This study has contributed to the development of the reference condition approach in
disturbed landscapes. The reference condition approach has been an important development
for the bioassessment of aquatic ecosystems by providing a practical tool for the accurate
assessment of river condition. The selection of appropriate reference sites is critical to the
success of the predictive model in terms of being able to distinguish between natural variation
in biota and the effects of human disturbance. Capturing natural variability and explaining it
is a key difference between the reference condition approach and other study designs (e.g.
before/after/control/impact). Natural disturbances such as drought or bushfire can
significantly alter the ecological condition of streams, and although the ecological condition
of streams affected by natural drought or bushfire is part of the natural cycle, this natural
variation of the ecological condition is rarely incorporated into many study designs because of
a mismatch in time scales. Human disturbance has also significantly altered the condition of
landscapes through the development of agriculture and urbanisation. In urban or agricultural
landscapes it can be impossible to locate streams that have not been modified by human
activity for use as a reference condition. This study looked at the effects of natural disturbance
on the reference condition, in terms of the way natural disturbance affects the prediction of
stream condition and also the incorporation of the condition of streams experiencing natural
disturbance into a predictive model. Additionally this study identified an alternative
benchmark for modified landscapes based on the presence of good management practices for
river protection, and tested this benchmark for the assessment of streams impacted by
urbanisation.
Drought and bushfire regularly disturb aquatic ecosystems in Australia, and affected reference
sites in the ACT and South Coast region of New South Wales in 2002 and 2003. Drought and
bushfire conditions affected macroinvertebrates and environmental variables across these
streams, and the majority of sites were assessed as significantly impaired using regional
AUSRIVAS (AUstralian RIVers Assessment System) models. This indicated the existing
reference conditions for these regions had not incorporated the ecological conditions of
reference sites suffering these natural disturbances. Many of the environmental variables used
to predict the condition of streams were also affected by drought or bushfire. The changes to
environmental variables affected how sites were assessed in models, but the overall
assessment was not significantly changed from the initial assessment that drought or bushfire
had significantly impaired the ecological condition.
To reduce potential assessment errors associated with changes to predictor variables an
attempt was made to construct new models with changeable variables excluded. However, it
was not possible to completely exclude these types of variables, and subsequent models were
no better than the original models in terms of changes to predictor variables affecting the
generation of expected taxa lists. The changes to environmental variables did not affect the
actual assessment of site condition because although group membership probabilities were
changed the probabilities of taxon occurrence did not change significantly. The different
reference site groups all contained some common taxa that occurred at most sites and even
when group probabilities changed this did not change the probability of these taxa occurring
at a test site. For regional models, such as the ACT or NSW South Coast, changes to predictor
variables may not significantly affect the assessment of site condition.
Incorporating reference sites under drought conditions into a predictive model was an
effective way of discriminating the effects of drought from human disturbance. The model
only provided two different ecological conditions, a single drought measurement and a single
non-drought measurement, so the model did not fully encompass the potential natural
variability. The model has value as a starting point and was effective in distinguishing sites
affected by human disturbance from sites affected by drought.
Good Management Practice (GMP) for river protection is any intervention that minimises
human impact on stream condition. Urban sites protected by GMP were used as an alternative
benchmark to a minimally impacted reference condition. The criteria used to select reference
sites were not sufficiently robust to detect a significant benefit of GMP on physical or
chemical characteristics of protected sites, compared to sites without GMP. In general
however, the physical and chemical condition of GMP sites was better than sites without
GMP and there were significant differences in macroinvertebrate assemblages of GMP and
non-GMP sites. A refinement to the site selection process is proposed to include a specific
assessment of GMP effectiveness for the protection it is designed to provide. This will
substantially improve the robustness of a GMP benchmark and provide a clearer picture of the
factors controlling biota in urban streams protected by GMP.
The GMP benchmark was developed into a predictive model for the assessment of urban
stream health, and in terms of the assessment of test site condition, it did not differ
significantly from a model using minimally impacted sites. The purpose of the GMP
benchmark was to provide an alternative reference condition for the assessment of stream
health in modified landscapes when minimally impacted sites are unavailable or provide an
unattainable benchmark. The GMP reference condition as an alternative can provide an
attainable and realistic benchmark. The development and application of the suggested site
selection protocol will improve the robustness of the GMP benchmark and better account for
natural variation in the biota and physical characteristics of the sites used to determine the
reference condition.
| Identifer | oai:union.ndltd.org:ADTP/202605 |
| Date | January 2007 |
| Creators | Sellens, Claire, n/a |
| Publisher | University of Canberra. School of Resource, Environmental and Heritage Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Claire Sellens |
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