Diverse drivers of phytoplankton dynamics in different phyla across the annual cycle in a freshwater lake

Abstract

An understanding of the annual variations in the phytoplankton community in freshwater lakes, and of the drivers responsible for these variations, is essential for lake management. In this study we collected and analyzed seasonal samples of phytoplankton and assessed environmental variables in Nansi Lake from 2011 to 2015, in order to identify the seasonal dynamics of the phytoplankton community and the main drivers in each phylum. The results showed that phytoplankton diversity in Nansi Lake followed annual cycles, which were interrupted by a water diversion in 2013. The disruption of equilibrium was clearly demonstrated by the Shannon–Wiener diversity index, Pielou’s evenness index, and Simpson’s dominance index, whereas the species richness and abundance showed resilience, maintaining regular annual cycles. The dominant species were frequently Synedra acus Kütz (Bacillariophyta), Closterium gracile Bréb (Chlorophyta), and Scenedesmus quadricauda Bréb (Chlorophyta) in summer and autumn. Non-metric multidimensional scaling (NMDS) analysis suggested that the phytoplankton was most widely distributed in summer, when conditions were more conducive to phytoplankton growth and reproduction. Redundancy analysis (RDA) indicated that the main drivers for the phytoplankton community varied in different taxonomic units. Specifically, the NP ratio and permanganate index (CODMn) had significant effects on Chlorophyta, whereas pH, dissolved oxygen (DO), and transparency significantly influenced Bacillariophyta. This study highlights the importance of seasonal phytoplankton succession and the need for identification of the main drivers in each phylum in order to achieve more effective control of phytoplankton blooms in freshwater lakes.

Keywords

• annual cycle
• environmental factor
• phytoplankton community
• redundancy analysis
• seasonal succession