Investigating periodic variations of salt-affected soil distribution from the perspective of salt absorption and migration pathway shifts induced by salt discharge zone

• Salt discharge zone located in areas with shallow groundwater and high evaporation. • Scattered salt discharge zone can accommodate salts and prevent further spread. • Salt discharge zones alternately accommodate salts, ensuring long‑term dry drainage. • Salt-affected soil undergoes salt accumulation, surge, reduction and backflow phase. Rational allocation and enhancement of saline soils can effectively counteract the growing soil salinization and the reduction of available arable land resources. However, some soils are challenging to improve and often remain ineffective due to factors such as evaporation and groundwater. Instead, they can function as salt discharge areas, accommodating salts from the surrounding land. This study aims to investigate how these salt discharge zones can regulate regional salt-affected soils by naturally altering their area and distribution patterns. Therefore, based on Landsat data, we analyzed the changes and interactions in the distribution patterns of salt-affected soil (soil salinity content (SSC) > 2 g kg −1 ) and salt discharge zone (SSC > 10 g kg −1 ) in the Hetao Irrigation District over the period from 2003 to 2023, at 5-year intervals. The results indicated that although salt discharge zones occupied only about 12% of the total area, they contained approximately 56% of the region’s total salt storage. The small, patchy salt discharge zones were closely linked to shallow groundwater depths, particularly in the northwestern part of the Hetao Irrigation District. The salt-affected soil area increased from 2003 to 2008, then declined from 2008 to 2023, ranging from 4.5 to 5.4 × 10 9 m 2 . Salt-affected soil area fell sharply in 2018 but rebounded in 2023, with total area dropping to 4.0 × 10 9 m 2 . Meanwhile, the proportion of small patches within salt‑affected soils increased between 2013 and 2023. The east–west distribution range of salt-affected soils (defined by the 25%–75% percentile interval) narrowed from 2003 to 2013, reaching its minimum width of 80000 m in 2013, before expanding again by 2023. Groundwater depths in salt‑affected soils and salt discharge zones varied over time, reaching their shallowest levels (∼2.0 m and ∼ 1.9 m, respectively) in 2008–2013, deepening slightly during 2013–2018, and returning to shallower depths by 2023. Salt‑affected soils showed a decline to a minimum in 2013, followed by a recovery to initial levels by 2023. Similarly, the anisotropy of the salt discharge zone increased significantly (P < 0.05) after 2013. For salt-affected soil influenced by groundwater, salt content fluctuates periodically, passing through four stages: accumulation, surge, reduction, and backflow. During the accumulation stage, enhancing salt drainage is key to preventing excessive salt accumulation. In the surge stage, efforts should focus on restoring soil quality in low-lying, salt discharge zones to control salt discharge. The reduction stage requires monitoring salt discharge zones for controlling potential salt backflow. And in the backflow stage, it is essential to perform regular remediation and prevent further salt accumulation.