title: Urea Release by Intermittently Saturated Sediments from a Coastal Agricultural Landscape.
abstract: 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, NH-N, and NO-N in the floodwater. Sediments were flooded with different N-amended solutions (distilled HO, 1.5 mg L NH-N, 3.0 mg L NH-N, 2.6 mg L NO-N, or 5.1 mg L NO-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.
authors.forename: Mason D
authors.initials: MD
authors.lastname: King
authors.forename: Ray B
authors.initials: RB
authors.lastname: Bryant
authors.forename: Louis S
authors.initials: LS
authors.lastname: Saporito
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Buda
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Allen
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Hughes
authors.forename: Fawzy M
authors.initials: FM
authors.lastname: Hashem
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: Kleinman
authors.forename: Eric B
authors.initials: EB
authors.lastname: May
mesh_terms: D000383:Agriculture; D004777:Environment; D055868:Floods; D019015:Geologic Sediments; D014508:Urea / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D053833:Wetlands
chemical_list: D014874:Water Pollutants, Chemical; D014508:Urea