Abstract
Tidal wetlands have been at the forefront of environmental changes in estuaries and coasts as they have been progressively reclaimed from their natural state into developed land. As one of the earliest colonial settlement regions in Australia, kanamaluka/River Tamar (1804–onwards) bears a long and complex history of anthropogenic impacts which have permanently altered the natural state of the estuary. To quantify these changes, we developed an adaptive multiple-criteria decision analysis (AMCDA) approach to map both the pre-colonial and current extent of tidal wetlands, changes in tidal wetland extent, and the apparent drivers and patterns of this change. To capture the entire temporal duration of changes post-colonisation, historical sources dating as early as 1809 were used in conjunction with environmental proxies and the earliest available aerial photography (circa 1945). We estimate that prior to European colonisation, kanamaluka supported the largest regional expanse of emergent tidal wetlands in Tasmania (~ 2231 ha), of which there has been a 52% reduction in extent. Much of the historical loss is concentrated in the upper estuary around the major regional city of Launceston with a significant proportion of its urban and industrial footprint (~ 587 ha) built on top of cleared tidal wetlands. These findings, along with our AMCDA approach, offer key insights for regional scale studies of estuaries that are without historical reference state assessments. We also expect that our high-spatial resolution mapping of both historic and current extent will assist in setting conservation and restoration targets, and in appropriate monitoring, assessment, and reporting.