The global environment has experienced rapid changes over the past decades, including global warming, global dimming and brightening, and abnormal climate fluctuations. However, direct evidence of global change in the regional physical environment of a lake is rare especially in China because long-term observations are lacking.
Recently, Prof. ZHANG Yunlin et al. from Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences demonstrated the profound changes in the physical environment of Lake Taihu on the basis of long-term observation since 1992, and their study was published in Water Resources Research.
The research team documented significant increasing rates of 0.36 °C/decade and 0.37 °C/decade for the yearly mean air and water temperatures, respectively.
Additionally, significant increase was observed for the yearly mean water level with the rates of 0.15 m/decade.
In contrast, significant decrease was documented for the yearly mean wind speed and Secchi disk depth with the rates of 0.27 m/(s·decade) and 0.21 m/decade for the macrophyte-dominated regions, respectively.
Therefore, the significant increasing ratio of temperature to wind promoted algal bloom formation and outbreaks (Fig. 1), while the decreasing ratio of Secchi disk depth to water level resulted in the loss of aquatic macrophytes (Fig. 2), which accelerated the shift from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state in Lake Taihu.
Their findings highlight the importance of long-term physical environment monitoring data for understanding ecosystem response to global climate change.
Fig. 1 Long-term trends in a meteorological index of algal blooms (a) and the yearly mean ratio of air temperature to wind speed (b) from 1992 to 2016 (Image by the research team)
Fig. 2 Long-term trend in the yearly mean ratio of Secchi disk depth to water level in the phytoplankton-dominated (a) and macrophyte-dominated (b) regions from 1992 to 2016 (Image by the research team)
Fig. 3 Schematic diagram of ecosystem succession driven by the profound changes in the physical environment of Lake Taihu (1) Global warming; (2) Decreasing wind speed decrease; (3) Increasing water level; (4) Decreasing Secchi disk depth; (5) ecosystem succession from macrophyte-dominated ecosystem to phytoplankton-dominated ecosystem (Image by the research team)
