Influence of Gypsum Amendment in the Nutrient Phytoremediation Potential of Three Native, Aquatic Plants Found in Agricultural Ditch Systems.

Agriculture is heavily scrutinized because of its nutrient contributions to global water quality.  Although no "silver bullet" management practice exists to completely remediate all agricultural pollutants, combinations of practices with a measure of demonstrated success hold promise as a means to reduce agriculture's contribution to global water pollution.  Twelve, 379 L mesocosms (1.32 m x 0.70 m x 0.66 m) were constructed by layering 16 cm of Lexington silt load atop a base of 22 cm of washed sand.  Three mesocosms (each) were planted with monocultures of either Leersia oryzoides L. Sw., Typha latifolia L., or Sparganium americanum Nutt. (n=9), while three mesocosms were left unvegetated to serve as controls.  Gypsum (167 g) was added to each individual mesocosm to simulate a recommended field application (reduced for scale).  Water amended with nitrate, ammonium, and phosphate (8 mg/L each) was pumped through each mesocosm using a metered piston pump to deliver an 8 h retention time for each system.  After the 8 h exposure, nutrient-amended water ceased, and the system was allowed to sit for 40 h.  Approximately 48 h following the original nutrient amendment initiation, the system was flushed with unamended water for another 8 h retention time to simulate effects of system flushing.  Overall phosphate mass mitigation was above 50% in all plant species, while control (unvegetated) mesocosms had 71±1% retention, likely due to the addition of the phosphorus-binding gypsum.   Ammonium mass mitigation was less efficient, ranging from 41±9% in T. latifolia to 56±18% in L. oryzoides.  Overall nitrate mitigation ranged from 12±49% in S. americanum to 49±7% in controls.  Based on comparisons to previous phytoremediation studies, gypsum amendments do not appear to enhance plants' abilities to mitigate diverse nutrients in runoff water.  In the case of unvegetated controls, however, gypsum did appear to enhance nutrient mitigation capabilities.