Thursday 21 Jan 2021

Sea-level rise is dangerous for mangrove forests

Increased combustion of fossil fuels likely to influence their composition

Sea-level rise is dangerous for mangrove forests

Mangroves are the only forests on the earth where land, freshwater and saltwater mix. They occupy less than one per cent of the world’s surface and are mainly found in the tropical and subtropical coasts covering an estimated 75 per cent of the coastline in 123 countries. The mangrove forests can be recognized by their dense tangle of prop roots that make the trees appear to be standing on aerial roots or pneumatophores that allow oxygenation of roots in hypoxic soils; and salt exclusion/excretion to cope harsh environmental conditions such as high salinity and temperature. Though they occupy only 152362 sq km areas of the world, mangroves are one among the most productive ecosystems on the earth.  There are about 80 species of mangroves and many associated species worldwide, and about 16 species and few associate species are found in Goa.

The intricate root system of mangroves makes their habitat attractive to terrestrial, estuarine and marine species (crustaceans, and shellfish) and other organisms seeking food and shelter from predators, and creates a barrier against storm and flood, prevent encroaching seas from gobbling up more land. On top of that, mangrove forests are even better at sequestering carbon dioxide from the atmosphere than rainforests of the same size. Their dense root systems trap sediment flowing in the rivers from land, thereby stabilizing the coastline and preventing erosion from waves and storms.

Mangroves serve as both a source and a sink for nutrients and sediments. Their roots are widely used in the treatment of malaria, diarrhoea, snake bites, ulcers, and skin infections. Due to increased combustion of fossil fuels, more greenhouse gas concentration is pushing up air temperature which is predicted to increase by about 4.8°C by 2081–2100 relative to 1986–2005.

This increase is likely to influence mangrove species composition, phenology, productivity, and ultimately the latitudinal range of their distribution. At present, mangroves forests are latitudinally confined by a minimum air temperature of 16° C. Temperature influence the ability of mangroves to assimilate carbon dioxide as a result of the limitations to biochemical reactions. Higher temperatures will increase evaporation rates, which would result in salinity increases; the synergistic impacts of salinity and aridity can influence species diversity, size, and productivity of mangrove forests. According to research published in Science, mangrove forests will be in danger of dying out when sea levels rise by more than 6 millimeters per year. Presently the sea level trend is 3.4 mm per year in comparison, the trend of about 1.8 mm per year during the 20th century. In fact, due to the rapid warming, this rate is projected to increase up to 5 mm per year over the next few decades, and reach 10 mm per year by 2100. So if their roots are completely submerged for too long, the mangroves will perish. This poses a major threat not only to mangroves, but also most species near the coasts, including humans. The mangroves can more or less survive as long as the sea-level rise is limited to 5 mm, which translates to 0.2 inches per year. But this scenario is only possible if low emission of greenhouse gases is maintained. If the sea levels rise by 6 mm per year, mangroves will disappear by 2050, the research warns. Governments should devise solutions to keep sea-level rise below that threshold to mitigate climate change and to protect millions of people who depend on mangroves for shelter, flood protection, etc. Switching to renewable sources of energy - clean energy generated from natural sources -could help in the long run to mitigate climate change. That means cutting back on fossil fuels and giving mangroves more time and space to adapt to the changing climate. 

(The writer is a scientist and researches global climate) 

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