Reedy Lake, near Geelong, is a large, brackish wetland, recognised as a Ramsar site in 1983. Since that time, high water levels were sustained during summer, to support community use of the wetland. In 2016, Corangamite Catchment Management Authority (CCMA) modified the water regime, to partially dry the wetland each summer and autumn by lowering water levels. This was to rebalance the diversity of habitats so that one habitat type does not dominate. In 2022, the CCMA wanted to understand whether the new water regime was maintaining the ecological character of the wetland within the Ramsar Limits of Acceptable Change (LAC).
Determining this required the changes in the extent and relative proportions of several different habitat types to be assessed between 1983 and 2022. To achieve this, we used Landsat and Sentinel-2 satellite imagery and applied an innovative semi-automated imagery classification technique using machine learning to detect vegetation types and extents for each timestep to generate a time-series of change.
Our analysis showed that the reed, sedge, and rush vegetation communities of Reedy Lake are dynamic, exhibiting strong seasonal and inter-annual variations in extents in response to water level changes; and that this pattern of variation has persisted since 1983. Importantly the range of variation was found to be within the Ramsar Limits of Acceptable Change.
Through this investigation, we demonstrated that analysing remotely sensed data is a cost-effective way to monitor historical change and inform management decisions in wetlands, providing critical insights that cannot be derived by other means.