Caboolture Region Water Quality Study - Moreton Bay Regional ...

Caboolture Water Quality Study
Table 3. Key to symbols used in the results of integrated assessment tables.
Integrated Water
Quality Rating
Good water quality
Moderate water quality
Poor water quality
Description
Insufficient data or the detection limit was greater than the guidelines and
median was equal to the detection limit
4.2 Assessment of Long-Term Trends
Long-term trends were assessed using two independent methods: statistical regression analysis and
change in integrated water quality assessments over time (years). The regression analysis detects
linear trends in water quality data over time, ie trends of increasing or decreasing concentrations of
indicators. However the small samples sizes of the data for this study (i.e. data for only two or three
years at monitored sites) reduces the power of this technique to resolve temporal patterns.
Consequently, most discussion on temporal trends in water quality is based on changes in overall
water quality assessment at a site over years (see Figure 5). This approach provides a robust method
of detecting changes in water quality based upon their compliance with the guidelines, and as such is
likely to represent real changes in water quality.
Site
Source Water
Type
Stream Name Trend 2001 2000 1999
CAB-1 CSC UC Caboolture Rv or
CAB-3 CSC LC Caboolture Rv
CAB-6 CSC ME Caboolture Rv or
CAB-7 CSC ME Caboolture Rv
Improvement
No trend
Deterioration
Variable trend
Figure 5. Example of trend analysis of water quality assessment. The change in water quality assessments (coloured dots) over
the years 1999 to 2001 were used to assess the direction of change (if any) of an indicator (green trend= improvement, red
trend= deterioration, black trend= variable trend, blank= no trend). The direction of the arrow indicates whether concentrations
of the indicators have increased or decreased.
4.3 Data used in water quality analyses
The data from the three programs were assessed for recent water quality condition, as well as water
quality condition over previous years. Usually 12 months of monthly data is required for an accurate
assessment of water quality. Some of the water quality programs did not comprise regular monthly
sampling. As such, the data used in the analyses presented in this report were treated as follows:
CSC- Bribie Island sites (3-monthly sampling)
CSC-all other sites
EPA – all sites
PRCMP– all sites
Data collected
3/2000 – 9/2001 2001
1/1999 – 11/1999 1999
10/2000 – 9/2001 2001
10/1999 – 9/2000 2000
1/1999 – 9/1999 1999
10/2000 – 9/2001 2001
10/1999 – 9/2000 2000
10/1998 – 9/1999 1999
10/1999 – 4/2000, 12/2000 – 4/2000 2000
10/1998 – 9/1999 1999
10/1997 – 9/1998 1998
Data
reported as
14