Lake health-status evaluation in the middle reaches of the Yangtze River based on the phytoplankton biological integrity index

Phytoplankton are key components of aquatic ecosystems, and critical for assessing the health-status of water bodies. Field surveys of phytoplankton communities in typical lakes in the middle reaches of the Yangtze River were conducted to establish a phytoplankton-based biological integrity index (P-IBI), for evaluating ecological health of these lakes. To ensure the reliability of the evaluation results, we performed a regression comparison with the comprehensive trophic level index (TLI), and used redundancy analysis with linear models to assess the relationships between P-IBI, TLI and their respective component metrics with environmental factors during the dry and wet seasons. Indicating that the overall structure of phytoplankton communities in typical lakes in the middle reaches of the Yangtze River is characterized by a Chlorophyte-Diatom-Cyanobacteria type, with Chlorophytes and Diatoms being dominant. Redundancy analysis revealed that ammonia nitrogen (NH3-N), total nitrogen, total phosphorus and Secchi depth were the primary environmental factors influencing P-IBI and its component metrics in this watershed. P-IBI and TLI correlated significantly and negatively during the dry season. Overall, P-IBI showed strong reliability for assessing the health status of typical lakes in the study region, thereby providing a reasonable assessment of water body-health status, responding sensitively to changes in water environmental factors within the watershed and providing relevant assistance for the research and management of eutrophic lakes and their similar counterparts in the middle reaches of the Yangtze River basin.