Analysis of Decadal Time Series in Wet N Concentrations at Five Rural Sites in NE Spain

Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH (4) (+) and NO (3) (-) whereby higher values were reached at the end of spring-early summer, except at the easternmost coastal site of Begur. Weekly NH (4) (+) concentrations decreased with time at all sites (except at La Senia) whilst NO (3) (-) concentrations increased at all sites during the same period. Rainfall SO (4) (2-) concentrations decreased with time at all sites. The opposite trends in NO (3) (-) and SO (4) (2-) concentrations determined a shift in the relative acid contribution of those anions during the 12-13-year period. To interpret the increasing trend, mean annual NO (3) (-) concentrations were regressed against NO2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha(-1) year(-1). When including estimates of dry deposition, total annual deposition rose up to 10-20 kg ha(-1) year(-1), values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems.