Microcystin concentrations can be predicted with phytoplankton biomass and watershed morphology

ABSTRACT

Anthropogenically derived increases in nutrient loads and climate change are considered the primary drivers of harmful cyanobacterial bloom expansion in freshwaters; however, watershed and within lake physical variables, as well as community interactions, mediate the response of the phytoplankton community. Thus, predicting when cyanobacteria are abundant and when their toxins have elevated concentrations is potentially dependent on a large suite of variables. We used a large spatial and temporal scale study to identify the best environmental predictors of microcystin concentrations in lakes and reservoirs in Ohio (Midwest USA). Additionally, we explored predictive models for a censored dataset that included phytoplankton community composition and abiotic characteristics of lakes and their watersheds. We found that lakes had elevated microcystin concentrations when phytoplankton biomass was high and when lakes had small watershed areas relative to lake surface areas, and that biovolume of potential toxin producers and phytoplankton biomass (chlorophyll a) both predicted microcystin concentrations. Seasonal patterns in microcystin concentrations suggested that a single annual sampling may miss microcystin maxima and, contrary to expectations, a late summer maximum in microcystin was not universal.

KEY WORDS:

• censored regression
• cyanobacterial toxin
• harmful cyanobacterial bloom
• microcystin

Acknowledgements

We thank E. Brownson for her indispensable assistance in the field and lab. E. Mette, A. Babler, E. Hagenbuch, L. Knoll, and A. Showalter also provided field and laboratory support. S. Hall and J. Denlinger provided logistical support and help with data interpretation. G. Simpson provided help with the statistics. The authors thank M. González, K. Downs, A. Rock, and T. Williamson for critical evaluation of previous drafts of the manuscript. This research was funded by a Committee for Faculty Research grant from Miami University to MJV, a grant from the National Science Foundation (DEB 0743192), and the Federal Aid in Sport Fish Restoration Program (F-69-P, Fish Management in Ohio) administered jointly by the US Fish and Wildlife Service and the Ohio Department of Natural Resources, Division of Wildlife to MJV and MJ González.

ORCID

Nicole M. Hayes http://orcid.org/0000-0002-5664-9939

Michael J. Vanni http://orcid.org/0000-0001-8690-9124

Additional information

Funding

This work was supported by Directorate for Biological Sciences [grant number 0743192], U.S. Fish and Wildlife Service [grant number F-69-P].