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Derivation of Limits of Acceptable Change



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4.2Derivation of Limits of Acceptable Change

In developing LACs as part of this ECD, a number of approaches were adopted, using existing data sets and information as well as national, state and local guidelines (see also Appendix B.2).

4.2.1Natural Variability and Probability Based LACs


Defining Baseline Conditions

As outlined in the National Framework, it is most preferable for LACs to be based on the known natural variability (over time) of a parameter. The LAC can then be set at the upper and lower bounds of that natural variability profile in the time period leading up to Ramsar site declaration. However, in most cases such data are unavailable or incomplete.

Recognising these information gaps, particularly with respect to natural variability prior to listing, we have adopted the following hierarchy (in order of preference) for establishing baseline conditions and natural variability:


  1. Empirical data (pre-listing) data describing natural variability prior to site declaration; or

  2. Empirical data (post-listing) for parameters that are unlikely to have substantially changed since listing; or

  3. Empirical data/qualitative data for parameters that may have changed since listing, but represent the only available data for establishing ‘baseline conditions’.

Where there are no data (or very few data), this has been identified as an information gap and a recommended LAC has been provided that could be used, should data become available as result of future studies.

Defining Baseline Data Quality

In characterising the baseline information used in deriving LACs, the following typology has been used:


  • Level A – This LAC has been developed from data and/or information (such as bird count data, fisheries catch data or similar) that has been reviewed by the authors and deemed to be sufficient for setting an LAC. This type of LAC is typically derived from long-term monitoring data;


  • Level B – This type of LAC is derived from empirical data, but is unlikely to describe the range of natural variability in time. This can include two sub-types:

  • Repeated measurements but over a limited temporal context;

  • Single measurement (no temporal context) of the extent of a particular habitat type, abundance of a species or diversity of an assemblage;

  • Level C – This type of LAC is not based on empirical data describing patterns in natural variability. This can include two sub-types:

  • Based on a published or other acceptable source of information, such as personal communication with relevant scientists and researchers, or is taken from referenced studies as part of management plans, journal articles or similar documents;

  • Where there are no or limited data sets and a lack of published information about the parameter, and the LAC has been derived based on the best professional judgement of the authors.

The LAC tables below provide a LAC quality rating incorporating both the baseline data characteristics (see Defining Baseline Conditions above) and data quality (Level A, B or C).

Measures Used to Describe LACs

Depending on the LAC parameter under consideration, several types of measures may be used to describe natural variability:


  • Percentile values. The use of percentile values allows for some change in the measured parameter, but still within the range of natural variability. Common examples of this type of LAC include water quality and biological indicator guideline values derived from statistical analysis of reference datasets. This approach is conceptually similar to the approach used for assessing water quality guideline values (for example, ANZECC/ARMCANZ 2000). Refer to Table 4 -20 for an outline of the approach used to define percentile-based LACs.


  • An allowable proportional change relative to a baseline value. While the use of percentile values to describe natural variability (and therefore LACs) is typically preferred, this is not always possible due to data limitations (such as insufficient baseline data to derive percentile values), and/or in some cases it is not meaningful to use percentiles due to the pattern in variability of the measured parameter (for example, the extent of some habitat types which show low natural variability). Similar to the approach used to define percentile-based LACs, professional judgement was used to set ‘proportional change’ based LAC values, based on criteria outlined in Table 4 -20.

  • Broad Ecosystem State and Function

This type of LAC is based on a broad change in an ecosystem from one state to another or on the basis of the wetland continuing to provide a particular function (such as provision of breeding habitat). An example of this type of LAC is a change in a particular wetland from a freshwater system to a brackish water system. This type of LAC has the advantage of encompassing a variety of indicators, and specifically addresses ecosystem end-points that can be directly linked to high level critical components and services. This type of LAC is particularly relevant where there is a lack of data and information to support a more quantitative LAC about ecological response or threshold.
Table 4 20 Statistical measures describing LACs

Degree of change

Description


Percentile values

% change

No change

  • Parameters where any change would be considered unacceptable.

  • Parameters that show low natural variability and where even a small change would lead to a change in ecological character.

Same measure used to derive baseline. No significant change.

0% change

Small

  • Within the range of natural variability;

  • Small to moderate variations from median baseline are acceptable, as:

    • Parameter has inherent low natural variability; and

    • Is considered to represent a direct measure of a critical service/benefit or component (e.g. bird abundance).

Upper = 80th

Lower = 20th



5% change

Moderate

  • Within the range of natural variability;

  • Moderate deviations from median baseline are acceptable, as:

    • Parameter has inherent moderate to high natural variability; and

    • A change in the parameter may not necessarily translate to an ecologically meaningful change in character. These are typically critical process-based LACs.

Upper = 90th

Lower = 10th



10% change

Large


  • At or outside the range of natural variability;

  • Large deviations from median baseline are acceptable, as:

    • Parameter has inherent high natural variability; and

    • A change in the parameter may not necessarily translate to an ecologically meaningful change in character.

  • These are typically:

    • Not direct measures of critical service/benefit, component or process-based LACs, but rather broad proxy indicators of ecosystem condition; or

    • Are critical service/benefit, component or process-based LACs where some degree of change outside natural variability is not considered to result in major change to ecological character.

Values outside the range of minimum and maximum baseline.

>20% change




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