PREDICTING RECOVERY IN ACIDIFIED FRESHWATERS BY THE YEAR 2010, AND BEYOND

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THE REGIONS

• Upland UK
• Germany
• Scandinavia
• Italy
• Czech Republic
• Slovakia
• Pan-European

RESULTS

• Upland UK
• Germany
• Scandinavia
• Italy
• Czech Republic
• Slovakia
• Pan-European

Czech Republic and Slovakia

Tatra Mountain Lakes

Bohemian Forest

All Czech sites are small lakes located in spruce-forested catchments in the Bohemian Forest along the border with Germany and Austria, in the largest woodland area in central Europe. Lakes are 200 km or more, south of major sources of emissions concentrated within the co-called Black Triangle of north-western Bohemia, southern Poland, and eastern Germany. Lakes Plesne and Zdarske are situated on granite, the rest on gneiss (mica schists). Rocks are usually covered by 1 to 5 cm of forest humus and total depth is only 0.1 to 0.5 m. Present (1998) S-deposition is ~ 1.3 g.m^-2yr^-1 , about 70 % lower than in the mid-1980s. Nitrogen deposition is variable (1 and 2 g m^-2yr^-1) and declined by 20 to 30 % around 1990. Long-term changes of the lake water chemistry are studied by regular sampling in summer (July), during the autumn overturn and irregularly in other seasons. Temporal changes of all major solutes and selected trace elements in water of lakes has been monitored since 1984. Four chronically acidified lakes (Cerné, Certovo, Prasilske and Plesne) exhibited a decrease in the concentration of strong anions at rates of 3.6 to 8.8 µeq L^-1 yr^-1 over the whole period 1984 - 1999. In addition to a decrease in SO₄ (by 56 to 101 µeq L^-1 , Fig.1) a decrease in NO₃ (18 to 35 µeq L^-1) and Cl^- (5 to 10 µeq L^-1) was also observed (Fig. 2). A multi-year decrease in NO₃ in acidified lakes was observed for the first time in the Bohemian lakes. Average SO₄ concentrations have been decreasing since 1986 and the annual decline of SO₄ in lake water was related to SO₄ concentrations in the acidified lakes. Lakes are now more sensitive to climatic variation causing ,e.g, temporal increase of SO₂ in winter 1995 - 1996. A limited amount of longer-term data suggests that the NO₃ concentrations have increased probably steadily in Cerné, Certovo and Prasilske lakes over the period 1936 to 1987 (Fig. 2). These data also suggest that NO₃ concentrations in Cerné and Certovo lakes peaked near the beginning of the study period (1985-1988) and contributed up to 50 % of the anthropogenically induced increase in strong anions (primarily SO₄ and NO₃) in the lake waters. The decrease in the NO₃ concentrations, especially in Certovo and Cerné lakes, has been relatively fast around 1990 (Fig.2). Besides nitrogen deposition, rate of organic matter decomposition, bioconsumption and 'acid stress' generally are factors affecting nitrate concentrations. The change of strong anions in Cerne, Certovo and Plesne lakes was accompanied by a decrease in Al, Ca, Mg and K contents (but not Na) and an increase in pH (rate of 0.009 to 0.023 pH yr-1).

Figure 1: Mean sulphate concentrations in epilimnetic waters in Bohemian Forest lakes

Figure 2: Changes in nitrate concentrations in Cerné, Certovo and Prášilské lakes from 1936 to 1999. - Cerné Lake, - Certovo Lake, - Prášilské Lake; 1936-1980 data taken from Jírovec and Jírovcová, 1937; Procházková and Fott (personal communication)

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References:

• Veselý, J., Hruška, J., Norton, S.A, Johnson,C.E. (1998 a) Trends in the chemistry of acidified Bohemian lakes from 1984 to 1995. I. Major solutes. Water, Air, Soil Pollut.108: 107-127.
• Veselý, J., Hruška, J., Norton, S.A, (1998 b) Trends in the chemistry of acidified Bohemian lakes from 1984 to 1995. II. Trace elements and aluminum. Water, Air, Soil Pollut.108: 425-443.
• Kopácek J., Hejzlar J., Stuchlík E., Fott J. and Veselý J.(1998). Reversibility of acidification of mountain lakes after reduction in nitrogen and suphur emissions in Central Europe. Limnol. Oceanogr. 43, 357-361.