Assessment of the health status of daye lake based on the phytoplankton integrity index (P-IBI)

As an important indicator for evaluating lake water environments, the phytoplankton biotic integrity index (P-IBI) has been widely used in recent years to assess aquatic ecosystem health. Based on field surveys and laboratory analyses, this study investigated the phytoplankton community structure and water quality characteristics of Daye Lake, a typical lake in the middle reaches of the Yangtze River, during the dry and wet seasons of 2023, and evaluated its ecological status using the P-IBI. The results showed that phytoplankton communities in both seasons were dominated by Chlorophyta, Cyanobacteria, and Bacillariophyta, with the Chlorophyta having the dominant species. During the dry season, P-IBI values ranged from 1.21 to 3.75, while during the wet season, values ranged from 0.14 to 3.00. Overall, the evaluation grade for Daye Lake was Fair during both the dry and wet seasons. However, the P-IBI exhibited temporal variability across different hydrological periods, with the evaluation results being better during the dry season than during the wet season. Redundancy analysis indicated that during the dry season, TP, Chl-a, NH₃-N, and TN were negatively correlated with P-IBI, while CODMn was positively correlated; during the wet season, NH₃-N, TP, Chl-a, TN, and CODMn were negatively correlated with P-IBI. TN and Chl-a were the primary factors influencing P-IBI during the dry and wet seasons, respectively. This study provides a scientific basis for the management of aquatic ecological health and restoration in the Daye Lake watershed.