The lower Yangtze basin

In this ESPA funded project, we take an evolutionary approach to studying the complex social-ecological systems. We combine long term time-series of social, economic and ecological conditions data to observe and assess changes of ecosystem services and the nonlinear dynamic of the regional social-ecological system towards the present in the Lower Yangtze river basin, China. Our results show that the study region has been undergoing a transient phase since the 1980s. Increasing trends in provisioning ecosystem services within the lower Yangtze basin over the past 60 years reflect economic growth and successful poverty alleviation. But these trends are paralleled by steep losses in a range of regulating ecosystem services mainly since the 1980s. Water quality services have already passed critical transitions in several areas. Relationships between economic growth and ecological degradation show no sign of decoupling as demanded by sustainable economic development.

Long term trade-offs between ecosystem services

Increasing trends in provisioning ecosystem services within the LYB over the past 60 years reflect economic growth and successful poverty alleviation but are paralleled by steep losses in a range of regulating ecosystem services mainly since the 1980s.

Figure 1: Tradeoff between provisioning services and regulating services in the LYB during the period 1900-2006. A) Map showing study site and locations with names. B-F) Indices of provisioning (red) and regulating (green) services based on aggregated and scaled data from official statistics, monitoring records and lake sediments for Huangmei (B), Shucheng (C), Wujiang (D), Yangtze tidal zone (E) and the LYB (F) respectively (Zhang et al. 2015).

Tipping points and early warning signals

Water quality records in all the studied locations show the most consistent evidence for critical transitions in the form of statistically significant breakpoints during the period 1979-1990. The Shucheng and Huangmei water quality records also show increasing variability starting in the 1950-60s that could be interpreted as early warning signals of the observed critical transitions.

Figure 2. Breakpoints, critical transitions and variance in water quality records across the LYB 1900-2006. A) Reconstructed time series (large panel) for total dissolved phosphorus  in Huangmei, Shucheng and Wujiang (left axis), dissolved inorganic nitrogen in the tidal Yangtze zone. The panel shows (vertical bars) the timings and relative strength of statistically significant breakpoints. B-E) (Upper panels) Optimized ARIMA model predictions (red lines) starting from each break-point  (Lower panels) Standard deviation of residuals after detrending, calculated on moving window (half time-series) and plotted to the right (Zhang et al 2015).

Zhang, K., Dearing, J.A., Dawson, T.P., Dong, X., Yang, X., Zhang, W. 2015. Poverty alleviation strategies in eastern China lead to critical ecological dynamics, Science of the Total Environment 506-507, 164–181.  doi:10.1016/j.scitotenv.2014.10.096 Open access download here