Ecological Succession of Wetlands: A Review of the Current Scenario

Background

Wetlands are regions in which land either remains covered by water, or hydrated throughout the year or for varying periods. They are characterized by varied life forms. Wetlands are intricately related to human civilization down the ages with major ancient settlements growing near a sustainable water source in the form of river or adjoining wetlands. The Mesopotamian civilization is recorded as the oldest civilization established 4000 years ago in the fertile region between Tigris and Euphrates (Morrisson et al., 2021). In Nile Valley, another ancestral civilization emerged in 3200 BC indicating the importance of water. The inhabitants of these regions are evidence of significance for biotic diversity, and thus prove that the wetlands are a very crucial ecosystem and are the most fertile habitats.The sunderbans form a distinctive wetland in the gangetic delta situated in the present day India and Bangladesh. They form the largest contiguous forested wetland in he world and covers about 10,000 square kilometres. Aside from the multilayered forest, the Sundarban has freshwater, brackish, and saline marshes, rice fields, and shrimp farms. The Sundarbans, which are extraordinarily rich in biodiversity, are the Royal Bengal tiger's sole known mangrove habitat (Gopal and Chauhan, 2018). A continual supply of sediment from the Mekong River keeps the Mekong Delta, one of South East Asia's Cenozoic river deltas, afloat. Natural inland wetlands constitute roughly 7% of the total area of the Vietnamese Mekong Delta (VMD), and are mostly restricted to regions of closed floodplains and back swamps due to broad-scale land use change (Quan et al., 2018). The Vietnamese Mekong Delta has a wide variety of wetlands, ranging from coastal systems like tidal flats, sandy ridges, and tidal back swamps to river floodplain areas like large depressions, peat swamps, and alluvial levees (Dinh, 2016). The Mahanadi delta also forms a wetland in Odhisha. Wetlands largely in the form of small fresh waterbodies evolved as depressions on both flanks of the Mahanadi and Brahmani rivers in the upper delta region, which has a fanning distributary system with intervening alluvial plains. Wetlands typically exist in the form of floodplains linked to active river channels as well as paleo-channels in the central delta, which has primarily clayey soil. Transient wetlands in the alluvial floodplain zones are also found in the central delta. Water and sediment distribution patterns within the delta have been considerably affected by extensive hydrological fragmentation and landuse changes, as well as a loss of connectivity between river channels and floodplains. Between 1975 and 2010, the wetland area decreased by at least 32% due to a variety of stresses (Kumar and Patnaik, 2016).The wetlands are different from other terrain or marine forms concerning their typical foliage of water flora (Butler, 2010) and their adaptation to distinctive hydric soil. They are formed when the water is in proximity to the land surface or where the land is covered by water (Ramsar Convention, 2018) and these are an exceptional ecosystem whose conservation is a global concern; and thus formed the Ramsar International Convention in 1971.

Wetlands imitate diverse behavioral responses to the surroundings since they are widely dispersed from polar to arid zones, peatlands, rivers coral reefs, deltas, lakes, rivers, mangroves, marshes, overflowing forests, and are intermediary regions between marine and terrain environments. Thus, when wetlands are classified, differences occur. Depending upon the water quantity, they are categorized into permanent or seasonally flooded; while construction style divides wetland into natural and man-made. However, factors like physical, chemical, habitat differences, topography, abiotic and biotic surroundings, and quality of sediment decide the role and classification of the wetlands (Finlayson and Spiers, 1999). Wetlands play a pivotal role in hydrology, distillation of water, water retention, dispensation of carbon and other nutrients, shoreline stabilization, and sustain an ecosystem. The performance of the function depends on specific features of that particular wetland, terrain, and aquatic bodies close to it (Dorney et al., 2018). Wetland loss occurs for a variety of reasons, namely urbanization, pollution, reduced biotic diversification, invasive species, terrain deprivation, and changes in climate. Multidisciplinary perception in basic and social sciences has proved effective for the evaluation of wetlands. The management reforms and its implementations of their capacity to absorb the majority of atmospheric carbon are considered to be approximately more than five times as compared to tropical forests; thus wetlands pave their way in betterment of future climate (Davidson, 2014; Sizo et al., 2015; Barros and Albernaz, 2014; Meng et al., 2016).