Relationship between dissolved organic matter and phytoplankton community dynamics in a human-impacted subtropical river

Abstract

Abstract Dissolved organic matter (DOM) is closely related to phytoplankton blooms, one of the most concerning environmental problems globally. DOM originates from phytoplankton production and metabolic activity and, in turn, can influence phytoplankton biomass and community structure. Therefore, clarifying the relationship between phytoplankton community dynamics and DOM has implications for bloom prevention and control as well as for aquatic ecosystem management. To understand this relationship further, we investigated phytoplankton communities at 110 sites in the dry and rainy seasons within the Dongjiang River basin, China, which is known for high rates of urbanization, industrialization, and agricultural intensification. The interaction between DOM (two humic-like DOM [C1 and C2] and two protein-like DOM [C3 and C4]) and phytoplankton community dynamics was investigated. Phytoplankton biomass and taxonomic composition were significantly related to C2, C3, and C4. The effect of C3 and C4 on phytoplankton taxonomic composition was prominent. C2 originating from agricultural wastewater increased phytoplankton biomass and changed phytoplankton taxonomic composition, whereas C1, originating from terrestrial soils and plants, did not stimulate phytoplankton biomass in rivers. There were clear change points, where phytoplankton abundance rapidly increased or decreased with changes in the concentrations of DOM components. Results suggested that DOM controls phytoplankton community dynamics and their relationship changes with variations in DOM chemical composition. DOM generated by anthropogenic activities may act as a potential warning of phytoplankton blooms.