A correction model for quenching effects on chlorophyll a fluorescence measurements in lakes

Abstract

Characterizing the vertical structure of phytoplankton biomass is key to understanding the light, nutrient, and mixing dynamics driving lake ecosystems. In situ fluorometry is widely used in limnology to obtain chlorophyll a (Chl a) measurements as proxies for phytoplankton biomass. Unfortunately, daytime fluorometry signals are biased by non-photochemical quenching, limiting the value of these measurements. Phytoplankton utilize this quenching process to dissipate excess light energy as heat, which contaminates daytime fluorometry measurements with reductions in measured Chl a. Despite the ubiquitous impacts of non-photochemical quenching on fluorometer measurements, there is no universal correction method for inland waters. We propose a novel model for correcting non-photochemical quenching impacts in lake systems as a simple exponential function of available light in the water column. This model was developed from data collected from two lakes representing the endmembers in terms of lake productivity and clarity, thus producing a model with possible application to other systems. The study sites are ultraoligotrophic Lake Tahoe, CA-NV, and hypereutrophic Clear Lake, CA. Our proposed non-photochemical quenching correction model demonstrates good performance (R² = 0.74) when tested on an independent dataset from Lake George, NY. We applied the model to vertical data profiles from Lake Tahoe and Clear Lake to more accurately evaluate the vertical distribution of Chl a in these lakes. The results of this research have wide-reaching benefits by enabling more accurate interpretation and application of Chl a fluorescence measurements in lakes with a range of conditions.