Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Oceanography

Degree Name

Master of Science

First Advisor

Kai Ziervogel

Second Advisor

Timothy Moore

Third Advisor

James Haney

Abstract

Lake Erie, the shallowest of the Laurentian Great Lakes, has been historically plagued with summertime blooms of potentially toxic cyanobacteria (Microcystis spp.) that originate in the shallow western part of the lake (average depth 10 m). The onset of Microcystis blooms often follow wind-driven resuspension events, indicating that internal loading of growth limiting nutrients (mainly phosphorus, P) may stimulate cyanobacterial growth. We hypothesize that wind-driven sediment resuspension releases particulate P (PP) in the form of organic (POP) or inorganic phosphorus (PIP), fueling cyanobacterial growth in the water. To test this hypothesis, we exposed replicate sediment cores from two sites in the western basin of Lake Erie (WE04, WE08) to increasing shear stress using an erosion chamber. Our results indicate site-specific differences in the release of PP from experimentally resuspended sediments. Sediment from the deeper site (WE4; high sand content) released lower levels of PP compared with the shallower site (WE8; high silt content). Laboratory culture experiments determined Microcystis can effectively access sediment bound organic P as a growth source. Growth rates were determined with Microcystis cultures amended with POP and PIP as well as dissolved inorganic P (DIP) and dissolved organic P (DOP). DIP growth rates were highest followed by DOP, POP, and PIP respectively. Potential activities of alkaline phosphatase enzymes that are used by cyanobacteria to remineralize inorganic P from organic P complexes, also increased during the erosion experiments and in the POP cultures. Our results indicate the potential for internal loading of PP following wind-driven resuspension event to promote blooms of Microcystis in the western basin of Lake Erie.

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