Toxic cyanobacteria blooms in freshwater lakes are an increasing problem worldwide, that are also impacting lakes in Washington and the Pacific Northwest. Identifying the potential biotic and/or abiotic factors associated with cyanobacteria bloom dynamics will provide critical information for natural resource managers to develop strategies for managing blooms based on empirical evidence. For example, if nutrients are found to be a primary factor associated with toxic cyanobacteria blooms in Washington state lakes, then a focus on measures to reduce nutrient loading into the lakes may be most effective for mitigating these blooms. Similarly, if a major control of cyanobacteria blooms is grazing impact from zooplankton consumers, then efforts to manipulate the system to maximize grazing pressure (e.g., via biomanipulation of fish stocks and cascading trophic effects) may be a possible approach to reduce toxic blooms. These results therefore benefit state and county agencies as they make decisions about our four lakes/reservoirs, but will also be applicable to regional and national resource management agencies who face similar challenges with cyanobacteria blooms in other temperate aquatic systems.

Results from this research provided new information about the dynamics of toxic cyanobacteria blooms in lakes across a eutrophication gradient in Washington state, which will be applicable to temperate freshwater systems more generally. In particular, this research addressed the interactive effects of nutrients (bottom-up) and grazing (top-down) on controlling the timing and magnitude of toxic cyanobacteria blooms in both eutrophic and oligotrophic systems.

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