Environmental Drivers of Harmful Algal Blooms in Montana Reservoirs

Abstract

Harmful algal blooms (HABs) can form when cyanobacteria grow to high density in aquatic environments. HABs introduce severe environmental health risks due to neurotoxins produced by cyanobacteria. Humans, pets, livestock, and fish that interact with or consume these neurotoxins are at risk of developing neurological diseases that may result in death. The goal of the Goemann Research Group is to identify where and what kinds of HABs are forming across Montana. Our research used nanopore DNA sequencing techniques to extract and amplify rRNA from the raw algae samples in four distant reservoirs across Montana. Sequencing data allowed us to visualize the growth patterns and population dynamics of the cyanobacteria throughout the summer. These growth patterns were then compared to environmental factors such as temperature, dissolved oxygen concentration (DO), and pH to identify what conditions select for growth of toxic species. Bloom initiation generally resulted in a spike in DO and pH, followed by a rapid decrease in DO, suggesting that certain environmental factors are closely linked to bloom dynamics. Further, cyanobacterial populations within individual HAB events were dynamic over time, with the major species changing between toxic and non-toxic cyanobacteria throughout the bloom. When comparing blooms between reservoirs, temperature was a key factor in the speciation of blooms. Cyanobacterial populations were distinct between many reservoirs; however, reservoirs with higher average temperature selected for common toxic species, including Microcystis sp., within HABs. Together, this data helps identify conditions that select for toxic HABs and can help to focus mitigation efforts.