Considerations for ecosystem receptors

Ecosystem receptor lines of evidence

At Step 3 of the Water Quality Management Framework, you could potentially select 3 ecosystem receptor lines of evidence:

  • biodiversity
  • toxicity
  • biomarkers, including biomarkers of exposure or effect and those that measure bioaccumulation.

Within each line of evidence, one or more indicators could be selected. When designing your monitoring program, consider specific requirements for different biological indicators.

Ecosystem receptors vary widely in nature, ranging from those measured solely using laboratory experiments to those that can only be measured using field surveys.

Here we address common issues relevant to ecosystem receptors when designing a water/sediment quality monitoring program.

Setting decision criteria to assess change

Irrespective of the monitoring program objective, the criteria used to assess change (including trend or ‘impact’) need to be set as part of the study design. Stand-alone guideline values for ecosystem receptors rarely exist so we usually base decision criteria on comparisons with reference or control conditions.
Procedures for setting decision criteria consist of 3 interconnected stages that need inputs from:

  • Steps 1, 2 and 3 of the Water Quality Management Framework, to select potential, relevant and sensitive ecosystem receptors (indicators)
  • Step 5 of the framework, to define water quality and environmental objectives.

Indicators are likely to vary in terms of specificity and cost so it is important to explore these issues when designing a monitoring program.
The terminology we use here will be familiar from traditional frequentist statistical methods. Similar considerations apply to Bayesian methods (Sahu & Smith 2006).

See also:

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How levels of protection affect decision criteria

The condition of an ecosystem may influence decisions about monitoring study design. We define 3 categories of ecosystem condition in the Water Quality Guidelines:

  • high conservation or ecological value systems
  • slightly to moderately disturbed systems
  • highly disturbed systems.

For high conservation or ecological value systems, the study design will need to set effect sizes and the ratio between α and β so as to be as precautionary as possible. Often there are scant baseline data for ecosystem receptors in such systems. The study design should maximise opportunities to improve baseline knowledge so that natural variation is sufficiently well characterised to allow effect sizes to be set (Mapstone 1995).

Humphrey et al. (1999) criticised aspects of the environmental impact assessment (EIA) process in Australia, saying that too often developments proceeded without adequate baseline data being gathered to detect and assess potential disturbances.

We strongly recommend that parties adopt a precautionary approach and respond wisely and in a timely manner to data gathered for ‘early detection’ indicators.

Slightly to moderately disturbed systems should be treated like high conservation or ecological value systems, acknowledging that there may be negotiated deviations from default guideline values (DGVs) prescribed for high conservation or ecological value systems. Nevertheless, any decisions on effect size should be based on sound ecological principles of sustainability rather than arbitrary relaxation of guideline values determined for high conservation or ecological value systems, or because of resource constraints.

For highly disturbed systems, our philosophy is that, at worst, water quality is maintained so that it can support the values identified by stakeholders (Step 2 of the Water Quality Management Framework). Ideally, the longer-term aim is towards improved water quality, in which case design considerations for remediation become relevant.

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