Frequently Asked Questions
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- What information can I get from the GDE Atlas?
The GDE Atlas shows the general location of groundwater dependent ecosystems. Each polygon represents an area within which groundwater interaction potentially occurs. This does not mean that the whole polygon is interacting with groundwater.
A set of attributes that describe the characteristics of each GDE is included and can be viewed by selecting an ecosystem or a group of ecosystems. Literature references that relate to individual GDEs can be viewed. Groundwater dependent ecosystems with specific literature associated with them will have more attributes than GDEs derived solely from GIS analyses.
- How should the GDE Atlas be used?
The GDE Atlas provides information to support the recognition and identification of GDEs in natural resource management, including water planning and environmental impact assessment. It indicates where ecosystems potentially interact with groundwater, and some of the characteristics of those ecosystems that may be useful in determining water requirements.
The GDE Atlas shows general locations where groundwater interaction may occur. It does not imply that an entire mapped ecosystem is using groundwater, but rather within the mapped ecosystem groundwater interaction may be occurring, since only part of the ecosystem may actually be interacting with groundwater.
The GDE Atlas makes no assessment of ecosystem value, condition, sensitivity, threat or risk. There are many external factors that need to be considered in these assessments at a more detailed scale. The GDE Toolbox provides a more detailed GDE assessment, including their identification, an assessment of ecological water requirements and determination of how changes in the groundwater environment impact on ecosystems.
- Which ecosystems are shown in the GDE Atlas?
The ecosystems shown in the Atlas are grouped into three classes:
- Ecosystems that may rely on the subsurface presence of groundwater including all vegetation ecosystems.
- Ecosystems that may rely on the surface expression of groundwater including all surface water ecosystems with a groundwater component, such as rivers, wetlands and springs. Marine and estuarine ecosystems can also be GDEs, but these are not mapped in the Atlas.
- Subterranean ecosystems including cave and aquifer ecosystems.
The ecosystems shown in the Atlas are derived from existing mapped ecosystem polygons. Therefore, if existing ecosystems mapping excluded certain ecosystem polygons, these will also be excluded from the Atlas.
- What does the remote sensing layer show?
The nation-wide remote sensing layer expresses the likelihood that landscapes are accessing water in addition to rainfall. The likelihood is expressed as a range of values between 1 and 10 (low to high), where 10 indicates landscapes that are most likely to access additional water sources. The additional water source may be soil water, surface water, or groundwater. A likelihood of 1 indicates landscapes that are most likely to rely solely on rainfall.
The remote sensing layer was constructed from multiple satellite sensors, namely MODIS and Landsat. While MODIS estimates evapotranspiration from land surface (van Dijk et al., 2011 ) and Landsat measures vegetation dynamics sustained during a prolonged dry period (Barron et al., 2011 ), the two sources were combined by converting these metrics into a standard unit based on likelihood of additional water use ranging from 1 to 10 (low to high). Within different landscapes, rules were applied to determine the combination of MODIS and Landsat data to develop a continental likelihood of IDE expressed at 25m resolution.
The limitations of the remote sensing are that the scale and resolution of the mapped information are only as detailed as the input mapping used; and features which do not influence a 30m Landsat pixel are not identified on the map. In addition, the data is dependent on the time period of the data used (2000-2010) and ecosystems water use can only be identified if active in the time period; it does not provide information on the future or the past.
- What does the Inflow Dependence (ID) layer show?
The ID layer shows landscapes that are likely to access water in addition to rainfall. The additional water source may be soil or surface water, or groundwater. The layer includes pixels from the remote sensing layer that have a likelihood of 6 or more. These pixels indicate that the landscape is more likely to be accessing an additional source of water than it is to be relying solely on rainfall (pixels with likelihood 5 and less). Pixels of likelihood 6 and more therefore include all landscapes that are likely to be inflow dependent, where 10 indicates landscapes that are most likely to be accessing additional water sources.
The IDs include a large variety of natural ecosystems (e.g. rivers, wetlands, and forests) as well as altered landscapes such as irrigated farming and channels.
- What does the Inflow Dependent Ecosystems (IDE) layer show?
The IDE layer shows ecosystems which are likely to use a source of water in addition to rainfall. This layer does not indicate whether the additional source of water is surface water, soil water or groundwater.
- What does the potential GDEs reliant on subsurface groundwater (vegetation) layer show?
The layer expresses the potential for groundwater and mapped vegetation communities across Australia to interact. It shows the vegetation communities that interact with groundwater from the watertable or in the capillary zone. The potential for other living organisms (e.g. faunal and microbiotic ecosystems) to interact with groundwater was not assessed (with the exception of burrowing crayfish in Tasmania). Information on the interaction of associated fauna or abiotic features would require additional assessment.
- What does the potential GDEs reliant on surface expression of groundwater layer show?
The dataset expresses the potential for groundwater interaction for rivers, springs, and wetland ecosystems across Australia. It shows the ecosystems that rely on groundwater that has been discharged to the surface, for example, as baseflow or spring flow.
- What does the Subterranean GDEs (cave and aquifers) layer show?
This layer shows areas where cave and aquifer ecosystems potentially rely on groundwater beneath the surface, either beneath the watertable, in the capillary zone, or the vadose zone. It generally outlines areas of karstic carbonate rocks which are known to, or potentially, host cave systems or aquifers containing subterranean GDEs.
- Are all groundwater dependent ecosystems captured in the GDE Atlas?
The mapping in the GDE Atlas relies on broad scale analysis, existing datasets and remote sensing methods. This means certain GDEs are not detected. Situations where GDEs may not be detected include:
- Very small vegetation ecosystems (less than 25m x 25m) may not influence an entire remote sensing pixel, and may therefore not identify as interacting with groundwater.
- In generally wet environments (e.g. southwest Tasmania), remote sensing techniques that rely on relationships between evapotranspiration and rainfall cannot accurately differentiate groundwater and surface water dependence. In many cases unsupervised classification of Landsat data has been successfully used to differentiate groundwater and surface water dependence within peatland and wetland environments. However, some areas of vegetation may remain less accurately differentiated.
- Vegetation or surface water ecosystems that were not represented on the existing ecosystem maps used to create the GDE Atlas maps. These ecosystems therefore do not have a mapped polygon available to represent them in the GDE Atlas.
- Vegetation ecosystems that interact with groundwater seasonally, but do not exhibit constant growth may not have been detected by the remote sensing techniques used. For example, ecosystems on discharge sands in the Northern Territory which rely on groundwater in the late wet season, but die off during the dry season.
- Vegetation ecosystems that did not interact with groundwater during the 10-year period of the remote sensing data (2000-2010) may not have been identified as GDEs.
- Is a whole polygon a GDE?
Each GDE polygon shows an area within which groundwater interaction may occur. For example, a large vegetation polygon may be assessed as having high potential for groundwater interaction, but the interaction may only occur in part of the polygon.
The larger the polygon, the less likely it is to accurately represent the spatial extent of the actual GDE. Large polygons indicate a broader grouping of landscape features. Not all landscapes indicate groundwater use, even if the polygon overall is considered to be a GDE.
- Do groundwater dependent ecosystems always use groundwater?
GDEs shown in the Atlas can use groundwater at rare intervals and still be classified as a GDE. The temporal nature of groundwater use by GDEs mapped in the Atlas was not assessed; however, where details on temporal groundwater use were available in existing data, this has been included in the attribution of groundwater dependent ecosystem polygons.
- Is the influence of river supplementation taken into account?
The influence of supplementation on rivers (e.g. by inter-basin transfers of water or flow regulation) has not been accounted for. Supplemented rivers may be represented as GDEs in the maps because they demonstrate several characteristics of baseflow rivers. This is due to additional flow from supplementation, rather than groundwater contributions.
- How accurate are the geographic locations?
The accuracy of the GDE mapping depends on the accuracy of input data. Several hundred input datasets were used so the accuracy varies across Australia. Details of the input data used are provided in the final GDE Atlas Methodology report.
- How well have the observations been checked?
Ecosystem polygons are represented as having high, moderate or low potential for groundwater interaction. There has been no field verification of the potential GDE mapping. The results were also reviewed by State and Territory representatives with groundwater and ecology knowledge of the mapped areas.
Attributes are assigned from published literature describing GDEs, and from previously existing spatial datasets. The accuracy of these attributes has not been verified.
- How do I download information from the GDE Atlas?
The following three layers can be downloaded:
- Potential GDEs reliant on subsurface groundwater presence
- Potential GDEs reliant of surface groundwater expression
- Subterranean GDEs (cave and aquifer).
Users can download the mapping, descriptive information and references.
To download large areas from the Atlas, please select the 'Download' tool from the main toolbar. This will open an export window where you can specify area and format of the download.