Assessment of the groundwater threshold of desert riparian forest vegetation along the middle and lower reaches of the Tarim River, China

Abstract

Abstract:Survival of desert riparian vegetation along the middle and lower reaches of the Tarim River in China depends almost entirely on groundwater. The aim of this project was to study the effect of various water table levels on desert riparian forest vegetation and to determine the groundwater threshold under which desert riparian forest vegetation can grow normally. Using data collected from 2 years (2006)(2007) of monitoring (groundwater, vegetation plots, and soil profiles) of the middle and lower reaches of the Tarim River, the relationship between vegetation and environmental factors was analysed using detrended canonical correspondence analysis (DCCA). The average depth of the groundwater table at the study sites was divided into six ranges (0-2, 2-4, 4-6, 6-8, 8-10, and >10 m) to compare the influence of groundwater level on species diversity. Using the ecological suitability theory and data from previous studies of several major plant species in the study area, a logarithm normal distribution relation model was built between the growth of plants and the depth of groundwater. The results of DCCA ordination indicated that groundwater depth (GWD) and soil moisture are the crucial environmental factors affecting the distribution of plants. Species diversity was the highest at the 2-4 m level, followed by the 4-6 m level, and then the 0-2 m level. When the groundwater level dropped to below 6 m, species diversity decreased greatly, and the slope of Hill's index (diversity ordering) tended to level off. Thus, the optimum groundwater level for major plant growth is 2-4 m and the threshold GWD is about 6 m. To restore the vegetation and ecosystem of the lower reaches of the Tarim River, the water table must be kept at a minimum of 6 m in depth. It should also be maintained at 2-4 m in the vicinity of the water way and at 4-6 m for the rest of this arid area.

Carbon Dioxide Fluxes and Their Environmental Controls in a Riparian Forest within the Hyper-Arid Region of Northwest China

“…However, we have a limited knowledge on the carbon source/sink intensity and its respective variability in arid ecosystems. In particular, due to the scarcity of precipitation, the groundwater is the main source required to maintain the current structure and functions in hyper-arid regions [6][7][8]. In addition, these ecosystems are highly vulnerable to climate change, e.g., invasive species success [9], therefore an understanding of the extent of carbon sequestration and emissions including the underlying driving forces behind this process is crucial for estimating the overall carbon balance in arid ecosystems.…”

“…The study of CO 2 fluxes and their environmental controls may provide insights into the health and activities of the riparian forest. Survival, growth and development of riparian forests have largely been dependent on the groundwater [6,8]. The overexploitation of water resources in the middle reaches of HRB since the 1960s led to a decrease in the discharge of water to its lower reaches, that was also likely contributing to a consequent decline in the groundwater and a degradation of ecosystems along the riparian habitats [29].…”

Development of agricultural land and water use and its driving forces along the Aksu and Tarim River, P.R. China

“…The absence of rainfall coupled with abundant sunshine provides ideal cultivation conditions especially for cotton. However, in recent years the negative ecological consequences of the intensive agricultural production became apparent (Hao et al 2010). In addition to the degradation of riparian vegetation, the overuse of surface and groundwater for irrigation of crops also led to an increased competition for water among farmers, often resulting in yield losses (Thevs 2011).…”

“…In addition to the degradation of riparian vegetation, the overuse of surface and groundwater for irrigation of crops also led to an increased competition for water among farmers, often resulting in yield losses (Thevs 2011). Since the beginning of the twentieth century several research groups studied the water resource issue of the Tarim region, with a strong focus on the development of the hydrological situation within the basin (e.g., Bai et al 2013;Turak et al 2007;Xu et al 2005), being influenced by climate change and human activities (e.g., Zhang 2001;Zhou et al 2012), as well as its impact on the natural ecosystems (e.g., Hao et al 2010;Xu et al 2003;. To improve the ecological situation in the region, the existing body of literature concludes that the irrational use of water resources related to the tremendous increase of irrigation agriculture, needs to be strongly reduced, by improving agricultural water-use efficiency (e.g., Zhang 2001), to be achieved through extensive implementation of effective water-saving technologies (e.g., Chen et al 2011).…”

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

“…One was interested in the hydrological controls of the desert riparian forests, mainly exploring the relationships between groundwater and vegetations, from leaf scale to communities level (Chen et al, 2003(Chen et al, , 2006Hao et al, 2008Hao et al, , 2010Zhang et al, 2011;Zhu et al, 2012;Wang et al, 2014;Li et al, 2008Li et al, , 2013. The other attempted to estimate ecological water requirements of the desert riparian forests for the water resource management (Wang et al, 2002(Wang et al, , 2005Liu, 2004;Ye et al, 2007;Chen et al, 2007;Chen et al, 2008a).…”