COASTAL wetlands around the world could have just 80 years left to live according to a warning issued by an international team of researchers who have worked on new impact modelling of sea level rise.
The lead researcher, Dr Jose Rodriguez, is based at the University of Newcastle and the research has been published in the journal Nature Communications.
The team has scrapped the previous ‘bathtub model’ that suggested tidal effects flow through the wetlands without interruption and developed a new model that shows the dire impact that man-made structures like roads, culverts and bridges will have as sea levels rise.
Dr Rodriguez said under the new model, there is increased inundation and attenuation — bad news for wetlands and salt marshes which rely on water coming in and then flowing back out in a regulated fashion.
“Both mangrove and salt marsh need a particular wetting and drying regime, both in terms of time and depth of inundation,” he said.
“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,” Associate Professor Patricia Saco said.
“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 … then at low tide, some areas of the wetland are not able to fully drain, resulting in ponding.”
Essentially, the vegetation drowns.
The modelling paints a bleak picture for the future of coastal wetlands, estimating a 50 per cent increase in their rate of loss.
“The impacts are going to start showing earlier, between 40 and 60 years from now. We’ll see considerable changes in the vegetation distribution.”
Human lifespans currently sit at an average of 79 years, and it is an international problem.
“These effects are going to be seen in all the areas, coastal areas that are heavily organised including all of the east coast of Australia, eastern China, the east coast of the US. It’s also relevant for Pacific islands and Indonesia,” Associate Professor Saco said.
In some areas, the scientists are predicting wetlands within one kilometre of the coast will disappear in 80 years, but it could be different in other areas.
“That’s what we are trying to understand really because it will be different for different areas and this depends on the entrance conditions to the wetlands, how close to the sea they are, how much attenuation there is,” she said.
Wetlands and salt marshes are a haven for bird life with herons and ibis among the species that head there to breed.
“Particular migratory birds depend on salt marsh, they use salt marsh for roosting, so any decline in salt marsh health is going to affect bird habitat,” Dr Rodriguez said.
The areas are also important for the breeding of crabs, bats, marsupials and fish.
The vegetation in question does have the ability to move in line with environmental changes — if there’s space further up the system.
“Salt marsh is particularly vulnerable because it’s at the upper end of the tidal regime and that area is typically where you start seeing development,” Dr Rodriguez said.
Buffer zones are needed.
“The obvious thing is whenever you are planning allow for a buffer radius for the vegetation to adapt to sea level rise and move to some other areas of the landscape where they can survive,” Dr Rodriguez said.
And ironically, other man-made structures such as gates or locks could help.
“The solution is to install gates that could mimic the effect of natural tidal flows,” Associate Professor Saco said. “It would be a gate that can be operated up and down.”
“It’s not a lost cause by any means,” Dr Rodriguez said.