Increasing River Temperature Shifts Impact the Yangtze Ecosystem: Evidence from the Endangered Chinese Sturgeon

Abstract

The Yangtze River has the third greatest water flow and is one of the most human-influenced rivers in the world. Since 1950, this river system has experienced drastic human interventions, leading to various environmental changes, including water temperature. In this study, based on observations during the past sixty years, we found that the seasonal temperature regime has been altered, both temporally (1-5 °C variation) and spatially (>626 km distance). Temperature shifts not only delay the timing of fish spawning directly, but also lead to degeneration in gonad development. Temperature regime alterations have delayed the suitable spawning temperature window by approximately 29 days over a decade (2003-2016). It confirmed that a period of lower temperature, higher cumulative temperature, and relatively higher temperature differences promoted the maturation of potential spawners based on the correlation analysis (p < 0.05). Also, thermal alterations were highly correlated with reservoir capacity upstream (R² = 0.866). On-going cascade dam construction and global warming will lead to further temperature shifts. Currently, rigorous protection measures on the breeding population of the Chinese sturgeon and its critical habitats is urgently needed to prevent the crisis of the species extinction. Increasing river thermal shifts not only threaten the Chinese sturgeon but also affect the entire Yangtze aquatic ecosystem.

Keywords: Acipenser sinensis; China; Yangtze River; cascade dam development; gonad development; river thermal regime; spawning time.

Figure 1

Study area of the Yangtze Basin. (A) Dams and five hydrological monitoring stations in the Yangtze main stem (Zhutuo, river km (rkm) 2474.2, rkm 0 is at the Yangtze estuary, Yichang, rkm 1669.2, Hankou, rkm 1043.2, Datong, rkm 553.9, and Nanjing, rkm 348.1). (B) Dams, hydrological monitoring stations, and longitudinal profile along the river.

Figure 2

Increasing river temperature shifts threaten the spawning of Yangtze fish. (A) Temporal shift in water temperature at Yichang station (spawning area of the Chinese sturgeon) during 1981–2016. (B) Spatial shift of temperature deviations from Yichang (i.e., Gezhouba Dam, the lowermost dam on the main stem) to estuary (Supplemental Table S2). (C) Spawning window delay in spring for the four major Chinese carps and autumn for the Chinese sturgeon due to the shifting temperature regime. (D) Gonad development failure of the Chinese sturgeon observed in 2014, probably due to the altered temperature regime.

Figure 3

Increases in dam construction (water impounding) and increasing temperature shifts and how they potentially impact the whole Yangtze aquatic ecosystem. The equation between total reservoir capacity (TRC) and year (i.e., x) assumed x = 1 in 1992. According to the developing trends (Sen’s slopes), the cumulative alterations of water temperature in year, M-Apr and M-Dec during 1956–2030 are +1.73 °C, −3.98 °C, and +8.03 °C, respectively.