Study on Index of Groundwater Ecological Function Crisis Classification and Early Warning in Northwest China

Abstract

The natural oases in the plain area of the northwest inland basin strongly depend on the groundwater depth. With the overexploitation and utilization of groundwater, natural oases are faced with the problems of serious degradation and rehabilitation. How to evaluate the degree of the degeneration crisis of groundwater ecological function has become one of the key scientific and technological problems to be solved. In this paper, the Shiyang River basin of Gansu Province was selected as a typical research area. The remote sensing interpretation, groundwater–soil ecology comprehensive investigation, and groundwater in situ monitoring were adopted to carry out the research. Based on the correlation analysis method of natural ecology and groundwater, the interactive relationship between the natural ecological environment and groundwater depth in different ecological types of the region were studied: (1) under the arid climate condition in northwest China, the relationships between the ecological situation and the groundwater depth in different ecological types of the region were obviously different, and as a result, the optimal or limit ecological water level of groundwater in different ecological types was also different; (2) in the natural wetland area, the suitable ecological water level of groundwater was between 0.5 m to 1.5 m, and the limit ecological water level was 8.0 m; in the natural vegetation area, the suitable ecological water level was between 3.0 m to 5.0 m, and the limit ecological water level was 10.0 m; and in the farmland area, the suitable ecological water level was between 2.0 m to 5.0 m, and the limit ecological water level was 2.0 m; (3) in order to effectively protect the natural ecology in different ecological types, a five-level early warning and control index system should be established for the ecological function degeneration crisis of groundwater. It may be beneficial to promote restoration and protection of the groundwater ecological function and natural ecology in the inland area of northwest China.

Study on the Suitable Ecological Groundwater Depth and the Suitable Well–Canal Combined Irrigation Ratio in the Weigan River Irrigation District

“…In this study, the maximum value of NDVI was measured in the groundwater depth of 3-5 m, followed by 2-3 m. When the groundwater depth was greater than 6 m, the value of NDVI was less than 0.2, and with increases in the groundwater depth, NDVI continued to decrease. In the research on the relationship between vegetation growth and groundwater depth response in the arid zone, it has also been shown that the reasonable threshold for the appropriate growth of vegetation crops in the arid zone is 3-5 m [52], and the vegetation begins to suffer from growth stress at a depth of 6 m in the groundwater depth [38,53,54]. the risk of soil salinization into the analysis of the ratio of suitable wells and canals for combined irrigation.…”

“…(2) The vegetation cover of the Weigan River irrigation district from 2012 to 2021 gen- According to the "Survey and Evaluation Report of Planned Groundwater Resources in the Weigan River Basin of Aksu Region, Xinjiang", Populus euphratica is the main ecological forest plantation species in the study area. The suitable groundwater depth for Populus euphratica is 3-5 m, and its stress water level is 6-8 m [54]. This is generally consistent with the pattern depicted in Figure 11, where NDVI shows a positive correlation with groundwater depths below 4 m and NDVI shows a negative correlation with groundwater depths above 4 m. Due to the low rainfall in arid areas such as the study area, groundwater is an important resource for supporting the growth of vegetation; however, the uncontrolled exploitation of groundwater will inevitably destroy the stability of the groundwater flow field in the natural vegetation area, meaning that the depth of the groundwater will continue to increase, resulting in drought stress of natural vegetation and even large-scale extinction [51,54].…”

The Impact of Groundwater Burial Depth on the Vegetation of the Dariyabui Oasis in the Central Desert

“…The over-exploitation of groundwater causes a decline in the water table, leading to an accumulation of soil salts and toxins, especially in drought years, in areas of high agricultural activity and increased water stress [15][16][17][18][19][20][21][22]. In China, the relationship between vegetation and groundwater burial depth, as well as the water table, water quality, and soil, has been studied in the Tarim River [23], Hei River [24], Shiyang River Basin [25,26], Sanguang River [27], Inner Mongolia Loop [28], Loess Plateau [29], Hulunbeier in Inner Mongolia [30], Ejina [31], and Gurbantunggut Desert [32,33]. Such studies have provided theoretical support for protecting the stability of vegetation in arid and semi-arid regions.…”

Rational Allocation of Water Resources in the Arid Area of Northwestern China Based on Numerical Simulations

“…Affected by changes in the natural environment and by human activities, the groundwater level in the Shiyang River Basin has dropped significantly in recent decades [11][12][13]. This lower groundwater level has resulted in a series of ecological and environmental problems such as water quality deterioration, vegetation decline, land desertification, and a decrease in the area of the spring water overflow zone [14]. A series of water transfer projects, including the water transfer from the Yellow River to the Jingdian phase II project and the water transfer from the upstream Xiying River, have been carried out in this basin since 2001.…”