The occurrence of phytoplankton blooms in estuarine and coastal waters is co‐determined by the export of fluvial nutrients and other water properties such as turbidity. In this study, the Changjiang River Estuary was used as an example to investigate the intrinsic link between river plume dynamics, riverine nutrient loading, suspended sediment concentration, and phytoplankton blooms with a coupled hydrodynamic‐sediment‐ecosystem numerical model. Suspended sediment concentration from the sediment module was used to parameterize light attenuation in waters, which, in association with river plume dynamics, was found to impact phytoplankton distribution. Data that was collected in situ, in addition to satellite data for chlorophyll, nutrients, and suspended sediments were used to validate the model, which performed well. The surface high chlorophyll centers exhibited a patch‐like pattern from the northeast to the south off the Changjiang River mouth. The high chlorophyll concentration within the river plume was mainly determined by riverine nutrient exports, and potential phosphate limitation occurred away from the river mouth. The chlorophyll concentration decreased dramatically shoreward of the sediment front, which was controlled by the bottom river plume front. The bottom plume front was an intrinsic feature of the Changjiang River plume and similar river plume systems, which set a boundary separating the well‐mixed (turbid) nearshore waters and stratified (clear) offshore waters. Without considering the sediment shading effect, the model yielded an unrealistic chlorophyll distribution with artificially high values in the turbid area. This indicated that light attenuation was a key factor limiting phytoplankton blooms in turbid river estuaries.

Estuarine saltwater intrusions are mainly controlled by river discharge and tides. Unexpectedly, an extremely severe saltwater intrusion event occurred in February 2014 in the Changjiang estuary under normal river discharge conditions. This intrusion cut off the freshwater input for 23 d into the Qingcaosha reservoir, which is the largest estuarine reservoir in the world, creating a severe threat to water safety in Shanghai. No similar catastrophic saltwater intrusion has occurred since records of salinity in the estuary have been kept. During the event, a persistent and strong northerly wind existed, with a maximum speed of 17.6 m s⁻¹, lasting 9 d and coinciding with a distinct water level rise. Our study demonstrates that the extremely severe saltwater intrusion was caused by this northerly wind, which drove substantial landward net water transport to form a horizontal estuarine circulation that flowed into the northern channel and out of the southern channel. This landward net water transport overpowered the seaward-flowing river runoff and transported a large volume of highly saline water into the northern channel. The mechanisms of this severe saltwater intrusion event, including the northerly wind, residual water level rise, landward water transport and resulting horizontal circulation, etc., were systematically investigated.

Qiu, C. and Zhu, J., 2015. Assessing the influence of sea level rise on salt transport processes and estuarine circulation in the Changjiang River estuary. Global sea level rise has been greatly concerned by government and society with its effects on saltwater intrusion and material transport in estuaries, which threaten freshwater habitat and drinking water supplies. A semi-implicit estuarine, coastal, and ocean model (ECOM-si) was used to assess the influences of rising sea level on salt transport processes and estuarine circulation patterns in the Changjiang River estuary, China. The variations of intruding saltwater and residual salt transport were simulated according to the variations of several sea level rise scenarios, and results in typical year and dry year were demonstrated, respectively. The modeled results are in good agreement with the observed data, and statistics show good correlation coefficient and Skill Score values. Results from the numerical experiments show that the intensity...