The response time of the Changjiang plume to river discharge in summer

A three-dimensional numerical model was used to study the response time of the Changjiang (Yangtze) River plume to river discharge by artificially increasing the runoff over a short period and investigating the variation of salinity in the plume region. The time lagged between the change of river discharge and the change of salinity that reaches the 10% of the adjusted value is considered as the response time in this study. The response times in the plume region differed slightly when the river discharge during the spring tide and the neap tide was increased. Specifically, the response times near the river mouth and in the plume edge were ~ 1 days and more than 15 days, respectively. The brackish water volumes were also calculated to determine the variations in the plume extensions over time. A tracer was released to study the transport time from the Datong station to the East China Sea using the concept of water age. The tracer transport time ranged from 10 days near the river mouth to more than 50 days at the edge of the plume, which is much longer than the response time of the surface salinity.