Incorporating Climate Change Predictions in Ecological Risk Assessment: A Bayesian Network Relative Risk Model for Chinook Salmon in the Skagit River Watershed

Climate change is expected to have widespread impacts on future ecosystem services in the Puget Sound and around the world. It is important that climate change be included in ecological risk assessment so that changing climate variables and potential interactive effects with chemical stressors can be taken into account. In this research, I focused on the question of how water temperature changes generated by climate change interact with organophosphate pesticide toxicity to affect Chinook salmon (Oncorhynchus tshawytscha) population size in the Skagit River, WA. To answer this question, I conducted an ecological risk assessment using the Bayesian network relative risk model (BN-RRM). It is a quantitative, probability-based approach that calculates complex relationships between ecological variables in a cause-and-effect framework to provide estimates of risk to valued receptors (endpoints). I used region and season specific measurement data for water temperature, dissolved oxygen, chlorpyrifos concentration, and diazinon concentration as the model input. Climate predictions were based on model output between the years 2071 and 2100 from an ensemble of global climate models (GCMs) selected from the Fifth Coupled Model Intercomparison Project (CMIP5). The probability of Chinook salmon population decline, before climate change predictions were taken into account, ranged between 77.1% and 64.0% depending on region and season. I found climate change caused changes in water temperature influenced risk in different ways depending on the region and season. The probability of Chinook population decline increased by up to 4.2% in different regions and seasons. I used sensitivity analysis of the BN-RRM to analyze which stressors had the most influence on Chinook salmon population size. I found that the environmental stressors of water temperature and dissolved oxygen had the most influence, which suggests habitat remediation may be an effective strategy for addressing risk to Chinook salmon in the Skagit River. This research demonstrates that climate change scenarios can be v successfully incorporated into ecological risk assessment using the BN-RRM. This approach can be easily adapted to other watersheds and allows for the inclusion of additional stressors and/or endpoints