Hawkesbury-Nepean River Environmental Monitoring Program

Figure 5.10: Oxidised nitrogen levels at Sharpes Weir
• Dissolved oxygen and temperature levels have largely remained steady, although
slight increases in temperature are suggested at sites upstream of Wallacia Weir.
• Conductivity levels appear to be increasing at the majority of monitoring sites 6 .
Although the absolute magnitude of this increase is not large and conductivity
levels are still well within ANZECC/ARMCANZ guidelines, the
ANZECC/ARMCANZ guidelines for conductivity in lowland rivers are quite broad
(125 to 2200 µS cm –1 ).
• Chlorophyll-a levels have mostly declined or remained stable at most sites.
• Cyanobacterial cell counts have largely remained stable, although some slight
increases are suggested (at sites N21, N38, N39, N57, N67 and N92). Most
recent blooms downstream 7 of the dams have not been dominated by Microcystis
or Anabaena, although Anabaena was the dominant species in the January 2007
bloom at Maldon Weir.
• Trends in other water quality indicators were variable among sites.
6. Trends in biological indicators
Aquatic ecology in the Hawkesbury-Nepean River system is affected by flow and
water quality, changes due to catchment disturbance and runoff, the discharge of
treated effluent, and flow regulation and modification. Long-term information on
biological indicators is much more limited than that on water quantity and quality. The
most well-developed and widespread of the available biological indicators are
macroinvertebrates collected by the methods of either Chessman (1995) or Turak et
6
This is in agreement with the findings of Wood, J. (2006) Western Sydney Salinity: Water
Quality Assessment. Report prepared for the Hawkesbury Nepean CMA, NSW
Department of Natural Resources.
7
At the time of writing, Microcystis was the dominant alga present on the surface of
Warragamba Dam.
22 Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report