Ecological effects and potential risks of the water diversion project in the Heihe River Basin

Highlights

• Integrated analysis of the effects of water diversion project is necessary.

• Quantitative analysis was used to assess the chain effects of water diversion.

• The deteriorated downstream environment has been improved preliminarily.

• Ecological risks still existed due to the simple administrative measure.

• Inability of the project to achieve sustainable development was highlighted.

Abstract

To curb the severe ecological deterioration in the lower Heihe River Basin (HRB) in northwest China, a water diversion project was initiated in 2000. A comprehensive analysis of the ecological effects and potential risks associated with the project is needed. We assessed the hydrological and ecological achievements, and also analyzed the potential problems after the project was completed. We found that since the project began the hydrological regime has changed, with more than 57.82% of the upstream water being discharged to the lower reaches on average. As a result, the groundwater level in the lower reaches has risen; the terminal lake has gradually expanded to a maximum area in excess of 50 km² since 2010, and there has been a significant recovery of vegetation in the riparian zone and the Ejin core oases, which represents the initial rehabilitation of the degraded downstream environment. Additionally, the economy of Ejin has developed spectacularly, with an annual growth rate of 28.06%. However, in the middle reaches, the average groundwater level has continuously declined by a total of 5.8 m and significant degradation of the vegetation has occurred along the river course. The discrepancy in the water allocation between the middle and lower reaches has intensified. This highlights the inability of the current water diversion scheme to realize further ecological restoration and achieve sustainable development throughout the whole basin. In future water management programs, we recommend that water allocation is coordinated by considering the basin as an integrated entity and to scientifically determine the size of the midstream farmland and downstream oasis; restrict non-ecological water use in the lower reaches, and jointly dispatch the surface water and groundwater.

Introduction

As the most important ecological and environmental resource, water is crucial for the development of oases (Chen et al., 2003). In the lower reaches of inland river basins, where precipitation is scarce, the upstream discharge is the main water resource available to oases ecosystems and for economic development. The majority of the world's river basins are dominated by human activity (Meybeck, 2003, Vorosmarty et al., 2010). This is particularly true for China (Zhai and Tao, 2017). River regulation by artificial water diversion enables the reallocation of water for ecological, societal, and economic uses, with such schemes intended to improve water use efficiency and achieve sustainable development (Everard et al., 2018). However, they also exert a profound impact on the hydrological regime, local ecosystems, and socioeconomic structures, and can lead to a chain effect among these systems, especially in water-deficient regions (Everard et al., 2018, Micklin, 1988). Hence, the accurate and timely evaluation of the positive achievements and potential negative influences of water diversion projects is a requirement for effective water management in inland river basins.

Recently, much attention has been given to the ecological response following water diversion projects. Experiments in the Murray Darling Basin, Australia, showed that large-scale flow diversion has stimulated greening of the riparian river red gum at Yanga National Park, and trees receiving supplementary flows were generally more vigorous (Nagler et al., 2016). Studies of environmental flows in the Colorado River, USA, have demonstrated that relatively low-magnitude flow deliveries had a limited effectiveness on the replenishment of groundwater and the ecological restoration of cottonwood and willow (Kendy et al., 2017, Shafroth et al., 2017). Water diversion projects in the lower reaches of the Tarim River, China, have resulted in significant achievements in forest recovery near the riverbed (Aishan et al., 2014), but there have been few positive effects on more distant sites due to the irregular and insufficient upstream water supply (Bao et al., 2017, Zhu et al., 2016). The lack of long-term monitoring and effective evaluation as well as the limited fundamental understanding of flow-ecology, are the main limitations impeding the ecological effectiveness of existing water diversion projects (Davies et al., 2014).

The Heihe River Basin (HRB) is the second largest inland river basin in the arid zone of northwestern China. As with the Tarim River (Chen et al., 2011), the HRB experienced severe water shortages and environmental deterioration in the 1980s (Xiao and Xiao, 2004). To restore the ecosystem in the downstream basin, the Chinese Government initiated the Ecological Water Diversion Project (EWDP) from 2000 onwards to ensure the delivery of minimum amounts of water to the lower reaches of the basin. As the EWDP proceeded, responses on the riparian vegetation, land use, and groundwater have been reported (Ao et al., 2012, Fu et al., 2014, Luo et al., 2016, Mi et al., 2016, Nian et al., 2014, Wang et al., 2014a, Wang et al., 2014b, Zhang et al., 2017, Zhao et al., 2016). Recently, Xiao et al. (2017) evaluated the ecological effects of the National Integrated Management Project in HRB. Cheng et al. (2014) comprehensively reviewed published studies of the ecologic-hydrologic-economic system in the HRB and made practical recommendations for the comprehensive management of the river basin to ensure its sustainable development. However, rather than providing a complete assessment, these studies focused primarily on the positive effects of water diversion projects and did not consider potential negative effects.

In this study, we aimed to: (1) examine the hydrological, ecological, and socio-economic effects of EWDP in the middle and lower reaches of the Heihe River; (2) address current positive achievements associated with water diversion, and (3) evaluate the potential risks and problems of the current diversion schemes. The results provide a reference for effective water resource planning and management, and can be used to maintain the stability of the oasis ecosystem and the effective functioning of the river, as well as promoting future regional development.