Response of sulphur dynamics in European catchments to decreasing sulphate deposition

A. Prechtel¹, C. Alewell¹, M. Armbruster², J. Bittersohl³, J. Cullen⁴, C.D. Evans⁴, R. Helliwell⁵, J. Kopácek⁶, A. Marchetto⁷, E. Matzner¹, H. Meesenburg⁸, F. Moldan⁹, K. Moritz³, J. Veselý¹⁰ and R.F. Wright¹¹
¹Department of Soil Ecology, BITÖK University of Bayreuth, 95440 Bayreuth, Germany
²Institute of Soil Science, Technical University of Dresden, 01735 Tharandt, Germany
³Bavarian Water Management Agency, 80636 München, Germany
⁴Centre for Ecology and Hydrology, Wallingford, Oxon OX10 8BB,UK
⁵Macaulay Land Use Research Institute, Aberdeen, AB15 8QH, UK
⁶Hydrobiological Institute, AS CR, and Faculty of Biological Sciences, USB, Na Sádkách 7,370 05 Ceské Budejovice, Czech Republic
⁷Consiglio Nazionale delle Richerche- Istituto Italiano di Idrobiologia, 28922 Verbania Pallanza (VB), Italy
⁸Forest Research Institute of Lower Saxony, 37079 Göttingen, Germany
⁹Swedish Environmental Research Institute (IVL), Dagjämningsgatan 1, P.O. Box 47086, 402 58 Göteborg, Sweden
¹⁰Czech Geological Survey, Geologická 6, 152 00 Praha 5,Czech Republic
¹¹Norwegian Institute for Water Research, P.O. Box 173, Kjelsas, 0411 Oslo, Norway

Full Reference

Prechtel, A., Alewell, C., Armbruster, M., Bittersohl, J., Cullen, J., Evans, C.D, Helliwell, R.C, Kopacek, J., Marchetto, A., Matzner, E., Meesenburg, H., Moldan, F., Moritz, K., Vesely, J., Wright, R.F. (2001). Response of sulphur dynamics in European freshwaters to decreasing sulphate deposition. Hydrology and Earth System Sciences Vol. 5, No. 3, 311-325.

Summary of Research

Following the decline in sulphur deposition in Europe, sulphate dynamics of catchments and the reversibility of anthropogenic acidification of soils and freshwaters became of major interest. Long-term trends in sulphate concentrations and fluxes in precipitation/throughfall and freshwaters of 20 European catchments were analyzed to evaluate catchment response to decreasing sulphate deposition. Sulphate deposition in the catchments studied declined by 38-82% during the last decade. Sulphate concentrations in all freshwaters decreased significantly, but acidification reversal was clearly delayed in the German streams. In Scandinavian streams and Czech/Slovakian lakes sulphate concentrations responded quickly to decreased input. Sulphate fluxes in run-off showed no clear trend in Germany and Italy but decreased in Scandinavia, the Czech Republic and Slovakia. The decrease, however, was less than the decline in input fluxes. While long-term sulphate output fluxes from catchments were gene rally correlated to input fluxes, most catchments started a net release of sulphate during the early 1990s. Release of stored sulphate leads to a delay of acidification reversal and can be caused by four major processes. Desorption and excess mineralisation were regarded as the most important for the catchments investigated, while oxidation and weathering were of lesser importance for the long-term release of sulphate. Input from weathering has to be considered for the Italian catchments. Sulphate fluxes in German catchments, with deeply weathered soils and high soil storage capacity, responded more slowly to decreased deposition than catchments in Scandinavia and the Czech Republic/Slovakia, which have thin soils and relatively small sulphate storage. For predictions of acidification reversal, soil characteristics, sulphur pools and their dynamics have to be evaluated in future research.

Introduction

As part of the EU project "RECOVER:2010 evaluated here are: (i) regional differences in long-term trends of SO₄ concentrations and fluxes in bulk precipitation/throughfall and freshwaters on an European scale; (ii) the catchment response to decreasing SO₄ deposition regarding SO₄concentrations and fluxes as well as budgets; and (iii) the processes responsible for SO₄ release in the investigated catchments.

The long-term data used in this study were collected within national projects described elsewhere. This study includes 20 European catchments, covering a wide variety of bedrock, soils, and vegetation types as well as deposition and acidification levels (Figure 1).

Input fluxes with total deposition at all European catchments started to decrease significantly during the late 1980s parallel to the decrease in concentrations (Figure 2). The decrease in input fluxes for the period 1988/89 (reference year) to 1998/99 ranged between 38% (Metzenbach, Schluchsee (1988-1996)) to 70% (Lange Bramke) at the German catchments, between 43-60% (Pellino - Cannobino) in Italy, between 53-64% in Norway and between 78-82% in the Czech Republic (for the Czech Republic reference year was 1990). The decreases at Slovakian (1980-1999) and Swedish sites (Gårdsjön, 1989-1999) were 48% and 51%, respectively (Figure 2).

Compared to the major decrease in input fluxes, output fluxes of German and Italian catchments showed no trend, partly caused by a high variability in water fluxes (data not shown). The Scandinavian streams, however, showed an overall decrease of output fluxes by 33% (Birkenes), 40% (Storgama and Gårdsjön) to 60% (Risdalsheia) between 1986-1999 (Figure 2) parallel to the decrease in deposition.

Fig.2.Input-output budgets1 Fig.2.Input-Output budgets2

The German catchments Lange Bramke and Lehstenbach along with the Czech lakes were impacted by the highest SO₄ deposition throughout the whole measurement period (for mean input fluxes see Figure 3). Lehstenbach and Lange Bramke and the Czech lakes also had the highest output fluxes. The catchment with the lowest input and output fluxes was Langtjern (Norway). There was a positive relationship between yearly mean input load and yearly mean output flux (Figure 3). An exception is the Italian catchment Pescone which had a higher output relative to input; this is probably due to weathering of S-containing minerals. Another exception is the catchment Schluchsee (Germany) with a medium output (106 mmolc m^-2yr^-1) and only a low input (56 mmolc m^-2yr^-1). Finally, Lange Bramke had a relatively low output compared to input values.

Fig.3.SO4 for European catchments

The dynamics of SO₄ budgets (defined as flux in total deposition minus flux out in run-off) indicated a trend towards negative values (ie net loss) in most of the catchments since the late 1980s (Figure 4). Many sites switched from net retention to net loss, except Pescone (Italy) and Schluchsee (Germany-Figure 4) which lost SO₄ since the beginning of measurements in 1985 and 1988 (average loss rates 107.6 mmolc m^-2yr^-1 and 49.9 mmolc m^-2yr^-1, respectively). The Italian catchments Cannobino and Pellino started releasing SO₄ in 1989 and 1990, respectively. Most German catchments started losing SO₄ in the early 1990s. The catchments with the highest annual loss rates were Pescone and Lange Bramke with -108 and -102 mmolc m^-2yr^-1, respectively. Villingen, Gårdsjön, Cannobino, Lehstenbach, Pellino and Schluchsee showed annual loss rates between 34 and 49 mmolc m^-2yr^-1. Lower annual loss rates were observed at Markungsgraben, Birkenes, Metzenbach, Pellesino and Storgama (release 24 mmolc m^-2yr^-1 or less). At Pellesino (Italy), input fluxes exceeded the output fluxes in run-off in most years, thus showing a net retention of SO₄ (14.9 mmolc m^-2yr^-1). Retention of SO₄ was also observed at Risdalsheia from 1995 to 2000 (Figure 4). The accumulation rate at Risdalsheia, however, was only around 10 mmolc m^-2yr^-1 and might be within the errors associated with flux measurements. The Scandinavian sites show no major changes in budgets and outputs track inputs closely.

Fig.4.Net retention of SO4 Germany and Scandinavia

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

The James Hutton Institute

THE REGIONS

RESULTS

Response of sulphur dynamics in European catchments to decreasing sulphate deposition