Field study on phytoplankton growth by using optical sensor

Abstract

An optical sensor was used for the measurement of chl-a concentration in the Shichigashuku Reservoir in order to clarify the growth and decay of phytoplankton bloom which is highly unsteady and non-uniform phenomenon. The measurement shows the followings: The plankton was stratified just above the thermocline, going down with their growth by the displacement of the thermocline. The period of the bloom was only one week and it was concentrated in a rather shallow area where nutrient may be supplied from the bottom.
Total mass of Chl-a integrated in the reservoir is compared with the time variation of phosphorus (P) which was estimated from water quality analysis. The result shows that most of P is consumed at the end of the bloom and that (P/chl-a) ratio of phytoplankton was almost unity which is consistent with the value of the ratio shown in a literature.