Acidic episodes retard the biological recovery of upland British streams from chronic acidification

Kowalik, Renata A., Cooper, David M., Evans, Chris D. and Ormerod, Stephen James ORCID: https://orcid.org/0000-0002-8174-302X 2007. Acidic episodes retard the biological recovery of upland British streams from chronic acidification. Global change biology 13 (11) , pp. 2439-2452. 10.1111/j.1365-2486.2007.01437.x

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Abstract

We tested two predictions required to support the hypothesis that anthropogenic acidic episodes might explain the poor biological response of upland British streams otherwise recovering from acidification: (i) that invertebrate assemblages should differ between episodic and well-buffered streams and (ii) these effects should differentiate between sites with episodes caused by anthropogenic acidification as opposed to base-cation dilution or sea-salt deposition. Chronic and episodically acidic streams were widespread, and episodes reflected acid titration more than dilution. Nonmarine sulphate (16–18% vs. 5–9%), and nitrate (4–6% vs. 1–2%) contributed more to anion loading during episodes in Wales than Scotland, and Welsh streams also had a larger proportion of total stream sulphate from nonmarine sources (64–66% vs. 35–46%). Sea-salts were rarely a major cause of episodic ANC or pH reduction during the events sampled. By contrast, streams with episodes driven by strong anthropogenic acids had lower pH (5.0±0.6) and more dissolved aluminium (288±271 μg L−1) during events than where episodes were caused by dilution (pH 5.4±0.6; 116±110 μg Al L−1) or where streams remained circumneutral (pH 6.7±1.0; 50±45 μg Al L−1). Both biological predictions were supported: invertebrate assemblages differed among sites with different episode chemistry while several acid-sensitive species were absent only where episodes reflected anthropogenic acidification. We conclude that strong acid anions – dominantly nonmarine sulphate – still cause significant episodic acidification in acid-sensitive areas of Britain and may be a sufficient explanation for slow biological recovery in many locations.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Biosciences
Uncontrolled Keywords:	Acid deposition ; Biodiversity ; Episodic acidification ; Invertebrates ; Reversibility
Publisher:	Blackwell Science
ISSN:	13652486
Last Modified:	17 Oct 2022 08:50
URI:	https://orca.cardiff.ac.uk/id/eprint/1214

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