New study shows mangroves may protect against sea level rise

22 July 2015

New research shows mangrove forests could play a crucial role in protecting coastal areas from sea level rise caused by climate change.

A joint study between Associate Professor Giovanni Coco from the University of Auckland’s School of Environment and colleagues at the Universities of Southampton (Dr Barend van Maanen) and Waikato (Dr Karin Bryan), used leading-edge mathematical simulations to study how mangrove forests respond to elevated sea levels.

The new model incorporates biophysical interactions to study the formation of tidal channel networks, how these channels are modified by mangroves and how mangroves are in turn affected by channel evolution.

The researchers studied the evolution of the channels by using a hybrid model that connects biotic (mangroves) and abiotic (currents and transport of sediment) processes, to simulate their interaction.

In particular the research focused on how estuarine environments with and without mangroves responded to sea level rise.

The study also used longer timeframes than have been incorporated into this type of modelling work than ever before, studying mangrove evolution for hundreds of years.

The research found that as a mangrove forest begins to develop, the creation of a network of channels is relatively fast. Over 160 years, tidal currents, sediment transport and mangroves significantly modify the estuarine environment, creating a dense channel network.

Within the mangrove forest, these channels become shallower through organic matter from the trees, reduced sediment resuspensions (caused by the mangroves) and sediment trapping (again caused by the mangroves)and the sea bed begins to rise, with bed elevation increasing a few millimetres per year until the area is no longer inundated by the tide.

In modelling of sea level rise in the study, the ability of mangrove forest to gradually create a buffer between sea and land occurs even when the area is subjected to potential sea level rises of up to 0.5mm per year. Even after sea level rise, the mangroves showed an enhanced ability to maintain an elevation in the upper intertidal zone.

“These findings show that mangrove forests play a central role in estuarine and salt marsh environments,” Associate Professor Coco says.

“As we anticipate changes caused by climate change, then it’s important to know the effect sea level rise might have, particularly around our coasts.

“Mangroves appear to be resilient to sea level rise and are likely to be able to sustain such climatic change. The implications for the New Zealand coastline are considerable and will require new thinking in terms of sediment budgets and response to climatic changes.”

This paper is the result of a series of papers to study estuarine morphodynamics initiated thanks to funding from NIWA and the University of Waikato.


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