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Clarifying the role of shallow groundwater systems in eco-hydrological processes is of great significance to agricultural production and ecological sustainability. In this paper, a lumped water balance model was proposed for the GSPAC (groundwater-soil-plant-atmosphere-continuum) system for different land use types under arid, shallow water table conditions. Model application was conducted in an irrigation district (Jiyuan) located in the upper Yellow River basin. A 13-year (2001-2013) water balance calculation was carried out to quantify the water budgets of different land use types. The effects of shallow groundwater on water and salt exchanges among different land use patterns were analyzed. Results indicated the shallow groundwater systems played a significant role in water storage and supply, water and salt redistribution, and the salt accumulation and drainage in Jiyuan. About 36% of the total applied water was first stored in a shallow groundwater system, and then redistributed. After redistribution, 63% of the total diverted water was consumed by cropland evapotranspiration (ET), 20% by natural land ET; the rest was discharged through drainage or groundwater exploitation. Finally, 67% of the introduced salt accumulated in natural land, while the rest was drained away, which helped maintain the productivity of the croplands. Overall, our results have quantitatively revealed the multifaceted roles of shallow groundwater systems, and also suggested the key management concepts for sustaining agroecosystems in arid irrigated areas.

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