Water Quality Guidelines Online - Introduction
Water Quality Guidelines - Trigger Values
What are Water Quality Guidelines ( 'Trigger Values' ) ?
* Water quality guidelines or trigger guideline values are lists of indicator values recommended
for various beneficial uses of water, and for the protection of aquatic ecosystems.
They are numerical concentration limits, physical measures or narrative statement
recommended to support and maintain a designated water use (eg primary contact recreation).
* Guideline trigger values are the concentrations (or loads) of the key performance indicators
measured for the ecosystem, below which there exists a low risk that adverse biological
(ecological) effects will occur. They indicate a risk of impact if exceeded and should
'trigger' some action, either further ecosystem specific investigations or implementation
of management/remedial actions.
The response required when the trigger value is exceeded is outlined in the Decision
Frameworks ('Trees") that have been developed for each Environmental Value list and for
various types of compounds.
The concept of a trigger is driven by the need to set a value that is low enough to ensure that
the signal to act to rectify the problem is made before significant damage has occurred.
That is the change detected is still within acceptable limits, for example for toxicants the
trigger is deemed to occur when more than 5% of species area likely to be affected.
The specific value used depends on how quickly a response can be made.
How are the guideline and trigger values developed?
* There is nothing mysterious about the process for developing the guidelines.
Protocols have been developed for the various indicators and Environmental Values.
* The procedures and protocols are clearly described in the published guidelines, which
also includes various software tools and tables showing the information that has been used
to develop each guideline value (see Volumes 2 and 3 on the CD, which also has the
Database for Physical and Chemical Stressors and databases and software for toxicants
‘BurrliOZ’).
What about Levels of Protection?
* A level of protection is a level of quality desired by stakeholders and implied by the
selected management goals and water quality objectives for the water resource.
The water quality objectives may have been derived from default guideline values
recommended for the particular ecosystem condition, or they may represent an
acceptable level of change from a defined reference condition; it can be formalised as
a critical effect size. ( see Vol 1 page 3.1-9 for more details)
* Three ecosystem conditions are recognised:
=> 1. High conservation/ecological value systems — effectively unmodified or other
highly-valued ecosystems, typically (but not always) occurring in national
parks, conservation reserves or in remote and/or inaccessible locations. While
there are no aquatic ecosystems in Australia and New Zealand that are entirely
without some human influence, the ecological integrity of high
conservation/ecological value systems is regarded as intact.
=>2. Slightly to moderately disturbed systems — ecosystems in which aquatic
biological diversity may have been adversely affected to a relatively small but
measurable degree by human activity. The biological communities remain in a
healthy condition and ecosystem integrity is largely retained. Typically,
freshwater systems would have slightly to moderately cleared catchments
and/or reasonably intact riparian vegetation; marine systems would have
largely intact habitats and associated biological communities. Slightly–
moderately disturbed systems could include rural streams receiving runoff
from land disturbed to varying degrees by grazing or pastoralism, or marine
ecosystems lying immediately adjacent to metropolitan areas.
=>3. Highly disturbed systems These are measurably degraded ecosystems of lower
ecological value. Examples of highly disturbed systems would be some
shipping ports and sections of harbours serving coastal cities, urban streams
receiving road and stormwater runoff, or rural streams receiving runoff from
intensive horticulture.
See Vol 1 page 3.1-11 for the framework for assigning a level of protection.
Can I Develop my own Guidelines for my local Area?
* Yes you can provided you meet the requirements of protocol specified for each type of
indicator.
* Two examples of the protocols are provided below:
Protocol for Physico-chemical Stressors
The approach depends on the availability of adequate monitoring data for a properly chosen
reference site. The minimum data requirement is 24 monthly readings taken over two years.
More frequent monitoring is desirable. The protocol used to develop low risk guideline values
depends on the level of protection:
=> High conservation/ecological value (condition 1 ecosystems)
For condition 1 ecosystems, the Guidelines advise that there should be no change
from ambient conditions, unless it can be demonstrated that such change will not
compromise the maintenance of biological diversity in the system. NOTE: All the
guideline values listed for physicao-chemical stressors are for slightly to
moderately disturbed systems.
=> Slightly to Moderately disturbed (condition 2 ecosystems)
The trigger values are derived from the 80th and/or 20th percentile values obtained
from an appropriate reference system. For stressors that cause problems at high
concentrations (e.g. nutrients, salinity), take the 80th percentile of the reference
distribution as the low-risk trigger value. For stressors that cause problems at
low levels (e.g. low dissolved oxygen in waterbodies), use the 20th percentile of
the reference distribution as a low-risk trigger value.
=> Highly disturbed (condition 3 ecosystems)
For condition 3 waterbodies, derive trigger values from site-specific biological or
ecological effects data or, when an appropriate reference system(s) has been identified
and there are sufficient resources to collect the necessary information, from local
reference data. In this latter case, depending on management objectives, define trigger
values using a conservative percentile value (e.g. 80th percentile value) to improve
water quality (preferred approach), or a less conservative percentile
(e.g. 90th percentile) to maintain water quality. Use professional
judgement to determine the most appropriate cutoff percentile.
For either condition 2 or condition 3 ecosystems, where there are insufficient
information or resources to undertake the necessary site-specific studies, use the
default values provided in the lists on this web site, that are derived from regional
reference data.
For more information see Vol 1 page 3.3-5.
Protocol for Toxicants
The published trigger guideline values are referred to as default values
because they are the ones you use if you cannot derive your own values using local
toxicity data.
If there is local toxicity data that meets the requirements specified
in the guidelines, then you can derive your own values using the software
provided by the guidelines. The minimum requirement is chronic toxicity data,
or the way of estimating it from acute toxicity data, or NOEC data (no observable
effect concentration) for a number of different species.
To do this you will require good toxicity data for a minimum of five different species from
four taxonomic groups (e,g. an alga, two fish, a snail, and a shrimp). Direct toxicity data
can also be used(see the published guidelines for this). The 'Burlioz' software is simply
a robust plotting tool. It uses the five more concentrations you have produced for chronic
toxicity for the various species to derive the best estimate of the concentration expected
to protect a specified percentage of species at a test site. The target percentage
depends on the level of protection.
=> High Conservation - The target level of protection is 99% of species
=> Slightly to Moderately Disturbed - The level of protection chosen for deriving the guideline
trigger values for slightly-moderately disturbed ecosystems was protection of 95% of
species with a 50% level of certainty, at least where there were sufficient data to
satisfy the requirements of the method.
=> Highly Disturbed - The target level of protection may be 90% or 80% depending on the
severity of the disturbance.
Three reliability levels have been assigned to the guideline values for toxicants, which depend
on the quality of the toxiciy data available:
=> Highly reliable estimates were derived using good NOECs
(no-observable-effect-concentrations) for more than three species, or equivalent
derived from Chronic toxicity tests, to derive the trigger values.
=> Moderately reliable estimates were derived Moderate reliability guideline trigger values
from acute LC50 data, when chronic data was not available.
=> Low reliability estimates - Low reliability guideline trigger values
were produced when datasets were too small for the above methods (i.e. too few species
or taxa), or if data did not satisfy requirements for completeness of information on test
parameters, it was considered preferable to derive tentative or low reliability guidelines
in the interim rather than have no working figures at all. Low reliability trigger values
should only be used as indicative interim working levels for interim guidance.
The Low Reliability Values are clearly labelled when displayed in the guideline lists.
See Volume 2 page 8.3-22 for more details.
Tailoring Guideline for Local Conditions
* The guideline trigger values were mostly derived using data from controlled laboratory test
in clean water. They represent the best current estimates of the concentrations of chemicals
that should have no significant adverse effects on the aquatic ecosystem. However there are
all sorts of local effects that may modify the toxic effects of the chemical locally.
The most obvious one is hardness. You should check that you have
applied the hardness multipliers for certain toxicants (the 'H' label and footnotes identify
when hardness corrections should be applied).
There may be natural substances that occur locally that affect the biological
availability of the substance to exert its toxic effect. For example if most of the substance
you have measured at the site is locked away by being bound to organic matter, then the toxic
effect may be over-estimated. Without considering bioavailability you may initiate a
management response before it is needed. In many instances this can be checked by using
the acid-soluble fraction as the trigger rather than the total concentration.
* The guidelines allow for these local effects to be considered by using what is called
a 'decision tree' or a 'decision framework'. There are decision trees for each type of guideline.
A Decision framework/ decision tree is a series of steps for tailoring guideline trigger
values to a specific site or region and for assessing water quality by considering the local
or regional environmental factors that will modify the effect of the particular water
quality parameter.
The decision frameworks begin with the simplest steps and finish with the most difficult
and expensive.
Each step requires a decision that involves a trade-off between initiating a management
action when it may not be required, or incurring the extra expense required to check
whether a value higher than the trigger value may not in fact be adversely affecting
the ecosystem.
* Click on the link below to find out more about the decsion trees and view the online
trees for the various guideline lists.