Olivia Muntz

Date Approved

2022

Degree Type

Open Access Senior Honors Thesis

Department or School

Biology

First Advisor

Kristin Judd, PhD

Second Advisor

Aaron Liepman, PhD

Third Advisor

Anne Casper, PhD

Abstract

Dams produce hydroelectric power and control flooding, but they also cause negative ecological consequences such as habitat fragmentation and altered water quality. The goal of this study was to determine whether dams alter rates of organic matter decomposition. Decomposition rates in impoundments and in free-flowing sections of the Huron River were measured using the cotton strip assay. We hypothesized that if water temperature is the main driver of decomposition rates, then higher rates of decomposition would be expected behind dams due to anticipated warmer water temperatures in the impoundment. If oxygen concentrations are a main driver of decomposition rates, lower decomposition rates would be expected behind dams due to lower oxygen in the sediments of the impoundment. To determine whether shifts in the relative importance of macroinvertebrate and microbial decomposer communities affected decomposition behind impoundments, we excluded macroinvertebrates from half of the cotton strips. We also measured temperature and oxygen levels to determine if there was a relationship with decomposition rates. We found decomposition rates were significantly greater in the impoundments than in one free-flowing section of the river. We did not find a significant relationship between decomposition and oxygen or temperature, however, average temperature was slightly warmer in the impoundments, suggesting a stronger effect of temperature than oxygen on decomposition. Dams have been found to alter important ecosystem functions, although the exact mechanism of their effects on decomposition requires further study.

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