Planning a Watershed Risk Assessment

Problem Formulation Phase

Problem formulation provides the organizing framework upon which the entire risk assessment depends. In this phase, the assessors use available information on ecological resources potentially at risk, stressors, and observed or anticipated ecological effects, to describe the nature of the problem and identify measurable traits of the ecological resources that can be used as indicators (note: due to the ambiguous use of this common term, risk assessment guidelines recommend using the more specific terms measure of effect, measure of exposure, and assessment endpoint, as appropriate). The problem formulation phase then produces a conceptual model of interrelationships among resources, stressors, and effects, and focuses the forthcoming analysis phase on answering one or more questions. When problem formulation is complete, the risk assessors should have a clear focus for the assessment and a plan for the analysis phase. Even if the remaining assessment phases are not carried out, the problem formulation alone is extremely valuable to watershed management because it summarizes often complex environmental risks, impacts and relationships in an organized manner.

Gathering available information about the watershed, its ecological resources potentially at risk, stressors and exposure opportunities, and ecological effects is a practical starting point. The type, quantity and quality of existing information determine whether problem formulation is easily completed, or if time must be spent filling key information gaps. In this phase, enough information must be available to define or conceptualize the watershed problems and risks, but not yet to analyze or quantify them. Existing information does need to be evaluated for data validity and information gaps, to guide further data collection. Evaluating available information will also help the assessors identify known and unknown relationships among stressors, exposure scenarios, and effects; much of the assessment will focus on improving the understanding of these relationships.

Ecological resources potentially at risk. In the planning process, stakeholders identified (possibly in non-scientific terms) the watersheds valued ecological resources of concern. These valued resources are an important focus of the problem formulation phase. Describing the basic characteristics of the watershed ecosystem is now necessary, as it provides a backdrop for evaluating the stakeholders concerns and then determining which of the valued watershed resources may be at risk. Important watershed properties to consider include the abiotic environment, biotic community structure, and ecosystem processes. After characterizing the watershed, assessors can restate the stakeholders concerns in scientific terms, including how and where in the watershed adverse effects might occur. Assessors should also begin to focus on specific watershed traits that are measurable and might indicate changes in the condition of valued ecological resources.

Stressor (and source) characteristics. Stressors are defined as any physical, chemical, or biological entity that can cause an adverse effect. Typically a wide range of stressors affects a watershed, and these may originate from stressor sources including a wide variety of human activities and natural processes. Here, too, it is important to note stressor characteristics that are measurable and potentially useful in developing measures of exposure. The stressor evaluation process should be made through the collective best professional judgment of an interdisciplinary team. Occasionally, a large number of stressors may be identified; the team may then focus on the ones most likely responsible for adverse effects on the watershed.

Example Stressor Characteristics:

• Type (chemical, physical, biological)
• Intensity (concentration or magnitude)
• Duration (short or long term)
• Frequency (one time, episodic, continuous)
• Timing (relative to seasons, life cycles)
• Scale (extent, spatial heterogeneity)

Ecological effects. In some cases ecological effects (e.g., fish kills, declining biodiversity) may already have been observed in the watershed. Other situations may involve expected effects, based on experiences elsewhere or on knowledge of the watershed and its ongoing changes. In any case, information on ecological effects is essential for the analysis of how stressors pose specific risks to the watershed.

Once the available information on ecological resources, stressors and effects has been gathered, it is used to:

• Identify and select the specific subjects of the assessment (the assessment endpoints);
• produce a conceptual model and associated questions that the assessment may address; and
• define a plan of action for the analysis phase and measurements that are needed.

Endpoint selection. Assessment endpoints are selected which provide a link between what can be measured (e.g., mussel species richness, used for the Clinch Valley assessment) and one or more management objectives (e.g., protecting threatened and endangered mussel species). Assessment endpoints are related to the management objectives and the valued ecological resources identified during planning, but they are more specific, and focus on a key characteristic of the valued ecological resource to be assessed. Three criteria for assessment endpoints are:

• relevancy to important traits of the ecological resource at risk;
• relationship to policy goals and resources valued by the community; and
• susceptibility to the stressor.

Several assessment endpoints may be used in one assessment to cover the range of management objectives and valued ecological resources, and also to help build stakeholder and manager acceptance. Assessment endpoints are often not easily measured. When direct measurement is not possible, the next step is to select measures of effect, formerly called measurement endpoints, which are measurable responses to a stressor. They are selected for their suitability in detecting changes to the broader assessment endpoint, singly or in groups (e.g. as an index), as well as for their ability to be measured accurately, consistently and economically. See the accompanying figure for examples of how objectives, valued resources, assessment endpoints, and measures of effect all interrelate.

Endpoint selection is of particular importance because this step translates abstract management goals to scientific measurements -- this is often a challenge in watershed management. Documenting the reasoning behind this linkage is also crucial when explaining scientific results at the end of the assessment.

Conceptual model development. The conceptual model consolidates all of the above and describes, in narrative and graphical form, relationships among human activities, stressors, and the effects on valued ecological resources. At this point in the assessment these relationships are based on best professional judgment, but usually not yet quantified; yet the framework for analysis and assessment is clearly described therein. This analysis plan then documents the exposure/effects relationships that will be quantified in the analysis phase, the data needed and measures to be used, and how risks will be described.

Developing the conceptual model provides a forum for discussion, a framework for understanding and explaining the problem's details, and a structure for the forthcoming analyses. Conceptual models may evolve as a better understanding of sources, stressors and pathways is acquired. Developing them also provides decision makers with a record of the opinions of the local and scientific experts and the references upon which the opinion is based. This record of supporting information later makes decision making more credible. The accompanying figure lists other positive contributions of conceptual model development observed in watershed ecorisk case studies.

When problem formulation is completed, the assessors should have:

• a conceptual model describing relationships among stressors, ecological resources, and effects;
• a set of questions that will be addressed in the assessment;
• assessment endpoints that identify what properties of the valued ecological resources will be assessed;
• identified measurements that will be needed to quantify risks or impacts;
• an analysis plan to guide the next phase of the assessment.

Ecological Risk Assessment Flow Chart