Time trends in the precipitation chemistry at a mountain site in Northeastern Spain for the period 1983–1994

Abstract

In the Montseny mountains (NE Spain), bulk deposition data from 1983 to 1994 revealed a significant decrease of SO 4 2− concentrations and deposition (of 19% for 5 yr means), but non-significant trends for N0 3 −, NH 4 +, the base cations or alkalinity concentrations or deposition. The pH distribution of weekly samples shifted to higher values: the median pH increased from 4.74 (H + concentration, 18.2 μeq l −1) in year 1983–1984 to 5.50 (H + concentration, 3.2 μeq l −1 in year 1993–1994. Base cations and alkalinity concentrations and deposition were strongly depedent on the occurrence of sporadic events of red rains from the Saharan region, which are rich in alkalinity and base cations. Excluding such red rains, SO 4 2−1 concentration still showed a significant decrease ( p = 0.014) over the study period while alkalinity increased ( p = 0.08). This is an indication that the reduction of S emissions due to the abatement regulations at an European scale of approximately 37% has had an effect on the bulk deposition over NE Spain, and that, leaving apart the high, but unpredictable, inputs of alkalinity and base cations from the Saharan region, there is an increase in the alkalinity of precipitation.