Describing the Daily Vertical Migration of a Blooming Freshwater Dinoflagellate and Simulating the Bloom by Coupling Migration Equation into Ecological Model

Freshwater dinoflagellate Peridiniopsis penardii has been reported blooming in a reservoir in western China annually. Being able to migrate autonomously is one of its major characteristic and is believed to have impact on its blooming development. A 24-hour field observation was conducted during the bloom in 2015 to quantitative analysis this feature, and the collected vertical profile of chlorophyll showed an evident migration rhythm. The blooming algae preferred to gather close to water surface during daytime and then dispersed through water column as night came. This process was proved to be independent to the mixing in top layer during night because the asynchronism observed between chlorophyll and temperature profile. An empirical equation was then proposed to describe the daily migration rhythm by fitting the field data to sinusoidal function, and the maximum migration speed of this algae was determined to be 0.35m/h based on derivation of this equation. Finally, the proposed migration equation was coupled into the ecological model in CE-QUAL-W2 to simulate dinoflagellate blooming. Field data collected during a whole blooming process was used to validate the modified model, and a maximum 9.4 % decreasing of modeling error was noticed by comparing the results of modified model to original one. This improvement also suggested that the consideration of algal migration feature in model could be helpful in algal bloom simulation if dominant species have migration ability. The presented migration equation and modified model in this research could be used as a reference to simulate similar algal bloom and offer scenario information for reservoir/lake management. Further research should focus on improving the migration equation by reveal physiological mechanism underlying the phenomenon.