irrigation, including canals, small sprinkler systems and paddy fields.
4 Seasonally flooded agricultural land, including flood river bed, meadows and pasture lands.
5 Salt exploitation sites; salt pans, salines, etc.
6 Water storage system over 8 ha; reservoirs/barrages/dams/impoundments.
7 Excavations; gravel/brick/clay pits; borrow pits, mining pools.
8 Wastewater treatment area including sewage farms, settling ponds, oxidation basins, etc.
9 Canals and drainage channels, ditches.
1.2 Importance of Wetland Ecosystem
Wetlands are vital for human prosperity and regulating the environmental system. Since the beginning of human civilization on this planet earth, wetlands have been a lifeline for human civilisations. Civilizations have flourished mainly along the periphery of the wetland ecosystems. The wetlands are ecosystem stems; they serve a range of purposes for the well‐being of humans and support the natural flow of ecosystem system, such as management and monitoring of the natural ecological and environmental processes (Figure 1.1). The regulatory system is essential for the protection of the human and planet health (Schuyt and Brander 2004). Wetlands are considered to be natural surface water and groundwater purifiers, water rechargers, recyclers of nutrients and human waste. They are essential to protect watersheds, to monitor climate and disasters such as floods, droughts, ecosystems for rich biodiversity, to stabilise shorelines, to desynchronize flood flows to constitute a major source of carbon sinks etc. (Kusler et al. 1994; Kraus 1995). Environment roles arise from a range of biological and physical interactions and interdependence of the socio‐ecological system. The wetland systems are a class of land cover that is ecologically fragile and highly susceptible to anthropogenic pressure and climate change. Through potential or close potential evapotranspiration, wetlands directly influence the global and local/regional ecosystems by exchanging water, heat and energy with surrounding as well as regional atmosphere composition and climate (Fan et al. 2010). Russi et al. (2013) observed that wetlands get engaged in the global biogeochemical cycle through greenhouse gas emissions and carbon dioxide sequestration and indirectly influence the environment from local to global scale. The collaborative environment of biological and geochemical processes in the wetlands contribute to emission of greenhouse gases. The wetlands systems are the largest source of methane (CH4) in the world, and the only one dominated by the atmosphere (Prigent et al. 2001; Bousquet et al. 2011). Many of these tasks are often essential for individuals, directly or indirectly, and are therefore continually influenced by human activities (Reis et al., 2017 & 2019).
Figure 1.1 Ecosystem services from wetlands system
Source: Ramsar Convention (2018) and Gardner and Finlayson (2018) © Ramsar Convention Secretariat.
Wetlands are resourceful for humankind as they perform many significant functions. Wetlands are essential for the provision of ecosystem system services for human beings' and they are survival and safeguard of the natural ecosystems. Wetlands system are world's most biological productive ecosystems and account for 47% of the global ecosystem's value. They provide essential tangible and non‐ecosystem services for biotic and abiotic components of the environment (MEA 2005; Russi et al. 2013). Wetlands, including natural and artificial wetlands, ponds, rivers, swamps, marshes, peatlands, mangroves, and coral reefs, are major sources of ecosystem services and contribute in regulating the ecological system and people's livelihoods. Wetlands are also known as “the kidney of the earth system” and believed to be the cradle of animals and plants. The wetlands are the most biologically diverse ecosystems and act as source and purifier of water on earth. Wetlands can filter pollution from the water and remove toxins and pollutants from the aquatic system due to their high and long‐term capacity to filter pollution from the water. These wetlands are helping to protect humanity by conserving natural resources from natural hazards like floods, droughts and many other disasters. Wetlands are the major storehouse of carbon than any other system and the production of food, fibre and ecotourism services (Mitsch and Gosselink 2000; Keddy 2010; Junk et al. 2013).
Since 1970, more than 35% of the wetlands have been lost which is more than three times greater than forest loss (Global wetlands Outlook‐2018). In controlling the hydrological process, wetlands play a vital role. The wetland systems regulate the movement of water supply, replenish groundwater, purify surface water, underground water, and manage and monitor the hydrological cycle phase. The ecology of wetlands plays a crucial role in well‐being of human beings and all other species of flora, fauna, climate change adaptation, biodiversity conservation, hydrology and soil conservation, and protection of the health of the planet (Ramsar Convention Bureau 2001). Centred on the principle of conventional medical practices and providing help for human health, 80% of the world's population relies primarily on health care services in these wetlands.
Wetlands are universally considered to be one of the primary natural pools of greenhouse gas methane (CH4) emission as they contributing 20–40% of the total annual emissions to the atmosphere, which adds a robust radiative forcing from CH4 (Bousqet al. al. 2011; Qin et al. 2014). Wetland ecosystem plays an extremely significant part in influencing the global climate system by biogeochemical feedback mechanisms (Seneviratne et al. 2010; Fisher et al. 2011).
1.3 Spatial Distribution and Potential of Global Wetlands
Globally, wetlands spread from the tropics to the tundra region across all climatic zones and are the most productive and vital habitats (Mitsch and Gosselink 1993). The spatial distribution of global wetlands might have occurred before the establishment of human civilization. Understanding the global distribution of wetlands will help to promote our understanding of the sustainable growth of wetlands, help in improving the wetlands, and the decision‐making processes to preserve and protect this important part of the ecological system. Globally seasonal inland wetlands account for about 6% of the world's terrestrial area, and about 89% of them are unprotected (as specified by IUCN I–VI and Ramsar protected areas) and provide <40 % of the global Species (Ramsar 2001; Mitra et al. 2003; Reis 2017).
Global wetland area range from 0.54 to 21.26 million km2, and the class‐specific spatial consistency of wetlands is less than 1% (Shenget et al., 2016). Ecologically wetlands, natural or artificial, represent one of the planet's most valuable and vital parts of ecosystems and are also one of the most vulnerable and threatened natural resources. As per the Global Wetland Outlook: state of the world's wetlands and their services to people Ramsar Convention 2018, “The most recent estimate of global inland and coastal wetland area is more than 12.1 million km 2 , an area almost as large as Greenland. Of this, 54% is permanently inundated, and 46% seasonally flooded. An estimated further 5.2 million km 2 are intermittently or occasionally inundated, but this is believed to include areas of formerly converted wetlands affected by extreme storm events. Approximately 93% of wetlands are inland systems, with 7% marine and coastal – although this coastal estimate does not include a number of wetland groups, such as near shore sub tidal wetlands, which also fall under the Ramsar definition. Global wetland areas are small in comparison: wetlands occupy an estimated 0.3 million km2 and rice paddy 1.3 million km2 (Davidson et al. 2018; Davidson and Finlayson 2018). The size of the global wetlands has increased considerably since the 1980s, primarily due to advancement in remote sensing, geographical information system tools and mapping methods but there has not been an increase in the actual size of the wetlands (Davidson et al. 2018). The largest wetlands region at the continental level are distributed in (Figure 1.2) Asia (32%), North America (27%) and Latin America &