Abstract:On the basis of the field measurements of changes in groundwater level and plant species abundance along nine transects crossing the Tarim River in Xinjiang, China, we examined the responses of groundwater and plant communities to a government-controlled 7-year recharge regime to the lower reaches of the river. Our results showed that the water recharges considerably lifted the groundwater table on both sides of the river course. The 6-8-m groundwater depths before the water recharges rose to 2-4 m after the recharges. In the transverse direction, the response of the groundwater table could be observed at as far as 850 m from the river course, and the affected Populus euphratica could be observed at 700 m. However, we did not observe significant influence of the water recharges on herbaceous plants. We infer that the plant communities will be benefited more from the combination of overbank flows and stream aquifer recharge than from sole stream aquifer recharge. Such a combination may maximize the ecological benefits of water conveyance and accelerate the restoration of the damaged arid ecosystems in this area.

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.

No abstract