title: Rapid immobilisation and leaching of wet-deposited nitrate in upland organic soils.
abstract: Nitrate (NO3-) is often observed in surface waters draining terrestrial ecosystems that remain strongly nitrogen (N) limited. It has been suggested that this occurs due to hydrological bypassing of soil or vegetation N retention, particularly during high flows. To test this hypothesis, artificial rain events were applied to 12 replicate soil blocks on a Welsh podzolic acid grassland hillslope, labelled with 15N-enriched NO3- and a conservative bromide (Br-) tracer. On average, 31% of tracer-labelled water was recovered within 4 h, mostly as mineral horizon lateral flow, indicating rapid vertical water transfer through the organic horizon via preferential flowpaths. However, on average only 6% of 15N-labelled NO3- was recovered. Around 80% of added NO3- was thus rapidly immobilised, probably by microbial communities present on the surfaces of preferential flowpaths. Transitory exceedance of microbial N-uptake capacity during periods of high water and N flux may therefore provide a mechanism for NO3- leaching.
authors.affiliation: Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Wales LL572UW, UK. cev@ceh.ac.uk
authors.forename: Chris D
authors.initials: CD
authors.lastname: Evans
authors.forename: Dave
authors.initials: D
authors.lastname: Norris
authors.forename: Nick
authors.initials: N
authors.lastname: Ostle
authors.forename: Helen
authors.initials: H
authors.lastname: Grant
authors.forename: Edwin C
authors.initials: EC
authors.lastname: Rowe
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Curtis
authors.forename: Brian
authors.initials: B
authors.lastname: Reynolds
mesh_terms: D015258:Acid Rain; D000327:Adsorption; D001965:Bromides / Q000032:analysis; D004463:Ecology / Q000295:instrumentation / Q000379:methods; D009566:Nitrates / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis; D009587:Nitrogen Isotopes / Q000032:analysis; D012621:Seasons; D017670:Sodium Compounds / Q000032:analysis; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis*; D014197:Trees; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D015258:Acid Rain; D001965:Bromides; D009566:Nitrates; D009587:Nitrogen Isotopes; D017670:Sodium Compounds; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C027938:sodium bromide; D009584:Nitrogen