title: Nitrogen fate in drainage ditches of the coastal plain after dredging.
abstract: Drainage ditches are a key conduit of nitrogen (N) from agricultural fields to surface water. The effect of ditch dredging, a common practice to improve drainage, on the fate of N in ditch effluent is not well understood. This study evaluated the effect of dredging on N transport in drainage ditches of the Delmarva Peninsula. Sediments from two ditches draining a single field were collected (0-5 cm) to represent conditions before and after dredging. Sediments were packed in 10-m-long recirculating flumes and subjected to a three-phase experiment to assess the sediment's role as a sink or source of ammonium (NH4) and nitrate (NO3). Under conditions of low initial NH4-N and NO3-N concentrations in flume water, sediment from the undredged ditch released 113 times more NO3-N to water than did sediment from the dredged ditch. When flume water was spiked with NH4-N and NO3-N to simulate increases in N concentrations from drainage and runoff from adjacent fields, NO3-N in flume water increased during 48 h compared with the initial spiked concentration, while NH4-N decreased. These simultaneous changes were attributed to nitrification, with 23% more NO3-N observed in flume water with undredged ditch sediment compared with dredged ditch sediment. Replacing the N-spiked water with deionized water resulted in two times more NO3-N released from the undredged ditch sediment than the dredged ditch sediment. These results suggest that ditch sediments could represent significant stores of N and that dredging could greatly affect the ditch sediment's ability to temporarily assimilate N input from field drainage.
authors.affiliation: Center for Agrarian and Environmental Sciences, Federal University of Maranhao, Chapadinha, MA, 65500, Brazil. francirose@yahoo.com.br
authors.forename: Francirose
authors.initials: F
authors.lastname: Shigaki
authors.forename: John P
authors.initials: JP
authors.lastname: Schmidt
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: Kleinman
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Sharpley
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Allen
mesh_terms: D004323:Drainage, Sanitary; D019015:Geologic Sediments / Q000032:analysis*; D008396:Maryland; D009584:Nitrogen / Q000032:analysis*
chemical_list: D009584:Nitrogen