Whether the ecological benefits will continue to increase as usual and improve under the background of continuous ecological water delivery?—Taking the Lower Tarim River in China as an example

Abstract

In arid regions, ecological water replenishment benefits in desert riparian forests are typically evaluated by assessing changes in hydrology (water area and groundwater depth) and vegetation growth before and after it is implemented. While continuous ecological water delivery may enhance ecological benefits, its trajectory remains uncertain. Under the backdrop of ongoing ecological water delivery, this study examines whether ecological benefits continue to improve and identifies strategies for optimal control and efficient utilization of ecological water. Based on an analysis of groundwater level changes and vegetation changes during early, middle, and late stages of ecological water conveyance in the Tarim River, China (2000–2021), ecological water consumption distribution was revealed. A notable observation is that a wide eco-water conveyance did not significantly impact forest growth indicators, such as tree ring density, crown width, and tree ring size, in Populus euphratica trees. Compared to a century ago, there were significant variations in the growth of P. euphratica tree rings over the 20-year ecological water transfer period. The vegetation coverage on riverbanks increased significantly in the early to mid-stages of ecological water conveyance (2000–2015), but then plateaued in the subsequent years (post-2015). There was a significant upward trend in plant diversity on riverbanks and tail lakes during the early stage (2000–2006), but it declined sharply thereafter (post-2006). A recommendation includes constraining the tail lake's water area and using ecological sluice gates and levees to disperse eco-water away from the river to enhance the efficiency of ecological water utilization. As a result of these findings, rational management systems can be developed in similar arid environments.

Keywords

• Tree-ring growth
• Plant diversity
• Groundwater depth
• Vegetation area/cover
• River bank
• Terminal lake