Recovery of an endorheic lake after a decade of conservation efforts: Mediating the water conflict between agriculture and ecosystems

Widespread water losses in endorheic river basins have triggered ecological disasters. Agricultural irrigation has been one of the major drivers of water losses. It is imperative to address the water conflict between agriculture and ecosystems in arid regions, but significant gaps remain in knowledge of the water-agriculture-ecosystem nexus. The Heihe River Basin, China's second largest endorheic river basin, lost its terminal lake in the 1990 s due to a rapid decline in river discharge to the downstream area, but the lake has returned quickly since the early 2000 s. A system analysis on the recovery of the lake is performed in this study, fusing field observations, remote sensing data, and ecohydrological model simulations. The major findings show that the waning and waxing of the lake are driven remotely by agricultural irrigation in the midstream area, rather than the climate. A one-decade effort involving diversion restrictions in the middle reach, starting from 2000, has recovered the lake to the condition of the early 1970 s. Under historical climate conditions, saving extra irrigation water may change the recovery trajectory but would not significantly enhance the stability level. The aquifer connected to the lake acts as a buffer, receiving leakage from the lake under normal conditions while discharging water to the lake under dry conditions. The overall water efficiency of water conservation for lake restoration during 2002–2012 is estimated to be only 3.5% due to significant riverbed leakage in the downstream area. Nevertheless, leakage loss is beneficial to the recovery of groundwater and vegetation downstream. Whether the diversion restriction needs modification depends on the tradeoff between ecological services provided by the lake and its related ecosystems and economic benefit produced by the midstream agriculture. This study provides insight into agricultural water management and ecological conservation in endorheic river basins in a fast-changing global environment.