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  • 1.
    Engström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weber, Christine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of river ice on riparian vegetation2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 6, p. 1095-1105Article in journal (Refereed)
    Abstract [en]

    1.  Many rivers and streams experience pronounced ice dynamics caused by the formation of anchor and frazil ice, leading to flooding and disturbance of riparian and aquatic communities.  The effects of dynamic ice conditions on riverine biota are little known.

    2.  We studied the formation of anchor ice in natural streams over 2 years, and assessed the effects of anchor ice on riparian vegetation by comparing sites with frequent or abundant and little or no anchor ice formation. We also studied the direct impact of ice on riparian plants by experimentally creating ice in the riparian zone over three winters, and by exposing plants of different life-forms to ‑18oC cold ice in the laboratory.

    3.  Riparian species richness per 1-m2 plot was higher at sites affected by anchor ice than at sites where anchor ice was absent or rare. Dominance was lower at anchor ice sites, suggesting that ice disturbance enhanced species richness. Species composition was more homogenous among plots at anchor ice sites. Experimentally creating riparian ice corroborated the comparative results, with species richness increasing in ice-treated plots compared to controls, irrespective of whether the sites showed natural anchor ice.

    4.  Because of human alterations of running waters, the natural effects of river ice on stream hydrology, geomorphology and ecology are little known.  Global warming in northern streams will lead to more dynamic ice conditions, offering new challenges for aquatic organisms and river management.  We expect that the results discussed here can stimulate new research, contributing to a better understanding of ecosystem function during winter.

  • 2.
    Weber, Christine
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Lovisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Alfredsen, Knut T
    Polvi, Lina E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Winter disturbances and riverine fish in temperate and cold regions2013In: BioScience, ISSN 0006-3568, E-ISSN 1525-3244, Vol. 63, no 3, p. 199-210Article in journal (Refereed)
    Abstract [en]

    Winter is a critical period for aquatic organisms; however, little is known about the ecological significance of its extreme events. Here, we link winter ecology and disturbance research by synthesizing the impacts of extreme winter conditions on riverine habitats and fish assemblages in temperate and cold regions. We characterize winter disturbances by their temporal pattern and abiotic effects, explore how various drivers influence fish, and discuss human alterations of winter disturbances and future research needs. We conclude that (a) more data on winter dynamics are needed to identify extreme events, (b) winter ecology and disturbance research should test assumptions of practical relevance for both disciplines, (c) hydraulic and population models should incorporate winter- and disturbance-specific aspects, and (d) management for sustainability requires that river managers work proactively by including anticipated future alterations in the design of restoration and conservation activities.

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    Weber et al_BioScience2013
  • 3.
    Weber, Christine
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Peter, Armin
    Success or Failure?: Do Indicator Selection and Reference Setting Influence River Rehabilitation Outcome?2011In: North American Journal of Fisheries Management, ISSN 0275-5947, E-ISSN 1548-8675, Vol. 31, no 3, p. 535-547Article in journal (Refereed)
    Abstract [en]

    Recovery indicators play a crucial role in the evaluation of river rehabilitation projects. Various types of biological indicators are used to address different ecosystem attributes (structure, composition, and function) at different levels of the biological hierarchy (population, guild, and community). Indicator values are evaluated against reference information from various sources, representing the conditions to be achieved (near-natural references) or to avoid (degraded references). We studied the extent to which investigators' conclusions on project outcome were influenced by the indicator and reference types used. We analyzed 40 selected studies dealing with the recovery of riverine fish assemblages after active rehabilitation of physical habitat and lateral connectivity. In 32 (80%) of the 40 studies, fish response was measured at the population level. Structural and compositional indicators dominated (31 and 24 studies, respectively), while functional indicators were underrepresented (5 studies). Eighteen studies used multiple indicator types for a given ecosystem attribute, a given hierarchical level, or both. Among these studies, we found only very limited evidence that project outcome differed among different indicator types (1 study). In contrast, highly heterogeneous results were found within the different indicator types at the level of the individual study (i.e., indicators addressing the same hierarchical level and ecosystem attribute resulted in different evaluations of project outcome). Such heterogeneity was related to the spatiotemporal variability of the results and species-specific responses to physical habitat rehabilitation. Most studies (73%; 29 studies) used a single type of reference, and the majority focused on degraded conditions. Among the 10 studies that applied multiple reference types, one-third (3 studies) showed inconsistent results (i.e., one reference comparison produced a positive assessment for a given indicator, whereas the second comparison indicated that the endpoint was not achieved). We discuss the implications of inconsistent project outcomes for future monitoring activities.

  • 4.
    Weber, Christine
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Scheuber, Hannes
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Alfredsen, Knut T.
    Detection and apparent survival of PIT-tagged stream fish in winter2016In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 6, no 8, p. 2536-2547Article in journal (Refereed)
    Abstract [en]

    Environmental fluctuations exert strong control on behavior, survival, and fitness of stream biota. Technical improvements increasingly allow for tracking the response of large numbers of individuals to environmental fluctuations, for instance, by remote detection of animals equipped with PIT (passive integrated transponder) tags. PIT tags were implanted into 393 juvenile and adult brown trout Salmo trutta L. and European sculpin Cottus gobio L. in a boreal stream subjected to considerable ice formation. With weekly trackings over 6 months, we quantified apparent survival and detection probability in relation to biological, environmental, and methodological factors. Individuals with a higher physical condition in autumn showed a higher apparent survival; this pattern was consistent across all species and age classes. Detection probability decreased with increasing thickness of the surface ice layer; this effect was most pronounced for juvenile trout and benthic-living sculpin, both tagged with smaller-sized tags. Detection probability was reduced in structurally complex habitats. Our study demonstrates that apparent survival and particularly detection probability may show pronounced spatiotemporal variation. In order to compare results from different sampling occasions and sites, a good knowledge of the study site and of the regulating factors is crucial.

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