Phytoplankton community evolution and driving factors in Lake Dali of Inner Mongolia over the last 1800 years

Lakes are important carriers of regional ecological evolution in geological history. Their sediments contain a rich information on the environmental evolution. Lake Dali is a closed inland lake situated on the northern edge of the East Asian Summer Monsoon (EASM). In this study, we collected about 238 cm sediment cores (GDL-1) in Lake Dali. Using 210Pb and 137Cs (top 20 cm of the core), AMS14C and other dating methods, we analyzed the content of sterols and other biomarkers in the sediment samples, and reconstructed the evolutionary history of typical algae, such as diatoms and cyanobacteria, in Lake Dali over the past 1800 years. The effects of total nitrogen (TN), total phosphorus (TP), salinity (Sr/Ba) and temperature on the algal communities were analyzed. The results showed that the mean total algal biomass in Lake Dali was 2.03 ng/g, with cyanobacteria accounting for an average relative abundance of 60%, green algae and diatoms with an average relative abundance of 20%. Environmental factors accounted for 47.7%, 55.20%, and 48.10% of the variation in the biomass of diatom, cyanobacteria, and total algae, respectively. Temperature, TN, and Sr/Ba ratio were identified as major influencing factors on phytoplankton community. The relative abundance of diatoms had a significant negative correlation with temperature, being the highest during the Little Ice Age and lowest in the Medieval Warm Period. In high-salinity conditions of Lake Dali, the influence of nutrient concentration on algae was limited, becoming a limiting factor for algae growth. With Sr/Ba ratio less than 0.9, the content of diatoms and the total amount of typical algae increased with the increasing Sr/Ba value. With Sr/Ba higher than 0.9, the total amount of typical algae was negatively correlated with Sr/Ba value, while diatoms showed a certain tolerance to salinity. The biomass of the typical algal communities in Lake Dali was affected by the combined effects of salinity, temperature and nutrient over the past 1800 years. During the warm period, the increase of lake salinity caused by enhanced evaporation became the main driver on the evolution of the typical algal community structure in Lake Dali. The reduction in nutrient concentration and temperature became the main factors affecting the phytoplankton biomass in the lake for the cold period. © 2024 by Journal of Lake Sciences.