Identification and characterization of toxic cyanobacteria in two forested maritime watersheds in North America

Abstract

Healthy forested watersheds naturally provide high quality drinking water to communities. However, the integrity and quality of these water sources may be threatened by climate change-exacerbated disturbances such as wildfires and hurricanes, which can lead to increased delivery of nutrients to receiving waters and increase in water temperatures. This can result in the proliferation of cyanobacteria that may threaten water quality through the production of toxins as well as taste and odour (T&O) compounds. Hence, it is important to detect the presence of potentially harmful cyanobacteria prior to any associated water quality shifts. In this study, a synoptic field sampling campaign was conducted in 2019 and involved the collection of one water sample per month in various watersheds. To evaluate the composition and relative abundance of cyanobacteria, water samples were collected from the Pockwock Lake watershed (Nova Scotia, Canada) in June, August, September and October, the Comox Lake watershed (British Columbia, Canada) in May and September, and the Leech River and Sooke River watersheds (British Columbia, Canada) in July and August. Microbial DNA was extracted from water samples for 16S rRNA gene sequencing and assigned taxonomy in QIIME2 using a SILVA classifier and resulting cyanobacteria ASVs were analyzed using the R package mirlyn. Lakes within the same watershed typically contained similar communities, though monthly variations in diversity were observed in some lakes. Most cyanobacteria ASVs resolved to the genus-level were assigned to Cyanobium PCC-6307 (NR_102447.1) and Rhabdogloea smithii SAG 47.91 (KM020002.1); across all samples, the relative abundance of reads from these genera was 51% and 42%, respectively. Other genera represented in the samples included cyanobacteria strains known to form blooms and produce geosmin, a terpene with an earthy odour, and microcystin, a regulated hepatotoxin. Findings from this study provide insights into the presence of cyanobacteria in water resources replied upon as drinking water supplies and underscores some potential commonalities for their potential to deteriorate water quality and challenge drinking water treatability in diverse forested watersheds in Canada.