Urea Production By Drainage Ditch Sediments in a Coastal Agroecosystem

Urea is a ubiquitous agricultural fertilizer implicated in the development of harmful algae blooms.  However, research shows that urea export from farm fields is unlikely, despite observations of high concentrations in coastal plain drainage ditches.  There is evidence that agricultural drainage ditches generate urea as flow stagnates following rainfall, a process that may be fueled by groundwater nitrogen.  Novel research that assesses the potential for autochthonous urea formation in ditches is underway at UMES.  The approach involves field monitoring of rainfall and ditch surface water, combined with an indoor mesocosm experiment.  The mesocosm experiment employed sediment samples to simulate stagnant, saturated field conditions.  Results indicate that urea was formed by mescosms’ saturated sediments within 8 hours of incubation for all replications and environments. The highest concentrations of urea were generated by agricultural drainage ditches, with lower concentrations generated by forest and wetland sediments. These results correspond with ongoing field monitoring data.  Certain ditch sediments may affect urea cycling and movement, and thus be an important driver of coastal dissolved organic nitrogen composition.  We postulate that urea formation is driven by microbial activity.  Our work is continuing to identify and characterize coastal plain ditches that generate elevated urea concentrations.