Modelling Soil, Carbon and Vegetation Dynamics in Estuarine Wetlands Experiencing Sea-Level Rise

Estuarine wetlands are among the most productive ecosystems in the world, providing unique habitats for fish and many terrestrial species. They also have a carbon sequestration capacity that surpasses terrestrial forest. In NSW, and most of south eastern Australia, they typically display a vegetation zonation with a sequence mudflats - mangrove forest - saltmarsh plains from the seaward margin and up the topographic gradient. Estuarine wetlands respond to sea-level rise by vertical accretion and horizontal landward migration, in order to maintain their position in the tidal frame. In situations in which accretion cannot compensate for sea-level rise and buffer areas for landward migration are not available, estuarine vegetation can be lost due to unsuitable hydraulic conditions. Predicting estuarine wetlands response to sea-level rise requires simultaneous modelling of water flow, soil and vegetation dynamics. This paper presents some preliminary results of our recently developed numerical model for wetland dynamics in wetlands of the Hunter estuary of NSW. The model continuously simulates tidal inputs into the wetland and vegetation types are determined based on their preference to prevailing hydrodynamic conditions. Accretion values based on vegetation types are computed and the topography is updated accordingly. The model is driven by local information collected over several years, which include estuary water levels, accretion rates, soil carbon content, flow resistance and vegetation preference to hydraulic conditions. Model results predict further wetland loss under an accelerated sea-level rise scenario and also under current conditions of moderate increase of estuary water levels.