Spatio-temporal Dynamics and Drivers of Phytoplankton Bloom in Dongting Lake from 2014-2022

Phytoplankton blooms are a major global issue affecting aquatic ecosystems, with negative impacts on aquaculture, food production, and reservoir water supply. In this study, the time-series floating algae index (FAI) products of Dongting Lake from 2014 to 2022 were generated using Landsat imagery through the Google Earth Engine (GEE). We analyzed the spatial and temporal dynamics of phytoplankton blooms and their responses to environmental and meteorological factors. Various statistical and spatial analysis methods were employed to examine the driving factors for blooms, such as the Theil-Sen median, Mann-Kendall test, Hurst index, and spatial autocorrelation analysis. Our results indicate that phytoplankton blooms more frequently occurred in the eastern and southern parts of Dongting Lake, with much lower occurrences in the western part. The largest bloom areas were observed primarily in summer and fall. The responses of blooms to environmental and meteorological factors varied by time scale. On a daily scale, total phosphorus concentration (TP), chlorophyll a concentration (Chl-a), and air temperature were the main factors promoting blooms, while total nitrogen (TN) and barometric pressure inhibited them. On a monthly scale, TP, Chl-a, and air temperature showed positive effects on the blooms. On quarterly and annual scales, Chl-a showed a strong correlation with bloom intensity. Bloom intensity and risk were further analyzed and rated at different levels, with 2014 recording the largest bloom area at 1,094.57 km2. This study provides valuable insights into the dynamics of phytoplankton blooms in Dongting Lake, which can contribute to the understanding of the bloom mechanism and offer guidance for improving water management and mitigating bloom-related risks.