James Cook University and CSIRO scientists have found that removing artificial barriers between wetlands and the coast can have a big impact on the environment – but the process is not straightforward.
Dr Nathan Waltham, Principal Research Officer at JCU's Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), said about 30 per cent of coastal wetlands in the Great Barrier Reef region are cut off from the sea by bunds, embankments, roads, culverts or floodgates.
"The coastal wetlands adjacent to the Great Barrier Reef are a vital nursery and feeding complex, supporting marine and freshwater fish, important native vegetation and a crucial bird habitat.
"But infestation by weeds has become a major issue within many of the wetlands modified last century. Weed control, using herbicides, has only seen limited success and infestation leads to a loss of habitat for many species of plants and animals – for example poor available oxygen for fish to breathe," said Dr Waltham.
The scientists tracked the changes in the environment after the removal of a bund on a property east of Ingham in 2013 allowed tides to once more flow upstream.
"In an earlier project by CSIRO and the traditional owners, the Nywaigi people, a section of the earth bund wall was removed. This resulted in the reintroduction of salty tidal water to the wetland. The result was a major reduction in weed infestation, the reappearance of native vegetation, improvements in water quality, and a tripling of fish diversity," said Dr Waltham.
But he said it wasn't quite as simple as removing the bund and letting nature take over, as particularly heavy summer rainfall can prevent tides from penetrating upstream and lead to the return of weeds and a degradation of water quality.
"We also saw the phenomenon of the return of native plant species – some of which were then summarily eaten by feral pigs. It's a complex system and these are vital lessons in how nature and restoration work,"said Dr Waltham.
He said the work is important particularly in the next few months, before we enter the United Nations decade on ecosystem restoration (2021 to 2030) – a global initiative that calls for the halt of further destruction of freshwater and saline wetlands along the coast.
"Many of those coastal wetlands left have been degraded and what we've seen here shows us that reintroduction of tidal flow by removal of an earth bund or levee could provide a cost effective and sustainable means of controlling freshwater weeds, rather than using herbicides, and improving coastal water quality into the future."
The Australian Government provided funding for this project through the National Environmental Science Program (NESP) Tropical Water Quality Hub.
Link to pictures of the Mungalla wetlands here.
