Biogeochemical origins of particles obtained from the inversion of the volume scattering function and spectral absorption in coastal waters
In the aquatic environment, particles can be broadly separated into phytoplankton (PHY) non algal par ticle (NAP) and dissolved (or very small particle, VSP) frac tions. Typically, absorption spectra are inverted to quantify these fractions, but volume scattering functions (VSFs) can also be used. Both absorption spectra and VSFs were used to estimate particle fractions for an experiment in the Chesa peake Bay. A complete set of water inherent optical prop erties was measured using a suite of commercial instru ments and a prototype Multispectral Volume Scattering Me ter (MVSM) the chlorophyll concentration, (Chl) was deter mined using the HPLC method. The total scattering coeffi cient measured by an ac s and the VSF at a few backward angles measured by a HydroScat 6 and an ECO VSF agreed with the LISST and MVSM data within 5 thus indicat ing inter instrument consistency. The size distribution and scattering parameters for PHY, NAP and VSP were inverted from measured VSFs. For the absorption inversion, the "dis solved" absorption spectra were measured for filtrate pass ing through a 0.2 um filter, whereas (Chl) and NAP absorp tion spectra were inverted from the particulate fraction. Even though the total scattering coefficient showed no correlation with (Chl) estimates of (Chl) from the VSF inversion agreed well with the HPLC measurements (r 0.68, mean rela tive errors 20 The scattering associated with NAP and VSP both correlated well with the NAP and "dissolved" absorption coefficients, respectively. While NAP dominated forward, and hence total, scattering, our results also suggest that the scattering by VSP was far from negligible and domi nated backscattering. Since the sizes of VSP range from 0.02 to 0.2 um, covering (a portion of) the operationally defined "dissolved" matter, the typical assumption that colored dis solved organic matter (i.e. CDOM) does not scatter may not hold, particularly in a coastal or estuarine environment.