Urea release by intermittently saturated sediments from a coastal agricultural landscape

Mason D. King, Ray B. Bryant, Louis S. Saporito, Anthony R. Buda, Arthur L. Allen, Lindsey A. Hughes, Fawzy M. Hashem, Peter J.A. Kleinman, Eric B. May

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Urea-N is linked to harmful algal blooms in lakes and estuaries, and urea-N-based fertilizers have been implicated as a source. However, the export of urea-N-based fertilizers appears unlikely, as high concentrations of urea-N are most commonly found in surface waters outside periods of fertilization. To evaluate possible autochthonous production of urea-N, we monitored urea-N released from drainage ditch sediments using mesocosms. Sediments from a cleaned (recently dredged) drainage ditch, uncleaned ditch, forested ditch, riparian wetland, and an autoclaved sand control were isolated in mesocosms and flooded for 72 h to quantify urea-N, NH4 +-N, and NO3 --N in the floodwater. Sediments were flooded with different N-amended solutions (distilled H2O, 1.5 mg L-1 NH4 +-N, 3.0 mg L-1 NH4 +-N, 2.6 mg L-1 NO3 --N, or 5.1 mg L-1 NO3 --N) and incubated at three water temperatures (16, 21, and 27°C). Urea-N concentrations in mesocosms representing uncleaned and cleaned drainage ditches were significantly greater than nonagricultural sediments and controls. While flooding sediments with N-enriched solution had no clear effect on urea-N, warmer (27°C) temperatures resulted in significantly higher urea-N. Data collected from field ditches that were flooded by a summer rainstorm showed increases in urea-N that mirrored the mesocosm experiment. We postulate that concentrations of urea-N in ditches that greatly exceed environmental thresholds are mediated by biological production in sediments and release to stagnant surface water. Storm-driven urea-N export from ditches could elevate the risk of harmful algal blooms downstream in receiving waters despite the dilution effect.

Original languageEnglish (US)
Pages (from-to)302-310
Number of pages9
JournalJournal of Environmental Quality
Issue number2
StatePublished - 2017

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Management, Monitoring, Policy and Law


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