Study on the Multiple Mechanisms of Hydroecological Effects in Lower-Middle Hanjiang River

This study utilized data on phytoplankton and benthic macroinvertebrates from the main stem of the Han River during 2011–2012, employing a functional linear model (FLM) to explore the hydroecological effects under different hydrological conditions. The results indicated that the impact of flow and flow rate changes on the density of phytoplankton and benthic macroinvertebrates is complex. In the short term, low flow and smaller flow rate changes favour the growth of phytoplankton, while high flow inhibits their growth. However, in the long term, high flow promotes the growth of phytoplankton. Although the flow change model for benthic macroinvertebrates was not statistically significant, their response to flow changes was also complex, with flow rate changes significantly affecting their density. There was a positive lag effect within a 1-year cycle, but this lag effect weakened over time, possibly due to habitat destruction or unstable food sources caused by severe or prolonged flow changes. Overall, the FLM identified statistically significant relationships with river flow over the past 12 months, providing a new perspective for predicting ecological flow scenarios. The research findings offer recommendations and a scientific basis for flow management in the Han River.