The Pearl River Delta (PRD) in Guangdong province is one of the most economically prosperous areas in China. A large number of domestic and industrial wastes are produced together with the economic development and 10% of waste output in growth rate has been estimated in the past few years. The complicated river web of the delta, which is characterized as criss-cross and multiple river channels, is the essential entrance for the Pearl River water entering into the South China Sea. Many studies have been focusing on physical and chemical factors of this region, but few referred to aquatic organisms, especially in recent years. To understand the temporal and spatial distribution pattern of Scenedesmus, a common green algal group of riverine phytoplankton community, seasonal investigation has been carried out in the river web area in 2012. The thirteen representative sampling sites settled covered almost the whole area and shaped in umbrella-type. The coherence between the biomass of each taxa and environmental factors was also analyzed using PCA method to evaluate the key factors for explaining the interaction mechanisms. Also, the regional characteristics of phytoplankton biodiversity pattern were evaluated from the genus level based on the results.
During the investigation, the total 24 taxonomic species (including variant and derivative) were identified, including 11 taxa with spines and 13 taxa none. Although several species showed high occurrence rate, their contribution to total phytoplankton biomass was low, and less than 1% in terms of averages. However, relative abundance between different taxa was closely related to their occurrence rate. Three species (S. armatus var. armatus, S. armatus var. boglariensis f. bicaudatus, S. dimorphus) showed relatively high values in both occurrence and biomass, which was assumed related to their special morphological features. Seasonal variation pattern of both species richness and biomass indicated high in wet seasons and low in dry seasons, water temperature and discharge have been found to be responsible for this through the PCA analysis. Water temperature mainly influenced the growth and physiological conditions of Scenedesmus, while discharge mainly determined the exterior supplement of the algae. The spatial distribution pattern of total species richness showed high in outside stations and low in central stations, but this pattern had apparent seasonal differences. The patterns of May and August were in accordance with that of the total, and the patterns of March and December just showed high values in sampling sites close to Guangzhou. Through the PCA analysis, discharge, water temperature and nutrients have been found to be the key factors to influence this spatial pattern. The spatial distribution pattern of biomass showed extremely higher in ZJQ than those in other stations. Nutrients, water stability and salinity have been found to be the key factors for the spatial pattern through the PCA analysis. In addition, the relationship between Scenedesmus biomass and species richness was analyzed, and it was in consistent with the global phytoplankton biodiversity pattern, and had an incline to ascending part of the model, which also promotes the grading and regional understanding of the global diversity pattern.