NZ, China Team Up On Caring For Coastal Wetlands As Sea Levels Rise

The University of Auckland and two Chinese universities have begun a three-year collaboration on caring for coastal wetlands as sea levels rise.

The New Zealand scientists are focused on computer modelling to guide wetland management, including the potential to restore mangroves and saltmarshes on low-lying farmland where sea water is encroaching.

Wetlands protect coastlines from erosion, provide habitats for flora and fauna, reduce flooding and store carbon. New Zealand has already lost more than 90 percent of them, mainly due to drainage and conversion to farmland.

“Understanding how wetlands can be adapted to sea level rise is a bit more complex than adjusting the sea level upward on a terrain map — otherwise called the ‘bathtub approach’,” says Professor Karin Bryan of the School of Environment.

Sophisticated models simulate tide flows and sediment shifts, even incorporating the effects on tide flows from friction with newly established vegetation. They predict ‘blue carbon’ effects such as carbon burial and emission changes. The Auckland scientists' use of one of these tools, called Delft3D, will benefit from the Chinese scientists' knowledge.

The Chinese team will stress-test some of their models in New Zealand conditions. As an example of common interests: This country has largely eradicated the pest grass Spartina from our coastline, while China is still in the process of removing it, and trying to reestablish native species.

Bryan’s team from Waipapa Taumata Rau, University of Auckland met with collaborators at Hohai University in Nanjing this month. Very different stretches of wetlands in Jiangsu province, on China’s east coast, and Northland will feature in the research, the Chinese area heavily altered from its natural state, the New Zealand site less so.

The University of Auckland researchers were awarded $300,000 from the Ministry of Business, Innovation and Employment under the New Zealand – China Strategic Research Alliance programme, while Hohai University and East China Normal University scientists are funded by the Chinese Ministry of Science and Technology.

“Each life stage of a plant in a wetland requires specific conditions to establish, survive and grow, so getting the flow pathways of the incoming and outcome tide correct, including during storms, is vital,” says Bryan.

Where tide flows are a problem, digging networks of channels and keeping some areas at high elevations can be solutions.

In New Zealand, the productive soils that harbour wetlands are suited to dairy farming but sea level rise has left many sites sitting in the intertidal zone, protected only by stop banks. Saltwater creeps up under stop banks and through soil, making paddocks less productive.

"There are many decisions to be made, like which land is simply too expensive to restore, and how should an ineffective stop bank be breached? In several places, and should we put a flow-control gate on it or not?"

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