A Guidebook to Environmental Indicators

Questions of risk are involved:

	how critical is the answer?
	is a surrogate or approximation acceptable?

Environmental indicators are measures of physical, chemical, biological or socio-economic factors which best represent key elements of complex ecosystems or environmental matters. To achieve their aim of accurately and relatively simply reflecting often complex realities, indicators need to be based on system knowledge and understanding and be embedded in a well-developed interpretive framework. A monitoring program of repeated measurements of the indicator, in various places and times and in a defined way, will give the basis for detecting environmental change, through comparison with a benchmark set or condition.

The indicator must reflect the aspect of the system that is the objective of the monitoring.

	It may be a key species (such as koalas on Kangaroo Island) which provides information about the system and other species dependent on it.
	Or it may be a key process (like watertable change) which reflects changes in ecosystem, landscape or catchment scale processes.

An assessment of risks associated with the choice of indicators should be made. This will be based on how critical it is to monitor a particular system and whether the indicator will provide sufficient information about the changes in the system to manage them better. Where it is too expensive to provide a desirable level of accuracy, it may be necessary to trade-off maximum benefits and use a less accurate indicator (a surrogate): the fact that a compromise has been made should be made clear.

To understand what indicators mean, it is usually necessary to have good knowledge of how a system behaves. What is the range of natural variation? What happens if the system strays outside this natural range? Will natural functions be slowly degraded, or is there a point at which the whole system will suddenly collapse?

Pitfalls of using environmental indicators
Environmental indicators are windows to highly complex and variable systems. They are tools for extracting what is critical, for synthesising multi-dimensional information, or integrating the influences of many processes. However, these characteristics can be a weakness. As in many arenas, great care must be taken not to over-interpret the story which a simple measure tells of a complex system and not to misinterpret or confuse short and long term trends.

Because the scope of any one indicator is usually limited, they should be used in suites to give a more complete picture of a system.

There is danger associated with trying to combine indicators into a single index of a system (an environmental counterpart of the Gross Domestic Product), and basing decisions on that single measure.

Without system understanding, it can be difficult to select and interpret indicators and to be sure they will provide useful, credible and statistically valid information. The better an ecosystem is understood, the easier to select the best indicators and assess what changes in them mean.

The level of gases in the air near industrial plants can indicate processes with potential impacts at various scales.

Normally, monitoring a complex natural system requires an integrated suite of indicators. The better our understanding of the system and the causal relationships within it, the smaller that suite can be. Understanding cause and effect relationships will also make it easier for managers to decide what action to take. For example, the relationships between the concentration of air pollutants in cities, emissions from vehicles and other sources, and weather events, are quite well understood. So, a manager could chose at some point to control industry emissions, use of wood stoves, or road traffic, based on weather indicators.

Some systems have emergent properties - of the system as a whole rather than individual parts. If emergent properties can be understood and measured, they are often better summaries of the state of the system than measures of individual components. For example, it is far easier to measure the pressure of a gas than to track the velocity of each molecule. Unfortunately, it is less clear how to identify and measure emergent properties of ecological systems. Suggested measures include the time taken to recover from disturbance, productivity trends, and biodiversity.