and 14 critically endangered.Footnote 1 Hakaluki haor is a very important wetland for its wide variety of waterfowl, particularly Anatidae (IUCN and CNRS 2006) (see Table 17.4). A variety of snakes, turtles, frogs, and tortoises are gradually getting extinct (Nishat et al. 1993), (e.g., Black Soft-shell Turtle, Aspideretes nigricans, is now extinct).

Table 17.4 List of amphibians, reptiles, birds, and mammals reported from Hakaluki haor
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2.2 Tidal Saltwater Coastal Wetlands

These wetlands cover almost 25% of the land area of Bangladesh and include mangroves, saltmarsh, lagoons, deltaic islands, sand dunes and beaches, barrier islands, seagrass, and coral habitats. The major coastal wetlands are the Sundarbans mangrove forests, the Chakaria mangrove forest, Sonadia Island, Moheshkhali Island, and St. Martin’s Island (Fig. 17.1). These coastal wetlands support a rich diversity of plants and animals (see Sect. 17.2.2.1). These habitats are dynamic and are susceptible to change due to coastal processes, lack resilience, and have a low threshold to irreversible damage. The physical and ecological characteristics of these habitats make them especially vulnerable to degradation. Coastal wetlands are also important for fishery, water resources, agriculture/land resources, and biodiversity.

2.2.1 Biodiversity of Coastal Wetlands

The coastal wetland vegetation in Bangladesh consists of 35 angiosperm species, 26 dicots, and 9 monocots. Ipomoea pes-caprae, Ipomoea spp., Leucas aspera, Clerodendrum viscosum, and Argyreia nervosa are common creepers that act as sand binders in the primary dunes. The grasses in these dunes include Cynodon dactylon, Panicum repens, Cynodon sp., Paspalum scrobiculatum, P. vaginatum, Cyperus sp., and Fimbristylis sp. The mature inland dunes consist of trees, shrubs, and herbs; common ones are Phyllanthus reticulatus, Cassia tora, Clerodendrum inerme, Vitex trifolia, V. pubescens, Ziziphus mauritiana, Z. jujuba, Casuarina equisetifolia, Streblus asper, Pandanus odoratissimus, Calotropis gigantea, Porteresia coarctata, Myriostachya wightiana, Avicennia officinalis, A. marina, A. alba, Sonneratia apetala, Aegiceras corniculatum, Ceriops decandra, and Aegialitis rotundifolia.

Vegetation

The mangrove vegetation of Sonadia Island consists of 27 species. The common ones are Avicennia officinalis, A. marina, A. alba, A. corniculatum, C. decandra, A. rotundifolia, and Sonneratia apetala. Unlike mangroves of the Sundarbans, Nypa fruticans and Heritiera fomes are completely absent in Sonadia. Sonneratia griffithii, which was once common in the Chakaria Sundarbans (Chittagong), including Sonadia Island, is no longer available in other existing mangrove areas in Bangladesh. The population of Porteresia spp. at Sonadia Island is more salinity tolerant than any of its other land races along the central and western coast of Bangladesh. P. coarctata formerly classified as Oryza coarctata, a wild relative of rice, is native to the coastal saline areas of Bangladesh and eastern India. This species of brackish water is often used as a substitute for cultivated rice.

Seaweeds

Common genera of seaweeds in Bangladesh include Hypnea (red seaweeds), Ceramium (red seaweeds), Acanthophora (red seaweeds), Polysiphonia (red seaweeds), Sargassum (brown seaweeds), Dictyota (brown seaweeds), Ulva (green seaweeds), Sphacelaria (brown seaweeds), Padina (brown seaweeds), Chaetomorpha (green seaweeds), Enteromorpha (green seaweeds), Caulerpa (green seaweeds), and Halimeda (calcareous green seaweeds). Species of seagrasses reported from the coastal wetlands of Bangladesh include ocean turfgrass, Halophila beccarii, H. decipiens, H. pinifolia, and Halodule uninervis, and beaked tasselweed, Ruppia maritima and Spartina sp. (Hoq et al. 2012). A total of 154 species of marine algae (including seaweeds) were reported from St. Martin’s Island of Bangladesh (Thompson and Islam 2010).

Corals

The rocky subtidal habitat supports diverse coral communities, of which 39 species have been identified as hard corals (reef-building corals) and 14 species as soft. Living corals (coral bleaching, ocean acidification, and diseases may cause mortality of corals) include species of Porites, Favites, Goniopora, Cyphastrea, and Goniastrea. The soft corals include species of Sinularia, Lobophytum, Anthelia, Dendronephthya, Palythoa, Nemanthus, Telemectius, and Discosoma. Besides, four coral species of the genus Acropora (A. pulchra, A. horrida, A. humilis, and A. variabilis) were reported from neritic waters of the St. Martin’s Island. In addition, Stylocoeniella, Pocillopora, Stylophora, Porites, Pavona, Favia, Favites, Pseudosiderastrea, Goniastrea, and Montastrea were recorded. Taxonomy of a good portion of corals occurring around the island is yet unknown. St. Martin’s Coral Island is the only continental island in Bangladesh with coral communities.

Fishes

The ichthyofauna of the coastal wetlands of Bangladesh includes 492 species (422 species are bony fish and 70 cartilaginous). About 89 fish species are coral associated. Major fish species are listed in Table 17.5.

Table 17.5 Major fish species reported from coastal wetlands of Bangladesh
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Sharks, Skates, and Rays

70 species of sharks, skates, and rays (Haroon 2010) and at least seven species of edible oyster are reported from Bangladesh (Siddiqui et al. 2007b).

Shrimps

Commercial shrimp and prawn species of coastal wetlands of Bangladesh are Penaeus monodon (jumbo tiger shrimp), P. indicus (Indian white shrimp), P. semisulcatus, Metapenaeus monoceros (speckled/ginger shrimp), Parapenaeopsis sculptilis (rainbow shrimp), and Macrobrachium rosenbergii (giant freshwater prawn).

Crabs

Seven species of crabs have been reported from the coastal waters of Bangladesh (Siddiqui et al. 2007b).

Molluscs

Gastropods, like Conus striatus, C. textile, and C. geographus, are abundant. Two economically important Gastropods, Trochus niloticus and Turbo marmoratus, are also reported.

Reptiles (Turtles, Snakes)

Five species of marine turtle (Chelonia mydas, Caretta caretta, Lepidochelys olivacea, Eretmochelys imbricata, and Dermochelys coriacea) have been reported (Hussain and Acharya 1994). Other reptiles include Varanus salvator and the sea snakes Laticauda laticauda, L. colubrina, and Enhydrina schistosa. Altogether, coastal area supports 27 reptile species. Entire coastal beach of 710 km from the Sundarbans in the southwest up to Teknaf in the southeast and the St. Martin’s Island is particularly important as nesting area for marine turtles.

Birds

More than 200 species of birds have been recorded from coastal wetlands, of which 67 species are resident and 53 migratory. Major bird species are Amaurornis phoenicurus, Anhinga melanogaster, Eurynorhynchus pygmeus, Ardea cinerea, Dendrocygna javanica, Egretta alba, E. gularis, Gallicrex cinerea, Gelochelidon nilotica, Ixobrychus flavicollis, Glareola maldivarum, Himantopus himantopus, Ixobrychus cinnamomeus, Metopidius indicus, Nettapus coromandelianus, Phalacrocorax niger, Porphyrio porphyrio, Porzana fusca, Rallus aquaticus, Sterna albifrons, Sterna aurantia, Tachybaptus ruficollis, Vanellus malabaricus, V. indicus, V. spinosus, Anastomus oscitans, Gallinago stenura, G. gallinago, Calidris alba, Limnodromus semipalmatus, Halcyon coromanda, Chlidonias hybrida, Leptoptilos dubius, L. javanicus, L. dubius, Limnodromus semiplamatus, and Tringa guttifer. St. Martin’s Island is particularly an important wintering area for a wide variety of migratory shorebirds, gulls, and terns. This island supports two globally threatened birds Vanellus cinereus and Sterna acuticauda and two marine mammals Sousa chinensis and Neophocaena phocaenoides. Common avian migrants and winter visitors are Anas acuta, Pluvialis dominica, Charadrius dubius, C. alexandrinus, C. hiaticula, C. mongolus, Numenius phaeopus, N. arquata, Tringa totanus, T. nebularia, T. stagnatilis, T. guttifer, Gallinago stenura, G. gallinago, Calidris alba, Chlidonias hybrida, Larus ridibundus, Philomachus pugnax, Sterna hirundo, Anastomus oscitans, Threskiornis melanocephalus, Pseudibis papillosa, Anser indicus, A. anser, Haematopus ostralegus, Calidris tenuirostris, Larus ichthyaetus, L. brunnicephalus, Rynchops albicollis, Eurynorhynchus pygmeus, Limnodromus semipalmatus, and Haliaeetus leucogaster.

Mammals

Important terrestrial mammal species include Canis lupus, Cuon alpinus, Catopuma temminckii, Neofelis nebulosa, Pardofelis marmorata, Melursus ursinus, Ursus thibetanus/Selenarctos thibetanus, Prionailurus viverrinus, Amblonyx cinerea, Lutrogale perspicillata, and C. hispidus (Khan 1986). Dolphins include Platanista gangetica, Sousa chinensis, and Neophocaena phocaenoide.

2.2.2 Case Study: Sundarbans Mangrove of Bangladesh

The Sundarbans, the largest continuous natural mangrove forest in the world, is located at the southern extremity of the Ganges river delta, i.e., bordering the northern margin of the Bay of Bengal spreading over the southern part of Bangladesh and West Bengal, India. The Sundarbans mangrove forest covers an area of about 10,000 km2 of which 62% falls within the territory of Bangladesh, while the remaining (38%) area belongs to West Bengal, India. Of the total area, approximately 70% is lands. This forest has been managed for more than a century (Curtis 1933). At present the forest is divided almost in a north-south direction into polyhaline (>10 ppt), mesohaline (≥5–10 ppt), and oligohaline (<5 ppt) zones. This happened since 1982 due to Farakka Barrage in West Bengal, India. The Sundarbans occupies a flat deltaic swamp rarely exceeding 0.9–2.1 m above mean sea level, with a maximum of 10 m amsl. It is generally tidally flooded on a twice-daily basis with most of the area being under water during the high spring tides of the monsoon. Some parts of the mangroves are characterized by the presence of acid sulfate soils, especially in the Chakaria mangroves of Chittagong. The World Heritage Convention (WHC) declared Sundarbans as the natural and cultural site of outstanding universal value. Over 3.5 million people live within 20 km boundary of the Sundarbans mangrove forest (SMF) and are directly or indirectly dependent on its fisheries resources (Hoq 2008; Kibria 2014).

Mangrove ecosystem is a suitable feeding, breeding, and nursery ground for several marine, estuarine, and freshwater species. The intermingled root system of the mangrove acts as a coastal stabilizer and binders of sediment, thus aiding in preventing erosion in the mangrove areas (Hoq 2008; Hoq and Haroon 2012). The name “Sundarbans” is due to the dominance of the plant Heritiera fomes, locally called as Sundari gach. Other major plant species are H. littoralis, H. minor, Excoecaria agallocha, Xylocarpus granatum, X. mekongensis, X. moluccensis, Bruguiera conjugata, B. gymnorrhiza, Sonneratia apetala, S. caseolaris, Avicennia officinalis, Ceriops decandra, C. tagal, Aegiceras corniculatum, A. corniculatum, Rhizophora mucronata, R. apiculata, Pandanus tectorius, Poresia coaractata, Myriostachya wightiana, Phoenix paludosa, Cynometra ramiflora, Hibiscus tiliaceus, Imperata cylindrica, Phragmites karka, and Nypa fruticans. Since 1989, timber extraction has been banned in order to conserve the natural resources, although exemptions have been made for the harvest of some species for poles, sawlogs and hardboard (e.g., H. fomes), pulpwood (E. agallocha), thatching material (N. fruticans), and some non-timber species for fuelwood. While mangrove formation of the St. Martin’s Island is quite different from other mangroves in the country in that, it is a pure Lumnitzera racemosa formation (large shrubs or small trees up to 8 m tall, locally known as Kirpa).

The Bangladesh Sundarbans supports diverse biological resources including at least 150 species of commercially important fishes, 270 species of birds, 42 species of mammals, 35 reptiles, and eight amphibian species. This represents a significant proportion of the species present in Bangladesh (i.e., about 30% of the reptiles, 36% of the birds, and 34% of the mammals) and includes a large number of species that are now extinct elsewhere in the country. Two amphibians, 14 reptiles, 25 aves, and five mammals are at present endangered. The Sundarbans is an important wintering area for migrant water birds and is an area suitable for watching and studying them. Eighteen snake species including Ophiophagus hannah, Naja sp., Python molurus, green vine snake, checkered keelbacks and rat snakes, vipers, and sea snakes are reported. Monitor lizards found are Varanus bengalensis, V. flavescens, and V. salvator.

Waterways of the Sundarbans mangrove forest are now considered as the global “hot spot” of endangered Gangetic river dolphin, Platanista gangetica gangetica, and Irrawaddy dolphin, Orcaella brevirostris (Fahrni et al. 2008). Although there is no global population estimate for either species, both have disappeared from major portions of their range. However, both species occur in the Sundarbans in sufficient numbers that it may serve as a global safety net for preventing their extinction. Besides, world’s second largest documented population, about 1,144 individuals of Indo-Pacific bottlenose dolphin, Tursiops aduncus, lives at the northern tip of the Swatch of No Ground in the Bay of Bengal, Bangladesh (Smith et al. 2008, 2010).

The varied and colorful birdlife includes about 315 species including 95 species of waterfowl and 38 species of raptors (Sarker 1985). Most readily seen are no less than nine species of kingfisher, including Pelargopsis amauropterus, P. capensis, Haliaeetus leucogaster, and Ichthyophaga ichthyaetus; raptors, the globally threatened Leptoptilos javanicus, Heliopais personatus, Pandion haliaetus, and Ichthyophaga ichthyaetus; herons; egrets; storks; sandpipers; whimbrel; curlew; and numerous other waders are seen along the muddy banks and on the chars or sandbanks. There are many species of gulls and terns, especially along the coast and the larger waterways. Apart from those species particularly associated with the sea and wetlands, there is also a considerable variety of forest birds such as woodpeckers, barbets, shrikes, drongos, mynahs, minivets, babblers, and many others (Salter 1984; Scott 1991).

The area is famous for the eponymous flagship species Royal Bengal tiger (Panthera tigris tigris) and leopard (Panthera pardus fusca), apart from the numerous faunal species. It is estimated that there are now about 500 Royal Bengal tigers and about 30,000 spotted deer in the area. In addition, there are several other threatened mammal species, such as the capped langur (Semnopithecus pileatus/Trachypithecus pileatus) (Vulnerable or VU), smooth-coated otter (Lutrogale perspicillata) (VU), Asian small-clawed otter (Aonyx cinereus) (VU), and large Indian civet (Viverra zibetha) (NT). The eco-region also harbors several smaller predators such as jungle cat (Felis chaus), fishing cat (Prionailurus viverrinus), leopard cat (P. bengalensis), Javan rhinoceros (Rhinoceros sondaicus), Indian rhinoceros (R. unicornis), water buffalo (Bubalus bubalis), C. duvauceli, and gayal (Bos frontalis, A. porcinus). Other mammals include chital/spotted dear (Cervus axis/Axis axis), barking deer (Muntiacus muntjak), wild boar (Sus scrofa), saltwater crocodile (Crocodylus porosus), mugger (C. palustris), gharial (Gavialis gangeticus), common gray mongooses, foxes, jungle cats, flying foxes, and pangolins.

3 Significance of Wetlands

3.1 Significance of Wetlands as Biodiversity “Hot Spots”

About 400 species of vertebrates and 300 species of plants in Bangladesh are solely dependent upon the wetlands for their life or a part of it. About 260 species of freshwater fish live in the wetlands and are the main source of daily protein supplement (70%) in the country. The deepwater rice or floating rice had been the main source of food supplement in those areas before the introduction of high-yielding varieties (HYV) in the 1960s. It is widely believed that Bangladesh’s aquatic diversity has not yet been adequately described. At any rate, the known levels of endemism in the Ganges-Meghna-Brahmaputra (GMB) basin are very high, 25% of the aquatic species found in this basin being endemic. Indigenous fish and prawn residents in wetlands of Bangladesh move into the floodplains to reproduce, and their offsprings use the wetlands for feeding and growth. Similarly, catadromous freshwater giant prawn (M. rosenbergii) and others needing an estuarine environment to reproduce migrate to the coasts from the rivers. Postlarvae of freshwater giant prawn again migrate upstream into the freshwater rivers and then laterally move into the floodplains to feed and grow. At the end of the flood season, fish and prawn on the floodplains move, with the receding waters, back into deeper permanent water bodies such as rivers, canals, and beels to survive through winter and dry season. They become the mother fishery stock to breed and multiply in the inundated floodplain in the following monsoon. In addition, several species of freshwater mussels and snails also occur in the floodplains. Several species of freshwater mussels bear pink pearls. Mussel/snail shells are also used to make lime for use with betel leaves and nuts. Snails are harvested to use their meat for feeding the freshwater giant prawn under cultivation. The country supports 650 species of birdsFootnote 2 within an area of 144,000 km2. This represents about 30% of the total number of bird species recorded from the entire Indian subcontinent and over 7% of the globally known bird species. The Assam plains in eastern Bangladesh are identified as Endemic Bird Area (EBA) by BirdLife International with the status of “urgent conservation priority.”

3.2 Significance of Wetlands as Livelihoods of People

Poorer section of the society near any wetland depends totally on the goods and services of the wetland for livelihood. The rich biodiversity in wetlands of Bangladesh (as discussed in Sects. 17.2.1 and 17.2.2) contributes significantly to diversify livelihoods of people. It is estimated that about two-thirds of people living in rural Bangladesh (mostly poor) depend on wetlands for a variety of purposes such as water for drinking, irrigation, food production (agriculture, aquaculture), fishing (fish, prawn, crabs), livestock grazing/fodder, bird hunting, medicines, snail, honey, vinegar, glue, wax, firewood, timber, thatching materials, harvesting grasses and seaweeds, and tourism/recreational business (Islam 2010; Kibria 2014). It has been estimated that over 60 million people are dependent on aquatic resources every day in Bangladesh, of which about a million are full-time and part-time fisher folk. The fishery and agriculture sectors employ 5% and 64.5% of the country’s total workforce, respectively.Footnote 3 Over 500,000 fishers are involved in catching hilsa, and over 2,000,000 people are indirectly involved in the distribution and sale of the fish and other ancillary activities such as net and boat making, ice production, processing, and export.Footnote 4 About 600,000 people are employed directly in shrimp aquaculture in Bangladesh that supports approximately 3.5 million dependents.Footnote 5 The Sundarbans alone provides livelihood and employment to an estimated 112,000 people (http://iucn.org/about/union/commissions/ceesp/?21654). Out of 3700 people on St. Martin’s Island, most are fishermen depending solely on fishing, shrimp fry collection, fish drying, exporting dry seaweeds, agriculture, and ecotourism business (Thompson and Islam 2010). About 200,000 people depend on resources of Hakaluki haor for agriculture (rice, oil seeds, pulses), fishing, duck rearing, cattle grazing, fish culture/aquaculture, snail collection, bird hunting, fuelwood collection (reeds), and sand extractionFootnote 6 (Islam 2010). Tanguar haor supports livelihood for more than 60,000 people (agriculture, commercial fishing, and trade in fuelwood, hunting/trapping waterfowl, the harvesting and sale of grasses and reeds, and coal collection). The principal activities of people living in Tanguar haor are agriculture (36.78%), fishing (21.56%), day labor (21.07%), business (7.55%), sand and coal collection (3.4%), and others (9.8%) (Alam et al. 2012). A significant number of people are employed in waterway transportation and ecotourism associated with wetlands across Bangladesh; but there is no statistics available on this.

3.3 Significance of Wetlands as Source and Sink of Greenhouse Gas

Wetlands used for rice farming (in waterlogged areas) emit significant quantities of methane (Yan et al. 2003). Dams/reservoirs emit GHG (greenhouse gas: methane, carbon dioxide) in several ways, from breakdown/decomposition of soil and plant carbon (by bacteria) and anaerobic conversion of organic carbon to methane and rotting/decay of vegetation at the bottom of dams/lakes (Bates et al. 2008). Though wetlands such as lakes/reservoirs are important sources of GHG emissions, they also provide an important role in climate change mitigation, for example, by exporting C and N, as fish biomass in fisheries and aquaculture. Afforestation, reforestation, and mangrove restoration remove CO2 from the atmosphere and act as carbon sinks (carbon sequestration). Mangrove forests store more carbon than any other tropical forests. In particular, mangrove-sediment stores about five times more carbon (Stecker and Wire 2012). Thus, restoration of mangrove forest would be an environment-friendly solution for mitigating climate change or global warming. Wetland systems have significant quantities of carbon stored in the vegetation and soil and hence have received increased attention for playing an important role to reduce GHG emissions (Box 17.1). As wetland soils are saturated with water creating an environment low in oxygen, the carbon that is sequestered is buried remaining relatively stable without decaying. When drained, such as through development, conversion to agriculture, or aquaculture, the carbon in the soil is exposed and oxidized, and that releases the stored carbon as CO2 into the atmosphere.

Box 17.1 Why Wetlands Are a Good Carbon Sink? (Lehmann et al. 2006)

  • Only 6% of the world’s land is wetlands and about 14.5% of the world’s soil carbon is found in wetlands.

  • Coastal wetlands (salt marshes, mangroves, and seagrass beds) can store large quantities of carbon. Some of the carbon that wetland plants capture gets added to soils either via internal transport in the plant or as plant parts, such as leaves and roots, which die and become incorporated into the soil.

  • Since wetland soils are largely anaerobic (without oxygen), carbon that is incorporated into the soils decomposes very slowly and can persist for hundreds or even thousands of years. Decomposition of organic plant material is much slower when oxygen is not present, so the carbon present in this plant material remains intact, rather than being broken down by microbes and respired back to the atmosphere. As a result, wetlands are very good carbon sinks (i.e., wetlands store a lot of carbon).

3.4 Significance of Wetlands in Disaster Mitigation

Wetlands such as mangroves play an important role in the protection of the coast from natural and climate change-related disasters (cyclones, storm surges, tsunamis, rise in sea level). Wetlands could act as a barrier (live seawalls) against disasters and help minimize damage to property and life. In India, the Philippines, and Vietnam, people have been protected and suffering less damage to lives and property from disasters like tsunamis, cyclones, and other natural disasters in locations where mangroves were intact (shielded with dense forest). On the contrary, people suffered extensively in locations where either mangroves were lost, cleared, or absent or mangroves have been converted to shrimp farms (MSSRF 2005). Bangladesh frequently experienced extreme cyclones, viz., Bhola cyclone 1970, Bangladesh cyclone 1991, Cyclone Sidr 2007, and Cyclone Aila 2009.

4 Conclusion

Wetlands provide a wide range of economic, social, and ecological benefits. Wetlands of Bangladesh are “lifeblood” since two-thirds of people (mostly poor) depend on wetlands for water, agriculture, aquaculture, fishing, wild food, medicines, fuelwood, furniture wood, honey, thatching materials, bird hunting, sand extraction, river transportation, and ecotourism business. Apart from biodiversity and livelihood support, wetlands of Bangladesh provide other ecosystem services such as flood control (store excess water), climate change mitigation (forests and wetland sediments as carbon sinks), and disaster mitigation (mangrove acting as live walls to reduce impact of cyclones, tsunamis). However, wetlands of Bangladesh and its ecology and biodiversity are under increasing threats due to pollution (pesticides, metals), climate change (rise in sea level), population increase, conversion and drainage of wetlands for agriculture and development, deforestation, irrigation and flood control projects, water diversion, nature siltation, overexploitation of resources (fish, water birds, plants), overgrazing by livestock, and transboundary water regulation.

Conservation, restoration, afforestation, and management of wetlands would be vital since a healthy biodiversity-rich environment is more resilient to climate and environmental shocks and various other stresses. In addition, livelihood diversification, awareness, and education of local communities on preservation and conservation of wetlands are needed to reduce pressure on wetland resources. Community-based participatory wetland resource management (bottom-up approach) looks good for conserving wetland biodiversity and aquatic resources and is being followed in Bangladesh since long. But this would not be just enough without comprehensive policies, strategies, and management plans combining political, economic, social, and technological approaches to prevent further degradation of wetlands.