Observation and Simulation of the Pearl River plume and its biological effects in a pre-flood season

A strong Pearl River plume occurred on June, 2015, which was caused by heavy precipitation in South China. A cruise survey was carried out to investigate the dynamics of the river plume and its effects on aquatic ecosystem. The freshwater was carried offshore in a strip and transported a long distance southeastward, when forced by the southwest wind. The edge of the plume touch the 100-m isobaths, over 100 km off shore. A phytoplankton bloom was observed to the south of Hong Kong Island. Along the longitudinal axis of the Pearl River Estuary, the low oxygen conditions was detected in the surface of the upper reach and bottom layers outside the estuary. A coupled physical-biological model was implemented to explore details of the plume dynamics and its ecological characteristics. Modeling results suggested that the strong stratification formed in the upper 10m layer of the plume. The low-oxygen, high-nutrient inflows entering the head of the estuary from four channels of Pearl River led to the hypoxia phenomena in the surface waters of the upper reach. The strong stratification caused by freshwater inflow together with excessive input of nutrients and organic materials were the main reasons for the occurrence of the phytoplankton bloom and low-oxygen in the bottom waters outside the estuary.