Assessment of Ecosystem Management Strategies and Stakeholder Needs for Harmful Algal Blooms in the Great Lakes

Abstract

This Master’s Project focused on improving the understanding of harmful algal blooms (HABs) within Lake Erie and Saginaw Bay as well as characterizing needs of water utility managers for information products. This research addressed four different topics: 1) In Chapter 2: Quantifying the impact of nutrient availability and form on the growth of HABs in Lake Erie and Saginaw Bay, we found that phosphorus was the main limiting nutrient based on nutrient addition treatments, but with nutrient reduction treatments, nitrogen appeared to be co-limiting, suggesting reductions in phosphorus alone may not eliminate blooms. 2) In Chapter 3: Mechanistic Assessment of Dreissenid Mussel Grazing Impacts on Phytoplankton Growth Rates, we found that the synergistic effect of nutrient excretion and dilution through grazing had the largest impact on total phytoplankton growth, followed by nutrient excretion and dilution through grazing, respectively. The overall impact of grazing by Dreissenid mussels on cyanobacteria growth rates was limited, and mussel-mediated nutrient recycling was the strongest explanatory mechanism. 3) In Chapter 4: Comparative Analysis of Microcystis Colony Buoyant Velocities in Western Lake Erie and Saginaw Bay of Lake Huron: Effects of Colony Size and Light Intensity, we show that Western Lake Erie and Saginaw Bay differ in the way that Microcystis buoyancy responds to light and may therefore ultimately affect how the bloom is transported throughout each ecosystem. Understanding the effects of light on buoyancy will help explain observed differences in vertical distribution and movement of Microcystis in the two lakes. 4) In Chapter 5: Characterization of Public Water System Needs and Attitudes Related to HAB Toxicity in Saginaw Bay and Western Lake Erie, we describe a focus group and survey of water system managers in Saginaw Bay about how HABs impacted them and if a HAB forecast model would be useful. Our results show that managers believed the forecast would be useful, and that they would be willing to use it. It also suggested that managers feel unprepared in the event of a HAB beyond what has occurred recently in the Bay, so efforts should be taken to increase their knowledge and preparedness.