In stratified lakes, a large portion of phytoplankton biomass is found—not at the surface, where sampling is easiest—but somewhere down the water column, in what is known as a subsurface chlorophyll maximum (SSCM). Researchers in Global Lake Ecological Observatory Network (GLEON) compared automated high-frequency chlorophyll fluorescence (ChlF) profiles with surface samples and discrete depth profiles. In 7 of the 11 lakes studied, automated sampling captured the presence of SSCM’s that would have been missed by conventional sampling.
These hidden blooms of phytoplankton can comprise up to 70% of the productivity in low-nutrient lakes and can come and go within days and move up and down the water column within hours. The new research is helping to motivate an update of the Plankton Ecology Group (PEG) model to include physical parameters, which can determine the strength, location and duration of such sub-surface blooms.