Characteristics of the ecological environment in the seawater off the Pearl River estuary in autumn

Nutrients, dissolved oxygen and chlorophyll a (Chl a) in different layers of the seawater off the Pearl River estuary were investigated in September 2015. Distribution patterns and relationships of these parameters were analyzed to study the ecological environment characteristics in this area. The results showed that the seawater ecosystems off the Pearl River estuary were generally in a good condition with the low concentrations of nutrients and Chl a, and the appropriate dissolved oxygen level. Their distribution patterns showed that the nearshore waters were influenced by river runoff to some extent. Because of the stratified water temperature and salinity, nutrients, dissolved oxygen and Chl a showed obvious vertical variations. Shallow waters (<~50 m) off the Pearl River estuary had relatively low concentrations of nutrients because of the photosynthesis of phytoplankton, while the deep waters (>~50 m) off the Pearl River estuary had generally high nutrient concentrations due to the release of nutrients from organic matter decomposition. Based on nutrient concentrations and their ratios, we found the phytoplankton growth in most of the shallow waters (<~50 m) off the Pearl River estuary may suffering both N and P limitation during the investigating period. The relationships among nutrients, dissolved oxygen and Chl a manifested that the water system off the Pearl River estuary in autumn was dominated by dissimilation processes.