The Waquoit Bay Watershed Ecological Risk Assessment Conceptual Model

Below, you will find a large drawing that is chock full of information about the Waquoit Bay watershed. The diagram is called a conceptual model, and it is a central part of the ecological risk assessment underway in the Waquoit Bay watershed. What is an ecological risk assessment (ERA)? It is a process that evaluates ecological effects caused by human activities, or the likelihood that adverse effects might occur. The U.S. Environmental Protection Agency developed guidelines for performing ERAs on watersheds and invited Waquoit Bay to participate as a case study, a site where the developed methodology could be tested.

The risk assessment method provides a step-by-step process for identifying valued natural resources and evaluating the risks to those resources, using information from the public, resource managers, and the scientific community. The process has three stages. During the first phase, all relevant information is gathered and summarized in a problem formulation document. During the second phase, the risk hypotheses are analyzed, and during the third phase, the risks to the system are characterized, including uncertainty estimates. Waquoit Bay has completed the first phase and is ready to begin the analysis phase. The conceptual model is our guiding diagram as we move from one step to the next. It is important to note that the conceptual model is dynamic; as we learn more about the systems, we adapt the model. It must also be understood that our ecological risk assessment is not all-inclusive. Constraints of time, data availability and funding have limited the scope of the Waquoit Bay ecological risk assessment case study.

The conceptual model diagram shows land use activities (top) that are sources of harmful agents or stressors (middle) that have adverse effects (lower middle) on valued resources (bottom). Because of space constraints, the conceptual model depicted here is simplified and does not show us how we think the stressors adversely affect the valued resources. In a more complete conceptual model, additional lines and accompanying text would actually diagram the risk hypotheses to be analyzed during the risk assessment process. For example, one hypothesis to be evaluated is that nutrients fertilize the water increasing the growth rates of opportunistic algae. These algae shade the water column or grow over the bottom of the bay decreasing the light available to eelgrass, causing a loss of eelgrass. As part of the analysis phase of the ecological risk assessment, scientists will use computer models to evaluate the relationships between nutrient loading and its affect on algae and eelgrass. This study, which we expect to begin in 1997, will provide resource managers with much needed information about how to manage nitrogen inputs to coastal bays. For the present, our analyses will be restricted to impacts on eelgrass meadows; if additional funding becomes available, we would like to evaluate risk to other valued resources in the Waquoit Bay watershed.

The conceptual model underlines the old adage that a picture is worth a thousand words. The diagram may look a little confusing at first, and if you think you could begin anywhere on it and follow the lines, you are correct! Let's begin along the bottom where you see the words, "Valued Resources." The hexagons contain the resources that the general public, local resource managers and scientists agreed that we want to protect. These valued resources have societal and ecological value and are at risk. Now skip to the middle of the model. Here you see ovals containing the agents or "stressors" that are causing problems. Different kinds of lines (solid, dashed, thick or thin) from each stressor extend down to the "Valued Resources." The same lines also extend up from the stressors to the sources of the harmful agents. Here along the top we see shaded rectangles containing land uses activities. What the conceptual model shows is that our every day activities and behaviors are sources for the stressors that impact the resources we value.