Sea-level rise, coastal salinity and vegetation changes in Sri Lanka

Sea-level rise is a key component of many climate change scenarios. Such increases are expected to cause greater coastal inundation by seawater, reduce the depth of the freshwater-saline water lens and have a range of consequences for coastal ecosystems. Soil salinity determines the distribution patterns of coastal vegetation across a sea-to-land gradient, and sea-level rise would be expected to alter these distributions. Our study done along the east coast of Sri Lanka shows that soil salinity decreases predictably from sea to land, varying between 21‰ and 30‰ over a distance of 50 m from the mean high water springs level. Soil salinity also showed declines with increasing soil depth (0, 10, 50 cm) although this was marginally non-significant. The emergence of terrestrial vegetation coincided with a cross-shore ecotone where the soil salinity approached 0‰. Our predictions suggest that if the mean sea-level were to increase by 1 m in the Batticaloa region (Sri Lanka), this would cause landward communities to be inundated with brackish water at various depths. The present permanent coastal vegetation front would likely shift landward by 30–45 m under scenarios involving a 1 m increase in sea level. Sea-level rise and its consequences could result in a variety of changes to coastal vegetation such as altered physiognomy and diversity, colonization of new territory, expansion of salt-tolerant species such as mangroves and saltmarsh and will therefore greatly influence adaptive management and future planning. This article is part of the theme issue ‘Developing resilient energy systems’.