Avoiding and correcting chlorophyll fluorescence quenching by photoinhibition

Abstract

In-vivo fluorescence measurements are ideal for monitoring phytoplankton biomass. However, as the PAR value increases under natural light conditions, phytoplankton protect the photosynthetic system by non-photochemical quenching (NPQ) process. Fluorescence quenching occurs during this process and the measured values using the fluorometer are lower than the actual phytoplankton biomass. To overcome this problem, the dark adaptation of the sample before measurement or thecorrection of the measurement results is required. The calculation equation considering the PAR developed in this study showed a good correction results. In addition, the effect on phytoplankton by diaphragm pump included in the dark adaptation method was insignificant, and similar results were obtained as the actual chlorophyll a concentration in the avoidance strategy of quenching by dark adaptation. However, considering the time and space constraints of the field survey, the method of calibration after observation using the underwater fluorescence sensor is more appropriate. In particular, it can help to obtain large and coherent calibrated phytoplankton biomass data monitored by autonomous platforms.