title: Examination of nitrate concentration, loading and isotope dynamics in subsurface drainage under standard agricultural cropping in Atlantic Canada.
abstract: Intensive agricultural farming practices have the potential to cause high levels of nitrate-nitrogen (NO(3)(-)-N) to be released from tile drainage systems. A better understanding of the temporal dynamics of NO(3)(-)-N loading, δ(15)N and δ(18)O from standard drainage systems is needed, in order to improve our understanding of NO(3)(-)-N transport and transformation processes; particularly, with regards to the imperfectly drained agricultural soils found within Atlantic Canada. Three conventional subsurface drainage plots (48 × 48 m) placed at a 0.80 m soil depth were monitored over a seven month period on sandy loam soil in Onslow, Nova Scotia. Each plot received similar applications of both organic and inorganic fertilizer. Water samples were obtained and analyzed for NO(3)(-)-N concentrations and isotopic signatures of δ(15)N and δ(18)O for NO(3)(-)-N. Maximum NO(3)(-)-N loads were observed in the winter and fall, when both discharge and concentration of the NO(3)(-)-N were highest. Mean isotope values in NO(3)(-) ranged from 3.1 to 8.5‰ for δ(15)N and -3.2 to 17.7‰ for δ(18)O. Results suggest that NO(3)(-)-N from the drainage water was derived from organic sources (i.e. manure and soil organic matter) and that loss via denitrification does not impart an identifiable signature upon the NO(3)(-)-N pool. The dual isotope approach examined here provides insight into N source and transformation processes which may be contributing to the NO(3)(-)-N found within the drainage water.
authors.affiliation: Agriculture and Agri-Food Canada, 361 Pictou Road, Truro, NS, B2N 2T6 Canada. erin.smith@agr.gc.ca
authors.forename: E L
authors.initials: EL
authors.lastname: Smith
authors.forename: L M
authors.initials: LM
authors.lastname: Kellman
mesh_terms: D000383:Agriculture; D005308:Fertilizers; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D009674:Nova Scotia; D010103:Oxygen Isotopes / Q000032:analysis; D011891:Rain; D012621:Seasons; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014874:Water Pollutants, Chemical