Distribution Characteristics and Environmental Impacts of Nutrients in the Dry Season of the Pearl River Estuary in 2016

Based on the field efforts in 2016 during a dry season (30 Nov-6 Dec) in the Pearl River Estuary (PRE)，south China, this study aimed to investigate the tidal changes of phytoplankton variability (in terms of chlorophyll a) and their responses to multiple environmental factors.Time series analysis，principal component analysis (PCA)，Pearson correlation analysis, and Delft3D model were carried out. A significant difference was found in the tidal variations of dissolved nutrients, covering both a spring tide and neap tide . Moderate differences in salinity and suspended sediment played different roles in the nitrogen and phosphate. The negative correlations of salinity and nitrogen ecologically implied a stronger diluting-mixing effect than that of phosphate, which has a large impact on the water quality. The adsorption of phosphorus by sediment particles was stronger than that of nitrogen. Nitrogen was mainly contributed by river discharge. DIN was constrained by tide-river dynamics and their mutual increase-decline trend, and a new source was supplemented along the transport from river to sea. The weak correlation between PO₄ and salinity suggested a different source contribution of the terrestrial emission from coastal cities; the contribution of river discharge was less compared with nitrogen. Over site, P-limitation was detected and was more frequently resulted in eutrophication and even bloom events. Characterizing the relationships among chlorophyll a, nutrients, and hydrological factors enables us to develop effective ecosystem management strategies, and to design studies more focused on ecological health and function.