Relating Cyanotoxin Occurrence to Environmental Cues to Inform Algal Toxin Monitoring and Management in Pennsylvania Lakes

Harmful cyanobacteria blooms (CyanoHABs) have become a common problem in freshwater ecosystems. Monitoring at the federal and state level in response to this threat has increased over the last decade across the United States. In 2018, Pennsylvania environmental agencies began collecting CyanoHAB data to inform state regulatory and management efforts. 998 discrete samples from 138 waterbodies were collected over four years. These data were used to determine if indicators often used in CyanoHAB monitoring co-occurred with toxic conditions. Cyanotoxins were detected in more than half of the samples in Pennsylvania’s monitoring program with anatoxin, saxitoxins, and microcystins detected in similar proportions. It is important to note that the monitoring program is not designed to be representative of all Pennsylvania lakes but instead is targeted toward sites with greater exposure (recreational beaches) or sites with suspected blooms. Our findings suggest that cyanobacteria growth and cyanotoxin production may be driven by independent variables, as only microcystins concentrations were positively correlated with cyanobacteria counts. While increased cyanobacteria counts were related to all environmental variables considered in this study (warmer water temperatures, increased dissolved oxygen concentrations, and reduced water clarity), the relationships between cyanotoxins and environmental variables were mixed. Our analyses highlight the complexities of bloom occurrence and severity, and the challenges of incorporating these factors into monitoring and management strategies. Long-term monitoring approaches like the one analyzed here can inform management strategies that rely on environmental cues and cyanobacteria enumeration to evaluate risk of cyanotoxin presence.