Harmful Cyanobacterial Aerosolization Dynamics in the Airshed of a Eutrophic Estuary

Abstract

In addition to obvious negative effects on water quality in eutrophic aquatic ecosystems, recent work suggests that harmful cyanobacterial blooms (CHABs) also impact air quality via emissions carrying cyanobacterial cells and cyanotoxins. However, the environmental controls on CHAB-derived aerosol and its potential public health impacts remain largely unknown. Accordingly, the aims of this study were to 1) investigate the occurrence of microcystin (MC) and putatively toxic cyanobacterial communities in particulate matter < 2.5 µm in diameter (PM2.5), 2) elucidate environmental conditions promoting their aerosolization, and 3) identify associations between CHAB events and PM2.5 concentration in the airshed of the Chowan River-Albemarle Sound, a eutrophic estuarine system in eastern North Carolina, USA. In summer 2020, during peak CHAB season, continuous PM2.5 samples and interval water samples were collected for targeted analyses of cyanobacterial community composition and MC concentration. Supporting air and water quality measurements were made in parallel to contextualize findings and permit statistical analyses of environmental factors driving changes in CHAB-derived aerosol. Several aquatic CHAB genera recovered from Chowan River surface water were identified in PM2.5, including Anabaena, Aphanizomenon, Dolichospermum, Microcystis, Pseudanabaena, and Tolypothrix. Cyanobacterial enrichment in PM2.5 was indistinctive at the subspecies level, but bloom state was an important factor in the enrichment of all CHAB cells in PM2.5. MC production was low throughout the study, but a CHAB dominated by Dolichospermum occurred from late-June to mid-July. In association with this CHAB event, the median PM2.5 mass concentration increased to 10.5 µg m-3 (IQR = 4.55), significantly above the non-bloom background of 5.81 µg m-3 (IQR = 5.48) (W = 1465, p < 0.001). Results underscore the need for highly resolved temporal measurements to conclusively investigate the role that freshwater algae, specifically CHABs, play in regional air quality and subsequent respiratory health risk.

Keywords: Water Quality, Toxic Cyanobacteria, Air Quality, PM2.5, Microcystis, Dolichospermum