Abstract:

The ecological water conveyance project was launched in 2000 to restore groundwater level and protect the “green corridor” from the continuous deterioration in the lower reaches of the Tarim River, Xinjiang, China. Until the end of 2020, the total water conveyance volume has reached 84.45×10⁸ m³. The monitoring results show that: (1) At the riverway-monitoring site (100 m away from the river), the groundwater depth in the upper, middle, and lower reaches of the Tarim River rises from 7.76 m, 9.31 m, 7.82 m in 2000 to 3.70 m, 4.48 m, and 2.69 m, respectively, in 2020. The average groundwater rise in the upper, middle, and lower reaches of the Tarim River are 4.06 m, 4.83 m, and 5.13 m, respectively. At a near riverway-monitoring site (500 m away from the river), the groundwater depth rises from 8.21 m to 6.61 m, 9.45 m to 5.46 m, and 9.08 m to 3.82 m, in the upper, middle, and lower reaches, respectively, during the past 20 years. At a monitoring site far from the riverway (1050 m away from the river), an increase in groundwater depth of 2.69 m, 1.38 m, and 1.59 m was monitored. (2) The surface water area expanded from 49.00 km² before the water conveyance project to 498.54 km², about four times the previous area; Taitma Lake has “resurged,” with a surface area of 455.27 km². (3) The surface ecological processes significantly responded to the water conveyance with the vegetation coverage, NDVI, NPP, and gross primary productivity of the lower reaches of the Tarim River (within 2000 m of riverway) increasing by 132 km², 0.07, 7.6 g C·m^-2 and 1221 g C·m^-2per growing season, respectively. (4) The influence of water conveyance on the surface vegetation in the lower reaches of the Tarim River is 1423 km² with the ecosystem service value increasing significantly. The carbon sink area increased from 1.54% in 2001 to 7.80% in 2020, the ecosystem health condition improved and ecological resilience increased significantly, as the soil carbon sink capacity increased. In short, the groundwater level has raised significantly during the past 20 years, and the desert riparian forest with Populus euphratica as the constructive species has been restored in the lower reaches of the Tarim River. The surface vegetation coverage has increased, and the trend of ecological degradation in the lower reaches of the Tarim River has been curbed significantly.

Key words: ecological water conveyance, groundwater depth, surface ecological response, Tarim River