Monitoring the hydrological and ecological response to water diversion in the lower reaches of the Tarim River, Northwest China

During the past twelve years, the assessment of hydro-ecological response of degraded floodplain ecosystems to the emergent water diversion practices in the lower reaches of the Tarim River has become a key research topic. This paper presents the current ecological conditions and analyzes what the water diversion has achieved. The limitations of this floodplain restoration program are discussed, based on the review of literature and long term field work data (groundwater data, eco-morphological parameters of riparian forests, Quick Bird remote sensing data) collected from three transects (Yingsu, Karday, Arghan). The results show that annual average groundwater depth responded to a certain degree after water diversion since May 2000. After a second water diversion, groundwater depth within 300 m distance from the river channel recovered significantly from 9.4 m in 1997 to 4.28 m in 2001 at Yingsu. With the exception of relatively favorable groundwater depth for floodplain forests within 150 m distance from the riverbed, groundwater depth at larger distances remained far below 5 m, and most forest plants excluding Tamarix sp. will suffer from water scarcity. The average crown loss (CL) and crown diameter (CD) of Populus euphratica trees in different distances from the riverbed have shown various degrees of responses. The effects of recovery were notable within 200 m distance to the riverbed. Distribution patterns of young seedlings, new shoots and root suckers of P. euphratica generated by water diversion also demonstrated that most were distributed close to the riverbed and reduced sharply with increasing distance. Twelve water diverting actions in the lower reaches of the Tarim River have made significant achievements in forest recovery near the riverbed, but had limited positive effects on more distant floodplain sites.