Inter-Annual Variability of the Turbidity Maximum Zone in Hangzhou Bay Based on Landsat Imagery

The areas of the turbidity maximum zone (TMZ) in Hangzhou Bay changed with the anthropogenic activities in the past several decades. Thirty Landsat images of the bay, covering the period from 1984 to 2015, were collected to examine the variation of the TMZ and surface suspended sediment concentration (SSC) in the bay. The surface SSC was retrieved from the Landsat images. The error between the retrieved SSC and the observed data was 23.3%. Then the TMZ areas were calculated using the remote sensing data. Results show that the SSC values had a more asymmetric distribution pattern from 1984 to 2015, with low turbid area increased, as shown by the coefficient of skewness. From 1984 to 2015, the SSC values decreased in almost the entire bay. The Luchaogang station in north shore witnessed the largest decrease of about 73%. The annual trend ratio of the TMZ areas was -4.57%, while the annual trend ratio of sediment load was -3.74%. Hence, the inter-annual variability of the TMZ areas is supposed to be affected by the combined effects of the reduction of the riverine sediment discharge, as well as the tidal flat reclamation around Hangzhou Bay.