Experimental study on acute impacts of hyper-concentrated flow on Gymnocypris Eckloni and implication for sediment management

Significant increases in suspended sediment concentration (SSC) always occur during dam removal or sediment flushing processes, which could result in acute impacts on aquatic organisms. An analysis of the potential impact of the Huangheyuan hydropower dam removal on the upper reaches of the Yellow River is required for adaptive management. But the reports on the impact of high SSC on fishes living in rivers in the plateau areas are limited. Further studies on impact factors, fish behavior, and assessment methods were performed in this paper. The acute response of a typical fish, Gymnocypris eckloni, was tested by experiments with sediment concentrations ranging from 3.3 × 10³ to 80.78 × 10³ mg·L⁻¹. The changes in fish aquatic surface respiration (ASR) behavior were analyzed under different SSCs. The cluster analysis of the environmental factors was conducted to analyze the relationship between the factors and fish mortality. The severity of ill effects (SEV) model was improved to assess the acute impact on fish. The results indicated that the SSC was the most related factor. The ASR could be induced by the SSC higher than 21 × 10³ mg·L⁻¹, and fish mortality was caused by SSC higher than 55 × 10³ mg·L⁻¹. The thresholds of SSC and exposure duration for fish protection were proposed to be less than 55 × 10³ mg·L⁻¹ and 6 hr, respectively. The findings could support the planning and regulation of dam sediment management on plateau areas.