Seasonal instability of phytoplankton community in extreme arid lake basin during interval period of large-scale ecological water transport.

Large-scale water transport helps solve the imbalance in water resources. Studies on ecological benefits after long-term EWT mainly focus on vegetation restoration and increase in water surface. However, the maintenance of aquatic communities in the EWT context is a major challenge. This study studied the seasonal dynamics of phytoplankton communities during the interval period of 22nd and 23rd EWT in a newborn lake generated by long-term EWT in an extremely arid zone. The 22nd EWT was carried out from August 2021 to November 2021, and the 23rd EWT was implemented from July to September 2022. Our research indicates that during the interval period, water temperature (WT), pH, dissolved oxygen (DO), suspended solids (SS), turbidity, total nitrogen (TN), NO₃-N, total phosphorus (TP), chemical oxygen demand (COD_cr), SO₄^2- showed seasonal dynamic changes. Meanwhile, the phytoplankton community also exhibits seasonal variations, including the succession of dominant phyla and dominant species, the decrease in density and α diversity, as well as the increased instability of functional groups and ecological networks. These phenomena are more pronounced in summer when the lake water evaporates and the water quality changes, suggesting that the phytoplankton community shows attenuation along with the changes of environmental factors during the interval period. Based on this, our study suggested that the coupling relationship between water quantity, water quality change and aquatic community succession should be considered for the precise control of EWT projects aiming at improving ecological benefits. Regular phytoplankton monitoring is recommended to track the evolution of aquatic ecosystems after long-term EWT.