Highlights

• For the first time, the Imaging FlowCytobot (IFCB) data is integrated with water quality models to interpret dissolved oxygen dynamics during algal blooms. This integration offers the first accurate prediction of dissolved oxygen (DO) levels during algal blooms.
• This work presented the first direct field measurements of carbon to chlorophyll-a ratio (CCHL) during an algal bloom cycle. It reveals that realistic values of CCHL, which are much higher than previously assumed in standard models, are necessary to account for the diurnal DO variations.
• By utilizing IFCB data for continuous estimation of CCHL ratios, the study demonstrates improved predictive accuracy for diurnal DO variations during bloom and non-bloom conditions. This advancement can benefit more accurate determination of carrying capacity of fish farms and hence fisheries management.

Summary

The dissolved oxygen (DO) during algal blooms can vary greatly over the course of a day – increasing to super-saturation levels during sunlight hours at the height of a bloom, and dropping to levels that cause massive fish kills when the bloom collapses.  The diurnal variation of DO is notoriously difficult and has been a longstanding challenge to water quality modeling.  One difficulty has been the non-availability of direct measurements of the carbon to chlorophyll ratio (CCHL).

This work investigates dissolved oxygen (DO) dynamics during algal blooms in subtropical coastal waters. In particular, this study employs the Imaging FlowCytobot (IFCB) for continuous direct measurements of cell volumes and reliable estimation of CCHL – and coupled with real time water quality measurements to study algal and DO dynamics.

A significant finding is the discovery of a diurnal pattern in algal abundance, with the carbon to chlorophyll-a ratio (CCHL) varying considerably throughout a bloom cycle. This observation challenges the constant CCHL values used in standard water quality models.

By integrating IFCB data with water quality measurements, the study successfully predicts DO level changes during algal blooms, enhancing the accuracy of environmental and ecosystem modeling.

This research emphasizes the need for dynamic water quality models considering varying CCHL ratios for better ecosystem modeling and environmental and fisheries management.

Ma, J. H. W. Lee, L. Chang, H. Tang, and H. Liu, “Field measurements of the carbon to chlorophyll-a ratio using Imaging FlowCytobot: Implications for dissolved oxygen modeling,” Estuarine, Coastal and Shelf Science, vol. 285, p. 108304, May 2023, doi: .