First Advisor

Yangdong Pan

Term of Graduation

Spring 2023

Date of Publication

5-5-2023

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Environmental Science and Management

Department

Environmental Science and Management

Language

English

Subjects

cyanobacteria, cyanobacteria blooms, harmful algal blooms, oregon lakes, phytoplankton

DOI

10.15760/etd.3563

Physical Description

1 online resource (ix, 122 pages)

Abstract

Cyanobacteria blooms are a growing issue worldwide and can be harmful to both aquatic life and human health. Warm temperatures, nutrient loading, stable water columns, and selective grazing of zooplankton and phytoplankton can contribute to cyanobacteria bloom formation. In this study, I characterized the algal communities and water quality differences in two physiographically similar lakes with relatively little human influences, Odell and Crescent Lakes, Oregon, to better understand potential contributing factors to cyanobacteria harmful algal bloom formation (cyanobacteria bloom) in Odell Lake.

There are three hypotheses in this study:

  1. If there was a cyanobacteria bloom in Odell Lake, but not Crescent Lake, then the algal community in Odell Lake would be representative of eutrophic conditions while Crescent Lake would not.
  2. If temperature was a contributing factor to community shifts in either Odell Lake or Crescent Lake, then temperature would have significant changes associated with phytoplankton shifts and cyanobacteria abundance.
  3. If nutrients were a contributing factor to cyanobacteria abundance, then the lake would experience increases in nutrient concentrations prior to cyanobacteria blooms formation.

Phytoplankton samples were collected from Odell and Crescent lakes on a weekly basis from June 2019 to September 2019 and characterized via microscopy. Multiparameter sondes were places in each lake at a fixed depth within one meter of the surface and recorded temperature (degrees C), pH, dissolved oxygen (mg/L and percent concentration), specific conductance (µS/cm), phycocyanin (relative fluorescence units; RFU), and chlorophyll-a (RFU) every 15-minutes throughout the study period. The phytoplankton community in Odell Lake was characterized by high abundances of eutrophic phytoplankton taxa, such as cyanobacteria, which had an average relative abundance of total density of 59.8 ± 30.3% (n=13; average ± standard deviation) throughout the sampling period. Crescent Lake was dominated by the phyla Bacillariophyta (diatoms) and Ochrophyta which had an average relative abundance of total density of 28.6 ± 14.0% and 20.9 ± 14.8%, respectively. Odell Lake transitioned from phytoplankton adapted to mesotrophic conditions and sensitive to stratification to phytoplankton found in eutrophic conditions and stratified water columns. Crescent Lake shifted from oligotrophic and mesotrophic algal taxa to a high abundance of cyanobacteria, however no visible bloom ever formed. A generalized additive mixed model of temperature data showed water temperature in Odell Lake was significantly warmer, on average 0.72 ± 0.92°C, than that of Crescent Lake as the bloom approached, which supported my second hypothesis. Nutrient measurements also supported the third hypothesis, as phytoplankton abundance in Odell Lake was significantly correlated with total phosphorus (TP; R-squared = 0.97; p < 0.05) and total nitrogen (TN; R-squared = 0.99; p < 0.05). Concentrations of orthophosphate peaked prior to cyanobacteria bloom formation, which when coupled with potential silica limitation in Odell Lake was likely responsible for promoting cyanobacteria abundance and cyanobacteria bloom formation dominated by N-fixer due to favorable nitrogen limiting conditions (TN:TP < 7) and reduced competition between cyanobacteria and diatoms due to silica limitation. Overall, this study found temperature was correlated with cyanobacteria bloom presence and intensity in Odell Lake, and nutrient conditions were more favorable to cyanobacteria dominance in Odell Lake versus Crescent Lake. The information provided in this study can be used with additional information could be used with additional information, such as lake orientation, wind patterns, and food web dynamics, to better understand factors contributing to cyanobacteria bloom formation in high mountain lakes.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/40422

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