Seasonal variations in suspended sediment concentration and its drivers in the radial sand ridges of China's Jiangsu coast

Abstract

Most studies on seasonal variations in suspended sediment concentrations (SSCs) only performed qualitative analyses and focused on the dynamic mechanisms of instantaneous SSCs rather than background SSCs and their contributions to seasonal SSCs. To quantitatively evaluate the seasonal differences in SSCs and their drivers in radial sand ridges (RSRs), we measured water depth, current velocity, SSC, wave parameters, and suspended and surficial sediment properties during summer and winter. Small grain size (fine sand, silt, and clay) was the dominant size class and suspension was the dominant transport mechanism in areas with a significantly higher SSC during winter than during summer (up to ∼2.5 times). Settling velocity, which was sensitive to temperature, grain size, and turbulence, had 0.39–0.89-fold difference between summer and winter. The stable background SSC (minimum SSC among tidal cycles) during winter was higher, with an average contribution of ∼74% to the total SSC, than that during summer. Combined with wave statistics, the lower sediment settling velocity acted in conjunction with the higher strong wave occurrence frequency and longer wave duration to sustain high background SSCs during winter. This study reinforces the utility of background SSC when estimating instantaneous SSC in different seasons.