Aggregation of diatom bloom in a mesocosm: Bulk and individual particle optical measurements

Optical measurements were acquired during a controlled, diatom-dominated, phytoplankton bloom and aggregation event engineered in a 1200 liter laboratory mesocosm. Observations included beam attenuation (c) at 660 nm and particle absorption spectra for phytoplankton and detritus. Despite intense bloom conditions in the mesocosm (chlorophyll a concentrations exceeding 165 mg/l and c exceeding 9 m-1), most optical parameters covaried linearly with biochemical parameters. There were significant positive correlations for dry mass versus the particle attenuation coefficient (cp) at 660 nm, particulate organic carbon versus the computed particle scattering coefficient (bp) at 660 nm, and chlorophyll a versus the measured particulate absorption coefficient (ap) at 660 nm, and chlorophyll a versus the measured absorption coefficient for phytoplankton (a.) at 673 run. le-component model simulations of optical and biochemical measurements accurately predicted particulate organic carbon (POC), particulate organic nitrogen (PON), and chlorophyll a concentrations using cp and ap measurements. Similar equations for cp and ap estimates using the biochemical measurements are also presented. New commercially available instruments to measure c(λ) and a(λ) should make remote PON, POC, and Chl a estimates practical upon measurements of site-specific relationships similar to those presented here.