A Desktop Assessment of Groundwater Dependent Ecosystems in Tasmania ‘A strategic framework for statewide management and conservation of Tasmania’s freshwater ecosystem values’ Report to the Conservation of Freshwater Ecosystems Values Project Water Development Branch Water Resources Division Department of Primary Industries, Water and Environment February 2004 © Department of Primary Industries, Water and Environment Author: Rolan Eberhard, Department of Primary Industries, Water and Environment Published by: Water Resources Division Department of Primary Industries, Water and Environment GPO Box 44 Hobart Tas 7001 Telephone: (03) 6233 6328 Facsimile: (03) 6233 8749 Email: [email protected] Website: www.dpiwe.tas.gov.au Citation: Eberhard, R. (2004). A Desktop Assessment of Groundwater Dependent Ecosystems in Tasmania . Report to the Conservation of Freshwater Ecosystems Values Project, Department of Primary Industries, Water and Environment, Hobart, Tasmania. Cover photograph: Phreatoicid isopods from Marakoopa Cave. Photo taken by John Gooderham. Copyright All material published in the report by the Department of Primary Industries, Water and Environment, as an agent of the Crown, is protected by the provisions of the Copyright Act 1968 (Cth). Other than in accordance with the provisions of the Act, or as otherwise expressly provided, a person must not reproduce, store in a retrieval system, or transmit any such material without first obtaining the written permission of the Department of Primary Industries, Water and Environment. Disclaimer Whilst the Department of Primary Industries, Water and Environment makes every attempt to ensure the accuracy and reliability of information published in this report, it should not be relied upon as a substitute for formal advice from the originating bodies or Departments. DPIWE, its employees and other agents of the Crown will not be responsible for any loss, however arising, from the use of, or reliance on this information. ii A Desktop Study of Groundwater Dependent Ecosystems in Tasmania Contents Summary.......................................................................................................................1 1. Definitions.............................................................................................................2 2. Methodology.........................................................................................................2 3. Results...................................................................................................................3 3.1. Karstlands ..........................................................................................................3 3.2. Deflation basins .................................................................................................8 3.3. Freshwater crayfish burrows..............................................................................9 3.4. Fractured and porous rock aquifers (excluding karst) .....................................10 3.5. Subsurface streams in talus and colluvium......................................................12 3.6. Groundwater Dependent Vegetation................................................................14 4. Conclusions.........................................................................................................16 5. References...........................................................................................................16 Appendix 1. Contributors .........................................................................................21 Appendix 2. Digital maps ..........................................................................................23 Appendix 3. Classification of Karst areas................................................................27 Appendix 4. GDE point features...............................................................................33 Conservation of Freshwater Ecosystems Values Project iii A Desktop Study of Groundwater Dependent Ecosystems in Tasmania Summary A desktop assessment of groundwater dependent ecosystems was carried out to identify classes of ecosystem where the species composition and natural ecological processes are determined by the permanent or temporary presence or influence of groundwater. It was recognised that groundwater contributes to the water balance of a vast array of ecosystems in Tasmania, including those associated with the majority of rivers and lakes as well as vegetation in many environmental settings. Identifying and mapping these ecosystems entails a range of practical and theoretical difficulties, and was not a viable objective for this project. Nevertheless, it was considered worthwhile to identify ecosystems where groundwater plays an obvious and critical role in the water balance of component organisms. The following classes of feature were identified as groundwater dependent ecosystems or features hosting groundwater dependent ecosystems: Karstlands (landform systems in limestone, dolomite and magnesite); Deflation basins (depressions formed through erosion by wind action); Burrows produced by freshwater crayfish (these host a characteristic faunal assemblage); Porous and fractured rock aquifers (especially coastal sand aquifers); Subsurface streams in talus and colluvium; and Vegetation types associated with shallow water tables. Examples of each class of feature were mapped digitally, although the comprehensiveness of the data varies considerably. For example, karstlands have been subject to considerable previous work including the preparation of a State-wide map of karst areas and studies of the distribution and ecology of karstic groundwater fauna. In contrast, Tasmania’s non-karstic stygofauna is virtually unknown, except for the fortuitous discovery of depigmented crustaceans in a spring at Devonport. This is a serious gap in our knowledge of groundwater dependent ecosystems in Tasmania and should addressed in an integrated way as part of regional hydrogeological assessments. Conservation of Freshwater Ecosystems Values Project 1 A Desktop Study of Groundwater Dependent Ecosystems in Tasmania 1. Definitions In accordance with definitions proposed in Environment Australia’s discussion paper on groundwater ecosystems (Sinclair Knight Merz Pty Ltd 2001) and the NSW government’s Groundwater Dependent Ecosystems Policy (Department of Land & Water Conservation 2002), this study defines a groundwater dependent ecosystem (GDE) as an ecosystem where the species composition and natural ecological processes are determined by the permanent or temporary presence or influence of groundwater. Following the Australian Natural Heritage Charter, an ecosystem is taken to mean a dynamic complex of organisms and their non-living environment, interacting as a functional unit (Australian Heritage Commission 2002). Groundwater is sometimes taken to include all subsurface water as distinct from surface water, and has been defined simply as ‘water below the earth’s surface’ (e.g. SDAC 1996). Tasmania’s Water Management Act 1999 defines groundwater as ‘(a) water occurring naturally below ground level; or (b) water pumped, diverted or released into a well for storage underground.’ More conventional definitions of groundwater refer to that part of the subsurface water that is in the saturated zone or phreas (i.e. below the water table). The water table is taken to include perched water tables (i.e. groundwater water resting on an impermeable layer that impedes its downward movement). Subsurface streams flowing through natural pipes or gaps between clasts in colluvium or talus are examples of perched water tables. This assessment has followed the more restricted definition of groundwater. Within its definition of a groundwater dependent ecosystem, Environment Australia recognises a spectrum of groundwater dependency (Sinclair Knight Merz Pty Ltd 2001). At the higher end of the spectrum are ecosystems that are entirely dependent on groundwater, where only slight changes in key groundwater attributes below or above a threshold would result in their demise. At the other end of the spectrum are proportionally or opportunistically forms of dependency, where changes in groundwater level or quality can be tolerated in the short term but will cause the ecosystem to decline and ultimately collapse if this state is prolonged excessively. Because of the short time available to this project and our rudimentary knowledge of the relationship between groundwater and ecosystems in Tasmania, this project focussed on ecosystems where groundwater was considered an obvious and critical factor in the water balance of the ecosystem. The ecosystems that were identified in this assessment would generally be classified as entirely or highly dependent on the spectrum of groundwater dependency proposed by Environment Australia. 2. Methodology Relevant specialists in the fields of earth science, zoology and botany were invited to workshops with the purpose of identifying groundwater dependent ecosystems (cf. Hatton & Evans 1998). A paper defining groundwater dependent ecosystems and discussing forms of groundwater dependency was circulated prior to the workshops. Some specialists who were unable to attend the workshops were consulted individually. Conservation of Freshwater Ecosystems Values Project 2 A Desktop Study of Groundwater Dependent Ecosystems in Tasmania Potential groundwater dependent ecosystems identified at the workshops were investigated through a literature review and in discussion