Deposition and Effects of Atmospheric Nitrogen and Ozone in Holm Oak Forests in Spain
Abstract
Atmospheric nitrogen (N) emissions in Spain, in the western Mediterranean basin, have followed an increasing trend since 1990 and have only started to decline recently. These trends have resulted in growing N depositions in some areas and in N enrichment of ecosystems, as described in previous studies by increasing records of nitrophilous species in herbaria and raising N content both in bryophytes and in leaves of forest trees. Tropospheric ozone (O3) background concentrations, formed as a result of photochemical reactions of N compounds in the atmosphere, have also increased during the last decades. Despite these evidences, limited information is available on N and O3 deposition and effects in Holm oak forests, important ecosystems in Spain. New studies are being developed to address this lack of data. First results on N deposition in a Holm oak forest in central Spain stress the importance of seasonal variations of N inputs in Mediterranean environments. Spring and autumn rainfall events added up to 80% of total annual bulk deposition and losses of NO3- in the soil water were detected when throughfall N pulses occurred during periods of low plant physiological activity. N uptake in the tree canopy was also observed. High O3 concentrations were also measured in this study. The exposure to both N and O3 is a common situation in Holm oak forests. The combined effect of N and O3 deposition on the annual pasture of the Holm oak forest understory has been studied in an open-top chamber study using a simplified community of six species. Results show that O3 can potentially reduce pasture growth, decrease its nutritive value for herbivores and cause shifts in species abundance. N deposition can partially counterbalance O3-induced effects on the pasture biomass, thus both O3 and N need to be considered together when studying air pollution impacts in these ecosystems. The studies presented here are intended for developing N and O3 critical loads and levels for the Mediterranean vegetation within the Long-Range Transboundary Air Pollution Convention of the UNECE. Critical loads and levels are used to evaluate the risk of air pollution damage to sensitive receptors and establish emission reductions to avoid critical level exceedances.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B42D..05G
- Keywords:
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- 0426 BIOGEOSCIENCES Biosphere/atmosphere interactions;
- 0469 BIOGEOSCIENCES Nitrogen cycling