Modeling Cyanotoxin Production, Fate and Transport in Surface Waterbodies

Abstract

Cyanobacteria exist throughout the world and are frequently associated with forming toxic blooms. The toxins produced by cyanobacteria, cyanotoxins, are harmful to both humans and animals. Rising temperatures due to global climate change, increased nutrient loading, and other anthropogenic impacts on waterbodies are expected to increase the prevalence of cyanobacteria. It is vital that we protect our drinking water supplies and natural water resources. Modeling the production and movement of these toxins is an important step in limiting exposure to them and evaluating management strategies to mitigate their impact. Cyanotoxins are diverse and the conditions under which they are formed are variable and depend on species, strain, and environmental factors. The research provided here offers an overview of some of the environmental factors and cyanobacteria species that are associated with toxin production, and the research also presents preliminary models for the transport and fate of cyanotoxins. Cyanotoxins can be either intracellular or extracellular and a model for each was developed. The models were first tested using published data from laboratory experiments, and then the models were incorporated into the two-dimensional (longitudinal and vertical) hydrodynamic and water quality model CE-QUAL-W2. The toxin models were tested using a model of Henry Hagg Lake (Oregon). Additional research was done to improve the water quality predictions of the CE-QUAL-W2 model of Henry Hagg Lake that had previously been developed. This involved updating the model simulation period through the end of 2020 and calibrating the model to better match field data through the new simulation period. The preliminary models were able to capture similar dynamics as the published data from the laboratory experiments, but the toxin data available at Henry Hagg Lake was minimal so it was difficult to compare the model results to the field data using the CE-QUAL-W2 model. Four scenarios were conducted to test the functionality of the toxin models in CE-QUAL-W2. The predicted results from each test scenario matched expected outcomes based on the parameters used in each scenario. Further applications of the toxin models to other waterbodies with more consistent toxin data will help verify the accuracy of the preliminary models. In addition, further research of the environmental factors that affect toxin production is necessary to incorporate variable rates of toxin dynamics. While the simulations of the Henry Hagg Lake CE-QUAL-W2 model closely match the field data for many water quality parameters, additional calibration of the model is required to