Modeling of plankton community dynamics characterized by algal toxicity and allelopathy: A focus on historical Prymnesium parvum blooms in a Texas reservoir
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A model is formulated to explore the dynamics of the harmful alga Prymnesium parvum, in a reservoir typical of those in the south-central U.S. where fish-killing blooms of this species frequently occur. Based on a previous model of growth in a well-mixed system, P. parvum competes for nutrients with cyanobacteria, which also excrete allelopathic cyanotoxin(s) that inhibit the growth of P. parvum. A new feature added here is a population of small-bodied zooplankton grazing on both types of algae, with the grazing rate on P. parvum inhibited by dissolved toxin(s) excreted by this species. In contrast to previous models that did not produce convincing calibrations, the new model is successfully calibrated using one year of forcing data on hydraulic flow, water temperature, salinity and nutrient supply from Lake Granbury, Texas. The calibrated model successfully reproduces the seasonal dynamics of P. parvum. Both allelopathy from cyanobacteria and toxic inhibition of grazers are necessary for fitting the calibration data, and produce dynamics in which blooms of P. parvum occur at low temperatures, below those optimal for growth. Long-term historical simulations of the new, calibrated model predict the observed occurrence of P. parvum blooms in cool weather, and suggest that low water flows during the late 1980s and early 2000s predisposed reservoirs to having such blooms. Respectively, these time periods correspond to the first known fish kills due to P. parvum in Texas, and to a series of annually recurrent blooms in several reservoirs. 2011 Elsevier B.V.
