Modeling cyanobacteria bloom formation and toxin production as a function of environmental N:P stoichiometry and hydraulic displacement

Cyanobacteria harmful algal blooms (HABs) are major disruptors of ecosystem functioning and are becoming increasingly problematic in some aquatic systems as climate change related impacts alter water column processes. In the work presented here, we focus on how N:P stoichiometry and hydraulic displacement, two lake characteristics influenced by anthropogenic activity and climate change, regulate cyanobacteria population dynamics and toxin production within a process driven numerical model. We also examine how phytoplankton diversity is altered under bloom conditions or periods of elevated toxin production to better understand the complex interplay between diversity, competition, interference strategies (e.g. toxin production) and environmental conditions that influence ecosystem functioning or loss thereof via bloom occurrence. For this work, we used a previously published plankton model, which produces seasonal phytoplankton dynamics and includes a population rich phytoplankton assemblage, allowing us to examine biotic interactions across a range of environmental gradients. The model was altered to include environmental conditions typical of warm monomictic systems in the southcentral USA, and a cyanobacteria state variable. Incorporation of the cyanobacteria state variable was coupled with production of cyanotoxins which negatively affected other biotic model populations. And, as part of model tailoring, we compared the usefulness of two equations which differently represent the relationship between toxin production and nutrient concentrations versus nutrient stoichiometry. Using both equations, we ran simulations over a gradient of N:P conditions using hydraulic displacement rates typical of systems spanning an East-West precipitation gradient in Texas (calculated using the Hydrologic and Water Quality System (HAWQS) for Texas reservoirs). Lakes in this region were the focus of previous work which produced empirical data against which the model results will be compared. This study will provide insight to factors important for maintenance of ecosystem health and functioning in the face of cyanobacteria HABs.

Primary Presenter: Sierra Cagle, Texas A&M University at Galveston (sec1414@tamu.edu)

Authors:

Daniel Roelke, Texas A&M University Galveston  (droelke@tamu.edu)

Crista Kieley, Texas A&M University Galveston  (ckieley@tamu.edu)

Royoung Park, Texas A&M University Galveston  (parkro9946@tamu.edu)

Smita Pal, Texas A&M University Galveston  (smita30@tamu.edu)

Kathryn Campbell, Texas A&M University Galveston  (klcampbell@tamu.edu)

Nathan Klobusnik, Texas A&M University Galveston  (nathanklo@tamu.edu)

Jordan Walker, Texas A&M University Galveston  (jronwalker@tamu.edu)

Kevin Stroski, Baylor University  (kevin_stroski1@baylor.edu)

Bryan Brooks, Baylor University  (Bryan_Brooks@baylor.edu)

Jessica Labonte, Texas A&M University Galveston  (lebontej@tamu.edu)