The vast majority of theses in this collection are open access and freely available. There are a small number of theses that have access restricted to the WWU campus. For off-campus access to a thesis labeled "Campus Only Access," please log in here with your WWU universal ID, or talk to your librarian about requesting the restricted thesis through interlibrary loan.

Date Permissions Signed


Date of Award

Fall 2020

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Sciences

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Landis, Wayne G.

Second Advisor

Matthews, Robin A., 1952-

Third Advisor

Rybczyk, John M.


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 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.




Climate Change, Ecological Risk Assessment, Toxicology, BN-RRM, Skagit River, Chinook Salmon, Organophosphate Pesticides


Western Washington University

OCLC Number


Subject – LCSH

Climatic changes--Skagit River Watershed (B.C. and Wash.)--Forecasting; Climatic changes--Risk management--Skagit River Watershed (B.C. and Wash.); Eclogical risk assessment--Skagit River Watershed (B.C. and Wash.); Fish populations--Skagit River Watershed (B.C. and Wash.)--Measurement; Chinook salmon--Skagit River Watershed (B.C. and Wash.)

Geographic Coverage

Skagit River Watershed (B.C. and Wash.)




masters theses




Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Lawrence_Skagit_BN-RRM_11-30-2020.neta (10 kB)
This is the Bayesian network model constructed in Norsys Netica software for this study. This model is viewable with a free version of the software available at