Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 9, 1205-1215, 2012
https://doi.org/10.5194/bg-9-1205-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
28 Mar 2012
Critical loads of nitrogen deposition and critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands
P. Pinho1,2, M. R. Theobald3,4, T. Dias1, Y. S. Tang4, C. Cruz1, M. A. Martins-Loução1,5, C. Máguas1, M. Sutton4, and C. Branquinho1 1Universidade de Lisboa, Faculdade de Ciências, Centre for Environmental Biology, Lisboa, Portugal
2Centre for Natural Resources and the Environment, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal
3Dept. Agricultural Chemistry and Analysis, E.T.S.I. Agrónomos, Technical University of Madrid, Spain
4Centre for Ecology and Hydrology, Edinburgh Research Station, Edinburgh, UK
5Universidade de Lisboa, Museu Nacional de História Natural, Jardim Botânico, Lisboa, Portugal
Abstract. Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds such as critical loads (deposition fluxes) and levels (concentrations) can be established. Few studies have assessed these thresholds for semi-natural Mediterranean ecosystems. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands. We have considered changes in epiphytic lichen communities, one of the most sensitive comunity indicators of excessive N in the atmosphere. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done for a Mediterranean climate in evergreen cork-oak woodlands, based on the relation between lichen functional diversity and modelled N deposition for critical loads and measured annual atmospheric ammonia concentrations for critical levels, evaluated downwind from a reduced N source (a cattle barn). Modelling the highly significant relationship between lichen functional groups and annual atmospheric ammonia concentration showed the critical level to be below 1.9 μg m−3, in agreement with recent studies for other ecosystems. Modelling the highly significant relationship between lichen functional groups and N deposition showed that the critical load was lower than 26 kg (N) ha−1 yr−1, which is within the upper range established for other semi-natural ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should aid development of policies to protect Mediterranean woodlands from the initial effects of excessive N.

Citation: Pinho, P., Theobald, M. R., Dias, T., Tang, Y. S., Cruz, C., Martins-Loução, M. A., Máguas, C., Sutton, M., and Branquinho, C.: Critical loads of nitrogen deposition and critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands, Biogeosciences, 9, 1205-1215, https://doi.org/10.5194/bg-9-1205-2012, 2012.
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