In the northern prairie region of North America, there are millions of small seasonal wetlands. The aquatic ecology of these wetlands is partly controlled by the salinity of the wetland pond water, which affects the vegetation and invertebrate communities. The objective of this study was to identify the key geochemical processes affecting water chemistry in prairie wetlands. We used the combined water and solute mass balance approach to quantify the rates of geochemical reactions in a typical prairie recharge wetland in Saskatchewan, Canada. Sulfate reduction, carbonate mineral dissolution, and processes adding carbon dioxide to the pond were identified as the key geochemical reactions. Sulfate reduction removed more sulfate from the pond than infiltration in each of the four years examined. The average rate of sulfate reduction, 0.07 g m⁻² d⁻¹, was greatest in spring and decreased during the year. Reduced sulfate remains in the sediments but is re-oxidized when the pond dries out and is dissolved into the pond water and sediment pore water when the pond re-floods. X-ray diffraction analyses of wetland soil and mass balance calculations indicate magnesium-calcite is dissolved into the pond water in the spring and precipitates out of solution later in the year, and dissolves into the pond the following year.