This paper is the result of hydrogeological survey engineering.

Obiective  Farmlands surrounding wetlands in the northwestern watershed are prone to salinization. Investigating difference characteristics and dynamic mechanism of synergistic water−salt variation in topsoil across different seasons is essential for ensuring both grain and ecological security.

Methods Based on data obtained from the in−situ multi− parameter high−frequency monitoring system in field−based groundwater regulation experimental site, a comprehensive comparative analysis was conducted on the variation characteristics of parameters such as topsoil moisture content, pore water electrical conductivity (ECp), and groundwater table depth during periods not directly affected by precipitation and irrigation infiltration.

Results From late spring through summer to early autumn, soil moisture content declined at 20 cm(shallow layer) and 40 cm(deeper layer) depths, while pore water EC (ECp) increased at both depths. Saturated paste EC (ECe) decreased in the shallow layer but increased in the deeper layer. During late spring, the shallow layer soil exhibited consistent daily trends in moisture content, ECp and ECe, whereas the trends for these parameters were inconsistent in the deeper layer. In summer, shallow layer soil moisture content and ECe changed synchronously on a daily basis, unlike ECp; in the deep layer, however, ECp and ECe varied in concert, a trend not shared by soil moisture content. In early autumn, soil moisture content, ECp, and ECe each showed distinct daily variation trends in both the shallow and deeper soil layers.

Conclusions Irrigation serves as the primary driver of inter−seasonal variations in topsoil moisture and salinity. Evapotranspiration directly drives intra−seasonal topsoil water−salt variations, and this effect is amplified by higher temperatures. The depth to the groundwater table is an important factor influencing topsoil water and salt dynamics. Increasing the groundwater table depth during summer significantly reduces topsoil salinity. In the prevention and control of salinization in the study area, the volume and frequency of freshwater irrigation can be appropriately increased during critical crop growth stages and the critical groundwater table depth during summer was determined to be between 1.7 m and 1.9 m.