Skip to main content
ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #331772
Title: Urea release by intermittently saturated sediments from a coastal agricultural landscape

Author
item KING, MASON - University Of Maryland Eastern Shore (UMES)
item Bryant, Ray
item Saporito, Louis - Lou
item Buda, Anthony
item ALLEN, ARTHUR - University Of Maryland Eastern Shore (UMES)
item HUGHES, LINDSEY - University Of Maryland Eastern Shore (UMES)
item HASHEM, FAWZY - University Of Maryland Eastern Shore (UMES)
item Kleinman, Peter
item MAY, ERIC - University Of Maryland Eastern Shore (UMES)

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2017
Publication Date: 3/17/2017
Citation: King, M.D., Bryant, R.B., Saporito, L.S., Buda, A.R., Allen, A.L., Hughes, L.A., Hashem, F.M., Kleinman, P.J., May, E.B. 2017. Urea release by intermittently saturated sediments from a coastal agricultural landscape. Journal of Environmental Quality. 46:302-310. doi: 10.2134/jeq2016.08.0304.

Interpretive Summary: Urea is linked to harmful algal blooms in lakes and estuaries, and urea-based fertilizers have been implicated as a source. However, direct wash off of urea-based fertilizers appears unlikely. Urea is rapidly converted to nitrate following application to soils. High concentrations of urea in tributaries of the Chesapeake Bay are most commonly found in surface waters outside periods of fertilization. To evaluate possible in-situ production of urea, we monitored urea released from drainage ditch sediments using mesocosms. Sediments from a cleaned (recently dredged) drainage ditch, uncleaned ditch, forested ditch, riparian wetland, and a sterile sand control were isolated in two-gallon buckets and flooded for 72 hours to quantify urea–N, NH4+–N, and NO3-–N in the floodwater. Sediments were flooded with different nitrate- and ammonium- amended solutions and incubated at three water temperatures (16°C, 21°C, 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. To corroborate mesocosm results, 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 urea–N in ditches is mediated by biological production in sediments and release to stagnant surface water. Consequently, storm-driven urea export from ditches could elevate the risk of harmful algal blooms downstream in receiving waters.

Technical Abstract: Urea–N is linked to harmful algal blooms (HAB) 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 control were isolated in mesocosms and flooded for 72 hours 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°C, 21°C, 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 degree 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 urea–N in ditches is mediated by biological production in sediments and release to stagnant surface water. Consequently, storm-driven urea–N export from ditches could elevate the risk of HABs downstream in receiving waters.