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3.9Conceptual Models


Several conceptual models have been prepared to support this ECD, in particular to illustrate the interaction of critical components and processes to produce ecosystem services/benefits.

In seeking to logically characterise the broad range of wetland habitats present in Kakadu National Park, the models reflect: the coastal and estuarine areas that are characteristic of the northern areas of the site around the mouths of the major rivers; the wetland environments within the floodplains themselves which link the estuarine and freshwater habitats; and the freshwater dominated wetland systems associated with the upper catchment of the floodplain leading into the escarpment and the Stone Country.

Figure 3 -47 provides an overview of the locations of wetland conceptual models presented in the ECD, noting the selection of the representative environments that have been chosen to demonstrate the interaction of critical ecosystem components, processes and services.

Figure 3-27 depicts the estuarine shoreline and island habitats that are characteristic of those wetlands found at and around the mouth of the South Alligator River. The wetland environments within this area are strongly influenced by tidal processes, noting the remarkable diversity of wetland environments (and associated ecosystem services) supported by Field Island.

Figure 3 -49 and Figure 3 -50 depict the floodplain wetland habitat characteristic of the South Alligator River near the tidal interface of the River with the Yellow Water area. Seasonal models have been presented (dry season and wet season) to illustrate the changes to use of the site during the seasonal cycle by waterbirds, crocodiles and other key wetland fauna. In the tropical monsoon environments of Kakadu National Park, these species and groups are heavily influenced by water levels, rainfall and other climatic conditions which control key life cycle processes such as migrations and breeding.

Figure 3 -51 depicts the freshwater wetland habitats characteristic of the upper catchment of the South Alligator and Magela Floodplains, leading through the monsoon forests into the escarpment and the Stone Country. As outlined in the critical services section, the pool habitats within the escarpment are particularly notable in this region of the Park, supporting a range of endemic invertebrate and fish species, freshwater crocodiles and various waterbird species.


Figure 3 47 Overview of wetland conceptual models





Figure 3 48 Shoreline and island conceptual model

Figure 3 49 River floodplains and billabongs (dry season) conceptual mode



Figure 3 50 River floodplains and billabongs (wet season) conceptual model



Figure 3 51 Upper catchment, escarpment and stone country conceptual model


4Limits of Acceptable Change

4.1Background

A key requirement of the ECD is to define the limits of acceptable change (LACs) for the critical components, processes and services/benefits of the wetland. LACs are defined as ‘the variation that is considered acceptable in a particular measure of feature of the ecological character of the wetland’ (DEWHA 2008). The LACs may equal the natural variability or may be set at some other value. LACs are based on quantitative information from relevant monitoring programs, scientific papers, technical reports, or other publications and information about the wetland or input from wetland scientists and experts.

Consistent with the above, the approach taken for the identification of LACs for the Kakadu National Park Ramsar site has been the following:


  • to assess natural variability and provide limits of acceptable change for each of the critical services/benefits and to identify, where relevant, particular aspects of the service for which LACs have been derived, and

  • to assess natural variability and provide LACs for critical wetland ecosystem components and processes specifically in the context of those wetland species (for example, species of conservation significance), populations (for example, waterbirds, fish) and habitat types (for example, seagrass, Melaleuca) that underpin the critical services/benefits.

It should be noted that in deriving the LACs as part of the current study, there are significant data and knowledge gaps and as a result, there are high levels of uncertainty associated with deriving the limits. As such, the LACs should be regarded by the site manager and other users of the document as being based on current knowledge and best professional judgement at the time of preparation of this ECD document, but need to be subject to further expert review over time and evaluated as knowledge about the site and it’s ecological character improves.

In interpreting and assessing compliance with the LACs, a change to ecological character will generally be deemed to have occurred where an LAC has been exceeded. In most cases this will need to be determined through monitoring of the extent and condition of key wetland parameters (refer Section 7.2) and may require several sampling episodes in order to determine that the change is not part of broader natural variability of the system (for example, LACs based on a percent reduction in the use of the site by waterbirds based on successive counts of waterbirds over a specified time period).

It should also be noted that there may be a range of processes occurring outside of the site that could affect the exceedance of a particular LAC; for example, the populations of migratory species that use the site. As such, in the future evaluation of LACs it is important to determine if the underlying reason for the exceedance of an LAC is attributable to natural variability, related to anthropogenic impacts on or near the site or alternatively a result of anthropogenic impacts off the site (for example, lack of available breeding habitat for migratory birds in the northern hemisphere).




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