Dynamics of surface accretion and surface elevation differ between river and tide dominated settings in tropical mangroves

Abstract

The maintenance of soil surface elevation in mangroves supports the persistence of mangroves with sea levelrise. The processes contributing to soil surface elevation have rarely been assessed in the humid tropics, despitemost mangroves occurring in river deltas and tidal estuaries within this climate zone. Using surface elevationtable (SET) with marker horizon methods over sites that occurred on either the main river channel or a tidalchannel, we assessed the role of rainfall and associated river discharge in moderating surface elevation in man-groves of the Daintree River, Queensland, Australia. In the sites in the main river channel close to the rivermouth, increases in soil surface elevation were episodic, with river flooding leading to greater accretion of sedi-ment and increases in surface elevation in years with high river discharge, while in the tidal channel furtherfrom the mouth, sediment accretion and surface elevation increments were variable among years and not linkedto river discharge. Our study finds that the 32.7 km 2 of mangroves of the Daintree River estuary have surfaceelevation gains that are variable but similar to current rates of sea level rise through trapping of around 40,000 tof sediment annually, mainly within the downstream mangroves and those in the main river channel. Extremerainfall and river flows have spatially variable influences on surface elevation in mangroves of the DaintreeRiver, which may lead to similarly variable responses to accelerating sea level rise