Study shows surprising results around coastal restoration, mangroves and sediment

“Don’t blame the mangroves,” is a key conclusion of an international collaboration on vegetation removal, sedimentation and coastal restoration. The study, published in Nature communicationshows that coastal restoration on a smaller local scale will not get through the mud without large-scale current changes.

Contributing author, oceanographer Professor Karin Bryan from the University of Waikato, says: ‘When we went to work we thought we knew what was going to happen, but the modeling showed surprisingly different outcomes: mangroves neither capture nor cause sedimentation as we would. expected.”

The researchers used computer models based on New Zealand’s estuaries to assess sedimentation inputs and the frictional effects of mangroves on sedimentation.

Professor Bryan worked within the NIWA Future Coasts Aotearoa program to build evidence of impacts and restoration efforts on local lowland coastal ecosystems.

“We know that land use changes upstream, such as deforestation, have significantly altered coastal and estuarine ecosystems downstream. We wanted to look at how levels of upstream sedimentation interact with downstream vegetation such as mangroves to assess the effectiveness of certain restoration efforts at a given time. local scale,” says Professor Bryan.

The results show that coastal mangrove removal initiatives, guided by knowledge of local-scale impacts, cannot stop or mitigate mud filling in estuaries to restore previous sandy ecosystems.

“Removing mangroves strengthens sediment at the estuary scale. This means that human interventions such as removing vegetation in estuaries can lead to counter-intuitive results that actually hinder restoration efforts, highlighting the need for more holistic management approaches,” says Professor Bryan .

Again, research points to the need to find solutions within the larger catchments, for example reducing sedimentation loss due to upstream land use.