Research Warns of Wetland Wipeout
A new study published in prestigious Nature Communications has found that the world’s coastal wetlands, which have existed for thousands of years, may now have the same average life expectancy of a human being - approximately 80 years.
Led by the University of Newcastle’s (UON) Dr Jose Rodriguez and Associate Professor Patricia Saco, the new study factors in for the first time, the role of attenuation (the ability of man-made structures to restrict the flow of water), predicting a decay far quicker than previously expected of coastal wetlands as sea levels rise.
Dr Rodriguez said the new model predicts a 50% increase in the velocity at which wetlands will disappear.
“Under a high sea-level rise scenario, most wetlands of South East Australia within a 1km coastal fringe will disappear due to submergence in about 80 years,” said Dr Rodriguez.
A New Model
Until now, scientists have used what is known as the ‘bathtub’ model to predict how sea level rise will affect coastal wetlands. The bathtub model assumes that, like a bath, water flows in and out of a wetland with no disruption.
Dr Rodriguez explained that man-made structures upset the movement of tidal waters and significantly increase a wetland’s vulnerability to sea level rise.
“Attenuation is how the tide, with its cyclic high and low tide periods, is disturbed as it flows through areas of the wetland with obstacles and impediments such as roads, drains, culverts and levies.”
“When we build a road across a wetland, the tide is forced to move from one side of the road to the other through culverts or bridges, instead of freely flowing over the tidal flat. As a result, it takes more time and energy for the water to reach the other side. This results in water sitting in the wetland longer and in a reduction of the high tide water level. Then at low tide, some areas of the wetland are not able to fully drain resulting in ponding.”
“Coastland wetland vegetation relies on a specific inundation regime to survive, and changes such as prolonged water exposure will essentially drown the vegetation,” said Dr Rodriquez.
The Impact of Sea Level Rise
Associate Professor Patricia Saco said that wetland vegetation would be more vulnerable to sea-level rise than previously thought, resulting in a much faster loss of coastal wetlands in heavily developed areas.
“Our results are particularly relevant for wetlands in heavily developed coastal areas including eastern Australia, eastern US, eastern China and Western Europe. As sea level rises we’ll see these attenuation effects exaggerate,” said Associate Professor Saco.
“We’ll start to see noticeable wetland decay in these areas in as little as 20 to 40 years and a total loss in 80.”
Why are Saltmarsh and Mangroves Important?
Mangroves and saltmarsh provide a critical role in ecosystem food webs, providing habitat for fish, crabs, birds, bats and marsupials.
A threatened ecological community itself, saltmarsh provides habitat for many vulnerable species including migratory birds protected under federal legislation and international treaties.
Both environmental engineers, Dr Rodriguez and Associate Professor Saco combined their strengths in hydraulic modelling with their passion for conservation as a key driver for the project.
“We have been looking at preserving migratory bird habitat. Our study site is an important roosting site for migratory birds in the estuary and we wanted to investigate the long-term evolution of the wetland and its suitability as a future roosting site,” said Associate Professor Saco.
“Coastal wetlands also offer important protection from erosion, storm surges and tsunamis. This valuable habitat is in decline globally and in Australia due to sea-level rise and human pressures. In fact, saltmarsh has been declared an endangered ecological community in NSW,” said Associate Professor Saco.
The research team hopes that by more accurately understanding the outlook for mangroves and saltmarsh, their survival can be assured.
“Our model can help assess different alternatives for saltmarsh and mangrove survival including removal of man-made structures and barriers to wetland migration and implementation of targeted tidal flow management strategies that minimise sea-level rise effects,” said Dr Rodriguez.
The research team also included postgraduate student Steven Sandi Rojas from UON, Professor Neil Saintilan from Macquarie University and Professor Gerardo Riccardi from the University of Rosario, Argentina.
Associate Professor Patricia Saco is also the Director of UON’s Centre for Water Security and Environmental Sustainability.