Trigger values, in the context of the ANZECC/ARMCANZ Water Quality Guidelines, are concentrations of key indicators, above or below which there is a risk of adverse biological effects . Default trigger values have been set for ‘core’ water quality indicators for different bioregions in Australia, and are based mainly on statistical distributions.
Section 220.127.116.11 (page 3.3-5) in the Guidelines outlines approaches for deriving trigger values. Percentile values (80th and 20th) derived from statistical distributions were used to set ‘default’ trigger values for different indicators (e.g. TP, FRP, TN, NOX, NH4, pH, chlorophyll a and dissolved oxygen saturation) in different bioregions.
The default trigger values have subsequently been adopted as default water quality targets for use in regional planning.
- ANZECC/ARMCANZ (October 2000) Australian Guidelines for Fresh and Marine Water Quality.