water Article Beyond Eutrophication: Vancouver Lake, WA, USA as a Model System for Assessing Multiple, Interacting Biotic and Abiotic Drivers of Harmful Cyanobacterial Blooms Gretchen Rollwagen-Bollens 1,2,*, Tammy Lee 1, Vanessa Rose 1 and Stephen M. Bollens 1,2 1 School of the Environment, Washington State University, Vancouver, WA, 98686, USA;
[email protected] (T.L.);
[email protected] (V.R.);
[email protected] (S.M.B.) 2 School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA * Correspondence:
[email protected]; Tel.: +1-360-546-9115 Received: 16 April 2018; Accepted: 8 June 2018; Published: 10 June 2018 Abstract: Eutrophication of lakes and reservoirs has contributed to an increase in the magnitude and frequency of harmful cyanobacterial blooms; however, the interactive effects of nutrient availability (eutrophication) and other abiotic and biotic drivers have rarely been comprehensively studied in the field. We undertook an eight-year (2005–2013) research program that assessed the interaction of multiple factors driving cyanobacterial blooms in Vancouver Lake, a large, shallow eutrophic lake in Washington, USA. Our program consisted of nearly continuous monthly or weekly monitoring of water quality and plankton community composition over eight years, as well as multiple zooplankton grazing experiments over three years. We found a relatively consistent seasonal succession of phytoplankton and zooplankton assemblages, and a pattern of interacting factors influencing cyanobacterial bloom dynamics. Typically, a combined effect of decreased dissolved inorganic nitrogen (N), a sudden increase of dissolved inorganic phosphorus (P), and a cascading effect of zooplankton grazing created a ‘perfect storm’ of conditions that promoted the rapid proliferation of cyanobacteria over the two to three weeks before a bloom.