Throughout southeastern Australia, management authorities are often challenged by public memory regarding what the ‘natural’ or ideal state of coastal wetland environments are. This is particularly exacerbated when local residents recall the record high rainfall years of the mid 1950s-60s and consider this to be the optimal state. Another obstacle may be the listing of a wetland under the Ramsar Convention, aimed at preserving the ecological character of significant wetlands. However, the condition at the time of listing may be far from pristine and thus the management guidelines recommend conserving a degraded or modified state.
Although meteorological records have been collected from weather stations for up to the last 150 years, condition reporting on Australian estuaries has only been considered in the last 30-40 years, at best. In addition, all estuaries considered here have been heavily impacted by changes in land use practices and hydrological modification since European colonisation in the mid-19th century.
Here we apply a combination of palaeocological methods to determine primarily the salinity, but also turbidity, nutrient flux and trophic state changes within a suite of estuaries along the southeast Australian coast. We use both ostracod assemblage changes and shell chemistry (δ18O, δ13C), diatom assemblages, and sediment geochemistry (iTRAX – XRF, δ13C, δ15N, C/N). These combined methods act to determine the state of the estuaries, including their natural variability, prior to extensive catchment modification. The sediment records also preserve the rate and trajectory of change of each of these wetlands, both in terms of management practices and climatic variability.
In each of these cases, our results have been taken into consideration to modify modern wetland management. Although it may not be possible – or desirable – to return to pre-impact conditions, the use of combined palaeoecological methods allows informed decisions about estuarine management to be made.