Harmful Algae Bloom (HABs) Dynamics in Mixing Zones of Lake Superior

Abstract

Phytoplankton, commonly referred to as algae, are found in water and create the base of the food web in aquatic ecosystems. When an ecosystem becomes unbalanced, phytoplankton can grow too much which can result in an algal bloom. Algal blooms can negatively impact the aquatic ecosystem by blocking sunlight while also taking up nutrients and other resources away from the natural plants and wildlife in the area. One species of phytoplankton, cyanobacteria (also known as blue-green algae), can produce and release harmful toxins into the water and concentrate into scum called a harmful algae bloom (HAB). Although Lake Superior is oligotrophic or nutrient-depleted, blooms have been more frequently observed within the St. Louis River Estuary (SLRE) throughout the last decade, which has bi-directional exchange with Lake Superior. This research was conducted to identify spatial and temporal patterns in phytoplankton species in the SLRE and southern shore of Lake Superior, with an emphasis on cyanobacteria. The results of this work help us understand the phenology of phytoplankton and what causes shifts in distribution and abundance throughout seasonal changes. Results of this study show brown algae species (diatoms) as the most abundant species at all locations over the sampling season, but overall algae community composition varies considerably among sampling locations. When present, peaks in cyanobacteria species were found at one sampling location at a time and their occurrence often lasted one day. This demonstrates that seasonality in environmental drivers and geographical location play an important role in phytoplankton community composition through time.