title: Quantitative study on nitrogen deposition and canopy retention in Mediterranean evergreen forests.
abstract: To assess the impact of nitrogen (N) pollutants on forest ecosystems, the role of the interactions in the canopy needs to be understood. A great number of studies have addressed this issue in heavily N-polluted regions in north and central Europe. Much less information is available for the Iberian Peninsula, and yet this region is home to mountain forests and alpine grasslands that may be at risk due to excessive N deposition. To establish the basis for ecology-based policies, there is a need to better understand the forest response to this atmospheric impact. To fill this gap, in this study, we measured N deposition (as bulk, wet, and throughfall fluxes of dissolved inorganic nitrogen) and air N gas concentrations from 2011 to 2013 at four Spanish holm oak (Quercus ilex) forests located in different pollution environments. One site was in an area of intensive agriculture, two sites were influenced by big cities (Madrid and Barcelona, respectively), and one site was in a rural mountain environment 40 km north of Barcelona. Wet deposition ranged between 0.54 and 3.8 kg N ha-1year-1for ammonium (NH4+)-N and between 0.65 and 2.1 kg N ha-1year-1for nitrate (NO3-)-N, with the lowest deposition at the Madrid site for both components. Dry deposition was evaluated with three different approaches: (1) a canopy budget model based in throughfall measurements, (2) a branch washing method, and (3) inferential calculations. Taking the average dry deposition from these methods, dry deposition represented 51-67% (reduced N) and 72-75% (oxidized N) of total N deposition. Canopies retained both NH4+-N and NO3-N, with a higher retention at the agricultural and rural sites (50-60%) than at sites located close to big cities (20-35%, though more uncertainty was found for the site near Madrid), thereby highlighting the role of the forest canopy in processing N pollutant emissions.
authors.affiliation: CREAF, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain. anna.avila@uab.cat.
authors.forename: Anna
authors.identifier: http://orcid.org/0000-0002-4137-0839
authors.initials: A
authors.lastname: Avila
authors.affiliation: CREAF, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Aguillaume
authors.affiliation: LICA, Universidad de Navarra, 31009, Pamplona, Spain.
authors.forename: Sheila
authors.initials: S
authors.lastname: Izquieta-Rojano
authors.affiliation: Ecotoxicology of Air Pollution, CIEMAT, 28040, Madrid, Spain.
authors.forename: Héctor
authors.initials: H
authors.lastname: García-Gómez
authors.affiliation: LICA, Universidad de Navarra, 31009, Pamplona, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Elustondo
authors.affiliation: LICA, Universidad de Navarra, 31009, Pamplona, Spain.
authors.forename: Jesús Miguel
authors.initials: JM
authors.lastname: Santamaría
authors.affiliation: Ecotoxicology of Air Pollution, CIEMAT, 28040, Madrid, Spain.
authors.forename: Rocío
authors.initials: R
authors.lastname: Alonso
mesh_terms: D000383:Agriculture; D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D064751:Ammonium Compounds / Q000032:analysis / Q000633:toxicity; D002947:Cities; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D005060:Europe; D065928:Forests; D009584:Nitrogen / Q000737:chemistry / Q000633:toxicity*; D029963:Quercus / Q000187:drug effects / Q000254:growth & development; D014197:Trees / Q000187:drug effects / Q000254:growth & development
chemical_list: D000393:Air Pollutants; D064751:Ammonium Compounds; D009584:Nitrogen
keywords: Canopy uptake; Critical loads; Mediterranean; Nitrogen; Throughfall; Wet deposition