Hawkesbury-Nepean River Environmental Monitoring Program

Sites upstream and downstream of dams, and at reference sites in the
Hawkesbury-Nepean River
An assessment of the effects of dams and weirs on diatom and macroinvertebrate
assemblages of the Hawkesbury-Nepean River system was undertaken by
AWT(1998) and Growns and Growns (2001). As part of the SCA’s Woronora
Environmental Flows Project, sampling of macroinvertebrates (and diatoms) was
repeated in 2002 at the same sites (with some additional sites in the Woronora
catchment) and using (as far as possible) the same design as Growns and Growns
(2001). This project has continued to sample macroinvertebrates over the intervening
time period, meaning that some sites have now been sampled over a period of
approximately 12 years (with a gap of about 5 years between 1997 and 2002).
Sampling in the later period has been undertaken consistently by Ecowise
Environmental under contract to the SCA (Ecowise Environmental 2007). A list of the
monitoring sites considered in this section is included in Table A5.1.1 (Appendix 5).
A complicating factor in the analysis of these data is the different organisations and
slightly different methodologies used to collect the data in different time periods.
Macroinvertebrate samples collected by Sydney Water/AWT were generally sampled
twice a year in autumn and spring using the methodology described by Chessman
(1995), AWT (1998) and Growns and Growns (2001). Samples collected by Ecowise
Environmental as part of the SCA’s Woronora Environmental Flows Project were also
usually sampled twice a year in autumn and spring but were collected using
AusRIVAS protocols. The latter methodology is further described by Turak et al.
(1999, 2004) and Ecowise Environmental (2007).
In order to compare the results from these programs, (at least) two assumptions
need to be made, i.e. that:
• the taxonomy is consistent between the two organisations and over the two main
periods of sampling
• the families or genera collected in samples are not greatly affected by slight
differences in the sampling methodology used by the two organisations.
The first assumption was addressed by matching the taxonomic levels used by
Growns and Growns (2001) with that of Sydney Water/AWT and Ecowise
Environmental. This involved pooling of some genera into higher taxonomic
categories (e.g. subfamilies of the Chironomidae) to achieve consistency with earlier
taxonomic resolutions. The taxonomy used is described further in Table A5.1.2
(Appendix 5). It still relies, however, on consistent identifications by individual
taxonomists/scientists (i.e. a lack of individual operator effects). The second
assumption has been investigated previously by Growns et al. (1997, 2006) who
found similar results were obtained when four live-sorting methods were used in
rapid biological assessments.
What these differences in sampling methodologies mean, however, is that any
putative temporal changes over time are confounded by changes in sampling
organization, sampling protocol and operator differences (assuming they are still
sampling the same site) 12 . This issue is returned to later in the discussion.
The impacts of river regulation have already been assessed by Growns and Growns
(2001) and Ecowise Environmental (2007). The objective of this section is therefore
12 Although every attempt was made to relocate the sites sampled by Dr Growns and
described by AWT (1998) and Growns and Growns (2001), there remains the possibility
that the stream reach sampled may be slightly different (but most likely within 100’s of
metres) from the site originally sampled.
Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report 33