Measurements of suspended particulate matter with laser in-situ scattering and transmissometry in the Jiaozhou Bay in China

A laser in-situ scattering and transmissometry probe (LISST-100) was used to estimate the spatial variations of suspended particle (aggregate) distribution, volume concentration and beam attenuation in the Jiaozhou Bay, Qingdao, China on 18 July 2003. One study site was located at the mouth (Sta. J1), with the other being within the inner bay (Sta. J2). Measurements of total suspended matter (TSM) and chlorophyll fluorescence and sampling of bottom sediments were carried out simultaneously. On the basis of the field data, the in-situ particle effective density, settling velocity and flux, and particle projected surface area (PSA) were estimated. The results demonstrate that both profiles have similar particle size distributions from surface to bottom within the water columns. Mean particle diameters for Stas J1 and J2 are 38～74 and 1～20 μm, respectively, particles within these ranges dominate over the particulate components. Suspended particle volume concentrations increase with water depth, with spikes near the bottom. At Sta. J1, the mean size of bottom sediments and those of suspended particles at 10.8 m below the water surface are almost the same, as well as their size distributions. This observation suggests that a special affinity exists between bottom sediment and suspended particles. In addition, the estimates show that the effective density, settling velocity and flux are higher in the inner bay. Beam attenuation coefficient correlates well with the volume concentration, positively. It is inferred that the optical scattering was mostly caused by 1～250 μm components, among which the particles finer than 20 μm dominate the beam attenuation. The PSA appears a proxy for the leaving reflectance estimation.