The effects of ecological rehabilitation projects on the resilience of an extremely drought-prone desert riparian forest ecosystem in the Tarim River Basin, Xinjiang, China.

The Tarim River Basin in Xinjiang, China, has a typical desert riparian forest ecosystem. Analysis of the resilience of this type of ecosystem under extreme drought conditions and ecological rehabilitation projects could provide a theoretical basis for understanding ecosystem stability and resistance, and provide new ecological rehabilitation measures to improve ecosystem resilience. We employed a quantitative framework to assess net primary productivity (NPP) resilience, emphasizing four aspects of NPP dynamics: NPP, NPP stability, NPP resistance, and maximum NPP potential. We compared ecosystem resilience across four time periods: before the implementation of ecological rehabilitation projects (1990-2000), during construction and partial implementation of ecological rehabilitation projects (2001-2012), during the initial project stage of ecological rehabilitation (2013-2015), and during the late project stage of ecological rehabilitation (2016-2018). There are three main finding of this research. (1) Mean NPP was increased significantly from 2013 and was decreased from 2016, especially in the main stream of the Tarim River and in the basins of eight of its nine tributary rivers. (2) Ecosystem resilience in 2013-2018 was greater than in 1990-2012, with the greatest NPP stability, mean NPP and NPP resistance, especially in part one of the river basin (the Aksu River, the Weigan-Kuche River, the Dina River, the Kaidu-Konqi River, and the main stream of the Tarim River). Ecosystem resilience in 2001-2012 was lowest when compared to 1990-2000 and 2013-2018, with lowest mean NPP, NPP stability, NPP resistance and maximum NPP potential, particularly in part two of the river basin (the Kashigr River, the Yarkand River and the Hotan River basins). Therefore, part one was most affected by ecological restoration projects. When 2013-2018 was divided into two distinct stages, 2013-2015 and 2016-2018, resilience in the latter stage was the lowest, with lowest mean NPP, NPP resistance and maximum NPP potential, especially in the main stream of the Tarim River. This may be due to unreasonable water conveyance in 2014-2015. (3) Ecological resilience has increased significantly in 2013-2015 after the implementation of ecological water transfer projects, river regulation, and natural vegetation enclosure projects. Ecosystem resilience could continue to increase even more in the future with the continued implementation of reasonable ecological water transfer projects.

Basic and target eco-environment water requirements of a dry inland river under typical flow frequencies in China.

Analysis of eco-environmental water requirements (EEWRs) and water resource allocation strategies for arid, inland river basins can provide the theoretical basis for sustainable water utilization and management. In this paper, an optimal water resource allocation strategy is proposed for Yarkand River Basin in Xinjiang, China, on the basis of a comprehensive analysis of runoff data collected between 1970 and 2016, three ecological environmental protection goals, basic eco-environmental water requirement (BEEWR) aimed at sustaining aquatic ecosystems within the river, and target eco-environmental water requirements (TEEWR) aimed at protecting various types of riparian vegetation along the river. The results showed that: (1) after the runoff in Kaqun reach subtracting the BEEWR, the annual average river loss (recharge), and the amount of water diversion for irrigation (51.43 × 108 m3) from flows along the Kaqun reach, the remaining water volume during wet years was able to meet all three TEEWRs; (2) during moderately wet years, the remaining water was capable of meeting the second and third TEEWRs; and (3) during dry and extremely dry years, there was little or no residual water available to meet TEEWRs. The proposed optimal water resource allocation strategy, based on the above findings, states that the water diversion requirement for irrigation and domestic use allocated from the total amount of runoff should not exceed the National Water Policy (Three Red Lines) standard first. Then, the BEEWR allocated from the runoff should be met second, and the annual average river loss, third. Depending on the amount of remaining water, the second and third TEEWRs can be fulfilled during wet years, but during moderately wet years, only the third TEEWR can be met. During dry and extremely dry years, only the BEEWR of the river can be met and only during the flood season.

Suitable oasis scales under a government plan in the Kaidu-Konqi River Basin of northwest arid region, China.

The Yanqi Basin and the Konqi River Basin of the Kaidu-Konqi River Basin were chosen as the study sites in this paper in order to investigate suitable scales of natural and artificial oases with a specified water resource and water quantity planned by the local government. Combined with remote-sensing images from 2013, water resources in 2013, 2025 and 2035, and weather and socioeconomic data, suitable scales of oases were analyzed. The results showed that: (1) The total available water quantities in the Yanqi Basin and the Konqi River Basin without river base flow, and the input of water into Bosten Lake and Tarim River, over high-, normal and low-flow periods, in 2025 and 2035, were 19.04 × 108 m3, 10.52 × 108 m3, 4.95 × 108 m3, 9.95 × 108 m3 and 9.95 × 108 m3, as well as 21.77 × 108 m3, 13.95 × 108 m3, 10.11 × 108 m3, 12.50 × 108 m3, and 9.74 × 108 m3. (2) The water demand of the natural oasis in the Yanqi Basin and the Konqi River Basin was 2.59 × 108 m3, and 4.59 × 108 m3, respectively. (3) The total water consumption of the artificial oasis in 2013, 2025, and 2035 were 10.51 × 108 m3, 10.99 × 108 m3 and 10.74 × 108 m3 in the Yanqi Basin, respectively, and 18.59 × 108 m3, 14.07 × 108 m3 and 13.30 × 108m3 in the Kongqi River Basin, respectively. (4) Under government planning, the optimal area in 2025 and 2035 should be 5,100.06 km2 and 5,096.15 km2 in the Yanqi Basin oases, and 6,008.53 km2 and 4,691.36 km2 in the Konqi River Basin oases, respectively, under the different inflow variations, and 4,972.71 km2 and 4,969.22 km2 in the Yanqi Basin oases, and 5,975.17 km2 and 4,665.67 km2 in the Kongqi River Basin oases, respectively, under the appropriate proportion. (5) The artificial oases in these basins should be greatly decreased in the future due to limited water resources.

Experimental study on water transport observations of desert riparian forests in the lower reaches of the Tarim River in China.

Studying the water use processes of desert riparian vegetation in arid regions and analyzing the response and adaptation strategies of plants to drought stress are of great significance for developing ecological restoration measures. Based on field monitoring and test analyses of physiological ecological indicators of dominant species (Populus euphratica and Tamarix chinensis) in the desert riparian forest in the lower reaches of the Tarim River, the water relations of P. euphratica and T. chinensis under drought stress are discussed and some water use strategies put forward. The results show that (1) concerning plant water uptake, desert riparian forests depend mainly on groundwater to survive under long-term water stress. (2) Concerning plant water distribution, the survival of P. euphratica and nearby shallow root plants is mainly due to the hydraulic lift and water redistribution of P. euphratica under drought stress. (3) Concerning plant water transport, P. euphratica sustains the survival of competitive and advantageous branches by improving their ability to acquire water while restraining the growth of inferior branches. (4) Concerning plant transpiration, the sap flow curves of daily variations of P. euphratica and T. chinensis were wide-peak sin and narrower-peak respectively. T. chinensis has better environmental adaptability.

Distribution pattern of plant species diversity in the mountainous region of Ili River Valley, Xinjiang.

In this paper, detrended canonical correspondence analysis was performed to analyze the relationships between diversity indices and environmental gradients, generalized additive model was employed to modal the response curves of diversity indices to the elevation, based on data from field investigation in the mountainous region of the Ili River Valley and a survey of 94 sample plots. Two hundred fifty-nine plant species were recorded in the 94 sample plots investigated, up to 235 species all appeared in the herb layer, and the species of woody plants were very limited. The communities with a complicated vertical structure presented higher values of indices. The distribution pattern of plant species diversity on the northern slope was affected by such factors as elevation, slope aspect, slope gradient, total nitrogen, total potassium, soil water content, organic matter, and that on the southern slope was mainly affected by such factors as slope gradient, elevation, available phosphorus, and soil water content. On the northern slope, Patrick index and Shannon-Wiener index of the plant communities presented a bimodality pattern along altitude; Simpson index and Pielou index showed a partially unimodal pattern. On the southern slope all the distribution pattern of species diversity indices showed two peaks, though Patrick index's bimodality pattern was not an obvious one. These altitudinal patterns were formed by the synthetic action of a variety of environmental factors with elevation playing an important role.