Date of Award

Winter 2018

Rights

Access is available to all users

Date Available to Non-EWU Users

February 2023

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

Abstract

This study analyzed macroinvertebrate communities of the Spokane River to determine: 1) accumulation of toxic trace metals in macroinvertebrate tissue, 2) effects of aquifer recharge, and 3) impact of urbanization. I predicted that aquifer inflows of cold, clean water would mitigate effects of pollution, and that reaches above the City of Spokane would be less negatively affected by urbanization; both were unsupported. I also predicted that effects of toxic trace metals would decrease within distance downstream; this prediction was supported. I sampled 12 riffles of the Spokane River between the Washington/Idaho border and Riverside State Park in late summer 2010. Six riffles were downstream of the City of Spokane (downstream), 3 were within suburban areas upstream of the City of Spokane with aquifer recharge (upstream gaining), and 3 were within suburban areas upstream of the City of Spokane without aquifer inputs (upstream losing). Four macroinvertebrate metrics indicated that the upstream gaining reach had the most anthropogenic degradation, with the highest proportion of dominant taxon (p=0.01), and proportion Chironomidae (p=0.0453), as well as the lowest proportion Clinger (p=0.01) and Shannon Weaver Diversity values (p=0.001). The downstream reach had the highest family taxa richness (p=0.01), EPT taxa richness (p=0.001) and proportion Trichoptera (p=0.01). These results supported the hypothesis that metal effects would decrease with distance downstream from the source, the Lake Coeur d’Alene basin, indicating that toxic metal effects are more significant than urbanization effects on Spokane River macroinvertebrates. Patterns of trace metal concentrations in macroinvertebrates tissues in this study are consistent with patterns from 1979-1981 and 1999. Concentrations in the tissues of Hydropsyche cockerelli declined with distance downstream of Lake Coeur d’Alene for Cd, Pb and a combined index of Cd, Pb and Zn (p=0.016; p=0.054; p=0.0426). The robust data in this study reflect an effective sampling protocol to address differences between reaches. With a large current investment in restoring the Spokane River, repeating this bioassessment could be an effective tool to address the ecosystem health of the river and effectiveness of restoration practices, particularly if the number of sampling sites can be expanded in areas of significant degradation.

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