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With the implementation of the South-North Water Diversion Project and the implementation of groundwater suppression, the local groundwater levels in the North China Plain have gradually rebounded. However, there is a lack of systematic studies of the trends of groundwater balance elements and their impacts on the ecological environment. This paper takes the Baoding Plain, a typical area in the North China Plain, as an example, and uses the water balance method to calculate the groundwater recharge and discharge terms, applies the factor analysis method to analyze the causes of the changes in groundwater balance elements from 1975 to 2019, and calculates the amount of recoverable and suppressed groundwater resources by using the optimal exploitation coefficient method, which provides a basis for the development and utilization of groundwater resources in the study area. The results show that in the past 40 years, the groundwater recharge term was smaller than the discharge term in the Baoding Plain, which is in a negative equilibrium state, and the main change elements are canal irrigation infiltration, canal system seepage, well irrigation return, river seepage, rainfall infiltration and artificial exploitation. The main factor affecting the change of groundwater equilibrium elements is human activity, with a contribution rate of 77.2%. After the groundwater recharge and discharge imbalance is slowed down, the increase of groundwater level burial depth becomes smaller, the area of groundwater level depression cone gradually decreases, and the area of the Baiyangdian wetland gradually recovers. The optimal exploitation coefficient of groundwater resources in the Baoding Plain is determined to be 0.64, the exploitable groundwater resources range from 8.89×108 to 11.35×108 m3/a, and the amount of compression exploitation ranges from 2.68×108 to 5.14×108 m3/a. The research results can provide a scientific basis for the sustainable development of groundwater resources and ecological environment in similar areas.

In arid and semiarid regions, lake-basin ecosystems are an important part of watershed security barriers, playing an important role in maintaining the stability of ecological patterns. However, the ecological environment of the lake-basin system has been gradually degraded in recent years, and its change process is accompanied by a complex dynamic mechanism. In the present study, we explored the spatial variability of the ecological environment of the lake-basin system and its drivers by taking Baozhainao Lake in the Mu Us Sandy Land of the Ordos Basin as the study area.In-situ dynamic monitoring, sample survey, statistical analysis and numerical simulation were employed. The distribution patterns of typical vegetation in the basin were determined and the mechanisms underlying the mutual feedbacks between subsurface hydrological process and lakeshore ecosystem was explored. The results show that the Baozhainao lake-basin ecosystem consists of four zoning types, namely, the lake zone, the lake nearshore fluctuation zone, the lakeshore beach zone, and the lakeshore wind beach zone. From the lake to the beach zone, the depth of water table increased gradually and the vegetation type transitions from water-loving and salt-tolerant to drought-tolerant. It was further found that the presence of vegetation on the lake shore significantly affects the circulation mode of the groundwater flow system. The conversion between lake and groundwater occurs mainly in the local groundwater flow system, resulting in a significant reduction in groundwater recharge to the lake.The results of this study can provide a scientific basis for the restoration and conservation of plant species diversity and vegetated ecosystems in the lake nearshore fluctuation zoneand lakeshore wind beach zone in arid regions.

Groundwater is of important ecological value. The changes in groundwater level, water quality, water content and salt content in the unsaturated zone in groundwater ecosystems drive the evolution of supergene ecological pattern. So far, the research on the ecological threshold of each variable is still at the starting stage, and the theoretical and methodological system is not perfect. In this study the Baoding Plain is taken as an example, and the driving force and ecological effect of groundwater level changes are analyzed from the perspective of time and space by using the historical regression method, GIS method and difference grid calculation method of groundwater levels and groundwater ecological environments. On this basis, the ecological water level thresholds of different hydrogeological units are determined. The results show that: (1) In the 1950s-60s, the ecological pattern of the study area depending on groundwater basically maintained a natural state; from 1959 to 2000, the groundwater levels continued to decline, and the groundwater depression cones appeared in some areas. From 2000 to 2008, the groundwater levels dropped sharply, the groundwater depression cones expanded rapidly, and the recharge and discharge relationship between groundwater and surface water changed. Since 2008, groundwater levels have gradually increased in some regions. (2) The depth of groundwater ecological water level in the piedmont zone of the study area is 10–15 m deep, the Juma River alluvial fan group and Cao River-Pu River alluvial fan group are 5–10 m, the Tang-Dasha River alluvial fan group is 3–5 m, the Dingzhou-Wangdu area in the alluvial plain is 3–5 m, the city of Baoding is about 10–15 m, and the rest are 5–10 m. The area around the alluvial lacustrine plain is less than 3 m. (3) Taking the determined ecological groundwater level as the standard, it is preliminarily estimated that the water demand for restoring the current groundwater level to the ecological water level in the study area is 57.14×108 m3. The research results are of important significance for restoring the local groundwater ecological environment pattern and for determining the ecological groundwater level in the North China Plain.