Drivers and controls of salinization in prairie ponds

High sulphate (SO 4 2− ) concentrations in ponds can support distinctive aquatic communities but can also promote salinization and disrupt aquatic ecosystem functioning, with implications for livestock watering. These contrasting effects are widespread across pondscapes of the Northern Great Plains, yet the interacting biophysical, limnological, and hydrological controls on SO 4 2− dynamics remain underexplored. We investigated SO 4 2− dynamics across upland soils, water columns, and sediments of prairie ponds comprising naturally occurring wetlands and artificially constructed dugouts (small, excavated water-storage ponds) spanning gradients in salinity, depth, upland vegetation cover, and hydrological setting. Wetlands exhibited higher SO 4 2− concentrations in water and sediment than dugouts, consistent with differences in pond morphology, hydrological connectivity, and longer-term solute accumulation. Hydrological setting was strongly associated with pond SO 4 2− concentrations, with discharge systems generally exhibiting higher concentrations than recharge systems. Across pondscapes, sediments had the highest SO 4 2− concentrations, followed by upland soils and the water column, highlighting sediments as an important long-term SO 4 2− reservoir. Structural equation modelling further identified hydrology, sediment and soil SO 4 2− , soil organic matter, total dissolved nitrogen, and water depth as important predictors of pond salinization. Upland vegetation cover was negatively associated with SO 4 2− desorption, suggesting a potential role in limiting solute mobilization, although its contribution appeared secondary to hydrological and geochemical controls. Collectively, these findings highlight the importance of hydrological setting, pond morphology, and long-term SO 4 2− storage in regulating salinization across prairie pondscapes and provide insights into processes that may influence the suitability of ponds as livestock-water resources.