Fate of gypsum surface — applied to an Appalachian hill pasture watershed

Low pH soils leached with gypsum solutions have been shown to sorb gypsum thereby increasing calcium and improving root growth of some crops. However, in some situations, exchangeable aluminum is leached which could enter waterways and potentially cause adverse off-site impacts. Due to relatively high solubility, gypsum itself has potential to impact stream water chemistry. In this study, 8250 kg ha−1 gypsum was applied to plots in a steep 4.3 ha-pasture watershed in central Appalachia. Changes in the 0–40 cm soil profile and changes in water chemistry at a flume below a seep which drains the watershed were measured in response to this application. After the end of the second growing season, and a total rainfall of 1.7 m, 46% of the applied gypsum calcium was still in the top 40 cm of soil. The rainfall had a 11.4% efficiency rate of transporting gypsum out of the top 40 cm compared to movement of a saturated solution through an inert medium. Of the applied gypsum sulfate, 3.4% exited the watershed through stream flow. Maximum gypsum concentrations in stream flow, which occurred during a storm event, were 34 ppm or <1.5% of saturation levels. No detectable aluminum was measured in stream flow at the flume. These findings indicate that as long as a minor part of watersheds such as this one has gypsum applied at rates less than 10,000 kg ha−1, off-site environment impacts should be minimal.