Problem Formulation

Problem formulation is a process for generating and evaluating preliminary hypotheses about why ecological and/or human health effects have occurred or might occur as the result of nutrient pollution. This process serves as the foundation of the assessment. Beginning with the conversations that occurred during the planning phase, this process should result in (1) assessment endpoints that adequately reflect management goals and the ecosystem they represent, and (2) conceptual models that describe key relationships between nutrients and assessment endpoints.

Formulating hypotheses and developing assessment endpoints and conceptual models starts with considering available information. Although integrating information is a continual and iterative process, initial evaluations can help generate preliminary conceptual models or assessment endpoints, which might highlight information gaps to be filled. Gathering appropriate information on sources, stressors, effects, and ecosystem and receptor characteristics can support evaluating data quality and quantity and further problem formulation. When data is limited or information gaps exist, either additional data can be collected or the assessment proceeds with available data while documenting limitations. Documenting limitations in data quality and quantity and how they relate to the uncertainty involved in assessment products is a critical step, not just in problem formulation, but also throughout the criteria development process.

Substantial amounts of nutrient pollution data have been collected over the past few decades. Many federal and state agencies have long-standing monitoring programs that make their data publicly available. Additionally, numerous academic sources are easily accessible. Many of those sources are accessible through the Data Library page.

When you are assessing available information, it might be useful to answer the following questions.

Source and Stressor Characteristics

  • What is the nutrient source? Is it anthropogenic, natural, point source, or diffuse nonpoint source?
  • What is the stressor? Is it chemical, biological, or physical?
  • What is the mode of action?

Exposure Characteristics

  • At what frequency does the stressor event occur?
  • What is its duration?
  • What is the timing of exposure?
  • What is the spatial scale of exposure?

Ecosystems Potentially at Risk

  • What are the geographic boundaries?
  • What are the key abiotic factors (e.g., climatic, geology, hydrology)?
  • Where and how are functional characteristics driving the ecosystem?
  • What habitat types are present?
  • Are there unique features that are particularly valued?

Ecological Effects

  • What type of information is available on ecological effects and how extensive is it?
  • What are the expected effects?
  • Under what circumstances will effects most likely occur?

After gathering key stakeholders and evaluating available information, problem formulation proceeds with the identification of assessment endpoints and the development of conceptual models.

  • Identifying Assessment Endpoints
  • Developing Conceptual Models

Case Studies

San Francisco Bay Endpoints

  • Increased chlorophyll a and decreased DO concentrations in recent years
  • Resilience of ecosystem appears to be weakening

Chesapeake Bay Criteria

  • Ecological conditions and associated values were identified for five bay habitats
  • Habitats’ sensitivity to nutrients was assessed
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