The flocculation of fine-grained suspended sediment and its impact on spectral characteristics based on in situ measurement in the Changjiang Estuary, China

Abstract

Flocculation of fine-grained particles dominates the fate of transportation, deposition, and resuspension of the large amount of estuarine sediment, organic matter, nutrient salts, trace metals, and even radioactive matter attached to the sediment. The flocculation processes change the physical characteristics of the original particles such as grain size, projected surface area, density, and settling velocity, as well as the spectral characteristics. In situ spectral reflectance and physical characteristics (sediment diameter and volume concentration) of fine-grained suspended sediment flocs in surface water (−0.5 m depth) were measured in the south channel turbidity maximum zone of the Changjiang Estuary from 23 May to 2 June 2009. The relationship between the spectral reflectance and the projected surface area (PSA) of fine-grained suspended sediment flocs was examined. Results showed that spectral reflectivity varied with the PSA of fine-grained suspended sediment flocs. The correlation between PSA and spectral reflectivity was larger than the correlation between suspended sediment concentration (SSC) and the spectral reflectivity. Because fine-grained suspended flocs exist in estuarine waters such as the Changjiang Estuary, special attention should be paid to the inversion model established by remote sensing data to extract SSC information.