Original paper

Patterning and predicting phytoplankton assemblages in a large subtropical river

Wang, Chao; Li, Xinhui; Lai, Zini; Li, Yuefei; Dauta, Alain; Lek, Sovan

Fundamental and Applied Limnology Volume 185 Nr. 3-4 (2014), p. 263 - 279

published: Dec 1, 2014

DOI: 10.1127/fal/2014/0684

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Abstract

Through time-series sampling during the whole of 2009, phytoplankton patterns and prediction models were built up with a self-organizing map (SOM) and Linear Discriminant Analysis (LDA) within the downstream region of a large subtropical river, the Pearl River (China). The excessive nutrient conditions resulted in a diatom dominant phytoplankton community. While green algae contributed more only in species diversity, as they were mainly dependent on inoculations from external resources, and their abundance remained low under fast and turbid flow conditions. The time periods of phytoplankton samples were classified into four clusters using a self-organizing map (SOM) based on species similarities. These clusters were clearly different with respect to species richness, biomass and indicators. The LDA predicting model indicated that these clusters of species assemblages could easily be differentiated by physical factors such as water temperature, discharge and precipitation. As for nutrients, only phosphate could have an occasional impact on phytoplankton assemblages. By using the environmental variables, the global score for predicting the assemblages was 64.2 %, with the predicting performance rates for clusters I, IIa, IIb1 and IIb2 at 50, 48, 62 and 74 %, respectively. Cluster I benefited from a combination of higher temperatures and low discharge, and had the highest species richness and biomass. Cluster IIb1 benefited from high discharge and diverse species inoculations, but interruptions in increases of biomass. Cluster IIb2 showed that low temperatures resulted in both low species richness and biomass. Cluster IIa, characterized by phosphate, indicated that phytoplankton assemblages were occasionally P-limited in the studied section. In conclusion, the annual patterns of the downstream phytoplankton assemblages in the Pearl River were mainly regulated by physical factors but occasionally limited by nutrients.

Keywords

environmentslinear discriminant analysis (lda)phytoplanktonriverself-organizing map (som)