Nitrogen Reduction Causes Shifts in Winter and Spring Phytoplankton Composition and Resource Use Efficiency in a Large Subtropical Lake in China

Liu X., Deng J., Li Y., Jeppesen E., Zhang M., Chen F.

Ecosystems, vol.26, no.8, pp.1640-1655, 2023 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 26 Issue: 8
  • Publication Date: 2023
  • Doi Number: 10.1007/s10021-023-00855-z
  • Journal Name: Ecosystems
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Aquatic Science & Fisheries Abstracts (ASFA), Artic & Antarctic Regions, BIOSIS, CAB Abstracts, Environment Index, Geobase, Pollution Abstracts, Veterinary Science Database
  • Page Numbers: pp.1640-1655
  • Keywords: eutrophication, phytoplankton, resource use efficiency, ammonium, fish, ecological thresholds, CYANOBACTERIAL BLOOMS, COMMUNITY COMPOSITION, FUNCTIONAL DIVERSITY, TROPHIC CASCADES, REGIME SHIFTS, NUTRIENT, AMMONIUM, EUTROPHICATION, ZOOPLANKTON, TOXICITY
  • Middle East Technical University Affiliated: No

Abstract

Aquatic ecosystems occasionally show ecological thresholds, defined as the point at which there is a sudden shift in production, trait or biomass or where changes in an environmental driver create nonlinear responses at the ecosystem level. Previous studies of lakes have mainly focused on how reduction in particularly phosphorus (P) concentrations helps to create a shift in lakes from a turbid to a clear state (re-oligotrophication), whereas the effect of nitrogen (N) reduction is less well studied. Here, by analysing a 28-year monthly monitoring dataset (from December 1991 to November 2019) from the subtropical, large eutrophic Lake Taihu, China, we identified a sudden shift in phytoplankton biomass and composition that coincided with a pronounced change in ecosystem functions, for example, resource use efficiency (RUE), during a period with reduction of the external nutrient loading. The changes were particularly strong in winter–spring where a sudden decrease in N concentrations was accompanied by a sudden increase in diatom biomass and phytoplankton RUE and a shift from green algae and flagellate co-dominance to dominance of diatoms. Structural equation modelling further indicated that ammonium reduction led directly to increases in winter–spring phytoplankton RUE and diatom biomass. Repeated fish stocking likely also contributed to the changes in biomass and RUE. Our study provides new insight into the ecological responses to N loading reduction and contributes to the understanding of lake responses to early re-oligotrophication, which was pronounced mainly in the colder seasons in subtropical Lake Taihu, similar to findings in the early phase of re-oligotrophication in numerous temperate lakes.