Limitations of the receptor impact modelling

Section 2.7.1 and companion submethodology M08 (as listed in Table 1) for receptor impact modelling (Hosack et al., 2018) detail the strengths and limitations of the expert elicitation process used in BAs for building qualitative ecosystem models and quantitative receptor impact models. There is no need to revisit these here, except to acknowledge that the qualitative models and receptor impact models that were developed to represent the landscape classes in the zone of potential hydrological change for the Gloucester subregion reflect the subjectivity and bias inherent in the knowledge base of the assembled experts (e.g. in defining the scope of the model; its components and connections; ecologically important hydrological variables; representative receptor impact variables; and magnitude and uncertainty of responses to change). Thus, each model represents ‘a view’ of a landscape class or ecosystem; a view that might brook argument about some of the specifics, but would generally be accepted as an adequate, high-level conceptualisation of the important components of the ecosystem(s) it represents.

However, some knowledge gaps and limitations were identified at the expert elicitation workshops, which limit the assessment of potential impacts from hydrological changes due to additional coal resource development for some landscape classes or components of landscape classes within the zone of potential hydrological change. In other words, they limit this BA and must be flagged as areas requiring further investigation.

While some models include salinity and/or nutrient components, the expert elicitations to define the results space for the receptor impact models are premised on changes in hydrology. Changes in water quality parameters that could occur with a shift in the relative contributions of surface runoff and groundwater to streamflow or due to enhanced connectivity between aquifers of differing water quality, for example, are not represented. Thus, the potential ecological impacts due to additional coal resource development reported in companion product 3-4 (impact and risk analysis) for the Gloucester subregion (Post et al., 2018) reflect the risk from hydrological changes only; they could differ if changes in key water quality parameters had been included in the model formulation.

Climate change is not included directly in the receptor impact modelling, but a mid-range climate projection is used and potential changes to precipitation factored into the process through the surface water modelling of hydrological response variables.

The signed digraphs for Gloucester subregion were elicited from participants present at the time of the qualitative modelling workshop, with a review process to confirm that the models reflected the knowledge conveyed. The purpose of the workshop was to provide a general description of the system that could be used as a focus for subsequent receptor impact modelling in follow-up workshops. Some of the variables ultimately used in the receptor impact modelling are not shown in the sign-directed graphs or are examples of more generic functional components. For instance, hydropsychids can be seen as an example of ‘high-flow macroinvertebrates’ in perennial streams. While the focus in the receptor impact modelling workshops across the Bioregional Assessment Programme closely followed the elements in the signed digraphs from the preceding qualitative modelling workshops, there were changes for some landscape classes in the Gloucester subregion. This reflected refinements to the receptor impact modelling process (the Gloucester subregion was the first) and the differences in the collective expertise between the two workshops.

There are opportunities for further refinement of the riverine signed digraphs, with some links and components subsequently identified that may be important. For example, with the intermittent landscape class some follow-up discussion as part of the review process has indicated that the ‘surface water regime’ (SWR) could also be linked with other components such as fine sediments (FS) and upstream recruitment (UR). Other discussion focused on the relationship between carp on submerged macrophytes, and the need to consider a predator-prey link between carp and small native fish (GS NF) or invertebrates (SW MI) in the signed digraph.

The canopy cover of woody vegetation, density of Hydropsychidae larvae, density of eel-tailed catfish and richness of hyporheic invertebrate taxa receptor impact variables for the perennial streams and intermittent streams were selected as indicators of instream ecosystems. They have been identified as sensitive to changes in hydrology and can represent the response of other components of the ecosystem to changes in hydrology. The criteria for selecting the receptor impact variables are discussed in detail in companion submethodology M08 (as listed in Table 1) for receptor impact modelling (Hosack et al., 2018). The receptor impact variables identified reflect those criteria and the ecological experts available at the workshops, but may benefit from testing and further consideration of their optimality over time. The extent to which the receptor impact variables are suitable indicators of ecosystem response for all instream ecosystems across the Gloucester subregion has not been established. The interpretation of results of the receptor impact models presented in companion product 3-4 for the Gloucester subregion (Post et al., 2018) is couched in terms of risk to instream habitat, rather than risks to the receptor impact variables themselves.

Qualitative models were developed for the ‘Forested wetlands’, ‘Wet sclerophyll forests’ and ‘Dry sclerophyll forests’. The ‘Forested wetlands’ landscape class focused on the role that the forest canopies play in providing flower nectar, habitat structure for nesting, and general habitat for various bird predators. There are opportunities for further refinement of the signed digraphs, including a stronger representation of the intrinsic responses of vegetation to groundwater even though the information on individual plant species response to shifts in depth to groundwater is limited. Discussion as part of the review process has focused on the link between forest fragmentation (FF) and forested wetland overstorey (FWOS), extending potential links from forest habitats' (FH) and flowers and nectar (FN) to other fauna (e.g. other birds, flying foxes), considering the potential absence of links to herpetofauna (e.g. frogs, reptiles) or insects, and the ecological role of organic matter cycling. Analogous opportunities around the qualitative modelling typically extend to ‘Wet sclerophyll forests’ and ‘Dry sclerophyll forests’. Receptor impact modelling could be conducted for ‘Forested wetlands’, ‘Wet sclerophyll forests’ and ‘Dry sclerophyll forests’.

The groundwater-dependent landscape classes cover fairly small areas within the zone of potential hydrological change, and none of these landscape classes are subject to drawdowns greater than 2 m. While there is uncertainty as to the frequency, timing and duration of groundwater use in the Gloucester subregion, the analysis would benefit from an additional elicitation process with experts around the potential implications of up to 2 m of drawdown.

A more comprehensive listing of the gaps and opportunities that have emerged during the Gloucester subregion BA is provided in Section 3.7 of companion product 3-4 (Post et al., 2018).

Last updated:
14 November 2018