Lagoons of Sri Lanka: from the origins to the present

Abstract

Sri Lanka, an island in the Indian Ocean, has lagoons along 1,338 km of its coastline. They experience low-energy oceanic waves and semidiurnal microtidal currents. The Sri Lankan coastal lagoons are not numerous but they are diverse in size, shape, configuration, ecohydrology, and ecosystem values and services. The heterogeneous nature, in general, and specific complexities, to a certain extent, exhibited by coastal lagoons in Sri Lanka are fundamentally determined by coastal and adjoining hinterland geomorphology, tidal fluxes and fluvial inputs, monsoonal-driven climate and weather, morphoedaphic attributes, and cohesive interactions with human interventions. Most coastal lagoons in Sri Lanka are an outcome of mid-Holocene marine transgression and subsequent barrier formation and spit development enclosing the water body between the land and the sea. This process has varied from one coastal stretch to another due to wave-derived littoral drift, sediment transport by tidal fluxes, fluvial inputs and wave action or, in other words, sea-level history, shore-face dynamics and tidal range as the three major factors that control the origin and maintenance of the sandy barrier, the most important features for the formation and evolution of coastal lagoons with their landward water mass. In certain stretches of Sri Lanka’s coastline, formation of the barrier spit was very active due to shore-face dynamics that resulted in chains of shore parallel, elongated lagoons. They are among the most productive in terms of ecosystem yield and show some similarities to large tropical lagoons with respect to sea entrance, zonation, biodiversity and ecosystem services. However, some of them become seasonally hypersaline due to lack of freshwater input and high evaporation. Functions and processes of some of these water bodies are fairly known.