Interactive Effects of Nutrients and Salinity on Phytoplankton in Subtropical Plateau Lakes of Contrasting Water Depths

Abstract

Eutrophication and salinization are serious global environmental problems in freshwater ecosystems, occasionally acting jointly to exert harmful effects on aquatic ecosystems. To elucidate the interactive effects of nutrients and salinity on phytoplankton assemblages, we conducted a four-season study during 2020–2021 of eight lakes from Yunnan Plateau (Southwest China) with a wide range of conductivities (Cond, reflecting degree of salinization), eutrophic states, and water depths and used General Additive Modeling (GAM) of the data. We found that: (1) species number (SN), density (DPhyt), and biomass (BPhyt) of phytoplankton showed stronger seasonal dynamics in shallow lakes than in deep lakes, all being, as expected, higher in the warm season; (2) annual and summer data revealed highly significant positive relationships between SN, DPhyt, and BPhyt with total nitrogen (TN) and total phosphorus (TP), which became weaker at high TP occurring when the N:P ratio was low, indicating N limitation; (3) SN, DPhyt, and BPhyt showed a unimodal relationship with salinity, peaking at 400–1000 μS/cm (Cond); (4) the two dominant taxa (cyanobacteria and chlorophyta) showed different patterns, with chlorophyta generally dominating at low TN and cyanobacteria at high TN and Cond, suggesting the synergistic effect of nitrogen and Cond on cyanobacterial dominance.

Effect of land use and environmental variables on phytoplankton community structure in high-elevation river, upper Yangtze river, China

“…In this study, Sal was significantly negatively correlated with Oscillatoria but had no significant effect on other dominant algae. This indicated that different phytoplankton had different tolerance responses to Sal, and Oscillatoria was not easy to grow and reproduce in the water environment with high Sal concentration (Wang et al, 2023). That's because the increase of Sal will affect the osmotic pressure within phytoplankton cells, leading to dysfunctional metabolism in phytoplankton (Redden and Rukminasari, 2008).…”

The Effects of Global Climate Change on Water Level and Salinity: Causes and Effects

“…This Special Issue of Water provides examples of the effects of salinization based on a variety of these approaches. Two of the studies [7,8] took a field observational approach. In [7], salinity-eutrophication interactive effects on the food web were studied in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia.…”

“…The interactive effects of salinity and eutrophication strongly depended on the size and depth of the lakes, and it was concluded that small shallow lakes will be the most vulnerable to the joint effect of increased salinity and eutrophication, with the degradation of ecosystem functioning and water quality at moderate salinities of 3-20 g L −1 . In the second study [8], the interactive effects of nutrients and salinity on phytoplankton assemblages were elucidated in a four-season investigation of eight lakes in Yunnan Plateau (southwest China), covering a wide range of salinities (conductivities), eutrophic states, and water depths. The species number, density, and biomass of phytoplankton showed stronger seasonal dynamics in shallow lakes than in deep lakes, all being, as expected, higher in the warm season.…”