Analysis and identification of sulfate sources in groundwater of a typical profile in the Yinchuan Plain

Abstract

Study region

The Yinchuan Plain in China.

Study focus

In large watersheds with diverse landforms, multi-level nested groundwater flow systems drive complex sulfate transport and transformation. Focused on a typical profile from the eastern Helan Mountain foothills to the Yellow River Tableland in the Yinchuan Plain. By using hydrochemical, multi-isotope, statistical, and microbiological methods on borehole samples of various landforms and depths, sulfate geochemical processes in groundwater were revealed and source contributions quantified.

New hydrological insights for the region

SO₄^2- concentrations rose along groundwater flow paths. Sulfate sources varied across groundwater flow systems. In the local groundwater flow systems, affected by topography, geomorphology, and human activities, sulfate sources were abundant, including soil sulfate, etc. Intermediate and regional groundwater flow systems had longer flow paths and reducing environments dominated by evaporite dissolution and bacterial sulfate reduction. Different landforms had distinct sulfate sources. In the alluvial-lacustrine plain's local groundwater flow system recharge zones, soil sulfate (35.7 %–48.9 %) and sulfide oxidation (21 %–28.6 %) contributions were higher. Human activities also enriched SO₄^2- in some shallow groundwater. These findings have theoretical significance for understanding sulfur biogeochemical processes evolution in multi-level nested groundwater flow systems at a regional scale and contribute to groundwater pollution control in arid and semi-arid regions.