Investigating Microbial Urea Production in Agricultural Drainage Ditch Sediments.

The increasing usage of urea nitrogen in fertilizers is a growing concern because of its association with harmful algal blooms and water quality. Urea - ammonium - nitrate fertilizers are commonly applied to crop fields on the Maryland Eastern Shore during April and May. However, increased concentrations of urea-N above 100 ug N L^-1 have not been found to occur until July or after storm events in the surface waters of the Manokin and Choptank Watersheds. Since urea is quickly hydrolyzed in the environment and urease inhibitors only last up to two weeks, it is unlikely that the urea-N measured in the surface waters downstream July through September is the same urea-N applied onto the crop fields in April and May. It is hypothesized that microbial communities contribute to the urea pool and influence the urea-N measured months after fertilization. Direct pathways leading to urea production originate from substrates in the dissolved organic nitrogen (DON) pool such as DNA and amino acids. Therefore, a mesocosm experiment using agricultural drainage ditch sediment was run to investigate if substrates from the DON pool are pre-cursors to urea production. Sediments were enriched with either untreated water, nitrate, or DON; and then incubated at 27^oC for a week. Sediment was collected at four time points for RNA and DNA extraction for microbial community composition and urease activity. Water samples were collected daily for nitrogen concentrations and determination of urea production. Results from the experiment will be used to generate gene targets from urea producing pathways, and to set-up another experiment to invesitgate mechanisms of microbial urea production in forest and agricultural drainage ditch sediments.