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What are the effects of natural versus human-caused acidity on stream species diversity and ecosystem functioning?
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human activities have caused acidification of freshwater systems on a large scale resulting in reduced species diversity and ecological functioning in many lakes and streams. However, many naturally acidic freshwater systems have also been found, for instance in northern Sweden. In regions where such naturally acidic aquatic ecosystems have prevailed over evolutionary periods, species diversity and ecological functioning are not automatically impaired due to possible adaptation to the putatively adverse environmental conditions. I studied species diversity patterns and ecological functioning in anthropogenically acidified, naturally acidic, circumneutral, and limed streams to test the adaptation hypothesis and examine the ecological effects of variation in naturally acidic water chemistry. Species diversity was studied using benthic macroinvertebrates, while functioning was modelled using the decomposition rates of leaf litter. In accordance with the evolutionary species pool hypothesis, species richness was reduced more strongly in regions with anthropogenic than natural acidity when compared to circumneutral streams, supporting the adaptation hypothesis. In contrast, the patterns in ecological functioning along the pH-gradients did not differ between regions with anthropogenic and natural acidity, likely resulting from compensation: the biomass of tolerant taxa probably increased which thus rescued the loss in functioning otherwise mediated by the more sensitive taxa. Furthermore, the naturally variable acidic water chemistry clearly supported distinct macroinvertebrate assemblages, as was reflected in differing patterns of species diversity and ecological functioning. Such naturally acidic waters that were rich in dissolved organic carbon supported higher ecosystem process rates and lower species diversity than waters that contained little dissolved organic carbon. Upon liming naturally acidic streams microbial leaf decomposition increased, whereas shredding decreased along with changes in shredder abundances. The abundance of large caddisflies decreased, while the abundance of small stoneflies increased. The results suggest that various types of benthic macroinvertebrates with varying levels of adaptation and tolerance inhabited the hydrochemically variable naturally acidic streams. The distributions of macroinvertebrates in response to different pH levels and differences in acid quality and how these distributions translate into varying patterns of species diversity and ecological functioning are worthy of further investigation. This will likely improve our understanding of how such naturally acidic streams and their biota can be successfully managed.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap , 2007. , p. 19
Keyword [en]
acid rain, aquatic insects, biodiversity, ecosystem function
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:umu:diva-1318ISBN: 978-91-7264-345-1 (print)OAI: oai:DiVA.org:umu-1318DiVA: diva2:140638
Public defence
2007-09-22, KB3A9, KBC, Ekologi, miljö och geovetenskap, Umeå, 10:00
Opponent
Supervisors
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2011-03-23Bibliographically approved
List of papers
1. Does freshwater macroinvertebrate diversity along a pH-gradient reflect adaptation to low pH?
Open this publication in new window or tab >>Does freshwater macroinvertebrate diversity along a pH-gradient reflect adaptation to low pH?
2007 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 11, p. 2172-2183Article in journal (Refereed) Published
Abstract [en]

1. The impacts of anthropogenic surface water acidification are much better known than those of natural acidity. Recent studies have indicated biodiversity is not degraded and species composition unaltered in naturally acidic compared to circumneutral watercourses.

2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.

3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.

4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.

5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups.

 

Place, publisher, year, edition, pages
Oxford: Blackwell Scientific, 2007
Keyword
acidity, aquatic insects, community ecology, generalized linear mixed models, taxonomic richness
Identifiers
urn:nbn:se:umu:diva-2485 (URN)10.1111/j.1365-2427.2007.01845.x (DOI)
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2017-12-14Bibliographically approved
2. Do natural acidity and anthropogenic acidification have different effects on species diversity and ecosystem functioning?
Open this publication in new window or tab >>Do natural acidity and anthropogenic acidification have different effects on species diversity and ecosystem functioning?
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2486 (URN)
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2016-02-25Bibliographically approved
3. Species richness, but not ecosystem functioning, is lost at a higher rate in recently acidified than in naturally acidic streams
Open this publication in new window or tab >>Species richness, but not ecosystem functioning, is lost at a higher rate in recently acidified than in naturally acidic streams
(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-2487 (URN)
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2016-02-25Bibliographically approved
4. Landscape-controlled chemistry variation affects communities and ecosystem function in headwater streams
Open this publication in new window or tab >>Landscape-controlled chemistry variation affects communities and ecosystem function in headwater streams
Show others...
2007 (English)In: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 64, no 11, p. 1563-1572Article in journal (Refereed) Published
Abstract [en]

We show that benthic freshwater communities of naturally acidic streams in boreal catchments differ depending on properties of the surrounding landscape. Although low pH usually is associated with negative impacts on species diversity and ecosystem function, here decomposition by insects and microbes as well as the abundance of leaf-eating insects were generally high at low pH and at humic sites influenced by mire-dominated compared with forest-dominated surroundings. Moreover, in situ growth experiments showed that the survival of two of the most abundant insect species was higher when they originated from mire-influenced sites, underscoring their tolerance to low pH. However, species diversity generally increased with pH and was greater at forest-influenced than at mire-influenced sites. Although less diverse, acidic and humic streams proved to be functional and supported distinct macroinvertebrate assemblages. Diversity and function in naturally acidic streams are apparently greatly influenced by the prevailing kinds of landscape-driven influences on water chemistry. In conclusion, well-known negative impacts of anthropogenic acidity on diversity and function may not apply to naturally acidic systems that are chemically and biologically heterogeneous.

Abstract [sv]

Nous démontrons que les communautés benthiques d’eau douce de cours d’eau naturellement acides dans des bassins versants boréaux diffèrent selon les caractéristiques du paysage environnant. Bien qu’un pH faible soit normalement associé à des impacts négatifs sur la diversité spécifique et le fonctionnement de l’écosystème, néanmoins dans notre étude, la décomposition par les insectes et les microorganismes, ainsi que l’abondance des insectes consommateurs de feuilles, sont généralement élevées aux valeurs basses de pH et dans les sites humiques influencés par un environnement dominé par les tourbières plutôt que par les forêts. De plus, des expériences de croissance in situ montrent que la survie des deux espèces d’insectes les plus abondantes est supérieure lorsque celles-ci proviennent des sites influencés par les tourbières, ce qui souligne leur tolérance aux pH bas. Toutefois, la diversité spécifique croît généralement en fonction du pH et elle est plus élevée aux sites dominés par les forêts qu’à ceux dominés par les tourbières. Bien que moins diversifiés, les cours d’eau acides et humiques s’avèrent fonctionnels et ils contiennent des peuplements distincts de macroinvertébrés. La diversité et le fonctionnement dans les cours d’eau naturellement acides sont apparemment fortement influencés par les effets du type dominant de paysage sur la chimie de l’eau. En conclusion, les impacts négatifs bien documentés de l’acidité causée par l’activité humaine sur la diversité et le fonctionnement peuvent ne pas s’appliquer à des systèmes naturellement acides qui sont hétérogènes des points de vue chimique et biologique.

Identifiers
urn:nbn:se:umu:diva-8474 (URN)
Available from: 2008-01-24 Created: 2008-01-24 Last updated: 2017-12-14Bibliographically approved
5. Mitigation or disturbance? Effects of liming on macroinvertebrate assemblage structure and leaf-litter decomposition in the humic streams of northern Sweden
Open this publication in new window or tab >>Mitigation or disturbance? Effects of liming on macroinvertebrate assemblage structure and leaf-litter decomposition in the humic streams of northern Sweden
2006 (English)In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 43, no 4, p. 780-791Article in journal (Refereed) Published
Abstract [en]
  1. Stream liming can alleviate the effects of anthropogenic acidification but itself constitutes a substantial ecosystem-level perturbation. Acidity in the humic streams of northern Sweden largely arises from natural causes but liming is extensively practised, with uncertain ecological outcomes.
  2. We investigated macroinvertebrate assemblage structure and leaf-litter decomposition in seven humic Swedish streams, each of which is limed at a single point using a dosing tower. Grey alder Alnus incana leaves were enclosed in replicate fine (mesh size 0·5 mm) and coarse (10 mm) mesh bags at three locations in each stream: upstream of the dosing tower, in the transitional ‘mixing zone’ immediately downstream of the tower, and at a site further downstream where the lime powder is completely dissolved, with marked changes to water chemistry. Benthic macroinvertebrate assemblages were characterized from each site via five replicate Surber samples.
  3. Alkalinity, pH, conductivity and calcium (Ca) concentrations increased following liming, whereas dissolved organic carbon and aluminium concentrations decreased.
  4. Decomposition in fine mesh bags, primarily mediated by microbes, was positively associated with pH and Ca and was significantly elevated by liming, probably attributable to stimulation of fungal pectin-degrading enzymes that require Ca as a cofactor.
  5. Decomposition attributable to detritivorous insects (shredders), assessed by subtracting decomposition observed in fine mesh bags from that observed in coarse bags, was reduced following liming, in concert with changes to shredder assemblages. Abundance of large caddisfly shredders declined in limed stream sections, whereas some smaller stoneflies increased in number. Shredder diversity declined following liming during spring. Species evenness fell overall, and richness was reduced in four of six streams.
  6. Synthesis and applications. Water chemistry changes following stream liming in northern Sweden appear to overcompensate for the limited acid deposition observed in the region, with important ecosystem consequences. The potential deleterious impacts of liming need to be balanced against its desired outcomes in regions where acidity is largely attributable to natural causes.
Place, publisher, year, edition, pages
Oxford: Blackwell, 2006
Keyword
alkalinization, biodiversity, ecosystem function, hyphomycete, natural acidity, restoration
Identifiers
urn:nbn:se:umu:diva-2489 (URN)10.1111/j.1365-2664.2006.01196.x (DOI)
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2017-12-14Bibliographically approved

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