Using a two-layered sphere model to investigate the impactof gas vacuoles on the inherent optical properties of Microcystis aeruginosa

[摘要] A two-layered sphere model is used to investigate the impactof gas vacuoles on the inherent optical properties (IOPs) of the cyanophyteMicrocystis aeruginosa. Enclosing a vacuole-like particle withina chromatoplasm shell layer significantly altered spectral scattering andincreased backscattering. The two-layered sphere model reproduced featuresin the spectral attenuation and volume scattering function (VSF) that havepreviously been attributed to gas vacuoles. This suggests the model is goodat least as a first approximation for investigating how gas vacuoles alterthe IOPs. Measured R_rs was used to provide a range of values for thecentral value of the real refractive index, 1 + ε, for the shelllayer using measured IOPs and a radiative transfer model. Sufficient opticalclosure was obtained for 1 + εbetween 1.1 and 1.14, which hadcorresponding Chl a-specific phytoplankton backscattering,b_bφ^*, between 3.9 and 7.2 × 10⁻³ m² mg⁻¹ at510 nm. The b_bφ^* values are in close agreement with the literatureand in situ particulate backscattering measurements. R_rs simulated fora population of vacuolate cells was greatly enlarged relative to a homogeneouspopulation. A sensitivity analysis of empirical algorithms for estimatingChl a in eutrophic/hypertrophic waters suggests these are robustunder variable constituent concentrations and likely to be species-sensitive. The study confirms that gas vacuoles cause significantincrease in backscattering and are responsible for the high R_rsvalues observed in buoyant cyanobacterial blooms. Gas vacuoles aretherefore one of the most important bio-optical substructures influencingthe IOPs in phytoplankton.

[学科分类] 地球化学与岩石