Mapping Changes of Saltmarsh and Mangrove Vegetation Communities in Wagonga Inlet, NSW South Coast

Saltmarsh and mangroves play a significant role within estuarine systems, with the extent and distribution of these communities being used as one of the indicators of the ‘health’ of an estuary. In NSW, two comprehensive inventories of estuarine macrophytes exist for the entire NSW coastline (West and CCA). Based on a comparison of these inventories, Wagonga Inlet, on the NSW South was identified as one of the NSW estuaries that exhibited significant change. Using GIS aerial photograph interpretation, changes in the extent mangrove and saltmarsh were mapped between 1957 and 2010. The analysis found that there has been a significant increase in both the distribution and extent of mangroves around the Inlet growing from 11.37 ha in 1957 to 23.83 ha in 2010, with mangroves expanding up-slope into saltmarsh areas, down-slope onto both prograding fluvial deposits and a marine tidal delta, and laterally along the foreshore. A loss of saltmarsh communities was found with 17.66 ha being identified in 1957 and only 8.99 ha remaining within Wagonga Inlet in 2010 with this loss being the result of reclamation, drainage of wetland areas, lawn mowing along the interface between saltmarsh and terrestrial communities, down-slope expansion of Casuarina glauca and up-slope expansion of mangroves. The study also assessed the validity of comparing the two existing Estuarine Vegetation Inventories to monitor changes in macrophyte distribution within estuaries, as a tool for estuarine management. For Wagonga Inlet, the study found that the comparison had produced erroneous results for both saltmarsh and mangroves. It was found that, by using aerial photographs scanned at a high resolution, a high level of accuracy is achievable in identifying and mapping mangrove communities. Saltmarsh was poorly identified in both the West and CCA inventories and it was found that without extensive ground truthing, even modern GIS based API will significantly underestimate the extent of saltmarsh.