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Arid Land Geography ›› 2021, Vol. 44 ›› Issue (3): 691-699.doi: 10.12118/j.issn.1000–6060.2021.03.11

• Ecology and Environment of Tarim River Basin • Previous Articles     Next Articles

Effects of ecological water conveyance on water use efficiency of desert riparian forest ecosystem in the lower reaches of Tarim River

HAO Haichao1,2,3(),HAO Xingming1,2(),CHENG Xiaoli4,ZHANG Jingjing1,2,3,FAN Xue2,5,LI Yuanhang2,5   

  1. 1. State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, Xinjiang, China
    2. Aksu National Station of Observation and Research for Oasis Agro-ecosystem, Aksu 843017, Xinjiang, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
    4. Taiyuan Normal University, Jinzhong 030619, Shanxi, China
    5. Xinjiang Normal University, Urumqi 830054, Xinjiang, China
  • Received:2021-02-07 Revised:2021-03-09 Online:2021-05-25 Published:2021-06-01
  • Contact: Xingming HAO E-mail:haohaichaol8@mails.ucas.ac.cn;haoxm@ms.xjb.ac.cn

Abstract:

Water use efficiency (WUE) refers to carbon absorbed per unit of water loss in the ecosystem. It is a comprehensive indicator used in evaluating the suitability of plant growth under water deficit and can well reflect the response of vegetation to ecological water conveyance. In this paper, the net primary productivity (NPP) estimated using the CASA model and evapotranspiration (ET) estimated using the SEBAL model are used to calculate the ecosystem WUE. Spatiotemporal changes in the ecosystem WUE in the lower reaches of Tarim River, Xinjiang, China are studied using slope trend analysis, Pearson correlation analysis, and grid time sequence synthesis, and the changes were found to be affected by ecological water conveyance, meteorological elements, and groundwater level. The results show the following: (1) from 2001 to 2018, the WUE in the lower reaches of Tarim River exhibited a significant fluctuation (P<0.05), whereas, the influence of NPP was greater than that of ET (CorNPP=0.76>CorET=0.10). The WUE of shrubs (0.49 g C·mm-1·m-2) is higher than that of Populus euphratica (0.30 g C·mm -1·m-2) and herbs (0.24 g C·mm-1·m-2). The spatial variation of WUE is based on the river channel and shows a decreasing trend to both sides and from northwest to southeast. The extremely significant increase in area accounts for 13.64% of the entire study area. (2) From 2001 to 2018, the WUE of various vegetations showed a significant upward trend with increasing ecological water conveyance (P<0.05). The average annual increase in the WUE of shrubs was 15 times that of P. euphratica and herbs. The response is also more sensitive. The WUE values of P. euphratica, shrubs, and herbs are positively correlated with ecological water conveyance and the duration of water conveyance and negatively correlated with the start time of water conveyance. The WUE of shrubs has the highest correlation with the three. (3) There is a positive correlation between the number of water conveyance times and WUE, NPP, and normalized difference vegetation index (NDVI) during the year (WUE: Cor=0.407, NPP: Cor=0.605, NDVI: Cor=0.657). In addition, the optimum temperature (TEM) and NDVI are related to WUE and NPP, and the spatial distribution of ET is highly consistent. Populus euphratica has an average annual optimum temperature of 25.62 ℃, shrubs have 27.07 ℃, and herbs have 23.22 ℃. At this time, the best combination of water and heat will be more conducive to vegetation survival. (4) There is a strong negative correlation between the annual WUE and the groundwater level in the lower reaches of Tarim River (Cor=-0.81), and WUE decreased by about 0.01 g C·mm-1·m-2 every meter. The correlation between the WUE of herbs and shrubs and groundwater level is greater than that of P. euphratica (|Corherbs and shrubs=-0.76|>|CorP. euphratica=-0.46|), and the average WUE of P. euphratica, shrubs, herbs, and groundwater level is 4-6 m, with a peak at 6 m. Above 6 m, the average annual WUE and WUE of each vegetation show a downward trend.

Key words: Tarim River, ecological water conveyance, water use efficiency, groundwater depth, vegetation type, optimum temperature