Inherent optical properties of suspended particulates in four temperate lakes: application of in situ spectroscopy.

摘要

Instrumentation measuring hyperspectral particle attenuation and absorption was used to assess particle concentration and size, chlorophyll, and spectral characteristics as a function of depth in four temperate lakes of different trophy. Partitioning the absorption coefficient permitted us to analyze properties of phytoplankton absorption as a function of ambient illumination and hydrographic conditions. Stratification was found to be a controlling factor in the size distribution and concentration of particles. Bloom cycles (chlorophyll >10 mg m-3) were observed to evolve over several weeks but on occasion did change rapidly. Total chlorophyll concentration revealed the majority of the lakes did not follow the typical seasonal succession of biomass associated with temperate waters. Particle and chlorophyll concentration maxima did not always coincide, cautioning the use of chlorophyll a as a surrogate for algal biomass. Phytoplankton near the base of the euphotic zone, including a deep chlorophyll maximum in an oligotrophic system, were found to exhibit significant chromatic adaptation. Unique absorption peaks identified the ubiquitous presence of cyanobacteria in all four lakes. Finally, particle resuspension and possible nepheloid layers were observed in the two smallest lakes.