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

Caboolture River Catchment
Figure 7. Box plots of results for dissolved oxygen for sites in the Caboolture River. Refer to Appendix B,
p. 54, for details on the interpretation of box plots.
STP
STP
Weir
Figure 8. Box plots of results for total nitrogen for sites in the Caboolture River. Refer to Appendix B, p.
54, for details on the interpretation of box plots.
Nutrient concentrations have increased over recent years at most estuarine sites (Table 5). An
analysis of changes in water quality assessments suggested that at most sites between 4.8 km and
17.1 km upstream, nitrogen (in all species) has increased (Table 5, Table 23). Some sites that had
good water quality condition ratings for ammonia and total phosphorus in 2000 had poor condition
ratings in 2001; this increase may represent a real increase in nutrient input to Caboolture River, or
may be related to changes in laboratory techniques. The regression analysis of long-term trends
indicated improving trends of secchi depth at many sites (Cab-1.6, Cab-7.6, Cab-15.1, Cab-18.8) and
nutrients at sites near the river mouth since 1994. (For example, at site Cab-1.6 total phosphorus
improved by 4% and ammonia by 21% annually; see Table 28 in Appendix F for full results).
Regression analysis also indicated that pH has decreased at some of the estuarine sites since 1994,
although the amount of change was small (Table 31, Appendix D).
A comparison of water quality condition with previous years shows that most freshwater sites (CAB-
1,2,3,4) have shown improvements in nutrients and that dissolved oxygen and turbidity have also
improved at some sites (Table 5).
The pattern of poor water quality at estuarine sites and better quality water at freshwater sites was
also evident in a number of other physical indicators, including the size and integrity of riparian
vegetation, reach environs, bank stability and channel diversity (Appendix, G, ANA, 1998; SoR, 2001).
Similarly, some upstream sites in the Caboolture River have fish communities classed as being in
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