Hawkesbury-Nepean River Environmental Monitoring Program

are also highly variable in terms of the temporal and spatial frequency of sampling.
Most data received from the SCA and Sydney Water date back to the early 1980s,
although data for some individual analytes may stretch further back in time.
Additional water quality data are available for a range of shorter term studies and/or
programs, but these are dispersed and of lesser value when attempting to interpret
longer term trends. They are nonetheless valuable in their own right for the time
periods and sites covered, but no attempt has been made to try to bring all these
data into a central location for this project. Data analysed for this project have
therefore been restricted to the long-term sites monitored by Sydney Water and the
SCA and summarised in Table 3.1. These data are illustrated graphically in Appendix
3.
In terms of water quality, many areas in the Hawkesbury-Nepean can be described
as being stressed, and some areas can probably best be described as being
eutrophic. Large amounts of water are diverted for water supply and irrigation, and
nutrient levels are often high, with outbreaks of algal blooms being common.
Introduced macrophytes also occur extensively throughout the river system. When
discussions of trends are undertaken here, it should be realised that although
improvements in water quality in recent times can be demonstrated, they are
improvements from what was a relatively poor condition; water quality in many areas
of the Hawkesbury-Nepean still has a long way to go before meeting water quality
objectives (e.g. ANZECC/ARMCANZ Guidelines).
Comparison of water quality with ANZECC/ARMCANZ (2000) guidelines
An initial assessment of changes in water quality in the Hawkesbury-Nepean River
was achieved by dividing the data into three periods: the period from 2003 to 2007;
the period from 1999 to 2003; and the historic period before 1999. The quartiles (25th
percentile, median and 75th percentile), maximum and minimum of the data at each
site (Table A4.1.1 in Appendix 4) were then compared with the ANZECC/ARMCANZ
(2000) Guidelines. The results of these comparisons are included in Table 5.1: the
colour coding indicates the conformance of measured values with the ANZECC
guideline trigger values (Tables 3.3.2 and 3.3.3 in ANZECC/ARMCANZ 2000). Here,
blue indicates 100% conformance with ANZECC/ARMCANZ guideline levels,
whereas bright pink indicates 100% non-conformance (i.e. 100% of the data
recorded at that site are outside ANZECC/ARMCANZ guideline levels).
An assessment of these results suggests that:
• improvements (decreases) in the number of samples exceeding ANZECC
guidelines are noticeable at many sites in the river system (e.g. red in the historic
period changing to orange, yellow, green or blue in later periods)
• nitrogen levels are often well above ANZECC guideline levels in many parts of
the river system
• the effects of individual sewage treatment plants can potentially be inferred from
these data (e.g. Penrith STP and changes in phosphorus levels at site N53)
although other sources such as urban and agricultural runoff also contribute to
water quality in these areas
• some sites appear to be experiencing a decline in water quality on the basis of
raw data summary statistics (e.g. inorganic nitrogen [NOx-N] and total nitrogen
[TN] at sites N75 and N53)
• nutrient levels are still an important issue in South and Eastern Creeks (sites
NS23 and NS081).
Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report 17