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 large-scale movement of urea fertilizer to surface waters is unlikely, despite observations of high concentrations in coastal plain drainage ditches.  There is evidence that stagnant agricultural drainage ditches generate urea once flow recedes following rainfall.  The potential for autochthonous urea formation was assessed by field monitoring and a novel indoor mesocosm experiment.  The mesocosm experiment took sediment samples from intermittent drainages and incubated them with prepared solutions to simulate stagnant, saturated field conditions.  Measureable urea concentrations appeared in mescosms’ surface water within 8 hours of incubation across all sediments and conditions, while control mesocosms produced little to no urea.  The highest concentrations of urea were associated with warmer temperatures and were generated by agricultural drainage ditches; lower urea concentrations were generated by sediments from forest and wetland drainages.  These results correspond with field monitoring data and support our hypothesis that urea is formed by ditch processes.  We postulate that urea formation is driven by microbial activity.  Agricultural ditch sediments may affect urea cycling and movement.  While urea fertilizer may not leach directly from fields, urea from agricultural drainage ditches may modify downstream nitrogen pool composition and thereby alter primary producer community structure to favor harmful algae bloom species.