Simulation of Populus euphratica root uptake of groundwater in an arid woodland of the Ejina basin, China

Authors: ZHU, YONGHUA - HOHAI UNIVERSITY, CHINA; REN, LILIANG - HOHAI UNIVERSITY, CHINA; Skaggs, Todd; LU, HAISHEN - HOHAI UNIVERSITY, CHINA; YU, ZHONGBO - UNIVERSITY OF NEVADA; WU, YANQING - SHANGHAI JIATONG UNIV

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2009
Publication Date: 5/27/2009
Citation: Zhu, Y., Ren, L., Skaggs, T.H., Lu, H., Yu, Z., Wu, Y. 2009. Simulation of Populus euphratica root uptake of groundwater in an arid woodland of the Ejina basin, China. Hydrological Processes. Available: http://www3.interscience.wiley.com/journal/122405848/abstract

Interpretive Summary: The Ejina Basin is an extremely arid region in Northwest China. The predominant natural tree species in the area is a deciduous poplar tree (Populus euphratica) that depends on groundwater for sustenance in the harsh arid environment. In recent decades, groundwater overdraft and increased water diversions from the Heihe River caused water table elevations to decline, such that large areas of P. euphratica withered, creating a highly visible symbol of ecological change and desertification in the Ejina Basin. Among other consequences, the disappearance of the trees has been cited as a cause of the unprecedented large sandstorms that have hit North and Northwest China in recent years. Ecological restoration efforts aimed at saving existing woodlands and cultivating new stands of P. euphratica are underway. To provide a better scientific basis for ecological restoration plan, it is necessary to understand the effect of water table elevation on P. euphratica water uptake. In this work, we used computer simulation models developed at the U.S. Salinity Laboratory to study groundwater movement into the root zone and the uptake of groundwater in a 10 year old P. euphratica woodland. Additionally, we examined the changes in uptake that would occur for different water table elevations. This work will assist researchers seeking to understand the effects of water availability on ecological change.

Technical Abstract: The Ejina Basin is an extremely arid subwatershed in Northwest China. The predominant natural tree species in the area, Populus euphratica (P. euphratica), depends on groundwater for sustenance. In recent decades, groundwater overdraft and increased water diversions from the Heihe River caused water table elevations to decline, such that large areas of P. euphratica withered, creating a highly visible symbol of ecological change and desertification in the Ejina Basin. Ecological restoration efforts aimed at saving existing woodlands and cultivating new stands of P. euphratica are underway. To provide a better scientific basis for ecological restoration plan, it is necessary to understand the effect of water table elevation on P. euphratica water uptake. In this work, we used the HYDRUS-1D software package to study groundwater movement into the root zone and the uptake of groundwater in a 10 year old P. euphratica woodland. Additionally, we examined the changes in uptake that would occur for different water table elevations. The model calibration was confirmed by comparing predicted soil moisture contents during the P. euphratica growing season (May 1 to October 31) with field measured values. The results indicate that in 2000, with an average water table depth of 2.64 m, P. euphratica at the study site obtained about 79% of its water from groundwater during the whole growth period. Simulations made with constant water table depths found that increasing the water table depth from 2 to 3 meters resulted in a 69% reduction in transpiration. Many factors can influence the optimal water table depth at a given site. An advantage of the modeling approach is that these factors can be systematically varied, creating a site-specific impact assessment of water management options that may alter water table depths, thus aiding ecological restoration efforts.