Internal conditions across the duration of a Euglena bloom in an urban stream1

Algal blooms are characterized by a rapid increase in abundance of a singular algal species and can have important consequences for human health. The increase of global temperatures, precipitation events, and eutrophication have only further exacerbated the frequencies of bloom events observed worldwide. Euglena blooms are commonly reported in southeast Asian aquaculture operations and not in northern latitude urban rivers. Identifying and understanding the conditions associated with this bloom in Ellicott Creek (New York, USA) is paramount given the frequency of human and domestic animal interactions within this water. We conducted regular collection of in situ conditions and whole water analysis during the summer of 2021. We assessed algal biomass, assemblage composition, and Euglena viridis cell density. Generally, increased rainfall resulted in excessive loads of phosphate that drove bloom formation. Other nutrients did not contribute significantly. This study provides key insights into the role that precipitation and excess nutrients can play in E. viridis blooms, which are increasing in number in this region. The information provided here can form the basis for future actions to mitigate these blooms.