Evaluation of reservoir-induced ecological flow with consideration of ecological responses to multiple hydrological alterations: A case study in the Feiyun River Basin, China

With rapid economic and social development, human activities, such as the construction of reservoirs, have satisfied many needs. However, these activities have also caused changes in the hydrological ecosystem of the basin, impacting river biodiversity. The establishment of the Shanxi Reservoir within the Feiyun River Basin has inevitably altered the hydrological system, which was previously shaped primarily by precipitation. This study comprehensively evaluates the impact of Shanxi Reservoir on the hydrological alteration of the basin. Two ecological flow indicators, ecosurplus and ecodeficit, were used based on flow duration curves, along with the Shannon Index of river biodiversity (SI) and several hydrological indicators: the Indicator of Hydrological Alteration (IHA), the Degree of Integrated Hydrological Alteration (D0), and the Dundee Hydrological Regime Alteration Method (DHRAM). The results of the study show that: (1) the previously observed correlation between ecological flow and precipitation was disrupted following the construction of the reservoir. As a result, there was a notable ecological deficit in the spring season, with a maximum of 0.43, and a considerable increase in ecological surplus during winter, reaching a maximum of 4.80. (2) The flow regime of the river has undergone significant changes, resulting in a combined hydrological variability of 66. 44% and an ecological hazard level of 4. This indicates a high risk to the river's ecological environment. (3) The total seasonal ecological surplus has increased and remained consistently high, which has contributed to a decline in the SI of river biodiversity, the river's biology has degraded over time (4) The use of ecological flow indicators is closely tied to IHA32 indicators. Combining ecological flow indicators with ERHIs has shown to be a successful approach for assessing ecohydrological regimes. These findings have significant implications for future studies in similar cases and offer valuable guidance for managing water resources.