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Potential and actual geomorphic complexity of restored headwater streams in northern Sweden
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2014 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 210, 98-118 p.Article in journal (Refereed) Published
Abstract [en]

Stream restoration usually relies on ecological theories presuming that increased habitat heterogeneity leads to higher biodiversity. However, to test this hypothesis a quantitative metric of overall geomorphic complexity is needed. We quantified geomorphic complexity using 29 metrics over five dimensions (sediment distribution, longitudinal profile, cross section, planform, and instream wood) of headwater streams in northern Sweden. We examined reaches with four different restoration statuses after a century of timber floating (channelized, restored, demonstration restored, and unimpacted) to determine (1) whether restoration increases complexity in all dimensions, (2) whether a complexity gradient can be quantified and which metrics can serve as proxies for the gradient, and (3) levels of potential complexity based on large-scale controls (drainage area, glacial legacy sediment, valley slope, valley confinement old-growth forest/buffer zone, and beaver activity). We found a significantly higher complexity in unimpacted and demonstration restoration sites than in channelized sites in all five dimensions except the cross section (based on the two metrics quantifying variability in the cross section). Multivariate analyses were able to elucidate an apparent complexity gradient driven by three complexity metrics: longitudinal roughness, sediment sorting, and cross section chain and tape ratio. The large-scale factors of valley and channel gradient as well as median grain size, along with restoration status, drive differences in complexity composition. Restoring a reach to its potential complexity is beneficial in regions without reference systems or sufficient data to model flow and sediment processes. Unimpacted and demonstration restoration reaches displayed not only more intrareach variability than channelized reaches but also greater interreach heterogeneity in complexity composition, which supports a focus on reach-scale controls on potential complexity and a landscape-scale view on restoration. (C) 2014 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
2014. Vol. 210, 98-118 p.
Keyword [en]
Geomorphic complexity, Stream restoration, Sweden, Boreal, Headwater streams, Channelization
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:umu:diva-88319DOI: 10.1016/j.geomorph.2013.12.025ISI: 000332820800009OAI: diva2:725749
Available from: 2014-06-17 Created: 2014-04-30 Last updated: 2016-05-18Bibliographically approved
In thesis
1. Gradients of time and complexity: understanding how riparian and instream ecosystems recover after stream restoration
Open this publication in new window or tab >>Gradients of time and complexity: understanding how riparian and instream ecosystems recover after stream restoration
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Why evaluations of the ecological outcomes of stream and river restoration have largely reported inconclusive or negative results has been the subject of much debate over the last decade or more. Understanding the reasons behind the lack of positive results is important for bettering future restoration efforts and setting realistic expectations for restoration outcomes. This thesis explores possible explanations for why researchers have failed to find clear and predictable biotic responses to stream restoration: recovery time has been too short, that restoration of habitat complexity is not clearly linked to instream biodiversity, that one monitored organism group is not representative of the entire community, that restoration effort was not intense enough to restore the potential habitat complexity of a system, and that reach-scale restoration done in the presence of catchment-scale degradation obscures restoration results. The overarching goal of this thesis is to study the holistic effect of reach-scale restoration of historic reach-scale simplification, due to timber floating in northern Swedish streams, thus avoiding the added pressure of catchment-scale degradation typically found at most restoration sites (e.g., non-point-source pollution and impervious cover). Using this model system, I was able to show that it took 25 years for riparian plant species richness at restored sites to increase above that of channelized sites. Furthermore, it was clear that restoration of these streams caused a large and rapid change in N-processing in the riparian zone and this alteration persists for at least 25 years. Additionally, multiple metrics of geomorphic complexity were needed to explain some of the more subtle responses of organism groups. Macroinvertebrates, diatoms, and macrophytes did not respond concordantly and cannot serve as surrogates or indicators for each other. I found that older best practice methods of restoration rarely restored the large-scale features needed to bring the sites up to their potential complexity because these elements were destroyed or removed from the system. Advanced restoration techniques used in more recent restorations added big boulders and instream wood and increased complexity to a level that elicited a biological response. By combining surveys of multiple metrics of structure, diversity of multiple organism groups, and process in this thesis I was able to get a holistic view of the effects of restoration of streams after timber floating. We now know that it takes at least 25 years for riparian plants and N-cycling to recover, we understand that multiple metrics of geomorphic complexity should be measured to be able to explain biotic responses, and that restored complexity should better match the potential complexity of the site in order to elicit a biological response. Finally, we know that multiple organism groups need to be assessed when evaluating the response of biodiversity to restoration.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2015. 36 p.
bioassessment, biodiversity, boreal, bryophyte, chronosequence, complexity, diatom, geomorphology, habitat heterogeneity, hydromorphological, macroinvertebrate, macrophyte, nitrogen cycling, river restoration, riparian buffer, stable isotopes, succession, Sweden
National Category
Research subject
biology, Environmental Science
urn:nbn:se:umu:diva-108079 (URN)978-91-7601-302-1 (ISBN)
Public defence
2015-09-25, Älgsalen, Uminova Science Park, Umeå, 09:00 (English)
Available from: 2015-09-04 Created: 2015-09-03 Last updated: 2015-09-03Bibliographically approved

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Polvi, Lina E.Nilsson, ChristerHasselquist, Eliza Maher
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