Critical loads of acidity to lakes in the Polish Tatra Mountains. Final report

Abstract

Major chemical compounds in precipitation and runoff have been intensively followed in two Polish, Tatra Mountain lakes (Dlugi Staw and Zielony Staw) since January 1993, to assess the degree of impact of acid precipitation. Since July 1995, even nitrogen and sulphur compounds in air have been measured, which means that most focus have been put on the year July 1995 - June 1996. Based on a dynamic, combined nitrogen and sulphur model (FAB), critical loads (CL) are exceeded for both lakes. While substantial reductionsof S and/or N are needed to reach CL at Dlugi Staw, only minor reductions are needed to obtain CL-level at Zielony Staw. Based on a nitrogen saturation index, both watersheds are in chronec stages of N-saturation. As long as the inputs of acid compounds are high, episodes particularly related to spring melt, may cause chemical conditions critical for aquatic life even at Zielony Staw with high acid neutralising capacity (ANC). This is primarily because the outlet streams might be totally dominated by melt water during such episodes, which means that organisms living in these streams have small changes to avoid episodes with extreme water quality. Because of far higher ANC at Zielony Staw, such episodes are both more uncommon and less extreme at this site compared with at Dlugi Staw. A surface water survey in the Karkonosze Mountains autumn 1995, documented strong impacts of atmospheric inputs of both S-and N-compounds in this area. Thus, CL is exceeded for all investigated sites.