Long-term effects of changing atmospheric pollution on throughfall, bulk deposition and streamwaters in a Mediterranean forest

Abstract

The abatement programs implanted in Europe to reduce SO₂, NO₂ and NH³ emissions are here evaluated by analyzing the relationships between emissions in Spain and neighboring countries and atmospheric deposition in a Mediterranean forest in the Montseny mountains (NE Spain) for the last 3decades. A canopy budget model was applied to throughfall data measured during a period of high emissions (1995-1996) and a period of lower emissions (2011-2013) to estimate the changes in dry deposition over this time span. Emissions of SO₂ in Spain strongly decreased (77%) and that was reflected in reductions for nssSO4² in precipitation (65% for concentrations and 62% for SO4²-S deposition). A lower decline was found for dry deposition (29%). Spanish NO₂ emissions increased from 1980 to 1991, remained constant until 2005, and decreased thereafter, a pattern that was paralleled by NO3(-) concentrations in bulk precipitation at Montseny. This pattern seems to be related to a higher share of renewable energies in electricity generation in Spain in recent years. However, dry deposition increased markedly between 1995 and 2012, from 1.3 to 6.7kgha¯¹year¯¹. Differences in meteorology between periods may have had a role, since the recent period was drier thus probably favoring dry deposition. Spanish NH³ emissions increased by 13% between 1980 and 2012 in Spain but NH₄⁺ concentrations in precipitation and NH₄⁺-N deposition showed a decreasing trend (15% reduction) at Montseny, probably linked to the reduction ammonium sulfate and nitrate aerosols to be scavenged by rainfall. NH₄⁺-N dry deposition was similar between the compared periods. The N load at Montseny (15-17kgha¯¹year¯¹) was within the critical load range proposed for Mediterranean sclerophyllous forests (15-17.5kgha¯¹year¯¹). The onset of N saturation is suggested by the observed increasing N export in streamwaters

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