VARIATION REGULARITY OF BOTTOM SUBSTRATE CHARACTERISTICS IN SPAWNING GROUND OF CHINESE STURGEON DOWNSTREAM THE GEZHOUBA DAM FROM IMPOUNDING OF THE THREE GORGE RESERVOIR

In order to investigate the changes of riverbed texture characteristics of Chinese sturgeon (Acipenser sinensis) spawning grounds under the Gezhouba Dam, we analyzed the correlation between the apparent characteristics of substrate and hydroacoustic characteristics. The analysis was based on hydroacoustic data and underwater video images collected from 2004 to 2020, covering the period since the Three Gorges water storage. The study aimed to analyze the changes of substrate characteristics and their causes. The results showed that (1) hardness, roughness and fractal dimension were found to be correlated with riverbed mass congestion, grain size and major composition, respectively; (2) the characteristic parameters of riverbed substrate at the spawning ground of Chinese sturgeon under the Gezhouba Dam showed significantly changes from 2004 to 2020. The mean values of hardness, roughness and fractal dimension showed an increasing trend followed by a decreasing trend from 2004 to 2012 (P<0.01). The three acoustic parameters also showed an increasing trend followed by a decreasing trend from 2012 to 2019. Between 2019 and 2020, all three acoustic characteristics mean values exhibited a significantly increase (P<0.01), followed by a significantly decrease (P<0.01); (3) the proportion of substrate containing sand in spawning grounds decreased by 33.08% between 2004 and 2008, increased by 12.69% between 2008 and 2012, and decreased 33.83% between 2012 and 2015. Subsequently, it continued to decrease until 2019 and increased by 39.37% during the period of 2019—2020. The substrate changes during this period were likely influenced by the Three Gorges water storage, sediment scheduling, water storage operation of newly constructed dams, floods, and the natural reproductive activities of Chinese sturgeon, which were obviously affected by the changes in riverbed substrate. The results of the study provide basic data for the extrapolation of the riverbed substrate of the Chinese sturgeon spawning grounds under Gezhouba Dam and the restoration and reconstruction of the spawning grounds.