Ecological Risk Assessment

Natural resource managers in the Alligator Rivers Region (ARR), and elsewhere in northern Australia, have few tools to determine what environmental assets are at greatest risk from multiple threats, where these range in scale from point source pollutants through to diffuse landscape-scale impacts of invasive species and, on a global scale, the impacts of climate change. However, Ecological Risk Assessment is a powerful analytical tool that allows objective comparison of the relative risk contributed by each specific ‘threat’ to ecological structures being managed. This permits risks from multiple stressors to be evaluated and communicated in a logical, robust and transparent manner. The process therefore facilitates optimum decision making for the management of natural resources through complete use of available information on potential environmental stressors, and through participative consultation with all stakeholders.

Kakadu National Park has Ramsar-listed wetlands and is a World Heritage site, but the mining and milling of uranium has occurred on a mineral lease within its boundaries for 25 years without any major off-site environmental impact. Nevertheless, Kakadu is exposed to other major ecological threats such as invasive species and climate change. For the past five years eriss has been undertaking a quantitative Ecological Risk Assessment of the Magela Creek floodplain, downstream of Ranger mine that encompasses threats identified from:

  • point source mining-related risks; and
  • diffuse landscape-scale risks.

A high protection level for the biodiversity of aquatic ecosystems was used as the assessment endpoint and, whilst measurement endpoints inevitably varied, they all encapsulate some metric of ‘species affected’ facilitating comparison between different risks. For minesite risks the focus was on three key chemicals (uranium, sulfate & magnesium) in the surface water pathway, and the focus for landscape-scale risks was wetland weeds, feral pig damage and unmanaged fire.

Additionally as part of the Tropical Rivers Inventory and Assessment Project, eriss is undertaking a broad-scale Ecological Risk Assessment of key threats to Australia’s tropical rivers.

The Ecological Risk Assessment process

Ecological Risk Assessment is the term ascribed to the method(s) for determining risk posed by a stressor (contaminant or perceived threat) to the survival and health of ecosystems. Under these procedures risk is defined as the probability that an adverse effect will occur as a result of ecosystem exposure to a particular ‘concentration’ of the stressor. Hence risk is determined by measuring two components: 

  • the consequences (also measured as effects)of an adverse event;  and
  • the likelihood or probability of the event occurring (exposure).

Using these criteria, risk is quantified as the probability of an adverse event, or the likelihood of exposure multiplied by the consequences or effects of that exposure (Prisk = Pexposure x Peffects).

Hence, the aim of Ecological Risk Assessment is to estimate the probability of adverse events from identified environmental stressors.  Traditionally, Ecological Risk Assessment has been used to investigate the effects of the release of particular chemical pollutants (toxicants) into the receiving ‘environment’. However, Ecological Risk Assessment is now applied more broadly to assess the relative impact potential of multiple ‘threats’ against measured and/or predicted impacts on environmental values (appropriate & measurable monitoring endpoints).

The systematic steps for performing Ecological Risk Assessment, as applied to an identified stressor, are outlined in Figure 1. Here it is important to emphasise the iterative nature of risk assessment in that results are updated periodically based on inclusion of new data and/or monitoring information.  Further, risk-reduction strategies are developed from improved understanding of both the risks posed by specific stressors and of the processes contributing to them. In this context Ecological Risk Assessment plays an important role in best-practice natural resource management based on adaptive management principles.

Figure 1 A basic framework for conducting Ecological Risk Assessment (adapted from US EPA1998)

Figure 1 A basic framework for conducting Ecological Risk Assessment (adapted from US EPA1998)

Consider the example of determining the risk of exposure to toxic levels of uranium to biota in Magela Creek waters downstream of Ranger mine. In this case there are two information sources for the assessment:

As illustrated in Figure 2 uranium levels for all exposure observations fall well under the effect thresholds and the risk probability for exposure to uranium at detrimental levels in Magela Ck is therefore close to zero.

 Cumulative probabily for exposure to uranium in Magela Ck, downstream of Ranger mine and for potential effects (No-Observed-Effect-Concentration) of uranium on six species of native aquatic fauna (from ecotoxicological studies). TV = monitoring trigger value for uranium in Magela Ck.

Figure 2 Cumulative probability for exposure to uranium in Magela Ck, downstream of Ranger mine (1998-2005) and for potential effects (No-Observed-Effect-Concentration) of uranium on six species of native aquatic fauna (from ecotoxicological studies). TV = monitoring trigger value for uranium in Magela Ck.

In this case the assessment endpoint used to evaluate impacts from off-site uranium contamination from Ranger mine is the conservation of the biological diversity of the ARR. Data from water quality monitoring of uranium and from laboratory toxicity testing for uranium using native aquatic species are the practical measurement endpoints used to represent potential exposure and effects, respectively. From this data risk of contamination by uranium via the surface water pathway can thereby be determined.

While risks of hazardous exposure to uranium (and other mine-related products) have been found to be extremely low in Magela Creek, a risk-reduction strategy is nevertheless in place.  Objectives for water quality management are based on minimum dilution requirements for mine-related products in receiving waters of Magela Creek. The uranium limit of 6 µg/L recommended by the Supervising Scientist has been derived using local ecotoxicological data in accordance with the Australian Water Quality Guidelines to protect 99% of the species present.  In the event that a limit is exceeded, an agreed and practical management response is identified.  In this case, therefore, risk-reduction management is intrinsically linked with the regulation and controlled release of mine waste-waters, offsite. When used in conjunction with timely monitoring information, these guidelines provide the basis for the ongoing management and re-evaluation of risks to Magela Creek biota. 

Depending on the information available for undertaking Ecological Risk Assessment, there are several approaches used to characterise risk. The classical quantitative approach, based on frequency information for effects and exposure uses null hypothesis testing & likelihood estimation (Figure 2). Where frequency data are not available a Bayesian statistical approach which involves assessing degrees of ‘belief’ using qualitative or semi-quantitative reasoning is often used.  In practice, a combination of techniques are used, where semi-quantitative assessments tend to be precursors to quantitative assessment (Figure 3). For example, conceptualising risk pathways to identify how and what risks may arise and to plan targeted monitoring is an important qualitative step from which quantitative data can then be acquired. Alternatively, applying a structured semi-quantitative approach to ranking risks (eg Table 1), which considers uncertainties, is a beneficial way of determining priorities, particularly when assessing risks from multiple stressors. This is often done using an expert technical panel to review available information.

Table 1  Risk matrix of consequences vs likelihood (adapted from AS/NZS 1999)
Likelihood Consequences
Insignificant
1
Minor
2
Moderate
3
Major
3
Unknown
4
A (Almost certain) H H VH VH U (H)
B (Likely) M H H VH U (M)
C (Possible) L M H VH U (L)
D (Unlikely) L L M H U (L)
E (Unknown) U (L) U (L) U (M) U (H) U

VH= Very High; H-High; M=Medium; L=Low; U=Unknown

Figure 3 The different levels of risk assessment (after Deere and Davidson 2005)

Figure 3 The different levels of risk assessment (after Deere and Davidson 2005)

Further reading

Andersen MC, Thompson B & Boykin K 2004. Spatial risk assessment across large landscapes with varied land use: lessons from a conservation assessment of military lands. Risk Analysis 24, 1231–1242.

AS/NZS 2004a. Risk management. AS/NZS 4360:2004, Standards Australia International, Sydney.

AS/NZS 2004b. Risk management guidelines companion to AS/NZS 4360:2004. HB 436:2004, Standards Australia International, Sydney.

Aspinall R & Pearson D 2000. Integrated geographical assessment of environmental condition in water catchments: Linking landscape ecology, environmental modelling and GIS, Journal of Environmental Management 59, 299–319.

Bayliss B, Brennan K, Eliot I, Finlayson CM, Hall R, House T, Pidgeon R, Walden D & Waterman P 1997. Vulnerability assessment of predicted climate change and sea level rise in the Alligator Rivers Region, Northern Territory Australia. Supervising Scientist Report 123, Supervising Scientist, Canberra.

Bayliss P, Camilleri C, Hogan A, Walden D, Boyden J & Begg G 2003. Uncertainty analysis of data, linking conceptual models to on-site management and communications. Discussion series on ARRTC Key Knowledge Needs: Powerpoint presentation and accompanying notes. Presentation for eriss Planning Workshop. Internal report 435, June, Supervising Scientist, Darwin. Unpublished paper.

Bayliss P, van Dam R, Boyden J & Walden D 2006. Ecological risk assessment of Magela floodplain to differentiate mining and non-mining impacts. In eriss research summary 2004–2005. eds Evans KG, Rovis-Hermann J, Webb A & Jones DR, Supervising Scientist Report 189, Supervising Scientist, Darwin NT.

Bayliss P & Walden D 2003. An ecological risk assessment of the major weeds on the Magela Creek floodplain, Kakadu National Park. Internal report 439, June, Supervising Scientist, Darwin. Unpublished paper.

Begg GW, van Dam RA, Lowry JB, Finlayson CM & Walden DJ 2001. Inventory and risk assessment of water dependent ecosystems in the Daly basin, Northern Territory, Australia. Supervising Scientist Report 162, Supervising Scientist, Darwin NT.

Bellio MG, Bayliss P & Dostine P 2004. Landscape analysis of the value of waterbirds in the Alligator Rivers Region, northern Australia. Internal Report 445. Supervising Scientist, Darwin. Unpublished paper.

Bellio MG, Bayliss P, Finlayson M & Dostine P 2004. Framework for assessing the values of waterbirds in the Alligator Rivers Region, northern Australia. Internal Report 479, July, Supervising Scientist, Darwin. Unpublished paper.

Billington K 2005. The River Murray and Lower Lakes Catchment Risk Assessment Project for Water Quality-Concepts and Methods. Environmental Protection Authority, South Australia.

Boyden JM, Walden D, Bayliss P & Saalfeld K (in prep) A GIS compendium for landscape-scale risk assessment of the Magela Creek floodplain and broader Alligator Rivers Region, NT. Supervising Scientist Report, Supervising Scientist, Darwin.

Burgman MA 2005. Risks and decisions for conservation and environmental management. Cambridge University Press, New York.

Burgman MA 2001. Flaws in subjective assessments of ecological risks and means of correcting them. Australian Journal of Environmental Management 8 (4), 219–226.

Burgman MA 2005. Risks and decisions for conservation and environmental management. Cambridge University Press, Cambridge, UK

Cain J 2001. Planning improvements in natural resources management. Guidelines for using Bayesian networks to support the planning and management of development programmes in the water sector and beyond. Natural Environment Research Council, Centre for Ecology and Hydrology (CEH) Wallingford, UK.

Davison D and Deere D 2004. Risk assessment in water supply. National Water Surveillance Conference, Dhaka, 4–6 July.

Deere D & Davidson P 2005. The Ps and Qs of risk assessment. Water March 2005.

Diamond JM & Serveiss VB 2001. Identifying Sources of Stress to Native Aquatic Fauna Using a Watershed Ecological Risk Assessment Framework. Environmental Science & Technology 35, 4711-4718.

Eliot I, Finlayson CM & Waterman P 1999. Predicted climate change, sea level rise and wetland management in the Australian wet-dry tropics. Wetlands Ecology and Management 7, 63-81.

Ferdinands K 2006. Assessing the relative risk of para grass invasion in the Magela Creek wetlands. Unpublished consultancy report to the Supervising Scientist Division, Darwin, NT.

Finlayson CM & Bayliss P 2003. Conceptual model of ecosystem processes and pathways for pollutant/propagule transport in the environment of the Alligator Rivers Region 2003

Finlayson CM & Bayliss P 2003. Conceptual model of ecosystem processes and pathways for pollutant/propagule transport in the environment of the Alligator Rivers Region. Discussion Paper prepared for the 11th meeting of ARRTC, 17–19 February 2003.

Finlayson CM & Spiers AG (eds) 1999. Techniques for enhanced wetland inventory and monitoring. Supervising Scientist Report 147, Supervising Scientist, Canberra.

Glicken J 2000. Getting stakeholder participation ‘right’: a discussion of participatory processes and pitfalls. Environmental Science and Policy 3, 305-310.

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Hart B, Burgman M, Webb A, Allison G, Chapman M, Duivenvoorden L, Feehan P, Grace M, Lund M, Pollino C, Carey J & McCrae A 2005. Ecological risk management framework for the irrigation industry. Report to National Program for Sustainable Irrigation (NPSI), Water Studies Centre, Monash University, Clayton, Australia.

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[Hart et al??? ]

Hayes EH & Landis WG 2004. Regional Ecological Risk Assessment of a Near Shore Environment: Cherry point, WA. Human and Ecological Risk Assessment 10, 299-325.

Hession WC, Storm DE, Haan CT, Burks SL & Matlock MD 1996. A Watershed-Level Ecological Risk Assessment Methodology. Water Resources Bulletin 32, 1039-1054.

Hogsett WE, Weber JE, Tingey D, Herstrom A, Lee EH & Laurence JA 1997. An Approach for Characterizing Tropospheric Ozone Risk to Forests. Environmental Management 21, 105-120.

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Landis WG & Wiegers JA 1997. Design Considerations and a Suggested Approach for Regional and Comparative Ecological Risk Assessment. Human and Ecological Risk Assessment 3, 287-297.

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Millenium Ecosystem Assessment 2003. Ecosystems and human well being – a framework for assessment. World Resources Institute, USA.

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van Dam R, Finlayson CM & Bayliss P 2004. Progress on the development of a conceptual model of contaminant pathways from Ranger uranium mine. Internal Report 474, June, Supervising Scientist, Darwin. Unpublished paper.

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van Dam RA, Finlayson CM & Humphrey CL 1999. Wetland risk assessment: a framework and methods for predicting and assessing change in ecological character. In Techniques for enhanced wetland inventory, assessment and monitoring. eds CM Finlayson & AG Spiers, Supervising Scientist Report 147, Supervising Scientist, Darwin, 83-118.

van Dam RA, Walden DJ & Begg GW 2002. A preliminary risk assessment of cane toads in Kakadu National Park. Supervising Scientist Report 164, Supervising Scientist, Darwin.

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Walden DJ, Bayliss P, Boyden JM & Ferdinands K (in prep) An ecological risk assessment of the major weeds on the Magela Creek floodplain, Kakadu National Park. Supervising Scientist Report. Supervising Scientist, Darwin.

Walden D 2000. Managing weeds in tropical wetlands: Wetland risk assessment and Mimosa pigra. Internal Report 337, Supervising Scientist, Darwin. Unpublished paper.

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