In situ study on the impact of total dissolved gas supersaturation on endemic fish in the Upper Yangtze River

Abstract

Total dissolved gas (TDG) supersaturation in the upper Yangtze River caused by high spill rates upstream of hydroelectric dams has become a serious environmental problem in recent years. TDG supersaturation downstream of the Xiangjiaba Dam was investigated during flood periods in 2014 and 2015. Alongside this, an in situ study was conducted to evaluate the impacts of TDG supersaturation on grass carp (Ctenopharyngodon idellus) and rock carp (Procypris rabaudi). TDG supersaturation levels ranged from 115% to 131% in 2014 and from 118% to 128% in 2015. During 2014, TDG supersaturation first decreased and then increased and finally remained relatively stable. In contrast, the TDG supersaturation level remained between 122-126% for a relatively long time in the 2015 study period. During 2014, grass carp confined to water depths of 0-1 and 1-2 m began to die after 45 hr of exposure, and most grass carp died between 90 and 130 hr when TDG supersaturation level was greater than 127%. The first observed death during 2015 occurred after 30-hr exposure. The survival of rock carp was greater than 50% when they were restricted to water depths of 0-1 m. Only three rock carp died when they were confined to water depths of 0-2 m, and no dead fish were recorded at water depths of 0-3 m. KEYWORDS acute lethality, endemic fish, high spill rates, in situ study, signs of GBD, TDG supersaturation

Field observations of the lethality characteristics of endangered and endemic fish under the stress of total dissolved gas supersaturation

“…The figure suggests that DO increased with increasing TDGS values, but a weak correlation between DO and TDGS can be observed. This unstable relationship between TDGS and DO was also observed during the flood discharge of other dams in China (Xue et al, 2019). However, although there is a linear relationship between the TDGS level and DO concentration in initial observations, there is no clear and stable relationship between TDGS and DO.…”

Tolerance and avoidance mechanisms of the rare and endemic fish of the upper Yangtze River to total dissolved gas supersaturation by hydropower stations

“…However, the flood discharge of dams in the upper Yangtze River fluctuates during the flood season, and as a result, the saturation of TDG in the upper Yangtze River varies with time (Feng, Li, Liang, & Shen, 2014; Qu et al, 2011). The fish tolerance and avoidance characteristics at varying TDG supersaturation may differ from those at constant TDG supersaturation (Cao et al, 2019; Xue, Li, et al, 2019). When the flood season ends, most of the water in the upper Yangtze River is used to generate power, and the saturation of TDG is much lower than that in the flood season (Bragg & Johnston, 2015; Qu et al, 2011).…”

“…First, previous studies were mostly conducted in the laboratory, and fish were confined at a constant water depth. Some in situ studies have been conducted in the upper Yangtze River, but the fish were also confined to constant water depths (Cao et al, 2019; Xue, Li, et al, 2019). The survival pattern, swimming behaviour and avoidance characteristics of fish in TDG‐supersaturated water under natural river conditions need to be studied further.…”

“…The horizontal avoidance percentage has been used to evaluate the ability of fish to avoid TDG‐supersaturated water in the horizontal direction, with the vertical water depth used to evaluate the ability of fish to use a depth compensation technique to avoid TDG‐supersaturated water. Several studies have examined the tolerance and avoidance characteristics of rare and endemic fish in the TDG‐supersaturated water of the upper Yangtze River over the past 10 years (Huang et al, 2010; Chen et al, 2012; Jiang et al, 2013; Zhang, Du, Wang, & Li, 2014; Wang, Liang, Tuo, Li, & Hodges, 2015; Wang, Li, et al, 2015; Wang, Zhang, Zeng, & Li, 2015; Cao et al, 2016; Xue, Li, et al, 2019; Xue, Wang, Liang, Li, & Li, 2019). However, studies of the tolerance and avoidance characteristics of fish are complicated and require extensive tests.…”

Effect of total dissolved gas supersaturation on the tolerance of grass carp (Ctenopharyngodon idellus)

“…In recent years, the problem of TDG supersaturation has attracted increasing attention due to the development of hydropower projects in the Yangtze River [10][11][12]. Many studies have been carried out to determine the effects of TDG on benthic species that inhabit the upper Yangtze River, such as David's schizothoracin Schizothorax davidi, Prenant's schizothoracin Schizothorax prenanti and rock carp Procypris rabaudi.…”