Estimation of Organic and Inorganic Matter in Inland Waters: Optical Cross Sections of Lakes Ontario and Ladoga

Abstract

The high degree of optical complexity of inland water masses necessitates the development of models which consider the optical competitiveness of several co-existing aquatic components. A model is described which was developed to simultaneously estimate chlorophyll a, suspended mineral, and dissolved organic carbon concentrations from a single measurement of the subsurface volume reflectance spectrum in the optically complex waters of Lake Ontario. To estimate such aquatic concentrations requires a quantification, as a function of wavelength, of the amount of scattering and absorption that may be ascribed to a unit concentration of each aquatic component (i.e., the pertinent optical cross sections). Cross section spectra are presented for Lake Ontario and it is illustrated how such cross sections may be utilized in conjunction with directly-measured subsurface volume reflectance spectra and optimization analyses to extract the organic and inorganic components. Cross section spectra obtained in a similar manner for Lake Ladoga are also presented and compared to those of Lake Ontario. Similarities in absorption, but differences in backscattering cross section spectra for suspended inorganic matter were observed for the two lakes. Near-identical absorption and very similar backscattering cross section spectra suggest that Lakes Ontario and Ladoga are characterized by optically-comparable populations of chlorophyll-bearing biota.