Hawkesbury-Nepean River Environmental Monitoring Program

Figure 6.6: Principal components analysis of water quality, illustrating differences
between sites upstream (US) and downstream (DS) of Yarramundi and among
individual sites
Temporal trends in SIGNAL-based assessments. Average SIGNAL-SG
(Chessman et al. 2007) scores were calculated for macroinvertebrates found at sites
on the main-stem of the Hawkesbury River, and these data are presented graphically
in Figures 6.7, 6.8 and 6.9. At sites upstream of Yarramundi (Figure 6.7) the average
SIGNAL-SG scores in edge habitats indicated a very consistent pattern over time
that does not suggest major changes have occurred in macroinvertebrate
communities (in terms of average SIGNAL-SG scores). Greater variation was found
at edge sites below Yarramundi (Figure 6.7), but there was an absence of more
recent macroinvertebrate data in these areas. Further sampling at these sites may
help determine whether these sites have also remained relatively stable over this
time period (in terms of average SIGNAL-SG scores).
The large variation between sampling events for the edge habitat may, at least in
part, be due to the types of microhabitats sampled. Sydney Water also sampled
submerged macrophyte habitat in the fluvio-tidal reaches of the Hawkesbury, finding
it a more stable habitat with a relatively extensive taxa list when compared with the
edge habitat (C. Besley (SWC) pers. comm. 2008). From 2003 onwards, the
macrophyte habitat was therefore replicated in this reach. Average SIGNAL-SG
scores in macrophyte edge habitats also indicated a very consistent pattern over time
(Figure 6.8), which again does not suggest that major changes have occurred over
time in macroinvertebrate communities in this stretch of the Hawkesbury-Nepean
River (in terms of average SIGNAL-SG scores).
Data from riffle habitats in the lower sections of the Hawkesbury-Nepean River were
less common, but, where they occurred, again there was little evidence of major
changes in average SIGNAL-SG scores over time (Figure 6.8). An unusual peak in
average SIGNAL-SG scores occurred at N53 (downstream of Penrith STP) in
autumn 2004; the reasons for this need further exploration (including potentially
looking at relationships with water quality at that time).
Although there appears to be a lack of temporal trends in the average SIGNAL-SG
scores at individual sites, there do appear to be longitudinal differences in average
SIGNAL-SG scores as you move down the river (i.e. from Maldon Weir (N92) to
Sackville (N26); Figure 6.9). The change downstream of Yarramundi is quite
Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report 29