Date Approved

8-2019

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

M. Megan Woller-Skar

Second Advisor

Eric Snyder

Third Advisor

Ashley Moerke

Academic Year

2018/2019

Abstract

This project quantified lotic periphyton community change from May 2018-October 2018 in five, first and second-order Lake Superior tributary streams. Using periphyton communities, land use, geology, and abiotic factors pertinent to stream ecosystems we evaluated periphyton community succession. Using periphytometers, periphyton communities were collected and identified monthly to quantify community succession. Total phosphorus and total Kjeldahl nitrogen were measured monthly during the study. Depth, velocity, specific conductivity, and canopy cover were measured to quantify some of the physical factors within the streams. Nonmetric multidimensional scaling analysis indicated that the periphyton communities were similar between streams (ADONIS p-value =0.73) but was changing seasonally (ADONIS p-value <0.001). Dominant diatom taxa found were Synedra, Nitzschia, Melosira, Navicula, and Diatoma. Principal component analysis found that most streams had similar characteristics throughout the sampling period but depth. Chemical analysis from the streams indicated that these systems contained low nutrients but were classified as oligotrophic based on the trophic state index. Nutrients in the streams were very low; total phosphorus ranged from 50-70 μg/L meaning the streams meet the oligotrophic threshold. Nitrogen concentrations within these streams peaked at 1.00 mg/L following leaf abscission from the riparian vegetation in the fall but was found to be <0.5 mg/L throughout the rest of the sampling period. It has been hypothesized that Lake Superior is beginning to undergo the process of ultra-oligotrophication or when total phosphorus levels are <1 μg/L within the water column. The Lake Superior basin could be greatly impacted by climate change, introduction of invasive species, and potential warming air temperatures, which could accelerate ultra-oligotrophication within the basin and cause a reduction in biodiversity of Lake Superior and its tributaries.

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