Identifying the relationship between algal blooms and key driving factors in a tributary backwater area of the Three Gorges Reservoir, China

Harmful algal blooms can occur in the backwaters of tributaries feeding large-scale reservoirs. Quantifying the contribution of the key environmental factors leading to algal blooms is challenging. In this study, we employed data-driven methods to identify and quantify the primary environmental drivers of algal blooms in the backwater area of the Xiaojiang River (XJR), a tributary of the Three Gorges Reservoir (TGR). The main results include: (1) Algal blooms in the backwater area of the XJR frequently occur in the spring and summer seasons, coinciding with the period of rising temperatures and decreasing water levels of the TGR. (2) The water level of the TGR has the greatest impact on algal blooms in the backwater area of the XJR, with a contribution percentage exceeding 30%. Followed by nutrients, where both TP and TN have contribution percentages exceeding 14%. Compared to TN, TP has a relatively significant impact on algal blooms. Moreover, the impact of temperature on algal blooms should not be overlooked, as it has a contribution percentage above 12%. Rising temperatures directly affect the physicochemical characteristics of water bodies, thereby accelerating the metabolic rate of algal blooms. The results indicate that appropriately increasing the water level of the TGR would help alleviate algal blooms in the tributaries.