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Contrasting effects of geomorphic complexity on diversity of three aquatic organism groups after stream restoration
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]
  1. Ecological theory states that greater habitat heterogeneity should support higher biodiversity. Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, little evidence has been published that supports this theory, especially with respect to stream restoration and aquatic organisms.
  2. Previous assessments of stream habitat restoration have suffered from four major limitations: (1) incomplete quantification of habitat complexity metrics, (2) assessment of the responses of only one organism group, most often macroinvertebrates, (3) mismatch between scale of restoration and scale of disturbance, and (4) limited number of restoration measures applied.
  3. We used 12 metrics of geomorphic complexity spanning five dimensions of complexity (sediment grain size distribution, longitudinal profile, cross section, planform, and instream wood) to evaluate if the diversity, abundance and community composition of three aquatic organism groups (benthic macroinvertebrates, diatoms and macrophytes) relate positively to complexity along near-natural, restored and channelised stream reaches in rural northern Sweden where disturbance to the streams has been primarily reach-scale channelisation to facilitate timber floating.
  4. We found that the variation in biodiversity and abundance within each of the three organism groups could be described by multiple regression models that included only geomorphic complexity metrics, but the variation within an organism group could rarely be described by only one metric of complexity in isolation. Rather, three metrics were needed on average to describe the variation in biodiversity and abundance, and rarely did all metrics relate positively to diversity. Sediment grain size distribution metrics were most often significant as explanatory variables, but were inconsistent in the direction of influence. The other four dimensions of complexity were less consistently significant but were nearly all positively related to our diversity metrics.
  5. Most of the variation in these metrics was driven by advanced restoration techniques and to a lesser extent older best practice techniques. Three complexity metrics were most often included in multiple regression models as well as described community composition in ordinations:  a metric quantifying heterogeneity of small sediment sizes, a metric that represents the variation in stream depth along the longitudinal profile, and instream wood metrics. Therefore, specifically these metrics could be targets for future restoration. The organism groups were not concordant in their patterns of diversity, abundance, or community composition; thus, none can be used as a surrogate in monitoring biodiversity of these sites.
  6. Synthesis and applications. Geomorphic complexity should be measured in multiple dimensions, and ideally in all five dimensions, to understand the full breadth of restoration impacts to which organisms could be responding. More than one organism group should be used in monitoring to ensure biodiversity goals are met. Finally, even though the scale of the restorations matched the scale of the disturbance at the reach scale, the older best practice methods of restoration rarely restored the large-scale features necessary to bring the sites up to their potential levels of complexity as these elements (large boulders, bedrock, log jams) had been destroyed or removed from the system. Although the advanced restoration sites were the youngest, advanced restoration techniques that added big boulders, coarse gravel and instream wood increased complexity to a level that elicited a biological response. Finally, the complexity level needed to elicit a biological response could be difficult to understand for a given system, so we suggest doing restoration work in an experimental way in collaboration with geomorphologists to determine what level of complexity is needed.
Keyword [en]
boreal, bioassessment, bryophyte, substrate heterogeneity, hydromorphological, large wood, river
National Category
URN: urn:nbn:se:umu:diva-108076OAI: diva2:850989
Swedish Research Council Formas
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2015-09-03
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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