A recent study has found that the Nukuhou Saltmarsh could become significant for carbon sequestration (or carbon storage). Potentially this could assist with the future management of climate change at Ōhiwa Harbour. And it would make the restoration of saltmarshes all the more important. Across the whole the Bay of Plenty 60 percent of saltmarshes were lost between 1840 and 2000, about 1400 hectares.
The research project conducted by the Bay of Plenty Regional Council, NIWA and and the University of Waikato mapped elevation profiles of coastal land across the region to identify potential locations for saltmarsh restoration projects. Apart from their potential as carbon sinkers, saltmarshes are vital for biodiversity and water quality in coastal areas.
Climate change impacts on the Bay of Plenty region include potential sea level rise of 0.7 m by 2070. Sea level rise might mean saltmarsh habitat will be pushed inland. However, “coastal squeeze” is also likely to occur where seawalls, roads, stopbanks and other human infrastructure limit such movement. There is likely to be an overall decrease in space available for saltmarsh due to land topography.
The researchers point out that ‘saltmarshes have some resilience to the impacts of sea level rise due to their ability to trap and store sediments: by stabilising emergent mudflats by slowing water velocity and causing sediment deposition out of the water, the plant roots bind sediments and improve resistance to erosion, and accumulation of organic material into the soil’. Yet on a less positive note, ‘if sea level rises too quickly, or the sediment supply or inundation through flooding is excessive, the saltmarsh may experience stress or deterioration’.
The report also noted that an additional complicating factor is the widespread increase of mangroves. Mangroves commonly grow in the upper intertidal zone, below the saltmarsh habitat. Localised landwardmovement of mangroves into saltmarsh habitat has been observed across the Bay of Plenty.
Options to preserve saltmarsh ecosystems include protecting and preserving inland regions, allowing for natural migration landwards and managing tidal reconnection in cases where human infrastructure is limiting the saltmarsh migration.
Estuarine wetland monitoring will help determine whether Bay of Plenty saltmarsh wetlands can adapt to rising sea levels, or if mitigation is required.
