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| Titel |
Long-term trends of water chemistry in mountain streams in Sweden – slow recovery from acidification |
| VerfasserIn |
H. Borg, M. Sundbom |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 1 ; Nr. 11, no. 1 (2014-01-10), S.173-184 |
| Datensatznummer |
250117112
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| Publikation (Nr.) |
 copernicus.org/bg-11-173-2014.pdf |
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| Zusammenfassung |
The water chemistry of streams and precipitation in the province of
Jämtland, northern Sweden has been monitored since the 1980s to study
long-term trends, occurrence of acid episodes, and effects of liming. The
acidity in precipitation increased in the 1970s, followed by a loss of acid
neutralizing capacity (ANC) and low pH in the streams. Sulfur deposition
began to decrease in the 1980s, until approximately 2000, after which the
decrease levelled out. Stream water sulfate concentration followed the
precipitation trend but decreased more slowly and since the late 1990s a
subtle increase was observed. Sulfate concentrations in the snow typically
have been higher than or equal to the stream sulfate levels. However,
during the period of rapid deposition decrease and also since 2005 stream
sulfate has sometimes exceeded snow sulfate, indicating desorption of
stored soil sulfate, possibly because of climate-related changes in run-off
routes through the soil profiles, following shorter periods of frost.
From 1982 to 2000, total organic carbon (TOC) increased by approximately 0.1 mg L−1 yr−1.
The mean trends in sulfate and TOC from
approximately 1990 until today were generally opposite.
Acidic episodes with pH 4.0 at flow peaks occurred frequently in the unlimed
streams, despite relatively well-buffered waters at baseflow. To evaluate
the main causes for the loss of ANC during episodes, the changes in major
ion concentrations during high flow episodes were evaluated. The most
important factors contributing to ANC loss were dilution of base cations
(Na+, K+, Ca2+, Mg2+), enrichment of organic anions and
enrichment of sulfate.
Wetland liming started in 1985 after which the earlier observed extreme peak
values of iron, manganese and aluminium, did not reoccur. The studied area
is remote from emission sources in Europe, but the critical load of acidity
is still exceeded. The long-term recovery observed in the unlimed streams is
thus slow, and severe acidic episodes still occur. |
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