Optical scattering properties of organic-rich and inorganic-rich particles in inland waters

We present the results from a study of the particulate scattering properties of three bodies of water that represent a wide range of optical properties found in inland waters. We found a positive linear relationship (R2 = 0.45, P < 0.005) between the mass-specific scattering coefficient at 532 nm (bp*(532)) and the ratio of the inorganic suspended material (ISM) to the total suspended material (TSM) in our study areas. In contrast to earlier studies in which bp*(532) was lower for inorganic particles than for organic particles, we found that the value of bp*(532) for ISM (bp*(532)ISM = 0.71 m2/g) was approximately 1.6 times greater than the value found for organic suspended materials (OSM) (bp*(532)OSM = 0.45 m2/g). We found that the dependence of the particle scattering coefficient (bp) on wavelength (λ) could be described accurately by a power law (with mean average percent error (MAPE) < 0.07) in waters dominated by inorganic particles. The model errors in waters dominated by organic particles, however, were much larger (MAPE > 0.1), especially in the spectral region associated with strong phytoplankton absorption. The errors could be reduced over this wavelength range by adding a term to the model to account for particle absorption, but the additional term tended to increase the error outside of this range. We conclude that information about the nature of the scattering particles in lake waters is necessary for the selection of an appropriate model for particle absorption and that a hybrid model that includes absorption over some wavelength ranges may be necessary.