Critical ecological assets in areas of highsalinisation hazard in the Tasmanian Midlands

A GIS-based assessment has been conducted to identify ecological assets in highsalinisation hazard areas in the NAP region of the Tasmanian Midlands. Relative hazardto aquatic ecosystems, wetlands, water bodies and streams, as well as to vegetationcommunities from salinisation was evaluated. The hazard analysis was based on thepresence of particular groundwater flow systems, and on rainfall and vegetationclearance. Hazard ratings were applied to these factors, and then to mapped polygonsdescribing each asset type by GIS overlay. Rule sets were applied to attribute each assetpolygon or streamline with an integrated hazard rating. High hazard ratings werecombined with information on asset features (e.g. wetland size, the presence of threatenedspecies etc) to develop a prioritised list of ecological assets in high salinisation hazardareas.148 wetlands (15% of the total) were rated as occurring in areas of highest hazard. 45 ofthese wetlands and two water bodies were rated as occurring in areas of highest hazardand being of high priority for management and/or monitoring. Around 7 - 8% of allstream sections in the study area (ca 1 100 km) were rated as occurring in areas of highhazard at low and median flows. These were primarily small headwater catchments ofseveral smaller river, creek and rivulet systems; and small floodplain or valley floortributaries of the lower Coal and Jordan and middle South Esk Rivers. Field evaluationconfirmed that high levels of stream salinity at baseflow were related to high hazardratings.Relatively small areas of priority vegetation (848 ha) or numbers of threatened species(100 populations) were located in areas of highest hazard. Only four of the highestpriority vegetation types (endangered/rare) were in the highest hazard category - lowlandPoa and Themeda native grasslands, Eucalyptus ovata forest and woodland, and riparianvegetation. There are seven vulnerable communities occurring in areas of highest hazard,with only inland Eucalyptus amygdalina forest with more than 50 ha in high hazard areas.Critical Ecological Assetsv Davies and BarkerIn comparison, relatively large areas of cleared agricultural land occur in areas of highesthazard (39 139 ha).Three groundwater flow systems were recognised as posing high salinisation hazard.These were local scale systems in alluvial plains, floodplain alluviums and deeplyweathered sediments. Alluvial plain and floodplain alluvial systems account for thegreatest proportion of ecological assets located in areas of highest hazard. Fieldassessment indicated that local systems in dunes are significant local sources of surfacesalinity and should be further evaluated.Recommendations are made with regard to future work, monitoring and assessment ofasset condition.