Effects of decreasing acid deposition and climate change on acid extremes in an upland stream
This study assesses the major chemical processes leading to acid extremes in a small, moorland stream in mid-Wales, UK, which has been monitored since 1979. Results suggest that base cation (mainly calcium) dilution, the "sea-salt effect", and elevated nitrate pulses, are the major...
| Main Authors: | , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2008-03-01
|
| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/12/337/2008/hess-12-337-2008.pdf |
| _version_ | 1811298950439763968 |
|---|---|
| author | C. D. Evans B. Reynolds C. Hinton S. Hughes D. Norris S. Grant B. Williams |
| author_facet | C. D. Evans B. Reynolds C. Hinton S. Hughes D. Norris S. Grant B. Williams |
| author_sort | C. D. Evans |
| collection | DOAJ |
| description | This study assesses the major chemical processes leading to acid extremes in a small, moorland stream in mid-Wales, UK, which has been monitored since 1979. Results suggest that base cation (mainly calcium) dilution, the "sea-salt effect", and elevated nitrate pulses, are the major causes of seasonal/episodic minima in acid neutralising capacity (ANC), and that the relative importance of these drivers has remained approximately constant during 25 years of decreasing acid deposition and associated long-term chemical recovery. Many of the chemical variations causing short-term reductions in stream acidity, particularly base cation dilution and organic acid increases, are closely related to changes in water-flowpath and therefore to stream discharge. Changes in the observed pH-discharge relationship over time indicate that high-flow pH has increased more rapidly than mean-flow pH, and therefore that episodes have decreased in magnitude since 1980. However a two-box application of the dynamic model MAGIC, whilst reproducing this trend, suggests that it will not persist in the long term, with mean ANC continuing to increase until 2100, but the ANC of the upper soil (the source of relatively acid water during high-flow episodes) stabilising close to zero beyond 2030. With climate change predicted to lead to an increase in maximum flows in the latter half of the century, high-flow related acid episodes may actually become more rather than less severe in the long term, although the model suggests that this effect may be small. Two other predicted climatic changes could also detrimentally impact on acid episodes: increased severity of winter "sea-salt" episodes due to higher wind speeds during winter storms; and larger sulphate pulses due to oxidation of reduced sulphur held in organic soils, during more extreme summer droughts. At the Gwy, the near-coastal location and relatively small extent of peat soils suggest that sea-salt episodes may have the greatest influence. |
| first_indexed | 2024-04-13T06:28:52Z |
| format | Article |
| id | doaj.art-070189c849df4b12b83683ce5d013e6c |
| institution | Directory Open Access Journal |
| issn | 1027-5606 1607-7938 |
| language | English |
| last_indexed | 2024-04-13T06:28:52Z |
| publishDate | 2008-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Hydrology and Earth System Sciences |
| spelling | doaj.art-070189c849df4b12b83683ce5d013e6c2022-12-22T02:58:16ZengCopernicus PublicationsHydrology and Earth System Sciences1027-56061607-79382008-03-01122337351Effects of decreasing acid deposition and climate change on acid extremes in an upland streamC. D. EvansB. ReynoldsC. HintonS. HughesD. NorrisS. GrantB. WilliamsThis study assesses the major chemical processes leading to acid extremes in a small, moorland stream in mid-Wales, UK, which has been monitored since 1979. Results suggest that base cation (mainly calcium) dilution, the "sea-salt effect", and elevated nitrate pulses, are the major causes of seasonal/episodic minima in acid neutralising capacity (ANC), and that the relative importance of these drivers has remained approximately constant during 25 years of decreasing acid deposition and associated long-term chemical recovery. Many of the chemical variations causing short-term reductions in stream acidity, particularly base cation dilution and organic acid increases, are closely related to changes in water-flowpath and therefore to stream discharge. Changes in the observed pH-discharge relationship over time indicate that high-flow pH has increased more rapidly than mean-flow pH, and therefore that episodes have decreased in magnitude since 1980. However a two-box application of the dynamic model MAGIC, whilst reproducing this trend, suggests that it will not persist in the long term, with mean ANC continuing to increase until 2100, but the ANC of the upper soil (the source of relatively acid water during high-flow episodes) stabilising close to zero beyond 2030. With climate change predicted to lead to an increase in maximum flows in the latter half of the century, high-flow related acid episodes may actually become more rather than less severe in the long term, although the model suggests that this effect may be small. Two other predicted climatic changes could also detrimentally impact on acid episodes: increased severity of winter "sea-salt" episodes due to higher wind speeds during winter storms; and larger sulphate pulses due to oxidation of reduced sulphur held in organic soils, during more extreme summer droughts. At the Gwy, the near-coastal location and relatively small extent of peat soils suggest that sea-salt episodes may have the greatest influence.http://www.hydrol-earth-syst-sci.net/12/337/2008/hess-12-337-2008.pdf |
| spellingShingle | C. D. Evans B. Reynolds C. Hinton S. Hughes D. Norris S. Grant B. Williams Effects of decreasing acid deposition and climate change on acid extremes in an upland stream Hydrology and Earth System Sciences |
| title | Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| title_full | Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| title_fullStr | Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| title_full_unstemmed | Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| title_short | Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| title_sort | effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| url | http://www.hydrol-earth-syst-sci.net/12/337/2008/hess-12-337-2008.pdf |
| work_keys_str_mv | AT cdevans effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT breynolds effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT chinton effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT shughes effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT dnorris effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT sgrant effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream AT bwilliams effectsofdecreasingaciddepositionandclimatechangeonacidextremesinanuplandstream |