Monitoring, quantifying, and controlling the effects of cyanobacterial blooms and toxins

Abstract

Cyanobacterial blooms and toxins have harmful impacts on global aquatic ecosystems. Within this, their impact on the water quality of freshwater systems are particularly troublesome. My research investigated methods to both monitor and control cyanobacterial blooms and toxins to assist resource managers with this pressing aquatic resource issue.

My monitoring research included identifying the environmental drivers of microcystin, a hepatotoxin produced by select cyanobacteria, using both a linear meta-analytical analysis and non-linear generalized additive modeling approach. Linear meta-analysis of 2,643 global fresh waterbodies indicated that chlorophyll, total dissolved phosphorus, total phosphorus, and Secchi disk depth were the strongest water quality parameters related to microcystin occurrence. On the other hand, non-linear analysis of 2,040 global fresh waterbodies indicated that total nitrogen, turbidity, pH, and Secchi disk depth were the strongest water quality parameters related to microcystin occurrence. Although similarities were found between these two approaches, my findings suggest trends in cyanobacterial data may be non-linear, and utilizing non-linear analyses to assess such data are recommended.

To control cyanobacterial blooms, I compared the effectiveness of 7 different algaecides (including copper-, hydrogen peroxide (H2O2)-, peracetic acid-, and clay-based products) in a 35- day field experiment, and also assessed the nuanced effectiveness of H2O2 under varying environmental conditions. In general, it was found that copper-based products remain the most efficient and cheapest choice to reduce total phytoplankton biomass in aquaculture systems. However, peracetic acid-based products effectively reduced cyanobacteria while having marginal effects on beneficial algae and zooplankton. Such algaecides could be effective alternatives to copper-based products depending on the outcomes sought by resource managers.

Lastly, my laboratory study of H2O2 assessed its effectiveness at reducing cyanobacteria under different environmental conditions, including varying dissolved organic matter concentrations, temperatures, and starting phytoplankton concentrations. Neither variation in dissolved organic matter concentration nor temperature influenced the effectiveness of H2O2 at reducing cyanobacteria. However, initial phytoplankton density as well as H2O2 dose greatly influenced the effectiveness of the algaecide. Thus, water resource managers are encouraged to consider how ambient conditions may alter the ability H2O2 to control algal blooms prior to treatment.