Sediment processes and mangrove-habitat expansion on a rapidly-prograding Muddy Coast, New Zealand

Document Type

Conference Proceeding

Publication Date



Mangrove-habitat expansion has occurred rapidly over the last 50 years in the 800 km2 Firth-of-Thames estuary (New Zealand). Mangrove forest now extends 1-km seaward of the 1952 shoreline. The geomorphic development of this muddy coast was reconstructed using dated cores (210Pb, 137Cs,7Be), historical-aerial photographs and field observations to explore the interaction between sediment processes and mangrove ecology. Catchment deforestation (1850s-1920s) delivered millions of m 3 of mud to the Firth, with the intertidal flats accreting at 20 mm yr-1 before mangrove colonization began (mid-1950s) and sedimentation rates increased to ≤ 100 mm yr-1. 210Pb data show that the mangrove forest is a major long-term sink for mud. Seedling recruitment on the mudflat is controlled by wave-driven erosion. Mangrove-habitat expansion has occurred episodically and likely coincides with calm weather. The fate of this mangrove ecosystem will depend on vertical accretion at a rate equal to or exceeding sea level rise.

Publication Source (Journal or Book title)

Coastal Sediments '07 - Proceedings of 6th International Symposium on Coastal Engineering and Science of Coastal Sediment Processes

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