Tendencies of changes in the chemical composition of precipitation in the Wielkopolski National Park

Abstract

The results are presented of chemical studies on precipitation based on multi-year observations (1992–2007) carried out in the Wielkopolski National Park (WNP). They are compared with the monitoring data obtained by stations grouped in the European Monitoring and Evaluation Programme (EMEP) network. It was found that over the study period the pH of precipitation tended to grow systematically, thus contributing to a decrease of the annual deposition of (H + ) ions. The trend lines of changes in the deposition of hydrogen ions have similar slope coefficients, which indicates similar rate of changes. The year with the lowest pH was 1994, in which the mean annual pH was 3.92. In turn, the acidification level was the lowest in 2006 with pH – 4.80. The deposition of hydrogen ions at all stations often exceeded 20 mg·m –2 ·year –1 , and at the WNP station it even reached 70 mg·m –2 in 1994. The deposition of acid-forming ions was also analysed. Predominant among them were sulphate ions, but their deposition showed a declining tendency with time. Their maximum values were recorded in precipitation in the WNP – 707 mg S-SO4·m –2 (2002) and 260 mg NNO3·m –2 (2007). It was found that the NO3/SO4 eq/eq ratio tended to increase, which is indicative of changes in the composition structure of precipitation. This effect resulted from the decrease in SO2 emission in the Wielkopolska region and from the increase in NOx emission caused by car traffic in the Park and along its border. Calcium dominated among the deposited alkaline cations – its share exceeded 50%. The figures recorded for potassium and calcium deposition by lowland EMEP stations were several times lower than those obtained in the WNP and lower than the mean for Poland. Over the last years one can note a stabilisation in the amount of deposited cations.