Coastal wetland elevation trends in Southeastern Australia
Situated within narrow elevation gradients, coastal saltmarsh is vulnerable to moderate rates of sea-level rise. Encroachment of saltmarsh by mangrove, documented for many estuaries of Southeastern Australia, has been postulated as evidence of the effect of relative sea-level rise over the historic timeperiod. In a large-scale experiment to test this hypothesis, sedimentation and surface elevation trends were studied in mangrove and saltmarsh wetlands in Southeastern Australia. A total of 81 surface elevation tables, each associated with feldspar marker horizons, were deployed in 12 wetlands across 7 estuaries, and monitored for three years. Saltmarsh and mangrove vegetation distribution were mapped for the same estuaries, and elevation characteristics of the wetlands were modeled. A positive relationship was demonstrated between saltmarsh subsidence and mangrove encroachment into saltmarsh, and between the rate of mangrove upslope migration and relative sea-level rise. The result suggests that saltmarshes vary in their capacity of respond to sea-level rise due to local factors such as groundwater flow, sedimentation and below-ground productivity.