Results of long–term observations of basic physico–chemical data of atmospheric precipitation in a protected area in Western Poland

The amount, pH, and electrical conductivity of precipitation, based on multi–year observations (1992–2013) carried out in the Wielkopolski National Park (WNP), are summarized. A systematic study of individual precipitation events in open terrain and in throughfall reveals that rainwater is still acidic here. As much as 78% of the precipitation tested had a pH of under 5.1; some very low pH values, even below 3.0, were observed occasionally. However, over the study period the pH of precipitation tended to grow systematically and electrical conductivity kept falling systematically. The mean electrical conductivity showed a slightly elevated level, but episodes with extremely high values (>1 000 μS/cm) could still be observed in throughfall. Studies of throughfall showed it to have a higher pH, but over the entire period its mean annual pH was lower than 5.1. Periods with a precipitation deficit are followed by those with excessive rainfall, which can be regarded as evidence for the instability of the climate. The results obtained were compared against long–term figures recorded at the stations monitoring background air pollution under the European Monitoring and Evaluation Program.