Untitled

Abstract

Sediment condition of the shoreward area in Tokyo Bay was mapped using sediment condition classification system based on echo features. This system enabled us to classify large areas of sediment in high resolution, with the echo trace output grouped by geometric pattern. The sediment condition was categorized by moisture content, which was correlated to the echo trace output. The high resolution sediment condition map showed that good condition sediments were intermittently spaced in the shoreward area that was previously presumed to be totally covered by sludge. This result provides important information about more efficient restoration of the shoreward area in Tokyo Bay because we can now zone the restoration area and carry out sand capping on localized areas.

Numerical Modeling of Long-Term Biogeochemical Processes and Its Application to Sedimentary Bed Formation in Tokyo Bay

“…Process-based coastal ecosystem models mainly consider physical processes, bioprocesses, and chemical processes. Other than those general processes, the mechanism of changing porosity with respect to POCC in sediment, which has emerged from the field data analysis [39], has been considered in this model. The processes in the water and sediment columns were considered independently, and the water column was coupled to the sediment column through the interaction of layer flux exchanges.…”

“…The model was initialized with inorganic sediment, which is free from POC and becomes polluted with the POC accumulation from the water column. The accumulated POC changes the sediment porosity [39] and thereby the active sediment layer thickness with respect to the POCC.…”

“…The pelagic model was composed of 20 σ-layers, and the benthic model was composed of 25 layers with different layer thicknesses in vertical direction. Based on the data analysis [39], the relationship between porosity and POCC was derived as shown in Figure 8, and it was applied to compute the new layer thickness in the benthic model at every time step with respect to POCC.…”

“…However, attempts to reproduce the spatial distributions of water and sediment quality through modeling approaches, which would support the management of water quality in the bay, are scarce or neglected. Meanwhile, the data show higher sediment water content (WC) at the inner part of the bay with a correlation to the sediment POCC [38,39], which in turn affects water quality deterioration.…”

“…The study area, which includes the river and sewer inputs and the data-collection locations, namely, Chiba lighthouse (CLH), Keiyo sea birth (KSB), and Tokyo lighthouse (TLH) is shown in Figure 1. The available data on vertical distributions of nutrients in water [43] and spatial distribution of POCC in the sediment [39] of Tokyo Bay have been used for validation of the model. The modeling approach in this study is the first of its kind to analyze water and sediment quality of Tokyo Bay by considering realistic processes of bed formation, with initial inorganic sediment that becomes polluted over time.…”