Temporal changes in south east Tasmanian saltmarshes

Coastal saltmarshes are unique and highly productive ecosystems. They form a major part of the enclosed waterways of south east Tasmania, especially within the Pitt Water, Pipe Clay Lagoon and Ralphs Bay areas. The Pitt Water saltmarshes are acknowledged to be the most diverse and extensive of Tasmanian saltmarshes with extremely high floristic and fauna! values, some recognised internationally while some remain unstudied. A study conducted in 1975 detailed the extent and vegetation community composition of the saltmarshes in the Pitt Water, Pipe Clay Lagoon and Ralphs Bay areas. More than 30 years since then, the change in these important ecological communities remained unstudied. Elsewhere in Australia and internationally, temporal studies of saltmarshes have reported substantial changes in morphology, extent and vegetation. This has led to several policy and management actions directed at conserving the function and values of saltmarshes. The objective of the present study was to investigate the spatial and temporal changes in saltmarshes mapped in 1975 to inform policy and planning concerning their management and conservation. Most saltmarshes have had losses in their areal extent, with nearly 17 hectares of area (5%) lost on the seaward side primarily due to coastal erosion. The saltmarsh shorelines have been eroding at about 6 cm to 20 cm a year, with erosion highest on the shorelines more exposed to wind-generated waves. Nearly 6% of the saltmarsh area had been lost due to land reclamation. While some area had been gained through accretion and landward transgression, it was less than a quarter of the saltmarsh area lost. Results for vegetation change show that low marsh plants, which are more adapted to waterlogging, have replaced long lived high marsh plants as the dominant vegetation community of the saltmarshes. A general shift of vegetation zones inland was observed, suggesting a response to sea level rise. Extensive areas within the marsh have been denuded of plant cover and have turned to salt pans/flats and \rotten spots\" possibly affected by an increase in tidal inundation increases in soil salinity related to climate change and increased nutrient inputs from irrigated land. These changes have several implications for the conservation of both the floristic and fauna! values of saltmarshes and their contribution to the health and productivity of the coastal waterways. This study highlights a compelling need for strategic planning for the future conservation and management of these important coastal ecosystems in a time of change and contributes key information and methods to assist these efforts."