Earth’s coastal wetlands disappearing, new Aberystwyth University maps reveal

Four thousand square kilometres of the world’s tidal wetlands have been lost over twenty years, but ecosystem restoration and natural processes are helping reduce total losses, according to Aberystwyth University researchers.

An international group’s analysis of more than one-million satellite images shows that global change and human actions are driving rapid changes of tidal wetlands.

The global intertidal change data indicates that 13,700 square kilometres of tidal wetlands — tidal marshes, mangroves and tidal flats – were lost around the world, offset by gains of 9,700 square kilometres. This meant there was a net loss of 4,000 square kilometres over the two-decade period, between 1999 and 2019.

Over one billion people now live in low-elevation coastal areas, and are vulnerable to losses of these wetlands, including through disruption of ecosystem services, such as biodiversity and coastal protection.

Professor Richard Lucas from Aberystwyth University said: “Tidal wetlands are of immense importance to humanity, providing benefits such as carbon storage and sequestration, coastal protection, and fisheries enhancement. Global-scale monitoring is now essential if we are going to manage changes in coastal environments effectively.

“Efforts to estimate the current and future status of tidal wetlands at a global scale are hindered by uncertainty about how they respond to drivers of change. Along with colleagues in Australia, we wanted to address that and provide a basis for conserving coastal ecosystems.

“To do this, machine-learning analysis of vast archives of historical satellite images was undertaken to detect the extent, timing and type of change across the world’s tidal wetlands between 1999 and 2019.

“The analysis found 27 per cent of losses and gains were associated with direct human activities, such as conversion to agriculture and restoration of lost wetlands.

“All other changes were attributed to indirect drivers such as human impacts to river catchments, extensive development in the coastal zone, coastal subsidence, natural coastal processes and climate change.”

‘Rapid change’

About three-quarters of the net global tidal wetland decrease happened in Asia, with almost 70 per cent of that total concentrated in Indonesia, China and Myanmar.

Dr Nicholas Murray, Senior Lecturer at Australia’s James Cook University, led the study. He added: “Asia is the global centre of tidal wetland loss from direct human activities. These activities had a lesser role in the losses of tidal wetlands in Europe, Africa, the Americas and Oceania, where coastal wetland changes were primarily caused by indirect factors such as wetland migration, coastal modifications and catchment change.”

The scientists found that almost three-quarters of tidal wetland loss globally has been offset by the establishment of new tidal wetlands in areas where they formerly did not occur – with notable expansion in the Ganges and Amazon deltas.

“Most new areas of tidal wetlands were the result of indirect drivers, highlighting the prominent role that broad-scale coastal processes have in maintaining tidal wetland extent and facilitating natural regeneration,” Dr Murray added.

“This result indicates that we need to allow for the movement and migration of coastal wetlands in the future to account for rapid global change.”