Atmospheric nitrogen inputs and cycling in Mediterranean evergreen broadleaf forests (Quercus ilex): Results from the EDEN project.

Héctor García Gómez1, Fernando Valiño1, Sheila Izquieta2, Laura Aguillaume3, Ignacio González-Fernández1, Héctor Calvete-Sogo1, David Elustondo2, Jesús M Santamaría2, Anna Àvila3, Rocío Alonso1
1 Research Center for Energy, Environment and Technology (CIEMAT)
2 University of Navarra (UNAV-LICA)
3 Center for Ecological Research and Forestry Applications (CREAF-UNAB)

P 3.3 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

The Mediterranean Basin presents an extraordinary biological richness but very little information is available on the threat that atmospheric nitrogen pollution can pose to biodiversity and ecosystem functioning. Mediterranean sclerophyllous woodlands represent a distinctive ecosystem and landscape of the Mediterranean Basin, including forests of Holm oak (Quercus ilex L.), the dominant tree species in the Iberian Peninsula. The main goal of the EDEN project was analyzing atmospheric nitrogen (N) inputs to this kind of forests in the Iberian Peninsula, and studying its cycling and possible effects.

Four Holm oak forests were monitored during more than two years. Concentrations of the main atmospheric N pollutants (NO2, NH3 and HNO3) were measured using passive samplers in open areas and inside the forests. Atmospheric particle were continuously monitored in open areas. Bulk and throughfall samples were collected weekly using conventional precipitation collectors, and seasonally using ion exchange resin columns. Dry deposition was estimated seasonally by means of rinsing techniques of both natural and lyophilized branches. Concentration of N in soil water was measured weekly through suction caps. Additionally, C/N ratio was assessed seasonally in leaves, litterfall and topsoil.

The atmospheric concentration of N pollutants varied largely among sampling sites for ammonia and N dioxide, with site-specific averages ranging 0.65-2.45 µg NH3 m-3 and 5.18-25.94 µg NO2 m-3 respectively. Smaller differences were found for ozone concentration, ranging 50.29-67.98 µg O3 m-3. The concentration of NH3 measured below canopy resulted systematically lower than in open field, with an averaged reduction of 31%-55%, depending on the sampling site. Smaller differences were found for the rest of pollutants when comparing open areas and inside the forest.

Atmospheric N deposition showed important seasonal variation and differences among sites. Annual nitrate and ammonium bulk deposition rates varied from 1.0 to 3.2 kg N ha-1 y-1 and from 0.8 to 4.9 kg N ha-1 y-1, respectively. Net throughfall rate of ammonium was in general around -50% of the bulk deposition, while the nitrate one was 150- 231% of the bulk deposition. Measurements obtained with conventional sampling methods are compared with those from ion exchange resin collectors. Finally, dry deposition estimations are exposed in combination with collected wet deposition data.

Letzte Änderung 19.06.2014