Date of Award

Spring 8-1-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Aaron Gooley

Second Advisor

Rusty Gonser

Third Advisor

Jeffery Stone

Abstract

Across the United States, dam removals are increasing in frequency. Despite this, the effects of dam removal on freshwater food webs are under-studied. Most existing studies investigate the impacts on fish assemblages, and very few investigate the impact on diatom, crayfish, and turtle communities. Furthermore, low-head dams are more abundant than large hydropower dams, yet the impacts of their removal are less studied than their larger counterparts. I used a Before After Control Impact (BACI) study design to survey populations of benthic diatoms, riffle-dwelling crayfish, and aquatic turtles. Species richness, species evenness, and Shannon Diversity Index values were used to quantify changes in biodiversity in all populations after the dam removal. Relative abundance and biomass were also used for crayfish and turtle populations. Habitat metrics such as stream width, depth, and conductivity were also measured. At the dam removal site, all biodiversity metrics significantly declined in diatom and turtle assemblages. At the control site, biodiversity metrics did not significantly decline, suggesting that changes can be attributed to the impact of dam removal. Riffle-dwelling crayfish expanded their range into newly formed riffle habitat, and abundance, biomass, and biodiversity metrics increased at the dam removal site but not at the control site. Stream width and depth significantly decreased at the impact site but not at the control site. Based on my results, I can conclude that the short-term impacts of the low-head dam removal were lowered diatom and turtle biodiversity in the year following dam removal. However, I hypothesize that diatom biodiversity will rebound and turtle assemblages will become dominated by species that prefer lotic environments. Crayfish abundance and diversity increased following the dam removal which is an indication that macro-invertebrate communities are shifting towards lotic assemblages. My results provide a more wholistic understanding of the impact of low-head dam removal on the riverine food web by quantifying the response of three under-studied groups of organisms. To understand the total ecological impact of such a disturbance event, all components of the foodweb must be considered.

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