Gosford City Council Historical Water Quality Review & Analysis

INTRODUCTION 1-7
The guidelines provide trigger values for freshwater and marine water. The guidelines recommended
moving away from relying solely on chemical guideline values for managing water quality, to using
an integrated approach which would involve chemical-specific guidelines coupled with water quality
monitoring, direct toxicity assessment, and biological monitoring. This approach ensures that water
management will focus on protecting the environment instead of focussing on meeting a number.
The trigger values provided by the ANZECC (2000) guidelines are presented as three grades of
trigger values; high, moderate or low reliability. These grades are dependent on the amount of data
available and hence the confidence or reliability of the final figure. Trigger values have also been
derived for four different protection levels; 99%, 95%, 90% and 80%. The protection level signifies
the percentage of species expected to be protected by monitoring concentrations below the define
values. These values were derived using the statistical distribution method.
1.3.5 Toxicants in Sediment
Sediment are important in aquatic ecosystems as they are a source and sink for dissolved
contaminants, they influence surface water quality, and they are a source of bioavailable
contaminants to benthic biota. Consequently it is important to identify areas were sediments present a
likely threat to ecosystem health. Recommended guideline values are provided as interim sediment
quality guideline (ISQG) values. Guidelines are not specified for some contaminants, which reflects
the absence of an adequate data set for that contaminant. A value for this contaminant can be derived
based on the natural background concentration multiplied by an appropriate factor (a value between 2
and 3 is recommended).
1.3.6 Application
A framework is provided for the application of guidelines for the protection of aquatic ecosystems.
The initial step involves two stages, which are common for the application of all of the indicator types
(biological, physiochemical, chemical and sediment);
1 determine the type of water body, the environmental values, the level of protection required, the
environmental concerns, the factors that are affecting the ecosystem and the management goals;
and
2 select the indicator types depending on the first step and then determining the appropriate trigger
values.
For the remaining steps it is convenient to consider guidelines application separately for biological
indicators and non-biological indicators (physical and chemical stressors and toxicants in water and
sediments). For biological indicators decision trees are used to derive the water quality guidelines.
Non-biological indicators are based on given water quality guidelines, however, there is the option to
refine guidelines using a decision tree. The ANZECC (2000) guidelines detail the method to derive
appropriate guidelines for a specific site, instead of using the trigger values provided within the
guidelines.
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