Using Gypsum to Affect Soil Erosion Processes and Water Quality.

A fundamental driving force in soil erosion is the low electrolyte content of rain water.  Various electrolyte sources have proven useful in serving as electrolyte sources such as phosphogypsum, lime and various salts, however, each has other potential problems.  We performed a number of studies on low cost gypsum from scrubbing air from coal fired power plants for pollution control (FGD gypsum) and found the neutral salt produced is an excellent electrolyte source which is slowly soluble in rainwater and has few if any potential environmental problems.  It has proven very useful in keeping soil clays flocculated and maintaining greater infiltration rates, therefore, reducing runoff and erosion.  During the studies we have conducted over the years we have found that during application to control erosion, gypsum addition also reduced some pollutants in the runoff water.  We have found that FGD gypsum application to the soil surface can reduce runoff, erosion and especially soluble phosphate concentrations in runoff.  One potential problem with the FGD gypsum compared to mined gypsum is that it can potentially contain over 100 ppt Hg from the original coal.  We conducted a water quality study with an FGD gypsum containing relatively high Hg and have found that the trace levels it contained did not significantly move into the shallow water table nor did they seem to pose a threat of increasing the concentration in corn tissue or grain.  The significance to these findings is that FGD gypsum can be used for erosion control and also to improve water quality while the threat of increasing Hg in the food chain does not appear to be a major problem.