Invited paper Using nitrogen concentration and isotopic composition in lichens to spatially assess the relative contribution of atmospheric nitrogen sources in complex landscapes * P. Pinho a, b, * , C. Barros a, c, d , S. Augusto a, e , M.J. Pereira b , C. M  aguas a , C. Branquinho a a Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ci^ encias, Universidade de Lisboa (CE3C-FC-ULisboa), Edifício C2, 5º piso, Campo Grande, 1749-016 Lisboa, Portugal b Centro de Recursos Naturais e Ambiente, Instituto Superior T ecnico, Universidade de Lisboa (CERENA-T ecnico/ULisboa), Av. Rovisco Pais,1049-001 Lisboa, Portugal c Laboratoire d’  Ecologie Alpine (LECA), Universit e Grenoble Alpes, F-38000 Grenoble, France d Laboratoire d’  Ecologie Alpine (LECA), CNRS, F-38000 Grenoble, France e ISPUP-EPIUnit, Universidade do Porto, Rua das Taipas, nº 135, 4050-600 Porto, Portugal article info Article history: Received 31 October 2016 Received in revised form 22 June 2017 Accepted 29 June 2017 Available online 13 July 2017 Keywords: Reactive nitrogen Eutrophication Isoscapes Multiple pollution sources abstract Reactive nitrogen (Nr) is an important driver of global change, causing alterations in ecosystem biodi- versity and functionality. Environmental assessments require monitoring the emission and deposition of both the amount and types of Nr. This is especially important in heterogeneous landscapes, as different land-cover types emit particular forms of Nr to the atmosphere, which can impact ecosystems distinc- tively. Such assessments require high spatial resolution maps that also integrate temporal variations, and can only be feasibly achieved by using ecological indicators. Our aim was to rank land-cover types ac- cording to the amount and form of emitted atmospheric Nr in a complex landscape with multiple sources of N. To do so, we measured and mapped nitrogen concentration and isotopic composition in lichen thalli, which we then related to land-cover data. Results suggested that, at the landscape scale, intensive agriculture and urban areas were the most important sources of Nr to the atmosphere. Additionally, the ocean greatly influences Nr in land, by providing air with low Nr concentration and a unique isotopic composition. These results have important consequences for managing air pollution at the regional level, as they provide critical information for modeling Nr emission and deposition across regional as well as continental scales. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Reactive nitrogen (Nr) includes all nitrogen forms capable of readily reacting and causing a number of cascading effects in the environment: reduced nitrogen as ammonia and ammonium (NH 3 and NH 4 ), oxidized nitrogen oxides (NO x ), nitrous oxide (N 2 O), ni- trate (NO 3 - ) and nitrite (NO 2  ). Reactive nitrogen is released from human activities and its levels already exceed those of naturally fixed N forms. This excess has negative impacts on ecosystem structure and functionality (Erisman et al., 2007; van den Berg et al., 2016). Knowing where excessive Nr is being deposited is important in order to take appropriate management actions. However, map- ping Nr deposition is not trivial (Hertel et al., 2012). On the one hand, Nr has multiple sources that can be diffuse (such as agri- culture or urban areas) or point sources (such as barns or chim- neys). These different Nr sources co-occur with other areas that emit little or no Nr (such as forests) e Nr sinks. On the other hand, some Nr forms such as atmospheric ammonia (NH 3 ) have a short dispersion range (albeit large impacts on biological systems; Sutton et al., 1998; Pinho et al., 2011), generating high spatial heteroge- neity in Nr deposition (Pinho et al., 2014a). Using monitoring sta- tions to map Nr deposition is very costly due to the large number of stations required to capture the spatial heterogeneity of Nr sources. Conversely, using passive samplers is not practicable, as they need to be frequently replaced to allow for temporal integration. To overcome these issues, modeling approaches have provided * This paper has been recommended for acceptance by Dr. Hageman Kimberly Jill. * Corresponding author. CERENA- Centro de Recursos Naturais e Ambiente, Instituto Superior T ecnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. E-mail address: ppinho@fc.ul.pt (P. Pinho). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2017.06.102 0269-7491/© 2017 Elsevier Ltd. All rights reserved. Environmental Pollution 230 (2017) 632e638