Are there signs of acidification reversal in freshwaters of the low mountain ranges in Germany?

C. Alewell¹, M. Armbruster², J. Bittersohl³, C.D.Evans⁴, H. Meesenburg⁵ K. Moritz³ and A. Prechtel¹
¹Department of Soil Ecology, BITÖK University of Bayreuth, D-95440 Bayreuth, Germany
²Institute of Soil Science, Technical University of Dresden, D-01735 Tharandt, Germany
³Bavarian Water Management Agency, D-80636 Munich, Germany
⁴Centre for Ecology and Hydrology, Wallingford, Oxon OX10 8BB,UK
⁵Forest Research Institute of Lower Saxony, D-37079 Göttingen, Germany

Full Reference

Alewell, C., Prechtel, A., Bittersohl, J., Moritz, K., Meesenburg, H., Armbruster, M. (2001). Are there signs of acidification reversal in freshwaters of the low mountain ranges of Germany? Hydrology and Earth System Sciences, Vol. 5, No. 3, 367-378.

Summary of Research

The reversal of freshwater acidification in the low mountain ranges of Germany is of public, political and scientific concern, because these regions are near natural ecosystems and function as an important drinking water supply. The aim of this study was to evaluate the status and trends of acidification reversal after two decades of reduced anthropogenic deposition in selected freshwaters of the low mountain ranges in the Harz, the Fichtelgebirge, the Bavarian Forest, the Spessart and the Black Forest. In response to decreased sulphate deposition, seven out of nine streams investigated had significantly decreasing sulphate concentrations (all trends were calculated with the Seasonal Kendall Test). The decrease in sulphate concentration was only minor, however, due to the release of previously stored soil sulphur. No increase was found in pH or acid neutralising capacity (defined by Reuss and Johnson, 1986). Aluminium concentrations in the streams did not decrease. Thus, no major acid ification reversal can currently be noted in spite of two decades of decreased acid deposition. Nevertheless, the first signs of improvement in water quality was detected as there was a decrease in the level and frequency of extreme values in pH, acid neutralising capacity and aluminium concentrations in streams. With respect to nitrogen, no change was determined for either nitrate or ammonium concentrations in precipitation or stream water. Base cation fluxes indicate increasing net loss of base cations from all ecosystems investigated, which could be interpreted as an increase in soil acidification. The latter was due to a combination of continued high anion leaching and significant reduction of base cation deposition. No major improvement was noted in biological recovery, however, initial signs of recovery were detectable as there was re-occurrence of some single macroinvertebrate species which were formerly extinct. The results of this study have important implications for water authorities, forest managers and policy makers: the delay in acidification reversal, suggests a need for ongoing intensive amelioration of waters, a careful selection of management tools to guarantee sustainable management of forests and the reduction of nitrogen deposition to prevent further acidification of soils and waters.

Regional Description

Regions investigated in this study are low mountain ranges in Germany (Figure 1). The Bramke area is located in the Harz mountains. The Lange Bramke catchment (51°52'N, 10°26'E) with an altitudinal range of 543 to 700 m a.s.l. has an area of 76 ha and is stocked with 54 years old spruce. Lange Bramke spring is a subcatchment of Lange Bramke. Dicke Bramke and Steile Bramke with catchment areas of 32 and 38 ha, respectively, are stocked with 20 to 110 years old spruce stands. The Steile Bramke catchment was limed in 1989 with 16 t ha^-1 of dolomitic limestone (Meesenburg et al., 2001). Bedrock consists mainly of sandstones with layers of calcareous sand and clay schist.

The Metzenbach catchment (240 ha, 49°54'N, 9°26'E) is located in the low mountain range, Spessart, southeast of Frankfurt at an elevation of 380-568 m a.s.l. Bedrock consists mostly of fine grained sandstones and the soils are predominantly Cambisols.

The Lehstenbach catchment (4.2 km², 50°09'N, 11°52'E) is located in the Fichtelgebirge area in Northern Bavaria close to the border with the Czech Republic at a height of 695-875 m a.s.l. The granite bedrock was deeply weathered during the Tertiary. 90% of the catchment is stocked with Norway spruce of various age classes.

The Markungsgraben catchment (48°57'N, 13°25'E) is a subcatchment of the catchment Große Ohe in the Bavarian Forest National Park on the Bavarian-Czech border. Markungsgraben has an area of 1.1 km² at an altitude of 890-1355 m a.s.l. Average slope inclination is 27%. Bedrock consists of coarse granite and gneiss. The catchment is completely forested with spruce in the highland region and mixed woodlands in the lower slope regions.

The Villingen (46 ha, 48°03'N, 8°22'E) and Schluchsee (11 ha, 47°49'N, 8°06'E) catchments are both located in the Black Forest at altitudes of 870 - 950 m a.s.l. and 1150-1250 m a.s.l., respectively. Both catchments are stocked with spruce with an average age of 110 and 55 years, for Villingen and Schluchsee, respectively. Bedrock is sandstone (geological formation Bunter sandstone) in the case of Villingen and granite (geological formation Bärhaldegranit) in Schluchsee.

Table 1. Average total deposition of S and N
Average total deposition at the sites investigated is presented in Table 1 (for calculation of total deposition see below).

Fig 2. pH in stream waters

Streams of the catchments investigated were acid and had pH < 6.5 most of the year with no temporal trend (Figure 2). The reason for the constant acidity in the streams and the delayed increase of pH can be attributed to the buffering capacity of the soils. All soils investigated have received considerable loads of acidity in the past and the stored SO₄ and acidity will be released under the currently low deposition regime.

Fig 3. Acid neutralising capacity(ANC)
Average ANC in streams (ANC as defined by Reuss and Johnson, 1986; levels calculated as arithmetic mean values) ranged from approximately 75 µmolcl^-1 at Lange Bramke, Dicke Bramke and Metzenbach, 33 and 15 µmolcl^-1 at Villingen and Schluchsee, respectively, around 0 µmolcl-1 at Markungsgraben, -50 µmolcl^-1 at Lehstenbach to an average of -140 µmolcl-1 at Lange Bramke spring (Figure 3, note that of the Bramke area only Lange Bramke is shown). At Steile Bramke, which was limed in 1989, average ANC was around 100 µmolcl-1 before liming (1987 to 1989) and 180 µmolcl^-1 thereafter (1989-1999, data not shown). According to the Kendall tau test none of the streams had significantly increasing ANC (Figure 3).

Fig 4. Aluminium concentrations in streams

Total Al concentration in streams responded similarly to pH and ANC. Kendall tau trend statistics and average stream concentrations of Al (Figure 4) indicated no decline except for Lange Bramke spring and Dicke Bramke. Although trends are not significant, a decrease in concentrations of extreme values and peak frequency is noticeable (Figures 2, 3 and 4). Nevertheless, the decrease in extreme values (both concentrations and frequencies) is clearly an indication of improved water quality in life conditions for the aquatic fauna. Thus, even though the decrease in acid deposition is so far not reflected in a major acidification reversal, the first signs of improvement are detectable.

Fig 5.Element budget for base cations When discussing the development of acidification reversal, the dynamic of base cations is of major importance because of the effect on ANC. Furthermore, a significant leaching of base cations will lead to a decrease in base saturation of soils and may cause problems with forest nutrition (Malmer, 1976; Ulrich et al., 1980; Baes and McLaughlin, 1984; BML, 1997; Riek and Wolff, 1998). Despite the significant decrease in acid deposition, leaching of base cations did not decrease. All catchments investigated showed continued high cation leaching, and a general increase in net release from the ecosystems is observed (Figure 5).

References

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BML, 1997. Deutscher Waldbodenbericht, 1996. Bundesministerium für Ernährung Landwirtschaft und Forsten, Bonn, xxx pp.

Malmer, N., 1976. Chemical changes in the soil. Ambio, 5, 231-234.

Reuss, J.O. and Johnson, D.W, 1986. Acidic deposition and the acidification of soils and waters. Springer, New York, 1-119.

Riek, W. and Wolff, B., 1998. Verbreitung von Nährstoffmangel bei Waldbäumen in Deutschland. AFZ/Der Wald, 10, 507-510.

Ulrich, B., Mayer, R. and Khanna, P.K., 1980. Chemical changes due to acid precipitation in a loess-derived soil in central Europe. Soil Sci., 130, 193-199.

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

The James Hutton Institute

THE REGIONS

RESULTS