Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 101

Chemical composition of the Tatra Mountain lakes: II. Recovery from acidification

Ninety−one lakes distributed across the Tatra Mountains (most lakes are >1 ha and 65% of lakes >0.01 ha) were sampled and analysed for ionic and nutrient composition in September 2004 (15 years following reductions in acid deposition). Eighty−one lakes were in the alpine zone and ten lakes in Norway spruce forest. The results were compared to similar lake surveys from 1994 (the beginning of recovery from acidification) and 1984 (maximum acidification). Atmospheric deposition of SO42− and inorganic N decreased by 57% and 35%, respectively, in this region from the late 1980s to 2000. Lake water concentrations of SO42− and NO3− have both decreased by ~50% on average (to 23 and 19 µmol L−1, respectively, in 2004) since 1984. While the decrease in SO42− concentrations was stable throughout 1984−2004, most of the NO3− decrease occurred between 1994 and 2004. The declines in SO42− and NO3 concentrations are related to catchment vegetation coverage, being most rapid for SO42− in lakes with forested catchment and for NO3− lakes in rocky catchments (alpine). Concentrations of the sum of base cations (dominated by Ca2+) decreased significantly between 1984 and 2004, with the highest change in alpine lakes. Most of this decline occurred between 1994 and 2004. Acid neutralising capacity (ANC) did not change in the 1984−1994 period, but increased on average by 29 µmol L−1 between 1994 and 2004, with the highest change in alpine lakes. Over the last decade, the proportion of lakes with ANC >150 µmol L 1 increased from 15% to 21% and that of ANC <20 µmol L 1 decreased from 37% to 20%. The highest decline in H+ and Al concentrations occurred in the most acid lakes. On a regional basis, no significant change was observed for total phosphorus, total organic nitrogen, and dissolved organic carbon (DOC) in the 1994−2004 period. However, these parameters increased in lakes with forested catchments, which exhibited an increasing trend in DOC concentrations, inversely related (p <0.001) to their decreasing ionic strength (30% on average in 1994−2004).

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