Effect of Introduced Flow and Aquatic Vegetation on Phosphorus Loads of Agricultural Drainage

Phosphorous (P) loads from anthropogenic sources increase eutrophication and reduce water quality. This study tested the management of two floating aquatic vegetation (FAV) species—water hyacinth (Eichhornia crassipes (Mart.) Solms)) and water lettuce (Pistia stratiotes L.)—and introduced flow facilitated by hydraulic pumps in reducing P loads exiting agricultural drainage ditches. The experimental design consisted of four treatment ditches equipped with hydraulic pumps to circulate farm canal water through the ditches prior to discharge. Treatment ditches 2 and 3 contained FAV that was physically introduced while treatment ditches 1 and 4 did not. In addition, two control ditches (ditches 5 and 6) were managed without hydraulic pumps or introduced FAV. Introduced flow was found to cause significant differences in total P, total dissolved P, and soluble reactive P concentration (p < 0.01) between inflow and outflow water. The treatment ditches reduced total P and total dissolved P by 13% and 33%, respectively compared with the control ditches, which increase total P by 9% and total dissolved P by 8%, respectively. Circulating farm canal water through ditches can be considered a treatment technology that reduces P loading via FAV uptake or particulate settling prior to being discharged.